The War on Truth: The Triumph of Newtonianism.

Battle o’ the specula; Orion 180mm  f/15 Maksutov Cassegrain versus the SkywWatcher 204mm f/6 Newtonian. The latter proved superior on all test targets.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

*** New testimonies recently added to the end of the article.

Preamble

For sheer brute force light gathering ability, Newtonian reflectors rate a best buy. No other type of telescope will give you as large an aperture for the money……For the sake of discussion, I have divided Newtonians into two groups based on focal ratio. Those with focal ratios less than f/6 have very deeply curved mirrors, and so are referred to here as ‘deep dish’ Newtonians. Reflectors with focal ratios of f/6 and greater will be called ‘shallow dish’ telescopes.

Pardon my bias, but shallow dish reflectors are my favorite type of telescope. They are capable of delivering clear views of the Moon, the Sun and the other members of the solar system, as well as thousands of deep sky objects. Shallow dish reflectors with apertures between 3 inches(80mm) and 8 inches(203mm) are usually small enough to be moved from home to observing site and quickly set up with little trouble………..Most experienced amateurs agree that shallow dish reflectors are tough to beat. In fact, an optimised Newtonian reflector can deliver views of the Moon and the planets that eclipse those through a catadioptric telescope and compare favorably with a refractor of similar size, but at a fraction of the refractor’s cost. Although the commercial telescope market now offers a wide variety of superb refractors, it has yet to embrace the long focus reflector fully.

From Star Ware, 4th Edition ( 2007), by Philip S. Harrington pp 32−33.

 

To savor stargazing we need to strike a balance between the time, energy, and expense devoted to this activity and what we channel  into other necessary human tasks. A contented evening of stargazing comes with this balance. ‘In medio stat virtus’, or, as this Latin rendition of Aristotle’s maxim has been translated into English, “All things in moderation.’

Otto Rushe Piechowski

Sky & Telescope February 1993, pp 5

The trend towards larger and larger reflectors is indeed exciting, and I can understand the need to keep them short focus( typically f/4 to f/5). But why are so many small ones made with these focal ratios? Such telescopes bring out the worst in the Newtonian design. The 6 inch f/8s and 8 inch f/7s common many years ago, were much better and more versatile reflectors than many commercially available today.

Alan French

Sky & Telescope, November 1993 pp 4.

Newtonian reflecting telescopes are great telescopes for observing Jupiter.

John W. McAnally, from Jupiter and How to Observe It, pp 152.

Indeed a high quality Newtonian reflector is a very powerful instrument, fully capable of superb performance in viewing the planets when the optics are kept clean and properly aligned. They have been amng the favorite instruments of serious planetary observers for many decades.

Julius L. Benton, Jr. from Saturn and How to Observe It, pp 57.

Newtonian reflector telescopes, apart from their complete freedom from chromatic aberration, can be made with much shorter focal ratios than refractors, usually between f/6 and f/8 so that even an 8 inch reflector is portable and easily affordable by most amateurs. An 8 inch refractor would be financially out of the question for the vast majority of amateurs  and would need permanent housing in a large observatory. As a choice for planetary observation, then, there is a lot to be said for the Newtonian reflector in the 6 to 10 inch aperture range.

Fred W. Price, from The Planet Observer’s Handbook 2nd Edition, pp 41.

It is true that such reflectors are considerably less expensive than are refractors of the same size. This does not mean that they are not as good; in fact, Newtonian reflectors are more widely used by more experienced observers than any other type.

David H. Levy, from Guide to the Night Sky, pp 61

The simplest, cheapest and overall the most efficient design you could choose to use as a richfield telescope is the Newtonian reflector. As ever, an aperture of 100 to 200mm and a focal ratio of f/4 to f/6 is most appropriate.

Nick James & Gerald North, from Observing Comets, pp 57.

It is not proposed to enter upon the controversial topic of reflectors versus refractors. If does not grudge the extra attention to keep a reflector in perfect adjustment, its performance in revealing planetary detail will equal that of a refractor of the same aperture, particularly if it is mounted with an open, lattice work tube, when a further improvement may be derived from the employment of an electric fan  to keep the column of air above the mirror well mixed.Moreover it has practically negligible chromatic aberration, whereas colour estimates made with a refractor are exceedingly unreliable.

Bertrand Peek, from The Planet Jupiter;The Observers Handbook, pp  37.

What is “over-expensive”? It depends on your point of view. A 106mm Takahashi flat field quadruplet refractor can be had, without mount, for only a little more than I paid for a high-end 12.5″ dobsonian Newtonian with state-of-the-art optics. If astro-imaging is your forte, the Tak will be the better choice. Don’t forget a high-end mount to go with it. For visual, though? Get real. The Tak will be severely limited–a well-machined, and beautifully-performing SMALL scope that can’t see much. If you buy your scopes for visual use, the Tak isn’t just over-expensive, it’s ridiculous. If you buy your scopes for photography, though, that Tak is an incredible choice.

Don Pensack from post no. 235 in an online a discussion on Why is Takahashi Overly Expensive?

Apochomats are expensive, particularly in the larger (repeated word ‘Larger’ omitted) apertures. Object the commonly available designs, reflectors are free of chromatic aberration since mirrors reflect all the colors identically. This means that a good quality reflector with a large aperture can be free of false color and yet provide the resolution and fine scale contrast while still being affordable. These Scopes have issues of their own..

Jon Isaac, from  post no. 14 in an online discussion entitled, Can An Apochromatic Refractor Use More Powerful Eyepieces than an Achromatic Refractor Of The Same Size?

So What telescope Should I Spend with My Money On?

All in all, if you can afford it, and if you have the room to house it permanently in some sort of observatory (perhaps a run off shed), I would say go for a Newtonian reflector of 10 to 14 inches (254 to 356mm) aperture and as large a focal ratio as you can reasonably accommodate……..If you can’t afford a 10 inch then go for a smaller Newtonian reflector. Remember this type of telescope is the cheapest of any but please do not compromise on quality for the sake of size. My second choice for an instrument intended for visual observation of the Moon would be a refractor of at least 5 inches (127mm) aperture…

Gerald North, from Observing the Moon; the Modern Observer’s Guide (2007), pp 52

 

A first-rate 130-mm Newtonian is roughly equivalent to a first-rate 102-mm refractor for planetary observing, but superior to the refractor for all other purposes.

Tony Flanders, former Associate Editor, Sky & Telescope, in an online discussion ( post no. 1837) of the Astronomers Without Borders One Sky Newtonian.

The Newtonian reflector is a popular choice. Money wise, they are cost effective, and most importantly, you can obtain a large aperture telescope  for a reasonable sum of money…..It is true the Newtonians can come with long tubes if a longer focal length and high focal ratio is required…..Although you will hear it said high focal lengths and ratios( example f/7 etc) are desirable for planetary work, telescopes with a focal ratio of f/5 can be very satisfactory.

Paul Abel, BBC Sky at Night Presenter, from his book, Visual Lunar and Planetary Astronomy (2013), pp 14/5.

The best view of Jupiter I ever had was at Peach State with a 12.5″ Portaball on an equatorial platform at 567x (10/10/2010). There was so much detail I tried to find a larger scope in use (no luck, alas). We could see albedo features on Ganymede and Callisto. Amazing what you can see on a night of exceptional seeing. Even when the seeing is not at its best, I find there are often times on any night when a larger scope has an advantage.

Alan French, from an online discussion (post no.14) entitled Large Telescopes and Jupiter.

Guan Sheng Optical (GSO) uses high-volume, state-of-the-art, high quality manufacturing and test lines. GSO guarantees diffraction limited performance, but their mirrors typically have a mirror surface quality of 1/16 wave RMS at least, and often better. This very smooth mirror surface results in excellent optical performance with practically no light scatter, while Antares Optics secondary mirrors are 1/15 P-V or better and come Zygo tested;

Rob Teeter, founder of Teeter’stelescopes.com

Amateur astronomers and telescope makers have debated from time immemorial the advantages and disadvantages of different telescope designs. In particular, mountains of hard copy and electronic articles are available on the merits of refracting and reflecting telescopes, more recently, apochromatic refractors vs. Newtonian reflectors. This debate has become rather rancorous (Newtonian telescopes as APO “killers” comes to mind.) and unscientific, to say the least. And when all is said and done, in a discourse without loaded words and acrimony, a discussion devolves to one concerning perfect optics. And isn’t this what we all want or wish we had?

From Ed Turco’s online article: The Definitive Newtonian Reflector.

Many people shy away from Newtonians because they have exposed optics that get damp and deteriorate. In this respect a good closed tube Newtonian wins hands down over an open tube one, as the tube keeps dew at bay. For the best planetary resolution, a telescope must, must, must must be precisely collimated!!! Also, the optics should be able to cool down quickly by fan cooling. Mirrors thicker than 40mm have serious cooldown problems unless fan cooling is employed. My 254mm f/6.3 Orion Optics Newtonian (plus mirror fan)is the best planetary telescope I have ever used. Some planetary observers line their tubes with cork too, to reduce currents. Many good planetary telescopes are comprehensively ruined by being in a huge unventillated dome with a narrow slit, a concrete floor and a metal dome.

Martin Mobberley, Author, from his webpage: Telescopes.

See also his review of the same instrument here.

Much has been written on the subject of the central obstruction and its impact on fine planetary detail. It remains a hot-button topic in on-line forums, and yet, despite the intensity of the debate, obstruction effects are well understood and fairly simple to quantify. The issue was most elegantly summarized by William Zmek in the July 1993 issue of Sky & Telescope magazine. Zmek’s rule of thumb states that if you subtract the diameter of the obstruction from the objective, you have the equivalent unobstructed instrument when it comes to contrast resolution. In other words, an 8-inch reflector with a 1.5-inch obstruction has the potential to resolve the same low-contrast planetary detail as an unobstructed 6.5-inch scope.

Gary Seronik, former Sky & Telescope Contributing Editor and Author, from his personal website.

I have the 12″ Orion as well (Truss, but the same thing otherwise). I have seen two other instances where optical quality on this model was excellent, and my own has perhaps the best mirror I have seen in a mass market dob.Star test with [2]3% obstruction shows an identical secondary shadow breakout, and the mirror had no zones or turned edge, and the smoothness was quite good. In other words, by anyone’s measure, the mirror in my own sample is a really fine mirror. If yours is in the same category for quality, be prepared for some awesome planetary views. The 12″ easily put up better planetary views than my 6″ Astro-Physics Apo and my C14. Views with 31mm Nagler and MPCC Coma Corrector are wonderful (I use the MPCC because it is 1x and while maybe not quite as sharp as the Paracorr, that 1x is important when trying to get the largest field possible out of today’s very expensive wide field eyepieces. I had fantastic views with my 12″ and it is my favorite larger aperture telescope ever. It does everything with excellence.

Ed Moreno, from an online thread entitled, First Light with my XT12G.

 

I tested the scope over a four week period, and found the optics to be very good, to excellent. I star tested the scope extensively, and found the mirror to be extremely smooth, with the slightest under correction.. I couldn’t put a figure on it, GS advertise 1/12 wave. Planetary images were rock hard. I tested the scope against my friend’s 12.5 Inch premium Dobsonian, which sports a “Swayze” mirror, and we couldn’t split the images over four different nights. On one particular night of excellent seeing, I had the magnification up to 500x, without any image breakdown.Our local club Telescope guy ran a series of tests on the optics, the main one being a Double pass Ronchi test, against a certified optical flat. He informed me the mirror was very well corrected, and very smooth. He didn’t believe the price I paid for the entire scope.

In summary, this scope has been a huge surprise. My experiences with “light Buckets” previously were not great. My intention was to use this scope for deep sky observation only, as I already have a Zambuto equipped premium scope for Planetary work, but it’s a lot more than that. Since purchasing my scope, I have looked through fourteen of these instruments at our club nights, and the images in all of them are almost identical. Guan Sheng seem to be producing a great mass-produced scope.

Con Stoitsis
Director
Comet Section
Astronomical Society of Victoria Inc
Melbourne, Australia

From a review of the Guan Sheng 12″ f/5 Dob (essentially identical to the author’s instrument pictured above). Source here.

I purchased a 15” Obsession from owner David Kriege on January 12, 2007 and took delivery in the first week of March of the same year. Since that time it has been my principle telescope for visual use. For comparison, I have owned two Takahashis (FS-102 and TOA 130), three Televues (TV85; NP127; TV85 again), a WO 10th anniversary 80mm, an 8” Celestron SC with Starbright coatings and a 6” Orion dobsonian.Despite the demonstrated affinity I have for apochromatic refractors, I had been to enough star parties to learn that aperture ultimately wins…………Those interested in purchasing a larger dobsonian may wonder what you see in a 15” scope. Having compared views with everything from 60mm refractors to a 30” dobsonian, I can honestly say “more than enough to keep you busy for a long, long time”. Globular clusters really seem to take life at about 12” and galaxies are already more than nondescript smudges by 15”. Of course local conditions make a huge difference. I have had nights with a 5” refractor that gave the 15” a run for its money. I have been at star parties looking at a galaxy in the 15”, then wandered next door to a 24” expecting to be utterly blown away by the difference and then been surprised by how little there was. That said, on any given night, the 15” tends to beat the socks off my small refractor nearly every night across the board, from planets to wisps.

From a review of the 15″ Obsession Dobsonian by Rene Gauge. See here for more details.

The Oldham optics on this Dobsonian are superb. A number of tests were carried out, the results of which are outlined below. The round airy discs of bright stars appear perfect. Faint stars are fine razor sharp points of light. On nights of good seeing I have been able to see faint diffraction rings around stars. Images snap into focus even at high power.

After extensive star testing, I could detect no major defects. There was no sign of any astigmatism, even close to focus. The test revealed near perfect correction and very smooth & high contrast optics. Given that the primary mirror is large and fast, and the star test is particularly sensitive, I consider these results to be very good. A particularly impressive aspect is the ability of the optics to handle very high powers. The results of the magnification roll-off test were excellent. First light revealed that the mirror could easily handle forty times per inch of aperture on planets. In good seeing conditions Saturn would reveal a high level of detail and remain sharp at magnifications in excess of 600X, and Jupiter showed no sign of image breakdown at 507X. Under no circumstances have I ever seen Jupiter soften at powers less than 450X. I have even enjoyed good views of the moon at 888X. I have also shared my experiences with a number of experts around the world who believe as I do that the optics are performing to a high specification.

Nick Koiza, from his review of a David Lukehurst 16″ f/4.4 Dobsonian detailed here.

Here’s what everyone wants to know. The primary mirror, as with all Zambuto-equipped Starmasters I’ve seen, is a jaw-dropper. Since quoting data on the mirror is often misleading and can cause flame wars, I’ve chosen to leave these out of this review. What I will say is that the Zambuto mirrors have an extremely smooth optical surface, with a near-perfect star test. Running through focus, the Fresnel rings are identical on both sides of focus and evenly illuminated. I can find no zones, no turned edge, and no astigmatism. There is perhaps a “slight” under-correction, however it’s often not even noticeable to me, which could indicate that I might have tested while the mirror was still slightly out of thermal equilibrium. If it is there, it’s very, very slight & I couldn’t begin to guess by what fraction of a wave.

However, that smooth surface correlates to what I believe to be the most important aspect of visual observing, and that is contrast. In a word – exceptional. The scope shows even the most subtle differences in illumination. There is definitely an emotional response with Carl’s mirrors, an underlying feeling that’s hard to describe, except to say sitting at the eyepiece is more like observing from space rather than the ground. The extremely fine details seen are amazing, and sometimes I seem to subconsciously pick up things that I don’t notice when looking through other instruments, only to go back to my scope & find that I wasn’t dreaming!

Jupiter usually shows 10 bands and massive amounts of detail within the belts & GRS, as well as the festoons & barges. And being able to see this kind of detail routinely at 400x, and many nights up to 600x is definitely like looking at a photograph. Polar regions & surface detail are visible on Io. Saturn shows the Crepe ring every night, as well as the Encke minima without fail.. Despite the short focal length it is a killer planetary scope. When Mars was last at opposition before the dust storms, picking out surface details was as easy as looking at our moon. In addition both polar caps were easily seen. Phobos & Deimos were also seen. On the planets I rarely use filters, so most of the views described above were natural.

No matter the conditions, the Trapezium easily breaks into 6 components, even at very low magnifications. The detail level seen in M42/43 is far better than any photo I’ve ever seen, from low-power views that show the entire nebula, to using a binoviewer at 500x on the Trapezium vicinity that reveals details in the nebula, which are reminiscent of the structure seen in cumulo-nimbus clouds.

With globular clusters, “resolved” takes on a new meaning & the scope provides “in your face” visual observing! Obviously M13 & Omega are completely resolved. One of my favorite globulars is M92 because of the super-dense core that seems to go on forever. One night I decided to push the scope to what our group likes to call “silly power” & view M92 at 700x. WOW – the core showed a tremendous amount of resolution, but again it’s so dense I couldn’t quite get it to go all the way. M13 at this power was like looking right through it to the other side. And I can’t forget the extra-galactic clusters, G1 & G2 in M31. G1 actually started show resolution at about 500x. Another extra-galactic object is NGC 604, the giant HII region in M33, about 2.5 MLY away. At 700x I can see much structure & filaments within the nebula. Seeing that in real time is spectacular.

Most galaxies within the local group show quite a bit of structure, knotting, & dust lanes. Those more distant objects do reveal detail well above being mere smudges. Many Virgo galaxies show spiraling. Every component of Stephan’s Quintet is always visible, and much easier to see than in many other scopes of similar aperture I’ve used. NGC 7331 is stunning. Closer neighbors like M51, M31, M33, M81/82, M104, NGC 4565 & NGC 891 take on photographic qualities in the eyepiece. I’ve been able to determine the rotational direction of a galaxy that NSOG stated was over 500 MLY distant. The scope is also quite capable of hunting the faint Abell planetary nebulae & galaxy clusters, and with an H-Beta filter, the Horsehead is a snap with direct vision. These are just a few of my experiences at the eyepiece. In short, once the mirror has reached thermal equilibrium, it’s like having a 14.5″ f/4.3 APO. Tight, pinpoint stars sharp across the FOV, and a nice “snap” to focus – there’s no mistaking it. The low f/ratio provides a nice wide field, at least for a scope of this size. I can get 1.4* with the 31 Nagler & using the Paracorr which boosts the focal length from 1584mm to 1822mm. (1.6* without it) Not a bad FOV for a 14.5″ mirror.

From a very happy and experienced owner of a 14.5″f/4.3 Starmaster Dobsonian. Details here.

 

Like every Sky-Watcher scope I’ve tested, this one arrived perfectly collimated out-of-the-box, and has held its collimation over the period I’ve been testing it. This speaks highly of the mechanical integrity of the scope, and alleviates the beginner’s greatest anxiety about Newtonians. No doubt the scope will require collimation at some point, but if it can make it to Canada to from China without losing collimation, it should be pretty stable.

I tested the telescope under the stars on four different nights, exploring a wide range of objects. Well, actually, one night and three mornings, as I was unable to resist the lure of using this scope on my old favourites, Jupiter and Saturn, currently in the predawn sky. I also spent time looking at the Moon, Mars, and Venus, favourite double stars like Epsilon Lyrae (split easily at 120x) and Rigel, and deep sky showpieces like the Ring Nebula and the Orion Nebula. All were well shown, as one would expect in a good quality 150mm scope. The supplied eyepieces, 25mm and 10mm “Super” modified achromats with 50° fields, performed quite well, yielding magnifications of 48x and 120x. This scope showed that it can handle much higher powers easily; I found myself using a 6mm eyepiece (200x) on the Moon and planets most of the time. Fans of deep sky objects will probably want to add a 2″ eyepiece to take in the wide field of view this scope is capable of.

As Terry Dickinson says in NightWatch, “There may not be a perfect telescope for the beginner, but the closest thing to it is the 6-inch Dobsonian-mounted Newtonian reflector.” The Sky-Watcher 150mm is an excellent example of this breed, at a very attractive price. My wife and I usually donate a telescope to our favourite charity to auction off each year, and this year this scope is our choice. Highly recommended!

Source here.

I put together one of his 6″ f8 telescope kits with the help of my kids. It’s still one of my favorite scopes. These days, I lend it to people who have shown an interest in astronomy, but can’t afford a telescope.

Barry Fernelius, from this online thread discussing Stargazer Steve’s kit ‘scopes.

Changing technologies have meant that amateur telescope making has largely been replaced  by the purchase of accessible high quality commercially produced instruments, but the Western world’s passion for the night sky is as strong as ever, and long may it continue.

Dr. Allan Chapman, from an essay entitled: The First Astronomical Societies, Astronomy Now, January 2018, pp 49.

 

Optical quality matters, but these days it’s usually not the main problem. Most of the commercial mirrors I’ve evaluated in the past 10 years have been pretty good — a few have even been excellent. That’s not to say there aren’t duds out there, but if your telescope isn’t performing, the items that top this list are more likely to be the reason.

Gary Seronik, from an online article entitled: Five Reflector Performance Killers.

In this department of astronomy, the names of Herschel, South, Struve, Dawes, Dembowski, Burnham, and others are honourably associated and it is notable that refracting-telescopes have accomplished nearly the whole of the work. But reflectors are little less capable, though their powers seem to have been rarely employed in this field. Mr. Tarrant has lately secured a large number of accurate measures with a 10-inch reflector by Calver, and if care is taken to secure correct adjustment of the mirrors, there is no reason why this form of instrument should not be nearly as effective as its rival.

W. F. Denning, from Telescopic Work for Starlight Evenings (1891), pp 290-291.

Since about a month this telescope is parked in my garage.
It is a Newtonian of 158mm aperture and a focus of 1240mm.The primary and secondary mirrors were made by David Hinds of UK.The telescope was home-made by my friend Tavi aka Erwin.Because he have other commitments, I was offered to give it a ride. I used the oculars seen in the second picture, from left to right: HM 6mm, Galilei – 50 mm, Galilei – 9mm , Baader Classic 6mm Ortho. This are the double.multiple stars observed on 23rd of December. All stars were split except 52 Ori where I believe to see a black space between main star and companion but not 100% sure.I was very pleased to see very well E and F stars in Trapezium.Good telescope, excellent optics, reliable mount……..I continued the testing on 26 of December when I made observations of 36 And, Delta Gem , Theta Aur and Eta Ori. All eas(i)ly split ,beautiful views……………..On 14 of January I targeted 7 Tauri double star. Unfortunately on the rare occasions when the stars were visible, the sky was hazy but still seeing was not better than 5 to 6 Pickering. Like with 52 Ori ,also at 7 Tau double star the Hind telescope showed at 248 x the two touching Airy discs but no black space bewteen them. I have high hopes in good seeing this telescope will split 0.7” double stars.

Mircea Pteancu from an online thread entitled: Double Stars in the Hind 158mm x 1240mm.

Visual report on the 12.5” f/6.5 Teeter Dob with Mike Lockwood mirror.

My eyepiece ‘fleet’ with the 12.5″:

31mm Nagler 67x

24 mm Explore Sci 86x

17.3mm Delos 119x

12mm Delos 172x

8mm Delos 258x

5mm Nagler 413x

6-3mm Nagler Zoom 344x to 688x

The first two nights (Tuesday and Wednesday) of observation were very foggy and absolutely dew-drenched – the most dew I have ever seen. Both nights the main mirror dewed up just after midnight – the joys of a thin 1.1” mirror which tracks ambient temperature very well, I suppose….

Along with the dew was some of the best atmospheric steadiness I have ever experienced. I would place the seeing at 9 to 9.5 (pickering) out of 10. With a 3mm eyepiece (688x) on a 4th mag star near the zenith, the full diffraction pattern was stable and almost unmoving. Unfortunately the transparency was mediocre and, towards midnight, increasingly poor….

The third night (Thursday) was very transparent and drier, with much more manageable dew but the seeing was extremely poor. The close pairs of Epsilon Lyrae were two touching fuzzballs (the night before you could have driven a HumVee through the blackness between…)

I looked at a bunch of double stars the first night… I used my Nagler 6mm – 3mm zoom which gives magnifications from 344x to 688x. Close pairs seen were:

STF 186: sep. 0.8”, mags 6.79/6.84
wide, dark sky split. The dark space was equal in width to the central discs of both components. very delicate first rings were present at all times…

A 1504: sep. 0.6”, mags 8.84/8.92
darkline split. Central discs ‘kissing’… first rings were pretty much too faint to see…

BU 525: sep. 0.5”, mags 7.45/7.47
very deep notch. a black or grey line seemed visible at times..

STF 346 AB sep.0.5” mags 6.19/6.21 This is triple star 52 Arietis. The ABxC pair is at 5” separation… Very nice to see three stars here. The AB pair was a deep notch, again with fleeting glimpses of a line between…

Dave Cotterell, Madoc, Ontario, from an online thread entitled: 12.5″ f/6.5 Teeter Dob with Lockwood Glass.

This report details my visual and photographic observations of some sub-arcsecond double stars that have been the subject of a few CN threads the past few months.  This document is necessarily heavy on technical details to support those who may wish to independently evaluate the results.

Visual observations were made with a 15-inch f/4.5 Dobsonian reflector setting atop an equatorial platform.  All observations were made between September 26th and October 26th of this year with a Paracorr Type I lens (setting no. 1) in the optical train.  In all cases, Pentax lenses were used to achieve the following magnifications:  ‘low’ (5XW; 398x), ‘moderate’ (3.5XW; 569x), and ‘high’ (2.5XO; 798x).

Imaging was accomplished using an ASI 178MC cooled camera [AVI files; mono mode] in an optical train consisting of a Paracorr Type I lens (setting no. 5) and a 5x Powermate.  The plate scale for imaging was previously determined to be 0.0553 +/- 0.001 “/pixel using calibration stars (n = 10) and 0.0553 +/- 0.002 “/pixel using a diffraction grating with monochromatic red light (n = 8).  Sharpcap 2.8 was used as the image capture software.  Fine focus was achieved using a Bhatinov mask [All-Pro, Spike-a brand] modified to fit over the Obsession UTA.  Separation values were determined using REDUC.  Images were stacked and processed using Registax with final presentation formatting in Gimp.

Bu 720, 72 Pegasi
magnitudes:  5.7, 6.1
position angle:  105 degrees
separation:  0.575” (orbital elements estimate); 0.505” (last precise measure; 2015)

The separation data are not in good agreement for this object.  This is, therefore, a good candidate for quantitative scrutiny.

Visual
At 398x the object vacillated on the border between elongated and just resolved to two golden-orange disks of similar magnitude in the correct position angle; 569x proved sufficient to show the stars as different magnitude and clearly resolved (but not yet split); a final increase in magnitude to 798x showed the pair as split, again with a golden-orange color and a small difference in magnitude.  The ease of resolution at modest magnification led me to think the larger separation value [0.575”] was more accurate for Bu 720.

Photographic
Bu 720 was easily imaged using an exposure of 10 ms [gain = 320].  Four movies were made and separation was measured by three methods using REDUC:  cross correlation of the top 5% of frames using S4 filter; simple measure of a Registax composite; and simple measure of a composite generated in REDUC.  There was good agreement across these methods, giving a measured separation of 0.61”.

STT 20AB, 66 Piscium
magnitudes:  6.1, 7.2
position angle:  176 degrees
separation:  0.598” (orbital elements estimate); 0.59” (last precise measure; 2015)

Good agreement between WDS listed separation values.  Should be able to split at moderate magnification.

Visual
Low magnification (398x) shows two white stars that are clearly resolved and are oriented in the position angle as stated in the WDS.  Moderate magnification (569x) shows that the components possess dissimilar magnitudes; the pair was barely split about 20% of the time at this power.

Photographic
STT 20AB was imaged using an exposure of 12 ms [gain = 400].  Four movies were made and separation was measured by two methods using REDUC: simple measure of a Registax composite; and simple measure of a composite generated in REDUC.  There was good agreement across these methods, giving a measured separation of 0.59”.  REDUC Correlation methods were not useful with this target for producing separation values because of the faintness of the secondary.

16 Vulpeculae, STT 395
magnitudes:  5.8, 6.2
position angle:  127 degrees
separation:  0.849” (orbital elements estimate); 0.81” (last precise measure; 2015)

This target possesses a wide discrepancy between WDS values and was discussed at some length in a prior CN thread.

Visual
This object was observed as split using an 8-inch reflector at 340x (3.5XW lens).

Photographic
16 VUL was imaged using an exposure of 14.5 ms [gain = 450].  Four movies were made and separation was measured by three methods using REDUC:  auto correlation of the top 5% of frames using S4 filter; stacked REDUC reductions; and simple measure of a composite generated in REDUC.  There was good agreement across these methods, giving a measured separation of 0.771 +/- 0.006”.  Previous REDUC autocorrelation measurements of this system using a 2x Powermate [plate scale = 0.143 “/pixel] gave a measure of 0.78 +/- 0.02”.

 

Mark McPhee, Austin, Texas, from an online thread entitled: Examination of Some Sub-Arcsecond Doubles: Bu 720, STT 495, Bu172AB, STT 20AB, and 16 VUL

 

Currently, my only objections to the short f/ratios becoming common are that the depth of focus is very short, making focus variability in mediocre seeing a bit more of a problem than in longer f/ratios, and that most eyepieces don’t perform as well at the edges at f/3 as they do at f/5, even when both are Paracorred with the latest Paracorr II at the correct setting. But, that being said, I would still unhesitatingly choose a fast f/ratio at the really large sizes of scope simply because it’s easier and safer to stand on the 3rd step of a step ladder than it is to stand on the tenth (!), and I’ve done that in a 36″ f/5.
Along the way of large scope progress have come better cells, thinner mirrors, better fans, and better collimation tools. Put those all together, and the performance level of the large scopes seems now to be only limited to the mirror qualities, and there are makers of large mirrors now who put the same quality into their mirrors as some of the better makers who stop with much smaller sizes.
I truly wish many of you had seen the poor quality large scopes over the years that I have seen. If you had, you’d realize how we truly live in the Golden Age of Astronomy right now.
Don Pensack, from a thread entitled: Large/Fast Newtonian Mirrors and Quality.
I thought I wanted a 140 class APO. The image and fantasy of it has been kicking around in my mind for most of the year. They’re such nice looking telescopes – what a telescope is supposed to look like. At a major star party a few weeks ago, I found a beautiful 140 – a very well-known top quality model mounted atop a big G11 and I asked the owner if he would please show me M15 in it. He was proud to do so and we looked. He raved and I was silent. I thanked him and walked back to my premium 16″ Dob. Looked at M15 in the 16 and raved to myself saying I’m so glad I have the 16. For the same amount of setup and money, what a difference!
Peter Natscher, Central Coast, California, from an online thread entitled; How much increase in aperture to see a difference?
 Ps. Peter is the proud owner of a couple of large premium Dobs and an Astrophysics 175 EDF apochromatic refractor.

yea sometimes (like this evening) I ask myself too: “why you silly id… buy all this expensive apo stuff???” :)

Cloudy for the whole day – this evening reported to be one of the most interesting of the year – Io & Europa before Jupiter – together with their shadows and crowned by the GRS. Before 1,5h I saw a break in the clouds and to be fast I just grabed my 8″ GSO Dob and took it out. After 30min cooling another break off – I could see so much detail in the bands, GRS shining in a bright red, both shadows, Europa just beginning to leave the planets disc and – man – I could swear to see a round structure in the band that could have been Io… – best experience for a looong time! :)

So go get a 8″ f6 Dob – Houston out

Donadani, Germany, from an online thread entitled; How much increase in aperture to see a difference?

 

 

Hello Peter [Natscher],

Hope you are well.

An 8 inch Portaball with a Zambuto mirror on a tracking platform is going to show you much more than a 130mm telescope, even a Starfire 130EDF. Both of these will be sit down and observe telescopes. If you were not going to get a tracking platform, I would go the refractor route. You will want tracking for dedicated planetary or lunar observing. Shoot, you could roll the dice and get a Sky-Watcher 8″ f/6 collapsible Go-To dobsonian. I have the non motorized version and it has a great mirror, however, your mileage may vary on the chinese mirrors.

Tony M, from an online thread entitled: 5″ Refractor or 8″ Newtonian for Lunar/Planetary Observing.

I would take a high-quality 8″ f/6 on a GEM over a 5″ refractor. The GEM will negate all the disadvantages of the Dob. My old Meade 826 easily gives me a sharp, detailed Mars at 400x (conditions willing). I wouldn’t trade it for any 5″ scope ever made.

Rick Woods, from an online thread entitled; 5″ Refractor or 8″ Newtonian for Lunar/Planetary Observing.

I may be too late to add my .02, but it should be valuable.

I have owned a AP130EDF and the GT model. I now own an 8″ f/5.5 Portaball.

My conclusion: The Portaball rips the APs to shreds. A perfect 8″ mirror over a perfect 5″ lens…no comparison, obviously assuming collimation and thermal equilibrium. Especially since the Portaballs are constructed with fans and other ergonomics to help with the thermal adjustment. And I’m solely talking about visual planetary, since that is almost exclusively what I do.

Markab,  Kansas City, from an online thread entitled: 5″ Refractor or 8″ Newtonian for Lunar/Planetary Observing.

One should never lean too heavily on sketchers. Although the vast majority are genuine, some go to an imaging website, study a particular image, and fake a sketch. In this way, they can make a 4 inch peashooter telescope look better than a Hubble image. I’d put more faith in the unlying eye of a CCD camera than any sketch, however elaborate.

Mr. Hardglass.

A major reason refractors give images with higher overall contrast than reflectors is that objective lenses may scatter only approximately 2% of the light passing through them. This is why I believe that the high refelectivity coatings that are now applied to many astronomical mirror surfaces are so important. With 95% reflectivity, not only will they give somewhat brighter images but they will also greatly reduce the amount of scattered light, so improving the overall contrast. A high reflectivity coating is well worth having even at an additional cost; not only will the telescope perform better but a second advantage is that the mirror surface allows far less moisture to penentrate and is likely to last perhaps 25 years before it has to be recoated. I have a 10 year old Newtonian whose mirror was one of the first to be given a high refelctivity coating and it still looks like new………The overall design of the telescope will affect the overall contrast as well. It is impossible to beat a well designed refractor, but Newtonian telescopes, where one observes across the tube assembly to the far wall, are almost as good.

Ian Morison, from An Amateur’s Guide to Observing and Imaging the Heavens (2014) pp 10.

 

A Newtonian for All Round Use

A very good compromise in designing a 200mm Newtonian is to use a focal ratio of f/6, and many such telescopes are sold with this basic specification. The focal length will thus be 1200mm, and the field of view when a low power, wide field, 2 inch eyepiece is used will be approximately 2 degrees. The secondary mirror willprobably be approximately 50mm in diameter, and this would give a percentage of obstruction of 25% and provide full illumination over the central 25mm diameter region of up to 46mm diameter field of view. This is a good compromise, but some manufacturers, such as Orion Optics in the UK allow the purchaser to choose other secondary diameters should he or she wish to optimise the telescope towards planetary (approximately 36mm) or widefield imaging (approximately 60mm). One could even purchase two flats for use depending on the type of observations planned for a given night!

Ian Morison, from An Amateur’s Guide to Observing and Imaging the Heavens (2014) pp 64.

 

Yes, I have active cooling for my 10″ Dob. For that scope, a fan in a baffle below the primary works fine. I have an EdgeHD 8″, a SW120ED and a 10″ solid tube Dob, and I know how Jupiter looks in all three. No 7″ APO in the stable, but aperture does count for something. Some of my best views of Jupiter have been through the 10″ Dob during early morning. All of my best views of Jupiter have been through the 10″!

Sarkikos, from an online review of the Celestron EdgeHD 8 inch SCT.

 

Making a good 8 inch Newtonian by Toshimi Taki (Japan).

I think I can speak with at least a little credibility on this subject, having owned numerous large refractors:
TeleVue 140
NP-127
One of only two Christen 6″ f/15 folded Triplets
Takahashi FC-125
Takahashi FCT-150
8″ Alvan Clark
and having used several other premium 8″, 10″ and 12″ refractors.
As a recovering “refractor-holic” I still crave their look, fit and finish. And inch-for-inch they can’t be beat. But an 8″ or larger refractor w/mount is a true BEAST to own unless you can leave it permanently mounted. Topping it off there’s that little thing called “COST”!
Once we started having master mirror makers like Carl Zambuto et.al. turning out mirrors that were simply without compromise, optically – the paradigm shifted!
A premium 12.5″ reflector today will simply blow away that beautiful old 8″ Clark. My present 14.5″ Ed Stevens mirror produces planetary images that are superior to anything I ever saw in a 10″ Zeiss triplet and pretty darn close to the 12″! And don’t even get me started on comparisons with my 28″ Starstructure w/Steve Kennedy mirror! This scope is fully driven and features GOTO, yet I can set it up, take it down and transport it (easily) all by myself. Try to picture what a 20″ refractor would look like and cost…that’s about what it would take to begin to match the performance!
Would I love to have a giant TMB set up in a dome behind my house? Sure! But not for ‘performance’ reasons.

Mike Harvey (Florida), from an online thread entitled: Refractor Versus Reflectors.

My 6″ refractor [AP 155] will show the arms of M51 from a dark site, but fairly subtly. It’s far behind what my 10″ Dob can do in that area.The inability of the refractor to show much spiral detail in galaxies is probably its greatest drawback as a deep sky instrument.

Joe Bergeron, (Upstate New York), from an online thread entitled: Refractor Versus Reflectors.

My advice to everyone wanting better planetary views is is to always spend money on a better instrument, or make their instrument better than it is.   An 8″ f/6 reflector with a high quality mirror is one of the best planetary scopes money can buy.  Period.  Don’t be duped into thinking a 6″ MCT is going to be better. Physics simply do[es]n’t permit it.

Ed Moreno, from an online thread entitled:8 inch f/6 Dob versus 6 inch Orion Mak on the Moon and Planets.

I’ve tried a single curved spider in my 8 f7.6, but went back to the straight 4 vane after a year. Didn’t notice even a tiny hint of more fine detail on Jupiter with the curved vane.

Planet Earth, from an online thread entitled: Curved Spider Vanes?

The idea of curved-vane spiders isn’t new — the concept has been around for a long time and several designs were detailed in the May 1985 issue (page 458) of S&T. For telescopes up to 12-inch aperture, a curved spider can be a good alternative to traditional 3- or 4-vane spiders. With larger scopes, the diagonal mirror typically becomes big and heavy enough that the greater rigidity offered by conventional spiders or more robust curved ones may be required. I’ve successfully used the design described here in numerous telescopes, including my 12¾-inch. My single-curve spider has the added benefit of being simpler than the ones in the 1985 article, and therefore easier to build.

Gary Seronik, from his online article: How to Build a Curved Vane Seconday Mirror Holder.

This is essentially an aesthetic issue. If you don’t like spikes, then go ahead and get a curved vane spider. It does eliminate the spikes. You will see an even glow around bright objects like Jupiter or Venus, and nothing around everything else……..If the spikes don’t bother you, then stick with a straight vane.

Jarad, from an online thread entitled: Curved Spider Vanes?

I have put a 6″ APO up against a mass market 8″ f/6 reflector and I can tell you that the 6″ APO overall is a better performer. It is sharper everywhere in the field, had better planetary contrast, and came SURPRISINLY close in terms of deep sky (Globular and Galaxy) performance.

But this didn’t have much to do with the fact that it was a refractor vs a reflector, but rather more to do with the fact that is is a virtually PERFECT refractor up against a telescope with optics that were only “Fairly good” optically.

But.. IF you were to put a TOP QUALITY mirror in your scope, along with the highest quality diagonal you could find, you would find that on axis, it would indeed take refractor very close in size to yours to give a better visual image at the center of the field.

Ed Moreno, from an online thread entitled: Refractor Equivalent to a 8″ Reflector.

A good 7.1″ refractor is very close to a good 8″ reflector on M13. For planetary resolution most of the time the 7.1″ refractor beats the good 8″ reflector. But, they can be very close on a good night.

Rich N (San Francisco Bay Area), from an online thread entitled: Refractor Equivalent to a 8″ Reflector.

As I mentioned earlier in this thread my experience is that a 7.1″ refractor is very close to an 8″ Newt.

I’ve had my AP 180EDT f/9 APO side by side with a friend’s well made 8″ Newt a number of times. My refractor is more consistant in giving high contrast, high resolution images but on the right night that Newt can give some fine planetary images. For deep sky the views are very similar.

Rich N(San Francisco Bay Area), from an online thread entitled:Refractor Equivalent to a 8″ Reflector.

 

I’m not talking about local seeing from night to night. I’m suggesting that if you set up a high end APO and a high end Newt of roughly the same size (maybe a 180mm APO and 8″ Newt) side by side over several nights, the APO (refractor) will more often show better high res, high contrast, planetary detail.

Rich N(San Francisco Bay Area), from an online thread entitled:Refractor Equivalent to a 8″ Reflector.

No, a well crafted 8″ reflector with a Spooner f/7 mirror will totally outclass not only 5 or 6″ achros, but 5 or 6″ apos as well. And look at the original posters question again. He was wondering if an 80mm refractor would equal a 6″ reflector or a 100mm refractor would equal an 8″ reflector. No, and it’s not really close. And if you can tie your shoe you can collimate a reflector and clean the mirror once a year.

And my 6″ $250 Orion 6″ f/8 Dob has run totally neck and neck with my buddy’s Tak 102 on more than a few nights on the moon and planets. And it’s beaten the 4″ apo on some nights. Same result with a TV102 and a Vixen Fluorite 102. And it beats my TV85 and his Tak 78 100% of the time. Myths die hard.

Quest Do Not Delete, from an online thread entitled.Refractor Equivalent to a 8″ Reflector.

I routinely compare 6″ APO to 7″ and 8″ Zambuto reflectors – see my sig for specifics. I am a dedicated planetary observer and really enjoy such comparisons.

Basically, I’ve found that the 8″ Z-mirror when cooled will be ever so slightly better then the 6″ APO. And the 6″ APO will edge out the 7″ reflector. The 6″ APO, an FS152, is a doublet and does not focus all colors to a common point as a matter of design. The blue is thrown way out of focus so the image has a slightly warmer look to it then that of the reflectors. I have often wondered if a triplet was compared to a the 8″ reflector how it would perform. Probably the same as the doublet as resolution is primarily a function of aperture.

The differences are quite minor in good seeing. But when the atmosphere is unsteady, I prefer the views in the FS152 over everything.

Peleuba(North of Baltimore, MD), from an online thread entitled: Refractor Equivalent to a 8″ Reflector.

I have a nice C6-R with a Chromacorr, and a nice 8″ f8 newt with a very fine Raycraft Primary, Protostar secondary, and flocked interior. I can’t recall offhand the size of the secondary, but it’s scaled for my 2″ EP’s, so it’e bigger than is optimal for planets.

Aestheticly, I find the refractor better, especially on evenings of dropping temps. I know the refractor has to cool too, but the views seem to be sharper sooner, and I never see tube currents.

The newt does reach deeper, though. But, I generally like to see sharper than deeper for the kinds of things I use the refractor for (planets and clusters). When depth is the concern, I opt for more aperture.

Under ideal conditions, I’m sure my 8″ newt will out-perform the refractor. But, conditions are rarely ideal, and so the edge goes to the refractor– tends towards better sharpness and better contrast due, I think, primarily to the lack of tube currents and cooling time.

Apples to Oranges, though.

Kerry R (Mid West Coast, Michigan), from an online thread entitled: Refractor Equivalent to an 8″ Reflector.

I will go toe to toe with any 7″ or 8″ APO with my 8″ F8 Newt and my Dan Joyce 8″ f/6.7 Newt. In the end I paid very litte for both Newts, and the 8″ APO owner has paid big time for the 8″ APO and it’s mount.

Had my share of 5″ to 7″ APO’s and they just dont cut it for such a high price. They do give that super fine snap to focus image, but my well built 8″ Newts can pretty much do the same thing and cost 50x less.

CHASLX200 (Tampa, Florida), from an online thread entitled; Refractor Equivalent to an 8″ Reflector.

8″ f/6. You’ll get a little better contrast with an unobstructed scope and imperceptibly brighter image because of light loss on a reflective surface. You won’t have coma on a refractive system, but you won’t have the huge amounts of CA with a Newt that you would have with an 8″ f/6 refractor.

Aperture, aperture, aperture. That’s what matters. A high quality, thermal controlled reflective system will give up very little to a similar size refractor.

Deep 13 (NE Ohio), from an online thread entitled: Refractor Equivalent to an 8″ Reflector.

 

Recognizing that everyone has their own opinions and preferences, here is my opinion and preference based upon 45 years of telescope ownership which by inventory would include something like about 40+ mounted telescopes and numerous guide scopes that would add about 15 or so more to the mix. I have had all types of scopes including both apo and achro refractors, maksutovs, schmidt-cass, newtonian reflectors (both equatorially mounted and dobsonian). While different telescopes are suited for different purposes, my overall preference is the refractor for a number of reasons, in particular the apo refractor of which I have owned 8 different apos. I also enjoy the classic long focal length achro refractor and have extensive use and ownership experience with Unitron refractors………………From my personal experience and in general for most applications my rule of thumb would be that a Newtonian would have to “out-aperture” a refractor by about 33% to be roughly equivalent for most applications. Accordingly the statement that a 6″ refractor is equivalent to an 8″ reflector is for the most part, pretty valid.

Barry Simon ( New Orleans, LA), from an online thread entitled; Refractor Equivalent to an 8″ Newtonian.

 

My guess is that a great 5 inch apo refractor would equal an average 8 inch mass produced mirror and it would take a great 6 to 7 inch refractor to equal a great 8 inch reflector. A generic 10 to 12 inch mirror will beat or equal any refractor under 8 inches. These guesses are based on real world observing at most objects. There are always exception.

Wade A. Johnson (North Central Iowa), from an online thread entitled; Refractor Equivalent to an 8″ Newtonian.

I have done the side-by-side during a couple of well attended starparties. My well collimated and optically very good C8 performed extremely similar to a very good Meade 6″ APO on Jup[i]ter on a night of exeptional seeing. The refractor edged it out with better contrast. No surprise. Compared to a home made 8″ Newtonian with a small 20% obstruction the images were almost impossible to tell apart.

So, my answer to the original question is: 6″ refractor.

I think we are finally well past the myth of a 4″ refractor being “sharper” or “showing more” than an 8″ reflector.

Contrailmaker, from an online thread entitled: Refractor Equivalent to an 8″ Reflector.

 

This old and tired conversation just seems to drag on and on, using the same old arguments that fly in the face of both common sense and physics. Drop it…let’s all agree that a 6″ Apo costing $7000 is a bit better than an 8″ F5.9 reflector costing less than $1000.
Which one would a sane person on a budget buy?

Covey32 (Georgia, USA), from an online thread entitled: Refractor Equivalent to an 8″ Reflector.

I would politely disagree to this. I looked through an excellent 5″ apo (my old Tak TOA-130S) and a very good 8″ Newt (8″ f/7) at Jupiter and Saturn. My Tak was soundly beaten by the views through the 8″ Newt.

Alvin Huey (Greater Sacramento) from an online thread entitled: Refractor Equivalent to an 8″ Reflector.

If you are talking about a ~5″ Apo like a 120ED, then yes they do give very nice views, but the 8″ f/6 Dob will still show you more detail and at 1/4 or less the price.

I think the views in the 5″ f/9.4 achro refractor I have are good, and on some nights they really are very good, but I have done quite a few side-by-side comparisons with my 10″ Dob over the past few months and as a result…the frac is back in it’s case in the shed and the Dob is by the back door ready for action whenever there is a break in the clouds.

RikM, (Gloucester, England), from an online thread entitled: 1st Planetary scope: Refractor vs Dobsonian.

Quote: “f-ratio is important. A 6″ f/11 might very well best an 8″ f/5 on most typical nights observing planets,” End quote.

Focal ratio is not relevant it’s the size of the obstruction that matters. So long as the secondary obstruction is under 20% of the primary diameter by area, the scope behaves like an unobstructed instrument. More than 20% and you start to see its effects. The effect you see isn’t due to light loss it’s due to increased diffraction caused by the large circumference of the secondary. This decreases contrast. However, there’s no reason a 25% or even 30% obstructed scope can’t perform very well. Why? If the scope is already a large aperture instrument with good optics then even with a hefty central obstruction it can still show superior contrast and detail. Optical quality and aperture matter more than focal ratio. I see this every time I observe Jupiter at f/4.

Umadog, (Basel, Switzerland), from an online thread entitled, 1st Planetary scope: Refractor vs Dobsonian.

My Skywatcher 8″ F/6 Dob beats my 5″ F/8 Apo [Takahashi FS 128] on the planets ……

post-13701-133877687106_thumb.jpg

Dweller, (Lancashire, UK), from an online thread entitled: 1st Planetary scope: Refractor vs Dobsonian.

 

Indeed, this is the point. The reason that beginners should be steered toward f/6 Newts is because this is a cheap way of getting good images. The mirrors are easier to make well and the eyepieces need not be expensive. Coma correctors aren’t necessary. Large (and fast) can be better, but quality is a lottery if you’re buying Synta or GSO, although those manufactures can produce some nice stuff. If you go home-grown you have a much better chance of a good mirror but you’re paying a lot more for it. In the end a lot of this comes down to economics not optics. Finally, there’s the hassle factor. To get the best out of a refractor you don’t have to do anything very special. To get a good view out of a Newt (particularly a big one) you have to plan ahead with cooling and collimation.

Umadog, (Basel, Switzerland), from an online thread entitled, 1st Planetary scope: Refractor vs Dobsonian.

If you have been dreaming of the day when the Chinese are able to make a portable 8 inch APO for under a thousand quid, keep dreaming! Seriously, this is not going to happen any time soon because APO-quality 8” ED blanks from the major suppliers (Ohara and Schott) don’t exist and if they did would be hideously expensive. Even if the glass was available, big APO lenses will always need a lot of highly skilled hand finishing along with very careful assembly in a sophisticated cell. The only major suppliers of big APOs today – TEC and APM/LZOS – charge the price of a new BMW for an 8” and if that situation changes it will be because they start charging even more! Then there’s always the Takahashi FCT-200 with a list price of $125,000 (but at least it includes the mount).

On the other hand, if you dream of getting similar performance to an 8” APO for under a thousand pounds, then dream no longer. Long focus Newtonians have always been simple to make well and with the advent of interferometer testing they can be made to an exceptional level of optical quality. Add in the possibility of a very small central obstruction, easy collimation and just two light scattering surfaces and a long-focus Newtonian has the potential to perform closer to a big APO than almost any other design.

Roger P. Vine (Welwyn, England), from an online article entitled;Orion Optics 8 inch Planetary Dobsonian Review.

In a Newtonian 8″ to 12″ with small central obstruction under 20%, very thin spider, longish F ratio above F6, excellent tube construction with well ventilated mirror and a decent flotation mirror cell (no mirror glued to plywood). Shorter F ratios require that the object be exactly centered in the field to avoid comatic aberrations. Also, the shorter the mirror, the more you will have to fiddle with the collimation. The mirror should have the best coating you can afford, avoid cheap coatings that lose contrast over time. Get a coating that you can clean without introducing pinholes. Add to that a smooth functioning focuser and you will have a very effective planetary instrument.

Roland Christen (founder of AstroPhysics, IL, USA), from his online article entitled: What is the Best Planetary Telescope?

I’ve compared my ED120 refractor (4.7″) with a number of Newtonians and have concluded that it will match a good 6″ Newtonian in planetary and lunar detail but the additional aperture will show deep sky objects just a little better.

John Huntley, from an online thread entitled: 150mm Refractor versus 200mm Reflector?

I am a confirmed dobaholic so the only choice is an 8″ dob between these two. The issue really is that unless spending 10x your budget or more, a 150mm refractor will provide less impressive views of low power faint objects and more faults with high power bright objects than an 8″ Newtonian. I’d also consider it more unwieldy and heavy/difficult to use than an 8″ dob. The one exception to the above is for wide open clusters where the frac will provide slightly more attractive views I think.

For me at that sort of budget an 8″ newt/dob is about as good as it gets.

Moonshane, from an online thread entitled: 150mm Refractor versus 200mm Reflector?

 

I’m a refractoholic but I have to admit that Shane is perfectly right on all counts.

Olly Penrice, from an online thread entitled: 150mm Refractor versus 200mm Reflector?

My STS and his have been under the dark skies of Landis a few times since. On one particularly memorable occasion, in May of 2015, our Teeters were out there alongside two world-class apochromatic refractors, the FS-128 and the comically coveted AP130. Given all the high-end gear, it felt like some star party of the aristocracy. My friend, who knows next to nothing about telescopes, was on hand. How could he possibly fathom the privilege of looking through such fine gear. Not until several years in the hobby, did I get my first eyepiece time with an Astro-Physics refractor or a Newtonian with Zambuto optics. There was, in fact, a 5th telescope on hand: a 4.5” Tasco — hey, every aristocratic star party needs a peasant scope. The FS-128 owner kept trying to pawn off the Tasco to my friend but he refused. (My friend later regretted not taking it). The modest scope did show Saturn nicely. In fact, on this night the seeing could not have been better. We were all treated to awe-inspiring views of the ringed gas giant, arguably the best I’ve ever had. On this night, Saturn would have looked great in about anything, but the two best views were to be had by the Teeters. My friend, who had no skin in the game (so to speak) or reason to be biased, attested to the “cannon ones” affording the best views of Saturn.

Daniel Quirin, from his online review of the Teeter STS18 (8″ f/6) Newtonian.

Once again, these Newts just floor me! Refractors will always be beautiful, but it’s hard to justify a $250,000 refractor to an $8,000 Newtonian that’s beating it. The fact is, is that if you dial the Newt right, your gonna win. Pons has been observing planets for 50 years. He’s earned the right to decide what he thinks is best and he’s got the best of both worlds to prove it.

When I asked him which scope he liked better on planets, he said the Newt was king, hands down and it’s as simple as that. He has no shame in saying so, d[e]spite the fact that he’s spent a good part of his life and a lot of money building the refractor.

People always try to challenge me in a debate. Then they look through one of these Newts and they’re quickly silenced. Pons always told me that they’ll always try to argue, but they’ll quietly go back to their garage and start trying to build a perfect Newtonian on their own.

Daniel Mounsey from an online thread entitled: Refractor vs. Reflector?

 

Yes, a 4-5″ APO will be very good, but the smallest detail it will resolve on a planet is around the 1 arc-second diameter mark. Resolution is tied intrinsically to aperture. It doesn’t matter how good the optics are or whether you’ve got 99.8% Strehl ratio optics etc, it won’t (indeed can’t) do better than this.

A clean, well-cooled and collimated, say 10″ f/6 or f/7 Newtonian with quality optics around 1/25th wave RMS mark and a secondary obstruction <20% in near perfect conditions will do twice as well as the 5″ APO in the same conditions — ie in the smallest detail to be potentially visible. It will probably cost little more than half as much. If the seeing is mediocre or poor there will be little difference in detail visible except in those occasional moments when clarity prevails for a moment or two — and the Newtonian wins again. The larger ‘scope will produce a significantly brighter image that will take much more magnification before it becomes unacceptably dim and uncomfortable to view.

Don’t get me wrong, refractors are beautiful telescopes inch for inch, but they are practically limited in aperture. (well they are aperture-limited by the depth of your pockets I guess). Aperture of the primary mirror/lens is the prime determiner of how much detail is potentially visible in a planetary image.

In poor, mediocre or average conditions a SCT of similar size to our Newtonian will perform about as well on planetary detail as the Newtonian. In very good conditions or excellent (rare) the Newtonian will produce a somewhat crisper image due to the much smaller secondary mirror used. It is a simple matter of physics due to the size of the secondary obstruction and the wave-nature of light. Increase the secondary mirror size and you push more light out of the Airy-disc and into the surrounding diffraction pattern. As Foghorn Leghorn said to the young chicken-hawk “Son yer can argue with me, but yer can’t argue with figures” — and that’s a fact, not an opinion!

Also, it is a simple fact of life that in a typical commercial SCT used with a diagonal, you need to get 5 optical surfaces right for it to work well. In a Newtonain there are only two.

If you are looking for a quality, visual-use, portable “APO killer” for an Eq6 mount, get yourself an 8″ f/7.5 Newtonian with a 25mm secondary. Longer focal length Newtonians are easier to collimate and much more forgiving of slight errors. Additionally, they are much easier to fabricate! Your eyes (and bank-balance) will thank you for a long time — it will flog the pants off any 4″ APO on any subject in the night-sky save perhaps ultra-wide field viewing. The image will be 4x brighter at a given magnification and will show twice as much detail in the right conditions.

Les D (Australia), from an online thread entitled; PLANETARY VIEWING ?? -aperature rules?or telescope type?

Unless your mirror is absolute and total trash, the reason is cool down, collimation, or seeing. Sounds like you took care of cool down and collimation so… Seeing.

Big scopes are able to resolve more, so they are subjectively more affected by poor seeing. I noticed this last night. I set up my 15″ next to so[me] nice Apo refractors, and stars looked better in their scopes. Seeing was exceptionally bad for me last night, stars were bloated little orbs over 150x, but they looked fine in the refractor. Peering at the moon, I didn’t see that shimmering you describe, but defocusing a star I could see very very fast upper air movement.

Now I know my mirror is not trash, it’s actually quite good and I’ve seen pinpoint stars at 300x in it and views of Jupiter that look like photographs. Last night, I couldn’t even see the GRS. So on nights of bad seeing, a small scope will be subjectively better because it isn’t big enough to resolve the poor seeing, at least not as well as a larger scope. That’s normal.

I[t] beat the pants of[f] the refractors on M13 though, and the Leo triplet, and M104, and M51… Shall I continue the list?

Brian Carter (Atlanta, Georgia), from an online thread entitled:Jupiter in my Dob vs Refractor?

Are those little apochromatic refractors really better than reflectors? They certainly have been advertised as such. In fact, refractor manufacturers have always alleged that reflectors are, well… just a little less than the ultimate – workable, useable, but really not first rate – images just a little sour. And in fact, many a view through a reflector confirms the sour image reputation. Views through refractors are invariably sharp and crisp, neat and gratifying to the eye. But are reflectors really a poor man’s telescope, a less than optimum instrument? As you might imagine, I don’t think so. And here is why I think not and why the “super little refractor” thing is just another load of advertising hype……….

While a Newtonian reflector of aperture and design proportions sufficient to function as a serious instrument for lunar and planetary observing is not going to be as readily portable as a small refractor or Schmidt Cassegrain or Maksutov instrument, such an instrument will optically match or out-perform all other forms of astronomical telescopes inch for inch of aperture in larger sizes. The problem is that such a Newtonian reflector requires slightly more care and consideration in use, but will be considerably less expensive to construct than any of the other telescope types. The point to emphasize here is that the Newtonian reflector is in no way a substandard instrument when compared to other compound reflecting optical systems or refractors. It is every inch the equal of these instruments, and, I believe, in many ways superior. Design the instrument well, construct it out of quality materials and with care, and fit it with quality optics. Give the instrument chance and it will absolutely amaze you.

Robert F. Royce (professional optician), from his article, Reflector vs. Refractor.

As early as 1972, the renowned British telescope maker E.J. Hysom conducted a careful series of experiments with mirrors of various diameters and thickness using a sensitive thermocouple. Hysom determined that a 30mm (1.2 inch) thick mirror cools at a rate of 3.3°C per hour, while a 76mm (1.8-inch) thick mirror cools at a rate of only 0.9°C per hour.
With the aid of a fan these rates could be increased by a factor of three.
Thomas Dobbins, from an online article entitled: The Recent Evolution of the Planetary Telescope: Part 2.

An 8″ mirror doesn’t have these thermal stability issues that are fundamental to larger apertures. Cool-down is relatively quick as long as you have a pyrex mirror. An 8″ plate glass mirror with a fan will also cool down quickly.

8″ f/8 newts (provided they have a solid/split tube design) can be staggeringly good planetary scopes. Wholly apart from the materials costs of refractor glass, you’re more likely to get a perfectly figured optic than you are with an apo. Refractors have more optical surfaces that have to be accurately figured (4 in a doublet, six in a triplet) whereas a newtonian only has one. At f/8, if using a low-profile focuser, the central obstruction is miniscule and the increase in contrast over a shorter focal length newt can be dramatic. Also, using a single-arc two-vane curved spider like a protostar can go a long way towards minimizing overall diffraction. Also at 8″ or less, the flexure inherent in that design is negligible enough not to affect performance.

Zamboni, from an online thread entitled: OPT 8″ f/9 Planet Pro Dobsonian.

 

The Astronomers Without Borders’ One Sky Newtonian; an affordable but good quality, ultraportable 130mm f/5 tabletop telescope.

We have 4 scopes that always see some use. A 8″ F8 Newt (Dob mount), a 111mm APO (actually, a lot of 4″ refractors), a 16″ SCT and a 17.5″ F4 Newt (dob). The 8″ has some of the best optics I have ever had the pleasure to use, a true one of a kind scope. Planets are fantastic through it. Actually, pretty much everything is. But, when I want to look at galaxy clusters or similar, the 17.5″ is the scope. When I want to study the details in planetary nebula or small single galaxies, I like the 16″ SCT. On exceptional nights, the 16 is great on the planets too but those nights are far and few between here in the Great Lakes State (only 1 really comes to mind in the last 10 years…).

Jason B, (Michigan, USA), from an online thread entitled: 1 inch Apo vs 12 inch SCT.

Under the stars, this telescope really shines now. It really is nearly the equal of my 10 inch f/6, a ‘scope I have been told by many who look through it, has Zambuto like quality. Planetary detail is excellent. Deep sky is just great. I find myself surprised over and over again by this telescope. The figure on that primary is just excellent. We did not touch what the original guys at Cave Optical did with the figure, we just recoated it. I reviewed this ‘scope on the Todd Gross astro equipment ratings site, and I’ll tell you now what I said then. If you like vintage ‘scopes and you don’t have one of these, try to find one. You won’t be disappointed! 

Edward Conley, (North Branch, MI, USA), from an online review of a Classic 8″ f/7 Cave Astrola Newtonian.

FWIW Rolando [i.e. Roland Christen] said the best view he ever had of Saturn was through a 12.5″ Cave – 800x was no problem.

deSitter, from an online thread entitled: Cave Telescope Estimate of Worth.

Jupiter on the morning of October 8 2010 by Jason H ( Central Florida, USA); afocal footage from a Criterion RV 8 f/7 Newtonian reflector.

When I rece[i]ved my 6″ F/8 Criterion RV-6 I was amazed at the detail I could see on Jupiter. Since then I have heard many others say how well their RV-6 scopes performed. Why did these scopes seem to perform so well? How do they compare to “modern”: Newtonians like Zambuto mirrored scopes?

Jim Philips (South Carolina, USA), on an online thread entitled: Criterion RV-6 Dynascope.

Well I always like to have an excuse to repost a picture of my restored 1960 or 61 original RV6. Yes the optics are as good as everyone reports. I agree with what others have written that the 6 inch at f/8 is relatively forgiving and if well made performs excellently even with a spherical curvature. After seeing a neighbors RV6 outperform my Astro Physics 6 inch f/8 triplet,(early model), I sold the refractor and restored my RV6 to almost like new condition.

Bill Nielson (Florida, USA), on an online thread entitled: Criterion RV-6 Dynascope.

 

Went to my club Saturday nite and happened to set up right next to a gentlemen who was using a 5 inch Takahashi refractor. I was using my 8 inch Orion Intelliscope. We struck up a conversation and soon began swapping scopes on different targets. Now as some of you know, i got the Dob to tide me over while saving fro a premium APO. Well, to make a long story short, my lowly, mas produced mirror beat the state of the art fluorite lens on every single target, planets included. Interestingly, it wasn”t i who first acknowledged this, it was the guy who owned the Tak. He kept bringing his own ortho eyepieces over to my scope, and shaking his head. As a recovering CRF, this was very validating for me. I am really no longer seeing any advantage at all to ultra expensive refractors. Not to mention that, while stunningly beautiful, and well made to say the very least, his scope and mount combo is a boat. Mine was out and ready in under 5 minutes. In conclusion, I am no longer aspiring to get the 4 to 5 inch APO, rather my next upgrade will be a 12 inch newt, which, because of cost, can happen a lot sooner. Personally, at this point, I see refractors as excellent, rugged, grab and go travel scopes. I am quite happy to be in the reflector camp at the moment.
Jonnyastro, from an online thread entitled 8 inch Newt vs 5 inch Apo.
Aperture rules and a lot always depends on the seeing which is the great equalizer, but a well made Newt with a reasonably small secondary mirror can be a great planetary scope. The secondary mirror will always lower contrast compared to the unobstructed Apo, but the higher resolution of an 8” brings something to the view that the 5” telescope can’t.

Snart, from an online thread entitled 8 inch Newt vs 5 inch Apo.

I just got back from a weekend star party and pretty much had observed the same thing. My well collimated DOB showed more and better than anything that had less aperature. Since I cant afford anything in the APO category, it left me pretty pleased with my equipment…….. VERY encouraging. I guess my homework and the help supplied from CN has led me to the right stuff!

 

Steve k, from an online thread entitled 8 inch Newt vs 5 inch Apo.
The hang up over reflector verses refractor seems to originate in the 1950’s-1960’s. Even Patrick Moore will say buy a three inch refractor or a six inch reflector.
However times and tech have changed. It just takes time for the astro community to accept this. I own a 14 inch reflector and I also own an 8 inch mak. I have also owned a five inch apo. The most used scope is the 14 inch reflector. I have been into astronomy for 30 years, I have been very active and I know my stuff.
Don’t forget if someone buys an apo for $2000 they want it to out do any other type of scope that costs a third less,their opinion will rely on the cost. It is human nature.
Gordon, from an online thread entitled 8 inch Newt vs 5 inch Apo.
It just boggles my mind that a piece of equipment costing in the three hundred dollar range can outdo one costing in excess of 5000 with mount.
Jonnyastro, from an online thread entitled 8 inch Newt vs 5 inch Apo.
 

Being a newt guy, I’d agree that an 8″ reflector can beat a 5″ apo refractor. However, I would point out a few things: The newt may require more cooldown time, and it may be more affected by seeing conditions, tube currents, etc. The newt will show diffraction spikes around bright objects unless a curved spider is used, while the refractor will obviously not. The refractor may show a “cleaner” image, but not necessarily more detail. This is especially true if the newtonian has a large central obstruction, isn’t flocked, etc….The great thing about newtonians is that they’re easy to modify. A flocked, collimated, cooled down newt with a curved spider, nice focuser (being perfectly in focus is important on planets!), and good optics will be right on par with an apo refractor of the same aperture minus the secondary obstruction, IMO.

Erik, from an online thread entitled 8 inch Newt vs 5 inch Apo.

 

like i always show my students; a 6″ unobstructed, perfect optic is creamed in resolution by a 10″ 20% obstruction 1/10 wave newt:

http://www.astromart…?article_id=473 (thanks darren!)

this is why i always wonder when people say refractors are best on planets…..

 

dave b, from an online thread entitled 8 inch vs. 5 inch Apo.

KWB said

like i always show my students; a 6″ unobstructed, perfect optic is creamed in resolution by a 10″ 20% obstruction 1/10 wave newt:
—————-
That’s fine, Dave but your skirting the issue. I’ve now been painted into the corner. Can you give the nod to a 6 inch
F/8 reflector against a 150mm Tak,AP,TMB,etc,?

if they both cost the same, i would take the 155mm AP.

if the 155mm AP and an 1/8 wave 8″ newt both cost the same, i would of course take the 8″ newt.

dave b, from an online thread entitled 8 inch vs. 5 inch Apo.

 

When I owned an 8″ Mag1 Portaball with a Zambuto mirror, I used to compare the views of the planets through my telescope with refractors. Over a two year period, there were a few refractors that came close to providing better views on a few exceptional nights, but I didn’t find a refractor that could compete head-to-head with my reflector. (The best refractor, the one that came the closest, was an AP 155, if I recall correctly.)

I now own a 12.5″ Mag1 Portaball (also with Zambuto mirror.) I’m still waiting for the night where the refractors demonstrate their clear superiority. I’m not holding my breath. Under crappy seeing conditions, I’ve seen the phenomena of a refractor providing what its owner called ‘a more aesthetically pleasing view.’ This is another way of saying when the seeing is bad, smaller aperture scopes don’t see the bad seeing as well as [a] large aperture scope. (In this type of condition, one can ‘stop down’ the larger scope and see the same sort of views that are seen by the refractor.)

When the seeing is good to excellent and when optical quality is excellent, aperture wins every single time. And dollar for dollar, high quality reflectors rule.

But don’t take my word for it. Check out Gary Seronik’s article “Four Infamous Telescope Myths” in the February 2002 issue of Sky and Telescope. You can also go to star parties and try a few experiments. Under good seeing conditions, take a look at the planetary views through a correctly collimated reflector equipped with a Zambuto, Royce, Swayze, Hall, etc. mirror. Then take a look at the views through a 6″ refractor that’s many times more expensive. I think that the results might surprise you.

Finally, consider this Mars image, made by Wes Higgins with a 14.5″ Starmaster. In the past, when the optics in most large reflectors were mediocre at best, I believe that high quality refractors provided the best views. Now, with high quality optics readily available in large reflectors, I believe the situation has changed.

Barry Fernelius, from an online thread entitled, Reflector versus refractor.

What more and more people are doing right now in France, is to buy those chinese 8″ or 10″ f/5 or f/6 Newtonians, play with them for some time, then have the primary mirror refigured to an exceptional quality for around €1,000 (US$ 1,250) with enhanced reflective coatings. They perhaps add a better focuser and tweak the spider a little bit. After that treatment on a 8″ reflector with 20% central obstruction, a 6″ APO can no longer match it for visual work.

Rhadamantys, from an online thread entitled, Reflector versus refractor.

At the risk of beating a dead horse, my experience is that an APO refractor delivers consistently a[e]sthetically pleasing results every time, with detail limited only by atmospheric conditions and aperture. A high-quality, well designed newt can also deliver [a]esthetically pleasing views, with detail limited only by atmospheric conditions and aperture. Everything else being equal, quality aperture wins, every time. Not surprising that (last time I checked anyway) Thomas Back’s personal scope for planetary viewing is….wait for it…. a 20″ Starmaster. Nuff said?

Gary in Ontario, from an online thread entitled, Reflector versus refractor.

 

A 130 mm F/5 with a decent mirror and a 2 inch focuser. No CA, much faster than the Mak or the refractor for EAA and very rugged.

I’ve owned several.. It’s scary sometimes how good they can be. I remember one night under dark skies.. I was doing the low power, wide field thing with my NP-101 and swapped it out for a 130 mm, F/5 Newtonian with the 31 mm Nagler and a paracorr. I wasn’t giving up much with the $200 scope.

Jon Isaac(San Diego, California), from an online thread entitled: 4″ refractor vs. 4″ Mak.

 

As John Browning was to argue in his ‘Plea for Reflectors’ in 1867, good silver-on-glass reflectors had tubes about half as long as those of refractors of similar aperture, they had a superior resolving power when used on dim double stars or planetary surfaces and often gave crisper star images, while unlike large aperture refractors, they were not ‘beyond the reach of all but wealthy persons’.

Allan Chapman, The Victorian Amateur Astronomer, pp 230, (1998).

James Francis Tennant, for example, had used a Browning mounted With 9 inch (silveronglass mirror) to observe the Indian eclipse of 1868, while in 1872 Joseph Norman Lockyer had one which produced ‘exquisite definition’. The With instrument in the Temple Observatory at Rugby School and one in a privately owned observatory in Sydney, Australia, were found superior to Clark and Merz refractors of similar aperture. By 1890, With’s mirrors were in use in Europe, Canada, Australia, Asia and elsewhere.

Allan Chapman, The Victorian Amateur Astronomer, pp 232233, (1998).

 

I find that the ideal planetary telescope is the largest quality aperture that you will use frequently. It can be fast or slow, in terms of f/#, so long as the optics are good. Ideally the primary is not too thick so it can cool and be cooled in a reasonable time. Proper mirror support and achieving and holding collimation are also very important.

Mike Lockwood (Philo, Illinois), from an online thread entitled: Help me pick a larger planetary scope.

I think that the ideal set up would be a 10″ F/7 Newtonian reflector on a GEM.

Stephen Kennedy (California), from an online thread entitled:Help me pick a larger planetary scope.

My best planet views came from all of my Zambuto and OMI 11 to 18″ mirrors and all were F/5 or faster. On the smaller size mirrors i like slower speeds in the 10″ and smaller sizes.

CHASLX200(Tampa, Florida), from an online thread entitled: Help me pick a larger planetary scope.
There is no way a 4″ apo will destroy a larger Newt!!  lol.gif Simple laws of physics are at play here.  My 6″ Newt with a 20% obstruction consistently shows more planetary detail than ANY of my 4′ Apos ever did!!  My former Takahashi TSA102 never performed as well on the planets as my large dobsonians did.  Aperture wins, every time! Small apos really shine in the portability department so they are eminently well suited to quick setup and teardown times.
Barbie, from an online thread entitled: Help me pick a larger planetary scope.

I am just not a APO fan in sizes over 4″. 3 and 4″ APO’s are my fav all around small scopes. Once you get into the 5″ and bigger sizes cost become a problem for me and 7″ and bigger the mount needed becomes pricey and big. A bigger Newt is many times cheaper and does what i need it to do. No 7″ or 8″ APO would give me the image at 1100x+ like my 14.5″ and 15″ Zambuto and OMI optics have done time and time again.

CHASLX200(Tampa, Florida), from an online thread entitled: Help me pick a larger planetary scope.
 
Last year I was privately discussing splitting some close doubles with a fellow Cloudy Nights member on the east coast. He was using a 175mm apochromatic triplet refractor that cost $20,000. I was using a 10 inch (250mm) Dobsonian that I bought used on Astromart 15 years ago for $240. One double in particular I had split cleanly with my $240 scope which had eluded the expensive refractor. This was due to the greater resolving power of the larger aperture and the more stable atmosphere (better seeing) of my location.
Jon Isaac(San Diego,California):from an online thread entitled, How much does a secondary affect the view?
I am not a bino viewer at all, and my particular vision doesn’t do binoculars, thru a telescope or even at the football field. But I do have personal experience comparing an Orion 120mm ED scope and a GSO 8″ newtonian on Saturn one night, probably some 11 years ago now. Hands down, the GSO (an old Meade LightBridge 8, back when they made them) beat the Orion 120mm ED scope on Saturn. The image was brighter and more detailed. I am certain a 10″ would have done even better, so if you think you’re a refractor guy now, a 10″ newt, should you figure out how to configure it, will convert you, for sure. The collimation and mechanics are the tricky things with these Chinese sourced newtonians, but I’m convinced the optics are actually pretty good. Not saying custom, American/European/Japanese mirrors aren’t better, but the standard Chinese mirror these days is really pretty good. Now the mechanicals associated with the scope are often not as good as the optics, so achieving the best views can be difficult to obtain, even tho the optics may, indeed, be quite good. My friend (who owned the 120mm ED) and myself were impressed with the mirror in the Meade LB8. I have a friend with an Orion Intelliscope 10″ and the views through it, at least on-axis cause he doesn’t own a coma corrector, are spectacular — Thor’s Helmet, Sculptor Galaxy, Jupiter, etc.
Colin in Alabama; from an online thread entitled:10″ Newtonian to upgrate an ED 120
 

I have owned a 1/2 dozen garden variety XT6/XT8 Dobs over the last 25 years. None of them were anything special, but they were consistently OK. I also simultaneously owned a sensibly perfect 4” APO and a custom 8” Dob with Zambuto optics.

The 6”f8 Dob consistently gave me better views of all objects than the 4” APO. The 8”f6 Dob consistently gave better views of all objects than the 6”f8 Dob. The 2” difference wasn’t a “wow,” but it was obvious.

The custom 8” Zambuto equipped Dob gave marginally better views than the 8” Synta Dob in excellent seeing, but the difference in the views was much more subtle than the difference that comes with 2” of extra aperture, which is why I would expect a typical, garden variety 10” Dob would probably give better views of anything than a sensibly perfect 8” Dob and cost much less

For reference, a complete XT10 costs $600 and is available off the shelf. An 8” Zambuto mirror starts at $1,100 with an 11 month lead time. A Zambuto equipped 8” Teeter starts around $3,300 with a 4 month lead time.

gwlee (California), from an online thread entitled: Premium mirror versus Chinese mirror.

Beyond that, the main thing is to get out there and use it. I don’t really worry much about whether a premium 8 inch would out perform my GSO 10 inch because the 10 inch does a reasonable job of doing what I ask of it. I do know that I have been able to split double stars with it that are beyond the Dawes limit for an 8 inch. Some pretty awesome planetary views at 410x.. And deep space.

Jon Isaac (San Diego, California), from an online thread entitled; Premium mirror versus Chinese mirror.

I have enjoyed Sky Watchers scopes for 10 years now in almost every circumstance, under light polluted or super dark skies, under ugly or really good seeing, side by side to terrible scopes or world class (Astrophysics) refractors, close the newbies or really experienced observers. They have never disappointed me, when conditions allow, they deliver terrific planetary and deep skies images.

Javier (Buenos Aires, Argentina), from an online thread entitled: Premium mirror versus Chinese mirror.

I had a 120 mm Orion Eon for two years. This is a 120mm F/7.5 FPL-53 doublet and probably better optically than your 120mm Binocular Telescope. I recently sold it because my generic 10 inch GSO Dob was the better all around performer and not just by a little. The Dob was better on the planets, it splits doubles not even worth looking at in the refractor. Globulars, nebulae, galaxies, for deep sky it’s a break through experience.

Jon Isaac(San Diego, California) from an online thread entitled: 10″ Newtonian to upgrate an ED 120.

After having large aperture Newtonians and Refractors, I would say yes, it’s possible to make a Newtonian as good as a a Mid priced apo.  My current(and final) scope, a 6″F8 newtonian provides refractor like images of the planets and double stars.  Everything snaps into focus and looks as good as in my former 4 and 5 inch apos.  At this point in my life, an arthritic back and knees prevent me from owning anything larger and I like the convenience of a dobsonian mounting. I’ve always said that if I could have only one scope, it would be a 6″f8 reflector.  It’s an outstanding performer and an excellent compromise between aperture and focal length!!

Barbie, from an online thread entitled; How hard is it to make a reflector as good as mid-price ED or Apo refractor?

The advantage of a reflector is that it scales to a larger size much more affordably; at small sizes that advantage is much less. That is why you see small refractors and large reflectors.  The notion that a 4-5″ reflector should be the same price as a 10-12″ reflector, though, is an unrealistic expectation. Next to a 12″ dob, a 127mm refractor looks like a kids toy… they are totally different leagues. Make no doubt about it, a 12″ premium dob will blow a 127mm refractor out of the water in every category except wide field views and ease of use. 

dgoldb, from an online thread entitled: How hard is it to make a reflector as good as mid-price ED or Apo refractor?

As Danny shows, the real world can be tamed a little or a lot. Cooling and boundary layers, collimation, and a few other variables are within our ability to minimize. In the tropics the real world is, at times, almost “lab like” with very good seeing and modest temperature differentials. So, even though we cannot talk about performance in isolation, we have a measure of control over “real world” performance except for seeing mostly. We can give our ‘poor’ scopes a fighting chance to perform better than they are often assumed to perform…in the real world, of course.

Asbytec(Norme)(Pampanga, Philliippines), from an online thread entitled, Premium mirror versus Chinese mirror.

I agree with Norme, often performance is all about location, location, location! What works well in the south, or out west might not be the ideal scope for the NE or other locations. You have to tailor your scope to your location and observing goals/habits to get the best consistent experience. There is no such thing as the perfect scope for any location, observing style etc. If there was we would all have it.

Richard Whalen (Florida), from an online thread entitled, Premium mirror versus Chinese mirror.

 

I have a superb TEC200ED and equally superb (optically, mechanically and coolingly…did I just make up a word?) Parallax/Zambuto 11″ F 7 Newt. Other than image brightness and a slight warmth in the TEC’s color tone, there is little difference between them for solar system viewing. Sometimes I prefer the TEC, others the Newt. The only “glaring” difference is the Newt’s diffraction spikes, especially on Jupiter and Mars. But I’ve learned to live with the spikes and ignore them much like I can ignore CA in achromats ( if it’s not too severe anyway), however there are also solutions for that too.

For me, the key to really enjoying my newts has been great optics & great mechanical and cooling designs. I want my newts to behave like an excellent APO and I’ve found that it is easily done if I pay attention to the big three: optical quality, mechanical design & execution, and cooling design & execution. Everything else is “sauce for the goose” for me (however, I freely admit to being one of those people who have sub-F5-phobia and yes, I am considering seeking therapy for it).

Jeff B, from an online thread entitled: How hard is it to make a reflector as good as mid-price ED or Apo refractor?

 I have one mount and two great scopes-an APO and a reflector. I usually go a month or so with one and then a month or so with the other.
After a month with the reflector I’ll switch to the refractor and notice how pretty the stars look all across the field.
After a month with the refractor I’ll switch to the reflector and achieve higher mag than is possible with the APO.

I’m not sure I could call one a favorite but I like the refractor for any outreach situation. It just seems easier for the uninitiated.

Steve O (Wichita, Kansas), from an online thread entitled: How hard is it to make a reflector as good as mid-price ED or Apo refractor?

I had a mid 1960’s vintage Cave Astrola Deluxe 10″F7 reflector and a GSO 10′ F5 dob and they both showed the same amount of detail on the planets. The ONLY difference was that the GSO showed a little coma whereas the Cave operating at F7 didn’t. They were both outstanding scopes and any differences other than the above noted were essentially splitting hairs. It is quite possible to get a Chinese optic that is outstanding. My current 6″f8 is a testament to this fact. I think over the last 15 or 20 years, the quality control has gotten a lot better and the chances of getting a lemon are far less but I’m sure the occasional one still gets through.

Barbie, from an online thread entitled: Premium mirror versus Chinese mirror.

***

I have also found that it’s much easier to find and purchase sensibly perfect (SP) refractors off the shelf than SP reflectors, which are usually only available from a few small custom shops. Custom SP reflectors are very expensive compared to off the shelf scopes. They have longer lead times, and some sizes, 6”f8 for example, are not available.

Why? I believe that most people are satisfied with the optics and mechanics of production reflectors at 1/10 the cost and don’t want to wait months for delivery, so the market for SP reflectors too small to be attractive to large manufacturers who stay in business by selling people what they want to buy at a price they are willing to pay and do it efficiently enough to make money.

For example, my factory 8”f6 Dob cost me $300 and was delivered to my front door by a big brown truck within 48 hours of placing my order. My custom 8”f6 reflector with sensibly perfect optics cost me $3,000 and delivery took a year. Its optics were better, but the improvement was subtle, usually requiring side-by-side testing in better than average seeing to confirm.

On the other hand, the optical improvements to be had from a 10” factory reflector costing $600 are immediately obvious, so more people are inclined to upsize their reflective optics rather than upgrade them. Other people who are basically satisfied with their massed produced factory reflector optics might prefer to spend the same $3K on a SP refractor, not because it’s better than a reflector, but because it complements a reflector so well, it’s available off the shelf, and it scratches the SP itch too.

gwlee (California), from an online thread entitled: How hard is it to make a reflector as good as mid price ED or Apo refractor.

Quid est veritas?

My world changed forever when I first took a modern SkyWatcher 8″ f/6 Newtonian for a serious spin under a dark sky. It was far less expensive than any of the other telescopes I had personally owned, including some fine refractors and Maksutovs, and it outclassed them all on every type of celestial target. It was the sweetest of revelations!  Modest and marvellous in equal measure, Newtonians are my instruments of choice, based solely on visual performance, when I want to pursue either serious or casual observing.

Mr. Hardglass.

 

Neil English is author of Choosing & Using a Dobsonian Telescope.

 

De Fideli.

 

The “Foot” ‘Scope Project: Part II

Foot sized powerhouse; the author’s 12″ f/5 Newtonian.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

April 13 2018

In a previous communication, I described my acquisition of a Revelation 12″ f/5 Dobsonian telescope, which delivered fine images of selected double stars and which was used to establish the Taylor hypothesis, namely, that if the seeing conditions are fair to average or better, sub–arc second pairs can be readily observed at appropriately high magnifications using the generous aperture of this telescope.

After conducting this body of work, I have had little time to enjoy the considerable benefits of observing with a big Newtonian system such as this, but in this blog I hope to report still more observations with the same telescope and improve its optical and thermal  performance in the field.

During the course of that previous communication, I described the optics in this telescope as being unreasonably good. Indeed, they far exceeded my expectations given the very modest cost of the telescope! I also described some modifications I made to the instrument, including the re–coating of the secondary mirror (just 70mm semi major diameter) with super–high (97 per cent) reflectivity coatings as well as the procuring of Bob’s Knob’s  to assist precise collimation in the field, but I postponed some other aspects of this project. In particular, I wished to also have the coatings on the large primary mirror similarly upgraded in order that it would increase light throughput to the eye as well as improving the overall contrast of the images so rendered.

Today, I endeavoured to resume work on the telescope and that meant removing the primary mirror from its cell in order that I could despatch it to the mirror coaters located south of the border in England. The mirrors for this telescope were sourced from GSO and seem to have been more or less consistently good, as judged by other experienced amateurs who had taken the time to assess one or more units of the same product. One such assessment is documented here and I would heartily agree with the conclusions of Mr. Stoitsis.

After removing the mirror cell from the rear of the optical tube, I was able to accurately measure its thickness, as well as assess the design of the accompanying cell. The thickness of the mirror was measured to be 36mm (so 1.5 inches), yielding a mirror thickness to aperture ratio of 1:8. This result is consistent with this author’s finding in respect of the ability of the telescope to acclimate adequately to ambient outdoor temperatures, allowing him to make those important observations with regard to resolving sub–arc second pairs.

 

The 30cm aperture GSO primary has a thickness of 36mm (1.5 inches).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The mirror cell is housed in an open cell. It appears to be well designed and incorporates a 9–point floatation system; just about perfect for a mirror with these dimensions.

The 9–point floatation system of the 30cm aperture GSO primary mirror cell.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The mirror was then carefully packed away for safe passage to the mirror coaters.

Packaging up the primary for re–coating.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I hope to despatch the mirror early next week, so hopefully I will have it back in a few weeks; just in time to explore the deep sky glories of spring!

 

April 14 2018

Time: 23:20UT

Almost forgot to tell you: several weeks after exchanging resources for the foot ‘scope, I received an envelope in the post. Curiously, I prized it open, and there it was! A small, battery powered fan; the same one that originally came with the telescope! As I explained in the opening blog, I wasn’t too bothered about not having it, nor did I really need it. But it was a warm gesture from the original owner of the telescope to send it on; something I appreciated!

The little fan.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 4:20 pm

As described in previous blogs, I also wish to line the inside of the 1450mm long tube with cork and overlay this with flocking material. Materials were ordered yesterday and should keep me busy until the primary returns home.

April 21 2018

Time: 5:45pm

Lining the 12 inch optical tube assembly with cork.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

With a decent spell of settled weather now upon us, I spent the afternoon lining the inside of the optical tube with a thin layer of cork. The product I chose has an adhesive layer on the underside of the cork substrate and adheres to the rolled aluminium tube fairly easily. The cork itself is very delicate though, and so some care must be taken not to tear it while preparing the strips. 3 full 100 x 45 cm rolls were used up today, but I needed to order up a couple of extra rolls to complete the job. These arrive on Monday so I can complete the task then. The flocking material has already arrived so that will be overlaid on the cork. This afternoon, I only flocked the inside of the focuser draw tube.

The mirror arrived safely at the coaters and on the invoice they noted its diameter to be 303mm. Hoping to have it back in a week or so.

Date: April 24 2018

Time: 3:10pm

The tube now fully insulated and flocked.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Well, I finally managed to complete the cork lining as well as covering it over with flocking material. Since the rolls are the same size ( i.e. 45 x 100cm), I can report that it will take 4 complete rolls of each material to insulate and flock the optical tube assembly of the 30.3cm F/5 Newtonian. I’m pleased with the result. All I need do now is wait for the arrival of the primary mirror and I’m back in business.

 

To be continued……

 

De Fideli.

What I’m Reading

 

 

 

 

 

 

 

 

 

 

 

 

Available now in paperback or kindle formats.

 

Few of us can venture outside on a clear, dark night without pausing for a silent, reflective gaze at the stars. For countless centuries, people have felt a sense of wonder about the heavens. How did our universe come into being? Has it always been here? Is our existence the result of chance or of supernatural design? Is God “out there”? If so, what is God like?

Whether you are skeptical of God’s existence or seeking scientific support for your faith, The Creator and the Cosmos will enable you to see how the heavens do declare the glory of God (Psalm 19:1).

Astronomer Hugh Ross makes an extensive update in the fourth edition of this modern classic. He explains recent scientific measurements of the universe that clearly point to its purposeful origin and development. An abundance of references to published research findings allows you to explore the evidence for yourself.

Endorsements
“Currently, it is fashionable to believe that the discoveries of science, one and all, are either hostile or simply irrelevant to the propositions of theology. For some time now, Hugh Ross has been one of America’s leading thinkers who has steadfastly refuted this claim with hard thinking and up-to-date scientific information. In The Creator and the Cosmos we have a treasure chest containing his most recent work, abreast of the latest findings of science, and packaged in an accessible form for a general audience. This book should be in the hands of every serious Christian who thinks about science and the Christian faith, and it should be given to interested inquirers outside the faith.”

J.P. Moreland, PhD
Professor and director of the Talbot M.A. in philosophy and ethics
Talbot School of Theology, Biola University

“It’s a thrill to see Hugh Ross update his influential book The Creator and the Cosmos. He chronicles the vast increase of scientific evidence for a designer that has emerged in recent times. And he shows quite convincingly how it uniquely points to the God of the Bible. I highly recommend this book for both Christians and seekers.”

Sean McDowell, PhD
Biola University professor and popular speaker
Coauthor of Evidence that Demands a Verdict
 

“Hugh Ross’s The Creator and the Cosmos, over the past 25 years, has risen to the status of ‘a classic’ concerning its profound influence upon Christian thought as it relates to modern scientific discovery. Many have come to faith citing their reading of The Creator and the Cosmos as one of the key elements that caused them to question their nontheistic positions, ultimately paving the way for their acceptance of the Gospel of Jesus Christ. In this edition, Ross lays down further evidence to the handiwork of God as displayed in the Bible. There are few authors that can take such complex scientific subjects and distill them down for the layperson, while maintaining the highest rigors of citation to substantiate the claims and to direct the reader to the primary scientific research literature. But even with all these scientific exactitudes, the sense of wonder in God’s creation is magnificently woven into each chapter in a way that draws the reader to the Creator Himself.”

James Tour, PhD
Professor of chemistry, materials science and nanoengineering, and computer science, Rice University

“Dr. Hugh Ross has spent a lifetime integrating his scientific intellect and his passion to represent Jesus Christ fairly in an increasingly cynical world. He speaks the language of the scientific world and he brilliantly navigates this world with Christian grace and deep commitment to both biblical authority and scientific evidence. In this updated version of The Creator and the Cosmos, Dr. Ross has acknowledged the growing spate of twenty-first century scientific discoveries that have significant theological implications. The sturdiness of this volume, as a foundational resource, has been given additional strength with its usage of the latest scientific research. Dr. Ross is a gift to Christ’s Kingdom, and this updated edition of The Creator and the Cosmos only serves to validate his status as a premier Christian apologist.”

Byron D. Klaus
President Emeritus
Assemblies of God Theological Seminary

 

Winds of Change: Some Comments on the SkyWatcher Evostar 72EDS Pro Refractor

Breaking the mould; the SkyWatcher Evostar 72EDS Pro.

 

 

For a good few years now, SkyWatcher has brought many quality telescopes to market at very reasonable prices. One of the major reasons for this success is the company’s  investment in better manufacturing technology, as well as improvements in quality control. This author can personally vouch for the fine Newtonian and Maksutov Cassegrain telescopes that are now available at prices that won’t break the bank. Apochromatic refractors have remained noticeably more expensive though, and while the same company has offered both doublet and triplet models at prices that are among the lowest in the market, I felt they still remained on the expensive side, especially when one considers their rather small aperture for purely visual use. Their relative expense still registers somewhat as an anomaly to my mind. Why, pray tell, should they command such high prices relative to other kinds of telescopes? That said, recently, SkyWatcher has marketed a few products that are significantly less expensive than even their earlier offerings; and one of them piqued my attention; the SkyWatcher Evostar 72EDS Pro Refractor.

So what does your £265 buy? Well, as it turns out; quite a bit! The telescope has a two speed Crayford focuser that can be locked for astroimaging applications, and it can also accommodate both 1.25 and 2 inch accessories, including diagonals and eyepieces. The machined aluminium dust cap screws on to the dew shield; a very nice touch!. It comes with dedicated tube rings and a universal dovetail plate for easy securing on a variety of light weight mounts. The optical tube is typical SkyWatcher, not overly showy and more practical than overtly ornate. While nearly all other similarly sized instruments come with a retractable dew shields, the Evostar 72EDS is of fixed length but is easily removed for transport. And you even get a nice custom fitted travel case for easy storage and transport. It also has a bracket for mounting a suitably sized finder ‘scope. Check out this youtube video for more details of what the package provides.

In a departure from previous marketing strategies, SkyWatcher has not disclosed the nature of the ED element their optical engineers have mated to the Schott glass crown lens of this 72mm ED doublet, but early indications are that it offers very good colour correction for its attractive price tag. All of this is very good news for the consumer, as it appears SkyWatcher is listening to their customers and bringing to market more economical ED refractors that offer significantly better overall value.

That said, considering the many nice mechanical features this new refractor offers, I wonder what percentage of the total cost of the telescope is divested to the objective? Are ED objectives really that expensive to manufacture? Judging by the modest cost of the entire package, the answer must surely be “relatively easy.”

In comparison to other models recently launched by companies like William Optics, who now offer a 61mm ED doublet for £400 UK, the new SkyWatcher will almost certainly be of greater utility owing to its significantly larger aperture (for many seasoned observers 61mm is just too small). This is especially the case for those amateurs who do not dabble in astrophotography.

I am personally comfortable about endorsing this product and see it as a significant and welcome move in the right direction for money conscious hobbyists. Will I be making a purchase myself? No, as I already have too many telescopes and, as I’ve already disclosed, I do virtually all my observing with modified SkyWatcher Newtonians which offer superior daylight and nighttime views to any small refractor in this aperture class. But I do think more folk can now enjoy the considerable charms of a small, short, high quality refractor.

The move by SkyWatcher will hopefully be part of a much greater impetus to drive down prices for apochromatic refractors generally. The hobby can only grow if more amateurs have access to decently priced products, and in making this move, SkyWatcher will surely impose pressure on other makers to offer their wares at fairer prices. The soon to be introduced ED 150 by the same company promises to continue this trend and I commend SkyWatcher for embarking on this very encouraging (and profitable) venture.

 

Neil English is author of Choosing and Using a Refracting Telescope.

 

 

De Fideli.

A Newtonian Travel ‘Scope

Wednesday, February 3 2016: SkyWatcher has established a solid international reputation for producing high quality Newtonian optics for the modern amateur astronomer, and at prices that won’t break the bank. Having been thoroughly satisfied with a 8″ f/6 Skyliner Dob, I became very curious about a smaller, model – the Heritage 130P (a 5.1″ f/5 Newtonian with a parabolic primary) tabletop Dobsonian – which promises to provide decent light grasp and resolution in an ultra-portable package for take anywhere travel and short grab ‘n’ go excursions to the back garden.

The telescope was purchased new from Rother Valley Optics on Tuesday morning, February 2, and arrived in the mid-afternoon today. The price, inclusive of postage, was £129.

The telescope came double-boxed and involved no assembly. The optics looked clean and streak-free. A neat instruction manual accompanied the instrument.

The Heritage 130P Dobsonian as received.

The Heritage 130P Dobsonian as received.

 

 

 

 

 

 

 

 

 

 

The ‘scope, weighing about 6 kilos with the mount, has a built-in carrying handle for swift transport into and out of the house.

Following along the same lines as their extremely successful flextube line of larger Dobs, the Heritage 130P can be extended to reveal the upper tube assembly, lengthening the tube from just 38cm to about 61cm. The lower assembly is adorned with the names of time-honoured astronomers, celebrating four centuries of telescopic astronomy. While some folk might find this ‘tacky,’ I rather liked it.

The Heritage 130P fully extended.

The Heritage 130P fully extended.

 

 

 

 

 

 

 

 

 

Remarkably, the telescope was almost perfectly collimated out of the box, as evidenced by the just slightly offset red dot from the centre-marked spot on the primary mirror. That’s a nice touch, as one can imagine the reaction of a complete novice were he/she to discover that the optics were delivering iffy views as a result of mis-aligned optical components. It might be enough to put someone off the hobby for good.

Note the position of the red dot from the laser collimator; just a shade out of whack.

Note the position of the red dot from the laser collimator; just a shade out of whack.

Once the collimation was tweaked, I investigated retracting and extending the tube assembly several times to investigate the rigidity of the structure. I am pleased to report that the collimation held quite well but might still require last-minute tweaking for more demanding tasks, such as obtaining the best lunar and planetary views, as well as double star work. Overall though, this is a very well thought out piece of kit and certainly better than I had anticipated.

 

 

 

 

The telescope primary and secondary mirrors are fully adjustable and can be aligned in a matter of minutes. Unlike the three ultra-thin spider vanes on larger models, the secondary mirror on the Heritage 130P is affixed to a single vane, which is a good bit thicker than the latter; a necessary design compromise to maintain that little bit more stability to the optical train.

The adjustment screws behind the f/5 parabolic primary mirror.

The adjustment screws behind the f/5 parabolic primary mirror.

The secondary support is of high quality and is easily adjustable with a user supplied hex wrench.

The secondary support is of high quality and is easily adjustable with a user supplied hex wrench.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The focuser is unusual. Unlike standard rack and pinion or Crayford type focusing mechanisms, the Heritage 130P employs a simple helical focuser which involves rotating the eyepiece either clockwise or ant-clockwise to bring objects to a sharp focus. In addition, the length of the upper tube can also be adjusted to accommodate cameras and other equipment. In short, any eyepiece will reach focus using a combination of these procedures. Only 1.25″ oculars can be used with the instrument, however.

The unusual helical focuser on the Heritage 130P Dobsonian.

The unusual helical focuser on the Heritage 130P Dobsonian.

 

 

 

 

 

 

 

 

 

 

Some observers may find reaching precise focus a little fiddly, but with a bit of practice, it works smoothly and accurately.

The Heritage 130P also came with a simple red dot finder (RDF) to aid in locating objects quickly under a dark sky.

The basic but useable red dot finder is easily attached to the upper tube assembly with a small screw driver.

The basic but useable red dot finder is easily affixed to the upper tube assembly with a small screw driver.

A particularly attractive feature of the instrument as received is the dovetail mounting of the optical tube assembly which enables one to remove the tube assembly from the mount proper for even easier storage.

The optical tube can be removed from the mount if necessary to aid storage/transportation.

The optical tube can be removed from the mount if necessary to aid storage/transportation.

In addition, the dovetail plate allows the user to mount the instrument separately on other types of mounts such as this author’s ergonomical Vixen Porta II alt-azimuth for an alternative style of observing. What a nice touch!

The SkyWatcher Heritage 130P mounted on the author's Vixen Porta II alt-azimuth mount; a particularly stable configuration.

The SkyWatcher Heritage 130P mounted on the author’s Vixen Porta II alt-azimuth mount; a particularly stable configuration.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Optical testing: Although the instrument suffers from the introduction of considerable amounts of stray light during daylight use without employing some sort of light shroud, I set the instrument up in the late afternoon, aiming the instrument at a roof top about 100 yards distant. I didn’t wait around to use the supplied oculars (which are adequate but not great for testing) but instead decided to push the ‘scope as hard as I could. To that end, I ran inside and affixed a good quality 6mm orthoscopic to a 2.25x Baader shorty Barlow lens, which would deliver a power of 244 diameters. Inserting these into the helical focuser, I carefully rotated it until best focus was achieved. Although the view was a bit drowned out with extraneous light, I am happy to report that the image of the terracotta roof tiles came into very sharp focus; a great initial sign that the optics were of potentially high quality.

After dark, more cloud encroached, but I waited for the odd sucker hole and was rewarded by a clear spot corresponding to Auriga, then high in the eastern sky. Relocating the instrument in a dark spot in the garden, I centred the bright star, Capella, using my multi-coated 32mm SkyWatcher Plossl in the field (yielding a true field of 2.5 degrees!) and was delighted to observe (with my eye glasses on)  a beautifully sharp vista, with pinpoint stars across most of the field. Then, I investigated the high power view of Capella at 244x and after refocusing, was thrilled to see a tight white Airy disk with diffraction rings a shade more prominent than what I have observed in my work horse telescope, a larger 8″ f/6 Dobsonian. This could be explained by the larger central obstruction of the Heritage telescope (~29 per cent by aperture) as compared with 22 per cent for the larger 8 inch.

On a whim, I moved the instrument north-eastward from Capella and centred the star, theta Aurigae. Focusing as accurately as I could, I was able to steadily hold its very faint companion at 244x, some 4 arc seconds away from the primary. Very encouraging to say the least!

It wasn’t long before the skies completely clouded over, and the drizzle came back, ending my first light vigil under the stars. Needless to say, the instrument performed surprisingly well under admittedly dodgy observing conditions.

More testing in the pipeline though.

Thursday, February 4, 2016

11:00am

Having collimated the telescope in situ and placed a makeshift light shround around the upper telescope assembly (UTA), I am happy to reaffirm that the telescope delivers tack sharp images of distant willow tree branches at 244x.

Friday, February 5, 2016

The Heritage 130P has a parabolic primary mirror, that is, it is figured into the shape of a parabola. Why is a parabolic shape responsible for such sharp images in a Newtonian reflector? It’s an interesting question, yet many amateurs accept it as a given. But we can do considerably better than that. We can analyse the properties of the parabola, one of the conic sections beloved to the mathematicians of classical antiquity, and thereby gain a deeper appreciation of why this shape, over all others, is chosen by opticians in the fashioning of high quality primary mirrors. Our analysis will borrow from the approach of the great French mathematician, Rene Descartes (1596-1650), who developed a way of investigating geometry using algebra.

A parabola is the set of all points which are equidistant from a given point called the focus and a given line known as the directrix.

The image below outlines the basic features of a parabola drawn on a x-y axis.

The Parabola

The Parabola

 

 

 

 

 

 

 

 

 

Let the focus be the point S( a,0) and the directrix be the line x=-a, as shown in the diagram. Consider any point on the parabola, P(x,y).

Thus, by definition, the length of SP = length of PM

So [(x-a)^2 + y^2]^0.5 = x + a

Therefore, (x-a)^2 + y^2 = (x+a)^2

Thus, x^2 -2ax +a^2 + y^2 = x^2 + 2ax + a^2

From which y^2 = 4ax ( Eq 1)

This is the standard form of the equation of a parabola.

Consider next the parametric equations x = at^2 and y = 2at.

Substituting the expression for x into equation 1 we obtain;

y^2 = 4a^2t^2 = 4a(at^2) = 4ax

So, x = at^2 and y = 2at represents the parametric coordinates of any point on the parabola y^2 = 4ax.

We can use this to derive two more equations that will enable us to arrive at the result we want. Consider the diagram drawn below.

The parabola with the point P defined parametrically.

The parabola with the point P defined parametrically.

 

 

 

 

 

 

 

 

y^2 = 4ax

Differentiating implicitly with respect to x we obtain;

2yf'(x) =4a

so f'(x) = 2a/y, which is the gradient of the tangent at any point.

Now since y = 2at, the gradient becomes 2a/2at = 1/t

And so the equation of the tangent to the parabola at the point P is given by:

y – 2at = 1/t(x-at^2)

Multiplying across by t  gives;

ty – 2at^2 = x-at^2

or  x – ty + at^2 =0 ( Eq 2)

Also, the gradient of the normal at P = -t and so the equation of the normal will be:

y – 2at = -t(x-at^2)

or tx + y – 2at – at^3 = 0 ( Eq 3)

Now we are ready to obtain further information from the parabola under discussion.

Let the tangent at P intersect the x-axis at R and the y-axis at U, and let the normal to the parabola at P intersect the x-axis at V, as shown in the diagram below:

parabola 3

The coordinates of R are obtained by setting y = 0 in equation 2

x – ty + at^2 =0 and so if y = 0 then x = -at^2 and so the coordinates of R are (-at^2, 0)

The coordinates of U are obtained from setting x = 0  into equation 2, from which it is easily shown that y = at i.e. U(0, at).

The x-coordinate of V can be obtained by setting y = 0 in equation 3;

tx + y – 2at – at^3 = 0 and when y = 0 we obtain:

t(x- 2a – at^2) =0,and since t cannot equal zero we have

x = 2a + at^2 and so the coordinates of V are given by (2a + at, 0).

From these results it is possible to verify the following:

(i)  U is the midpoint of PR

(ii)  length of SR = length of SV = length of SP

(iii) US is parallel with PV and that PU is perpendicular with SU

I will leave these as exercises for the interested reader.

Now, to the meat of the analysis. Consider a line PZ drawn parallel to the axis of the parabola as shown in the diagram below:

parabola 4

 

 

Since  length SP = length SV so too must angle SPV = angle SVP

But angle SVP = angle VPZ since PZ is parallel with RV

So angle SPV = angle VPZ

But ZPV is the angle of incidence of a ray of light incident upon a reflective parabolic surface and so the law of reflection requires that the angle of reflection be the same i.e. angle VPS.

But since P is independent of S, the result implies that any ray of light parallel to the axis will be reflected through the focus, S.

This is the reason why parabolic mirrors work so well, as they completely avoid a phenomenon known as spherical aberration, which can can plague other kinds of optical designs.

That’s enough math for one evening eh.

After a day of more or less constant rain, the sky appears to be clearing up and so I’ll get some more time under the starry heavens using my little parabolic Newtonian.

Thank goodness for small mercies!

Saturday, February 6 2016

Time: 00:05h

The telescope was collimated perfectly before use and left to cool in a dry, unheated shed. Initially, I had intended to use my Baader zoom and dedicated 2.25x Barlow to observe Jupiter, now 31 degrees above the horizon. To my chagrin, I discovered that this combination failed to reach focus. Due to the constant interruptions from clouds and with the rain never far away, I did not want to retract the UTA enough to get it to focus. Instead I chose a 7.5mm Parks Gold ocular and 2.25x Barlow yielding 195x.

Though the helical focuser is a bit fiddly and takes some getting used to, I am happy to report that the Jupiter images were wonderful in this telescope, with lots of nice detail showing up under moderate scrutiny. The planet’s enormous equatorial belts were seen in their faithful colours and many shades of tan were observed. A Baader Neodymium filter took away a little bit of glare surrounding the planet, helping to bring out more subtle details. Although I felt 195x was a little too high, and would have been happier with 160x, I was most impressed by what this inexpensive Newtonian was delivering.

Jupiter as seen through the Skywatcher Heritage 130P Dobsonian at midnight of February 6.

Jupiter as seen through the Skywatcher Heritage 130P Dobsonian at midnight of February 6.

Turning then to some brighter stars appearing from behind the clouds, I was equally impressed by how well the instrument focused them down to tight round Airy disks at the highest powers pressed into service (244x). The telescope seems quite immune to atmospheric turbulence as judged by the calmness of the images. Returning to a 32mm Plossl, I enjoyed a spell binding few minutes drinking up the famous Double Cluster (Caldwell 14) in Perseus. The 20x delivered by this eyepiece provided a very generous field of view, allowing both star clusters to be easily framed in a most beautiful portal.

This is certainly not a toy telescope! It is impressively powerful with high quality optics. Indeed my initial impressions were very similar to this assessment made by Ralph Bell back in 2009.

Monday, February 8 2016

Time: 18:30-45 UT

I enjoyed another brief vigil under the stars with the Heritage 130P Newtonian.  Charging the telescope with a 32mm Plossl (20x), I first visited the Pleiades, now high in the southern sky. Its constituent stellar components focused to fine points of light, pure white as the driven snow, with excellent contrast. Though I did not do a side by side comparison with my 80mm f/5 shorttube refractor, I was immediately aware of the Heritage’s significant advantages in light gathering power, with many more fainter members coming through at a glance. Then, I moved the instrument southwards, where majestic Orion was just about to culminate. The view of M42, the Great Nebula, was a sight for sore eyes. Cranking up the magnification to 81x with my Baader Zoom, I enjoyed a sumptuous field of view dominated by the emission nebula and Trapezium stars at its heart. The hinterland of the nebula was jewel encrusted with brilliant white stars set against a jet black sky.

Before packing up, I examined three higher resolution targets; first Rigel, just a few degrees to the southwest of M42. Using a power of 108 diameters, I was delighted to see the faint companion to this brilliant giant star cleanly and steadily. Then I swung the telescope over to Cassiopeia, now high in the northwestern sky. First I centred eta Cassiopieae and keeping the power at 108x I was able to easily split this pair, consisting of a beautiful yellow primary of magnitude +3.5 and its ochre companion some 13 arc seconds away, shining considerably more faintly at magnitude 7.4. Finally, I moved the Heritage 130P over to iota Cassiopeiae and could make out two of the three components of this system at a glance at 108x. The third member remained somewhat more elusive though, so I attached the Baader 2.25x Barlow yielding a higher magnification of 244x, refocused, and was overjoyed to see all three components clearly and precisely!

The Heritage 130P enjoying a dry afternoon.

The Heritage 130P enjoying a dry afternoon.

The imminent arrival of another student meant that I had to end the short vigil there, but it was very rewarding nonetheless. The telescope has great potential as a deep sky instrument and appears to be no slouch on moderately difficult double stars.

Tuesday, February 9 2016

Time: 19:00-30 UT

After a cool but crisp day, I continued my Newtonian education by fielding two telescopes; the Heritage 130P and a high quality 90mm f/5.5 ED doublet on loan for a a magazine review. Both instruments were given plenty of time to thermally acclimate and placed in the darkest spot in my garden to minimise stray light flooding into the open tubed reflector.

The multicoated objective of the f/5 ED90 'scope.

The multi-coated objective of the f/5.5 ED90 refractor.

The sky after sunset was clear but the stars were corruscating fairly wildly. Transparency was excellent though, so I decided to assess the seeing conditions some more by turning the 130P on Castor, now quite high in the eastern sky. Charging the telescope with a power of 195x, both the A and B components were resolved but there was quite a bit of turbulence which made the stars bloat significantly from their calmer appearances under better seeing conditions.  Comparing the same target in the ED90 charged with a power of 188x, both components were also resolved but there was still noticeable turbulence. It was not quite as unsettled in the refractor though, a consequence I suppose of its smaller aperture. This demonstrated to me that poor seeing can (though thankfully rarely at my location) adversely affect small telescopes. I judged the image in the refractor to be slightly more aesthetically pleasing under these conditions.

The reader will also note that the refractor comes equipped with a state-of-the-art 11:1 dual speed micro-focuser and so was considerably easier to focus finely than with the comparatively crude helical focuser on the Heritage 130P. This may also have contributed to my conclusions regarding Castor A & B. Accurately focusing f/5-ish instruments is never a walk in the park.

Turning to M42 once again, I compared and contrasted the images in both telescopes matching their image scales as best I could (~100x). Both telescopes delivered good images but the superior light gathering power of the reflector gave it a distinct edge. More nebulosity was seen and the stellar images were noticeably brighter in the reflector. This was despite the fact that the refractor had superior contrast, with a blacker sky background.

I am hoping that conditions will improve by the time Jupiter rises in the sky in a few hours from now.

22:45 UT

The sky has completely clouded out and the forecast predicts that it won’t clear again until the wee small hours. I am very tired though, so will leave further testing for another night.

Thursday, February 11 2016

Time: 00:50h

I fielded the same two instruments tonight as last night; the 130P reflector and the ED90 refractor. I finally found a good eyepiece to optimise the 130P’s capabilities on Jupiter; a 4mm Plossl delivering a power of 165x.The ED90 was charged with a power of 150 diameters.

Seeing was only marginally improved over last night (Antoniadi III-IV) but it was nonetheless a good test of what both instruments could deliver on Jupiter under these sub-par conditions (we have a north westerly air flow here which almost invariably brings more turbulent conditions but with excellent transparency).

I fitted a Baader Neodymium filter (with very high light transmission and virtually no colour shift, more a moon and skyglow filter than anything else)  to the 130P to reduce the glare a little.

Comparing the images in both telescopes over a period of about half an hour, I gathered my thoughts.

Both showed some nice details in the equatorial belts. The ED90 image revealed hints of more subtle details at higher and lower latitudes but in the end I felt the 130P showed that little bit more. In particular, it was easier to see those details at temperate latitudes, as well as the more delicate polar shadings. One very striking difference was the colour of the Jovian disk presented in the telescopes. The ED90 was noticeably yellower in overall hue – a consequence of its imperfect achromaticity in comparison to the perfectly achromatic reflector. The latter presented a brighter disk in its true colour; much more creamy white than yellow. The Neodymium filter showed that the colour in the ED90 remained the same but with a little more light loss.

In retrospect, this should not have come as a surprise; while the refractor has a low dispersion element, which improves colour correction, it still can’t deliver perfectly achromatic images. Yes, it’s a sizeable improvement over the traditional achromat but still not perfect. Only a reflector image – which brings all wavelengths of light to the same focus – could really reveal this. In addition, a brighter image can also help the eye see finer details. You need light to see such details.

That being said, I do know the ED90 is capable of showing more on better evenings ( data not communicated) but so must the 130P, as they were both compared under the same conditions. I am eager to conduct further tests in this capacity as soon as the seeing conditions return to normal.

This was an instructive vigil. The 130P should  give very decent images of Jove when the seeing is fair to good.

15:50UT

SkyWatcher has also brought to market a related telescope called the 130PD-S, which, as far as I can tell, features the exact same optics as those possessed by the Heritage 130P but retails for about £30 more. The optics are housed in a closed tube and the spider vanes are akin to what is seen on a traditional Newtonian. It also features a low profile 2-inch dual speed focuser for precise focusing and the secure mating of a CCD camera to the instrument. The 130P-DS has proven a huge hit with astro-imagers who have used it to good effect to capture stunning views of the night sky. Featured on this link is a plethora of deep sky objects captured by this modest telescope, but the reader will also take note of the lunar and planetary images captured by the same instrument.

Although not a visual assessment, I hope you will agree that the unlying camera shows just how good the optics are in these telescopes.

Friday, February 12 2016

Time 00:01UT

The seeing was vastly improved tonight, frosty but no wind. I only had time for one target; Jupiter. Like last night I fielded the same telescopes and employed the same magnifications etc.

Both telescopes served up some excellent images, but this time there was a clear winner – the 130P.

Though the image flitted somewhat between perfect focus and slightly out of focus in both telescopes, both instruments revealed excellent details in the equatorial and temperate belts. Details in the more prominent NEB were more finely resolved in the Newtonian than in the ED90. But what clinched it for me was the sighting of the Great Red Spot (GRS) near the western limb of the planet (at 00:01UT) that was picked off in the 130P but was not seen clearly in the ED90.

As always, I would be very grateful if someone could repeat these observations if you have the 130P and a good 90mm refractor.

The 130P is turning out to be a fabulous little telescope and I am overjoyed to have made its acquaintance!

19:30 UT

I have noticed that the price of the ED90 has been bumped up by £48 in the short time since I acquired it for review. It now retails for £868?! I don’t know why this was done (it was £820 just last week, remember?), but I can tell you I do not consider these telescopes good value for money and do not understand some people’s obsession with them. Under good conditions the Heritage 130P will outperform it and for 1/6th of the price. And if the classical achromat is the prince of telescopes, Newtonians are the ruling monarchs.

I would like to keep this telescope and learn how best to maximise its potential. I have bestowed a name on her; Plotina.

After another beautiful, crisp day, the firmament was glorious after sunset, with a gorgeous crescent Moon adorning the western sky. I set up Plotina at the side of the house and trained her on our life-sustaining satellite. She cools super quick, faster perhaps than the ED refractor that now sits in its case. The view of Luna at 20x was simply breathtaking, with razor sharp crater fields and the most wonderful earthshine from its dark side. Cranking up the power to 165x, the image remained razor sharp with excellent contrast and without a trace of chromatic aberration.
After that, I headed over to eta Orionis, a fairly tricky double star and was rewarded by a good clean split of the A and B components, the primary shining about a magnitude brighter than the secondary (3.8 and 4.8, respectively) and separated by a mere 1.7 arc seconds. Because of its f/5 relative aperture, it is very important to examine such high resolution targets at the centre of the field. This can be achieved by placing the system at the eastern edge of the field and letting it drift into the centre. The procedure is repeated several times until one is certain that the duplicity has been unveiled.

Some haar moved in a short time ago but hopefully it will clear later. I hope to field my most powerful telescope, Octavius, to continue my study of the Giant Planet.

Saturday, February 13 2016

13:00UT

My luck ran night overnight, as instead of clear skies, we got a fall of snow.

The final step in keeping anything in my family is to get my wife’s approval. For that, I had to get all my facts together to make a convincing case lol:

The optical tube assembly weighs just 3.2 kilos

The little lazy Susan weighs 2.8 kilos

The telescope can be collapsed to half its length.

The tube assembly can be used with a variety of other mounts.

The telescope is easy to tweak; involving a couple of minutes with a laser collimator.

The telescope is easy to carry about using one hand, so even when I’m feeling lazy it will not overtax me.

The telescope cools rapidly, so no waiting around or extensive pre-planning involved. Just set it out 15 or 20 minutes before use and you’re cooking with gas.

Because the tube is open, the optics can be accessed to remove dust and other grime easily.

The telescope gathers a very decent amount of light to go that little deeper than my short-tube refractor; very good for deep sky viewing.

The telescope takes high magnification well; images remain sharp and well defined up 244x (higher powers not yet tested) when conditions are average to good, so will perform well on lunar, planetary and double star targets.

The telescope can be improved in a number of ways; for example, the mirrors could be re-coated to give both higher reflectivity and increased durability, the secondary size re-assessed, ways could be found to refine the helical focuser, a permanent light shroud can be installed  etc. Any amount of tomfoolery is permissible!

The instrument exudes charm and is popular with the kids.

The entire package cost only £129.

I think these points will be enough to win her over. Fingers crossed eh!

16:00 UT

Improving the Focuser:

As mentioned earlier, the focuser on the Heritage 130P is of the simple, helical variety. One simply twists it one way or another to attain a good focus. But in the field at night, it can be a little frustrating to focus precisely, especially when using high magnifications. Manhandling the focuser almost always causes the telescope to move a little, necessitating re-centering of the object under study.

Fortunately, I was able to find a very simple solution; about six inches of string!

A new improved focuser!

A new improved focuser!

 

The string is tied in a single knot around the focuser, gripping the top thread, and leaving two overhanging ends which can be pulled in either direction causing the focuser to move inward or outward, as desired. This enables both course and fine focusing with much less vibration or annoying image shift. I tested it out during the day on a variety of targets at various distances from about 40 yards to infinity and it worked really well! This will allow more quality time observing and more precise focusing from moment to moment.

I’m well happy with the improvement!

Sunday, February 14 2016

10:50UT

St. Valentine’s Day and the first Sunday of Lent.

Last night I fielded Plotina just before midnight. After snowing for much of the day, the late evening sky cleared up to reveal the hosts of the second heaven. Seeing was very good but bitterly cold(-4C), but I was rewarded by quite an extraordinary view of Jupiter and its magnificent satellite system. I watched the planet for about 40 minutes, beginning at 23:50UT and ending at about 00:35UT.

This instrument continues to humble me in many ways. The optics are unreasonably excellent in this telescope; something I was not really prepared for, but hand on heart, it has thus far given me the finest views of Jupiter in any small telescope that has passed through these parts. I made a quick sketch depicting the planet’s appearance at 23:50UT (CM II 217 degrees), when it was 33 degrees above the horizon. The Great Red Spot (GRS) was plainly seen in the eastern hemisphere of the planet. The magnification employed was 165x and a Baader Neodymium filter threaded to the 4mm Plossl.

Jupiter as it appeared though the Heritage 130P shortly before midnight on February 13, 2016. North is at the bottom and west is to the left.

Jupiter as it appeared though the Heritage 130P shortly before midnight on February 13, 2016. North is at the bottom and west is to the left.

 

 

 

 

 

 

 

 

 

Indeed, I was able to use this telescope to establish the most accurate longitude of the GRS during this apparition. The GRS was observed transiting the centre of the planet at 00:32 UT where the system II longitude was 243 degrees. Not bad eh?

In the immortal words of Alexander Pope;

Nature and nature’s laws lay hid in night;
God said “Let Newton be” and all was light.

Monday, February 15 2016

19:00UT

I subjected the 130P to a high magnification test on the first quarter Moon, at an ambient temperature of -1C. I am very happy to confirm that it handled 244x without flinching, with the craters, mountain ranges, maria and valleys  remaining tack sharp and colour free throughout. This is about as high as one would like to go with this telescope in the vast majority of applications and a testament to the quality of the underlying optics.

I would warmly encourage other individuals to test each and every one of the claims I have made about this telescope. Test everything; hold fast to that which is good.

Sound Biblical advice that!

23:15 UT

Way hay! I found me an online thread about the same telescope;  Enter the One Sky Newtonian from Astronomy Without Borders .

250K+ hits ……..Crikey!

Seems like I don’t need to say anymore, eh.

Watcha think?

Tuesday, February 16 2016

00:20UT

What a thread! The things they say about this telescope warms my heart.

That thread has saved me months of blogging; Laudate Dominum!

Gary Seronik of S&T also found the telescope a joy to use; see here.

And yet another independent review can be read here.

Here my story ends.

Thank you for viewing.

Post Scriptum: 

Thursday, February 18, 2016

10:25UT

Having just acquired the latest issue(March 2016) of Astronomy Now (pp 63), I read with interest that the current longitude (system II) of the GRS is 238 degrees. That’s just 5 degrees shy of my best estimate made with the 130P shortly after midnight on Sunday February 14 (see above). I’m thrilled to bits to have gotten so close with this nifty little travel Newtonian.

Monday March 14, 2016

I have found that the Televue bandmate planetary filter is a great match for the 130P whilst studying Jupiter.This filter will be used in all future observations of the planet with this telescope.

The Televue Bandmate Planetary Filter.

The Televue Bandmate Planetary Filter.

The primary and secondary mirrors of the Heritage 130P have been despatched to Orion Optics UK. Both mirrors will be re-coated with Hilux enhanced aluminium reflectivity coatings and a slightly smaller secondary (35mm @27% linear obstruction) is to replace the original flat.

Will report back on progress.

Tuesday, March 22 2016

The mirrors arrived back from Orion Optics UK this afternoon and I immediately set to work putting it all back together again.

Out came the matt black paint to darken the periphery of the new secondary mirror to further reduce stray light and increase contrast.

The primary mirror has been rocaoted with 97 per cent reflectivity Hilux coating. The smaller secondary ( also Hilux coated) is seen in the middle beside the original secondary.

The primary mirror has been re-coated with 97 per cent reflectivity Hilux. The smaller secondary ( also Hilux coated) is seen in the middle beside the original secondary.

 

 

 

 

 

 

 

Applying a coat of matt black paint tot he periphery of the new mirrors cuts down on unnecessary stray light entering the optical train.

Applying a coat of matt black paint to the periphery of the new secondary mirror cuts down on unnecessary stray light entering the optical train.

 

 

 

 

 

 

 

 

 

 

Side view of the recoated 130mm primary mirror.

Side view of the recoated 130mm primary mirror.

 

 

 

 

 

 

 

 

 

 

 

 

 

The primary mirror had to be re-spotted at its centre but this can easily be done by placing the mirror shiny side down on a sheet of paper and tracing round its circumference. Next, the 130mm diameter circle was carefully cut out and folded first in half, and then once again into quarters. When the paper is unfolded the centre is marked by the intersection of the two crease lines. A scalpel (lol!)was used to excise a very small hole at the centre of the unfolded paper and then it was placed over the mirror, being secured in position with some cellotape. Finally, a doughnut shaped sticker was placed on the spot exposed by the hole. Job done!

Marking the centre of the mirror for collimation purposes.

Marking the centre of the mirror for collimation purposes.

 

 

 

 

 

 

 

 

The optics were then rehoused in the tube, collimated using an inexpensive laser collimator (SkyWatcher) and briefly tested with an eyepiece. Everything looked dandy!The telescope should now deliver brighter, more contrasty images on all celestial targets. And those special coatings will last at least a quarter of a century!

Surely now Plotina will be as durable as any high quality refractor nay?

All I have to do is wait for a decent clear spell to see how well she performs under the starry heaven.

Plotina pining for a clear sky.

Plotina pining for a clear sky.

 

 

 

 

 

 

 

 

 

Wednesday, March 23, 2016

Jupiter as it appeared in the modified Heritage 130P travel Newtonian on the evening of March 23, 2016.

Jupiter as it appeared in the modified Heritage 130P travel Newtonian on the evening of March 23, 2016.

Beginning about 20:30 UT this evening, I took advantage of a clear spell after a few hours of light rain. Jupiter was about 34 degrees above the horizon and rising, and I continued observations through to 21:15 UT before more cloud rolled in. I captured some beautiful detail on the Jovian disk, including the appearance of the GRS at the planet’s eastern limb. As the minutes passed, the view of Jupiter got ever better as it gained in altitude. The 130mm f/5 performed flawlessly. The planet was brighter, crisper and cleaner than I had ever seen it before with this instrument under these conditions (Ant II). To say that I’m pleased with the modifications would be an understatement, but we’ll leave it at that.

I heartily recommend this telescope to my amateur friends across the world.

Wishing you all a very blessed Easter.

March 31, 2016

23:50 UT

I enjoyed a half hour with the Heritage 130P this evening after I had observed Jupiter. After spending some time in Leo hunting down some spring galaxies, I started looking at some double stars. Gamma Leonis was easy, Castor A and B just as easy, iota Cassiopeiae triple lovely and all three components resolved. Mizar & Alcor were glorious at 150x as was Polaris A & B. Izar (epsilon Bootis), a summer favourite, was high enough in the east for me to split it. These were all seen at 183x save for Mizar & Alcor. I then decided to try a pair of stars I haven’t visited in a while; Alula Borealis and Alula Australis in Ursa Major. They are high overhead this time of year. Aiming is quite difficult using just the RDF but with my 32 mm Plossl delivering 20x, I was able to frame them both in the same field. Starting with the orange star Alula Borealis, I employed 183x using my most comfortable ocular; the Mark III Baader Hyperion zoom set to 8mm with its 2.25x Barlow. Although this does not show the highest contrast views (but only by a surprisingly small margin!!), I was able to see the very faint spark of its companion. The primary is magnitude 3.5 but the secondary shines at magnitude +10.1 and only 7.4″ separating them! I was chuffed to see this in such a humble little reflector. Then came the icing on the cake; I moved south to Alula Australis (Xi UMa) and could see that the star looked ‘entangled’ but I knew I needed a little more power to get a clearer view. So I ran in and fetched by 6mm orthoscopic and coupled it to the little 2.25x Barlow yielding 244x, centred and focused carefully: Voila! The pair (1.6″ split) were beautifully resolved (magnitudes 4.3 and 4.8), the components round as buttons, with a kind of diffraction halo encircling them; kind of like an ‘aura’ encasing two luminous eggs in a wafer thin handkerchief lol.

I was absolutely beside myself in admiration for what this little telescope can do! I believe Newtonians have been terribly maligned as unsuitable for high resolution work relating to double stars but I now know that this is another myth. The telescope takes very high power well under reasonable seeing conditions and totally exceeded my expectations.  I feel privileged to finally ‘know’ and  to share this personal discovery with my peers.

If no one bothers, how can one ever discover the truth? The Heritage 130P is unreasonably excellent on everything; a great little bundle of joy!

April 7, 2016

Mr. Adam Blake from Pennsylvannia USA, was kind enough to share some video footage of Jupiter he captured with his One Sky Newtonian, as seen on the evening of April 5, 2016 during a spell of good seeing. He used an inexpensive 5X GSO Barlow and standard UV/IR filter on the camera at prime focus to capture the images, which have only been very lightly processed to show the telescope’s potential. See below.

Mighty Jupiter as captured by Adam Blake using the 130mm f/5 Newtonian on the evening of April 5, 2016.

Mighty Jupiter as captured by Adam Blake using the 130mm f/5 Newtonian on the evening of April 5, 2016.

 

 

 

 

 

 

 

 

 

 

21:30UT

I aimed the Heritage 130P at iota Leonis, now high in the south. Using 244x I was able to quite easily resolve A-B. The primary shines with magnitude +4.06 and the secondary +6.71 with 2.1″ separating the components. I would warmly encourage others to try this system, as well as the aforementioned star systems with this telescope.

A Portable Dew Buster: Are you concerned about dew building up on the open tube of the Heritage 130P? Nae worries! I never let any heating devices within a country mile of my telescopes, just like my forebears. I bought a portable three-speed fan for about £10 that zaps dew in seconds from the secondary and primary using cold air. Now you can enjoy the telescope under the stars for as long as you like!

Laudate Dominum!

 

 

 

 

 

 

 

 

 

April 28, 2016

00:30h

At an ambient temperature of -1C, the Skywatcher Heritage 130P worked flawlessly to bag epsilon 1 and 2 Lyrae, eta Bootis (with its 10th magnitude companion), pi Bootis ( AB:  4.9, 5.8  separation  5.4″ and  AC: 4.9,10.6, separation 127″), alpha Herculis ( AB:3.5, 5.4, separation 4.6″ and a corker, AD: 3.5, 11.1, separation 79″)

For lunar and planetary studies, I can also recommend the Baader single polarising filter to use with this adorable little telescope. Retailing for £32.00, it significantly enhances belt detail on Jupiter, reduces glare and presents the planet in its natural colours.

The superlative Baader single polarising filter.

The superlative Baader single polarising filter.

 

 

 

 

 

 

 

 

 

 

Sunday, May 15, 2016.

The view from the sandy beach at Luss, on the western shore of Loch Lomond. May 14, 2016.

The view from the sandy beach at Luss, on the western shore of Loch Lomond. May 14, 2016.

 

 

 

 

 

 

 

 

 

 

During a relaxing weekend away with a group of old friends in the picturesque and historic village of Luss, on the western bank of Loch Lomond, I took the little SkyWatcher Heritage 130P along with me, as it was so easy to transport and set up. After long sunny days outdoors, I set the instrument (on its Dob mount) up on the garden table for a look at Jupiter and the first quarter Moon, which were perfectly positioned in the evening sky.

The Skywatcher Heritage 130P on holiday.

The Skywatcher Heritage 130P on short vacation.

 

 

 

 

 

 

 

 

 

 

As this was an annual event away, the crew were expecting me to bring along a telescope, but it is usually of the short refractor variety. I got some odd looks from the gang as I extended the upper stage of the ‘strange’ reflecting telescope, but I was sure glad I made the effort; they were all mightily impressed by the images the little portable reflector served up:- and even more gobsmacked when I told them how relatively inexpensive an instrument of this quality cost to acquire!

That's it guys: form a nice orderly queue.

That’s it folks: form a nice orderly queue.

 

 

 

 

 

 

 

 

 

A close encounter with the first quarter Moon: Kenny's face says it all!

A close encounter with the first quarter Moon: Kenny’s face says it all!

 

 

 

 

 

 

 

 

 

 

 

July 21, 2016

 LightBridge Mini 130 5.1" tabletop altazimuth mini-Dob reflector by Meade Print Home Telescopes The Meade LightBridge. Image Credit: Meade Instruments.

The Meade LightBridge Mini 130 5.1″ tabletop alt-azimuth mini-Dob reflector
 Image Credit: Meade Instruments.

My collegaue at Astronomy Now, Steve Ringwood, has independently reviewed the New Meade Light Bridge 130 Mini Dob for the August 2016 issue of Astronomy Now (now in the shops) on page 108-10. Although a slightly different design to the Heritage 130P featured in this blog, the optics are essentially the same but features a solid tube and a more traditional four spider-vane secondary support for even more rigid collimation maintenance in the field. Steve found that the optics were very good indeed, being capable of powers in excess of 200x, in agreement with my findings. At $200, it is priced at the same as the One Sky Newtonian from Astronomy Without Borders, discussed above.

So more choice for the discerning amateur.

Brian Schultz, from his YouTube channel Cool Space, describes how the One Sky Newtonian can be fitted to an inexpensive go-to mount for added versatility. See here for a video clip.

August 8-9 2016

The Old Man of Storr, Isle of Skye, as seen in the opening scenes of the block buster movie, "Prometheus".

The Old Man of Storr (elevated in the distance), Isle of Skye, as seen in the opening scenes of the block buster movie, “Prometheus”.

Our family ventured to the remote Isle of Skye, a place of outstanding natural beauty, for our summer vacation. My trusty 130mm f/5 Heritage Newtonian travelled with us. Though the weather was mostly damp and windy, I did enjoy a bout of observing with the instrument during brief clear spells on the evenings of August 8 and 9. The sky is truly glorious at this location, presenting some of the darkest and most transparent skies in all of Europe. And the (not so) little 130mm did not disappoint, serving up jaw-dropping views of the northern Milky Way high overhead, once the crescent Moon fell out of the sky. Deep sky objects were a joy to behold, including M31,Caldwell 14, M57, M13 and M92. The North American Nebula in Cygnus was as plain as the nose on the your face, as were the eastern and western Veil nebulae nearby.

Plotina ready for action on the remote island of Skye.

Plotina ready for action on the remote island of Skye.

I can also report that high resolution targets – including a batch of close test double stars – presented very well indeed. Images of systems such as Izar, delta Cygni etc, were calm and well resolved at high powers (243x), showing that this island has good seeing conditions for such work. Scotland has many such places(as I continue to discover) if one is intrepid enough to find them out!

September 30, 2016

My experiments with the Skywwatcher  Heritage130P continue apace. A while back a kindly gentleman from the USA alerted me to a potential issue with the instrument; the loss of precise collimation as the instrument is pointed to different parts of the sky. In a series of experiments conducted over the last six weeks or so, I discovered that while tightening the shaft that holds the secondary mirror in place seems to solve this problem for lightweight eyepieces, it doesn’t always hold collimation for heavier oculars such as the rather bulky, Baader Hyperion zoom.

As a consequence, I have reassessed the suite of oculars I use with the instrument and have switched entirely to smaller, more lightweight units. Below is an image of my current experimental set up; a 32mm Plossl, delivering a power of 20x and a 2.5 degree true field. Using the tiny, screw-on 2.25x Baader Barlow, I can couple the 32mm ocular to give a power of 45x and a true field of ~1.1 degrees – just large enough to frame the entire Double Cluster in the field!

For higher power work, I use a Parks Gold 7.5mm delivering 87x, a 6mm Baader classic orthoscopic yielding 108x, and a 4mm Revelation Plossl (fully multicoated) giving 163x. Finally, using the 2.25x Barlow I can achieve 243x and even 366x when mated with the 6mm and 4mm oculars, respectively. I also have an old 1.6x screw-on Barlow made by UK Astro Engineering, which gives me still more options to play with.The Barlows will increase the eye relief of the short focal length of the short focal length eyepieces too.

Plotina with a suite of lightweight oculars and low profile Barlows.

Plotina with a suite of lightweight oculars and low profile Barlows.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Over the winter I hope to fine tune this set up some more, but I am very happy with the range of powers available to me and the relatively low cost of its operation.

I also intend purchasing some Bob’s Knobs collimating screws to fit to the secondary assembly in order to make collimation even more easy to achieve.

I will report back later in the year to tell you how I got on!

The instrument continues to inspire in so many ways and needless to say I have grown very fond of using it.

Thursday, October 13, 2016

Plotina received her new set of Bob’s Knobs secondary screws to make fine adjustments to collimation easier. I consider these to be a quality acquisition going forward.

Bob's knobs for easier adjustment of the secondary mirror.

Bob’s knobs for easier adjustment of the secondary mirror.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Monday, October 17, 2016

Upon further investigation, I have been able to tighten up the stalk holding the secondary mirror in place by inserting a small washer, as shown below.

A simple washer tightens up the secondary support.

A simple washer tightens up the secondary support.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This increased rigidity allows the instrument to maintain precise collimation even after moving the telescope wildly in altitude and azimuth. This was verified using a laser collimator. The telescope can now use larger oculars once again, including the Baader zoom.

Monday & Tuesday, October 18 and 19, 2016

A break in the wet autumnal weather over the last two nights has allowed me to conduct further tests with the SkyWatcher 130mm f/5 Newtonian. I fielded a 90mm apochromat (retained for further testing) side by side with the instrument and studied how both performed on a variety of high resolution targets located in different parts of the sky.

Test instruments: a 130mm f/5 Newtonian (left) and a 90mm apochromatic refractor (right).

Test instruments: a 130mm f/5 Newtonian (left) and a 90mm apochromatic refractor (right).

Yesterday evening, shortly before midnight, I compared and contrasted both instruments in respect of their ability to maintain crisp, bright images of a waning gibbous Moon. Once our satellite achieved a decent altitude, I cranked up the magnifications on both instruments and examined the cratered terrain along the day-night terminator. Both instruments performed well but the larger aperture of the Newtonian allowed me to employ significantly higher magnifications (in excess of 300x) before the image became unsatisfactorily dim for my liking. The 90mm refractor, in contrast, maxed out about 200x.

Tonight, with better seeing but in colder(+4C) and hazier conditions, I ran the two telescopes to a variety of double star targets at various altitudes; gamma Delphini, theta Aurigae, Iota Cassiopeiae and delta Cygni; these systems were deliberately chosen so as to test how the 130mm Newtonian would hold collimation as it was adjusted in altitude and azimuth. My results show that the insertion of the washer in the stalk supporting the secondary mirror (described above) worked perfectly well, the stellar images remaining crisp, round and tiny. In every case, the Newtonian produced brighter, more convincing splits of these systems under equivalent magnification regimes – 200 to 250x.

These results show that the Newtonian is a wonderful, cost-effective and versatile instrument for all celestial targets and is noticeably superior to a much more expensive 90mm refractor, which quickly runs out of both light and resolving power in comparison.

I continue to highly recommend this instrument to those who are looking for excellent performance on a limited budget.

Nothing more to say really.

Thanks for following this blog.

Best wishes,

Neil.

Update: February 15 2017

My colleague at Astronomy Now, Ade Ashford, is helping to change culture by writing an excellent four page article on how to tune up the SkyWatcher Explorer 130PDS, mentioned in the blog above, and essentially the same telescope optically as the Heritage 130P (but with a closed tube) for better visual and photographic use. You can read this VERY interesting article in the March 2017 issue (page 98 through 102), out now.

Update: July 17 2017

Time: 00:09 BST

Location: Wigtown, Southwest Scotland.

Seeing: ( I to II): generally excellent, very calm

Instrument: 130mm f/5 Newtonian

Comments: A fabulous bout of double star observing. See notes below.

 

 

 

 

 

 

 

 

 

 

Update: July 18 2017

Time: 00:45 BST

Comments: Just in from another excellent session with the 130mm Newtonian. Highlight of the night was tracking down and resolving the lovely Mu Cygni. Tight pair, even at 244x and a fainter ‘companion’ wide away making it seem more like a triple system. Generous aperture and solidly good optics made very light work of this system. Like I said, this is arguably the best grab ‘n’ go ‘scope on the market today.  Details below;

 

 

Update: July 21 2017

Time: 00:35 BST

Instrument: 130mm f/5 Newtonian, aka ‘Plotina’

Seeing: Excellent (I); very clear before midnight. Some cloud moved in after midnight.

Comments: Still in Wigtown. Third night where conditions have been excellent.

Some very tricky systems resolved once again this evening with this modest telescope. Textbook perfect results!

 

 

 

 

 

 

 

 

 

 

Update: April 4 2018

The Astronomers Without Borders, One Sky Newtonian thread has now exceeded 300,000 hits!

 

 

De Fideli.

Further Adventures with a 3″ Achromatic..

An amazing performer; the Orion SpaceProbe 3 reflector.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dedicated to John Wall (1932–2018).

a chromatic: literally, without colour.

There has never been a better time to begin the hobby of telescopic stargazing. In past generations, owning a good telescope often proved to be an expensive venture, typically involving many months or even years of saving up. Thankfully, such days are well and truly behind us. Today, you can purchase a decent quality telescope for a very light financial outlay. Indeed, I always advise novices not to spend a great deal on their first telescopes, especially if they are unsure whether or not they intend to pursue the hobby in the longterm. In addition, many people will end up being ‘casual’ or ‘occasional’ observers and so splashing out lavish sums of money on an instrument that sees little net use doesn’t make a whole lot of sense.

In this capacity, one of the best novice ‘scopes I have personally come across is the Orion SpaceProbe 3 reflecting telescope (pictured above, fully assembled), which set me back about £70. That money bought me a very good 3 inch (76mm) telescope, together with a decent mount and two good quality eyepieces delivering magnifications of 28x (using the 25mm ocular) and 70x (when the 10mm eyepiece is employed) and an excellent instruction manual written by an experienced astronomer to show you how to set up the telescope properly, as well as guidance on how to keep the optics in tiptop condition.

All good starter ‘scopes need a good instruction manual.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Orion SpaceProbe 3 is the latest incarnation in a long line of Newtonian reflecting telescopes, so called because its ingeniously simple design was invented by Sir Isaac Newton around 1668. Over the years, the Newtonian telescope has been steadily improved and refined so much so that today it is arguably one of the most popular kinds of astronomical telescope on the market. Generations of skygazers have enjoyed the crisp, bright images served up by these telescopes, allowing them to conduct detailed observations of a wide range of celestial real estate, from the Moon and the the bright planets, to pretty star clusters, nebulae and distant galaxies in the depths of space.

The optical tube displays the basic optical information of the telescope, including its aperture (76mm) and focal length (700mm).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Space Probe 3 telescope has a focal length of 700mm and we need to know this number in order to calculate the magnification being used with any given eyepiece. Fortunately, it’s a simple calculation; just divide the focal length of the telescope by the focal length of the eyepiece. So the 25mm ocular produces an enlargement of 700/ 25 = 28x and the 10mm eyepiece provides a power of 700/10 = 70x. Although these will give very pleasing views at ‘low’ and ‘medium’ power, one will eventually need to stretch the magnification some more to get the best views of high resolution targets like the Moon and bright planets. Furthermore, by dividing the focal length by the aperture, i.e. 700/76, we obtain a quantity called the focal ratio of  9.2 or f/9.2. The significance of this number will become important as I elaborate on the optical quality of the telescope in due course.

My field testing over the last two months has clearly shown the potential of this little telescope. A good instrument ought to garner sharp images at powers of 50x per inch of aperture. So according to this reasoning, a 3 inch reflector ought to handle 150x. But I can assure the reader that this telescope can handle considerably higher powers and these high powers can prove very useful for certain kinds of astronomical observations. I have used the instrument profitably at powers of 210x or more but one must also bear in mind that as one pushes the magnification to these high values, the images become rather dim owing to the small 3 inch mirror gathering the light.

By far the most economical way to achieve a greater range of magnifications is to invest in one or two Barlow lenses. Typically they will boost the power of any eyepiece by a factor of anywhere from 1.5 to 3 times. You can get a decent Barlow for just a few tens of pounds (it’s always worth watching out for one on the secondhand market too) and when skillfully chosen, can turn two eyepieces into four or even six. For example, a 2x Barlow will enable the two eyepieces supplied to give additional powers of 56x and 140x. For this particular study, I employed 2.25x and 3x Barlows, providing high powers of 158x and 210x, respectively, when coupled to the 10mm eyepiece supplied with the telescope.

The eyepieces and Barlows used with the telescope. From left to right: the 25mm ocular, the 10mm ocular, the 2.25x and 3x Barlow lenses.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

One of the most attractive features of the telescope and its mount is its overall weight; just 8.4 pounds (3.8 kilos)! That means that most anyone can move the fully assembled instrument about. The lightweight, but strong aluminium tripod can be collapsed or extended for seated for viewing or by standing. I decided to use the instrument without its accessory tray so as to maximise the stablity of the tripod. In addition, I elected not to attach the slow motion control bar. This is a strategy I have adopted for many years now, as I like to keep the up−down (altitude) and sideways (azimuth) motions to be as free as possible whilst in ue. With many hours of practice, I have learned to nudge the telescope along smoothly and with minimal vibrations, even at high power. I accept that this is essentially a learned skill and that others may not be happy with it. Only time spent at the telescope can ultimately sway you in one direction or another, and I would encourage as much experimentation as possible in this regard.

To get the very best images out of this telescope, the user must ensure that the optics are accurately aligned. The user manual with the supplied collimation cap and Philips screwdriver will enable you to accurately execute such a task. Experience shows that once this is done, the telescope retains very accurate optical alignment, even after being moved from indoors to the outside many dozens of times. This fine tuning of the optical train will make a noticeable difference to the high power views especially.

By and large, telescopes are not status symbols. How they look counts for practically nothing in the scheme of things. That said, this telescope is well made and is handsomely finished. It ‘looks’ like a ‘proper’ telescope and performs like a ‘proper’ telescope. The rolled aluminium tube is finished in an attractive British ‘racing green’. Some readers concerned more with appearances than anything else (an ugly reality for some, unfortunately) will no doubt fuss over whether or not it ‘looks the part’ and may falsely ascribe importance to what ‘others’ might think. This rather sad state of mind can be entirely dispensed with however, when one realises that amateur astronomy is very much a small ‘goldfish bowl’. The vast majority of folk I have shared my telescopic experiences with know next to nothing about telescopes and can’t discern anything from its appearance. Indeed, you’re as likely to find a telescope like this in a New York penthouse balcony than in a tenement of a working class community. Telescopes are just not like cars! So, if you’re concerned about something as trivial as ‘looks,’ you’re probably in the wrong hobby!

To get an idea of how good the optics are in these telescopes, it pays to take the instrument out during daylight hours. I like to observe nature with as many of my telescopes as possible and usually select a good spot in my garden, out of direct sunlight, and give the instrument a few minutes to settle down in its new environment. To work at its best, any telescope must be allowed to equilibrate with its ambient environment. Failure to do so will provide less than optimal (read disappointing) results, especially when the telescope is ‘pushed’ to high magnifications. I recommend starting with the lowest power eyepiece; this will be the 25mm Explorer II ocular supplied with the telescope delivering 28x. I usually select a distant tree top a few hundred yards distant or some such which I can zoom in on. Care must be taken to avoid observing targets over possible heat sources, such as rooftops and the like.

Once a suitable target is chosen, crank up the magnification gradually, carefully touching up the position of best focus by moving the drawtube housing the eyepiece slowly back and forth until the sharpest possible images are produced.

Good focusing is an essentail skill, especially when attempting to ‘push’ the magnification of the telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

By engaging in such an activity, I have discovered that the telesope can take high powers in its stride. The images remain crisp and sharp right up to 210x and beyond, especially on bright sunny days. This comes at the expense of image dimming though; higher powers yield progressively dimmer images. This image quality is no doubt facilitated by the high focal ratio of the telescope (f/9.2 in this case). When the focal length is long in comparison with the aperture of the ‘scope, geometrical aberrations are minimised; less field curvature, coma, distortion, spherical aberration, astigmatism etc. This alows for the use of simpler and less expensive eyepieces so that using the telescope will not create a ‘black hole’ with your resources.

Oh deary me!

 

 

 

 

 

 

 

 

 

 

 

In this way, you will discover that this telescope is a very sharp shooter that will embarrass owners of much more expensive telescopes of comparable aperture. The images you will enjoy are true and honest; a simple consequence of the laws of optics and good execution. Here’s an image taken my the US−based amateur, Joe Roberts, who took the time to image the first quarter Moon at prime focus (be sure to click on the image for a good close up) with the same telescope albeit on a sturdy motorised equatorial mount. I hope you will agree that this little telescope is no toy!

More a hindrance than a help: the EZ finder that comes with the telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

One of the Achilles’ heels of this telescope package might not be uncovered until one spends a good few hours in the field. Specifically, many decent−sized telescopes come with the equivalent of a ‘rifle sight’ or ‘finder’ telescope, which usually attaches to a bracket found on the top of the main telescope, adjacent to the focuser draw tube. Once aligned with the main telescope, it serves as a very useful tool to find and centre objects quickly. But the ‘finder’ supplied with the Orion SpaceProbe 3 is not a  telescopic ‘finder’ as such, but a non−magnifying device (the EZ finder) that projects a small red dot onto a plastic screen which the user is required to co−align with whatever object is to be observed in the telescope. However, a few sessions of active use with the EZ finder will convince most of its inadequacy. For one thing, the EZ finder can only be used with the brightest stars and for those who live in towns and cities, where light pollution may be a concern, using it will prove more an exercise in frustration than anything else.

For this reason, I would strongly recommend the user swap this device out for a regular finder telescope; a small traditional finder ‘scope magnifying perhaps five or six times and having an objective (front lens) of about 30mm. These can be purchased on the used market for very little money. Indeed, if you play your cards right, you may find a sympathetic amateur who will provide you with one for free! Mounting such a finder ‘scope will greatly enhance the enjoyment one can have with the telescope. You’ll be able to focus in on much fainter targets, and learn how to ‘star hop’ from one object to another.

Close up of the finder I mated to the scope; note the matching colour and texture of the finder bracket with the focuser and rim of the optical tube assembly. Schmokin’

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Before you can use the finder, it must be aligned with the main telescope. This is easy to do in daylight. Just select a distant target (as far away as posible and at least a few hundred yards in the distance) and centre it the main telescope. Now look through the finder ‘scope and  move the cross hairs of the finder so as  they coincide as precisely as possible with the image in the main telescope. This is usually done by tigtening or loosening a set of screws in the bracket mounting the finder. Once that’s done, move the telescope to a different target and check to see that the subject you have centred in the main instrument is also centred in the cross hairs of the finder ‘scope. If so, you’re ready to rock ‘n’ roll!

The position in which the observer looks into the telescope has a direct bearing on viewing comfort. And the more comfortable the telescope is to use, the more you will use it. In this capacity, the convenient location of the focuser drawtube makes it easy to observe objects situated at low altitudes but it is while viewing targets high in the sky that the great utility of the Newtonian design shines through. As a former refractor enthusiast, I certainly do not miss the extraordinary degree to which one has to crouch down into very uncomfortable positions near the ground in order to view a high altitude target for any length of time. The simple truth is that Newtonians dispense of much of this hardship. Because I value my back and my posture, observing with the Orion Spaceprobe 3 provides a good way forward.

Every budding telescopist needs a guide book of sorts. It can be hard to know what’s what, observing from a bright, suburban sky, and from a dark site, where the full glory of the heavens is manifested, it’s very easy to get confused. That’s where a simple guide to the night sky is so useful. It will be prove indispensable as your knowledge and observing skills develop. There are many good literary guides available to the modern amateur. I especially like Ian Ridpath and Wil Tirion’s Stars & Planets (Collins 2017). It’s strength lies with its simplicity. You can use the seasonal and monthly maps to find the outline of a constellation you wish to explore and then home in on your selected target(s) for the evening. The lunar maps are very good too. Overall, I have found it an invaluable aid to small telescope forays in the northern hemisphere, but is equally at home under an antipodean sky.

The new edition ( October 2017) of a favourite observing guide.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Finally, though it may seem a bit old fashioned nowadays, I recommend that all observers adopt a culture of regularly recording the sights and sensations one experiences while at the telescope. Notes are an important thread to the past.  It’s amazing how much one forgets as the years go by, and it is so reassuring to have the means of consulting earlier work in matters that may prove important at some later time.

 

 

 

 

 

 

OK. With all that said, we’re now ready to begin an adventure together under the stars, exploring something of the extraordinary riches of the heavenly creation. It is fitting to begin this journey with the brightest and most accessible object in the night sky; our glorious Moon.

Oona: a perfect ‘scope for moongazing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: January 31 2018

Time: 22:00 UT

Conditions: Clear, bright sky, very little cloud, bright full Moon.

Temperature: 0C

Tonight is a Super Blue Moon. This means that the Moon is bigger and brighter than average (that’s the ‘super’ bit). It is also the second full Moon in the month (making it’ blue’), the last one occurring on January 2nd last. Inserting the 25mm Explorer II eyepiece and focusing the telescope shows a big bright orb. Indeed it’s almost dazzlingly bright, prompting some observers to reach for a neutral density filter to cut away some of the glare and reduce eye strain. Notice also that the reflected light from the full Moon makes the background sky very bright, drowning out the light of many of its fainter stars.

Did you notice that the image of Moon is both upside down (meaning north is at the bottom and south is at the top) and back to front (meaning east and west are the wrong way round)?

All of this is completely normal with a Newtonian telescope. Indeed, spatial orientation is of little importance in the pursuit of astronomical bodies. You’ll soon get used to it!

Now, looking at the Moon itself with the 25mm eyepiece delivering 28x. Notice how big the entire field is. Indeed, you can easily see that it will fit about three full Moons from one side to the other. Since the full Moon subtends an angular size of about half a degree on the sky, this gives you an idea of how large the field is in the 25mm Explorer eyepiece; about 1.75 degrees. That’s plenty big enough to see the vast majority of deep sky objects, as we shall see on other evenings.

Chances are you’ll have also witnessed two ray craters on the lunar surface. Down near the bottom of the Moon (as you observe it in the northern hemisphere) is Copernicus and the one near the top is called Tycho. Can you see how rays of bright matter seem to stream from these craters? The rays are caused by ejected material gouged out when a large, rocky body collided with the lunar surface in the distant past, ejecting huge quantities of material away from the crater and in all directions (that is, radially). Such ray craters are very old: Tycho is believed to have formed some 100 million years ago, while Copernicus is thought to be 10 times older still (so a billion years or so).

The two prominent ray craters visible in the telescope; seen here in the correctly orientated view.

 

 

 

 

 

 

 

 

 

 

 

Because your telescope is a reflector, it shows the true colour of the lunar regolith. Looking closely at its surface will convince you that it has many shades of white and grey, revealing something of its mineral content and age.

Next, remove the 25mm eyepiece and replace it with the 10mm. After centering the Moon and refocusing; you will note that the field of view is considerably smaller and yet it’s still larger than the size of the full Moon. Indeed, this 70x eyepiece serves up a fairly generous field of view of about 0.7 degrees.

It follows that as the magnification increases for a given eyepiece design, the field of view shrinks.

This observing session will have familiarised you with the magnifications and field sizes for your two eyepieces. These will be useful data as we plan our observations of other celestial bodies.

Alas, observing the Moon while it is full is the absolute worst time to see many of its most inspiring features. To see the great mountains, valleys, craters and rilles; we’ll have to wait until the Moon proceeds through its last quarter and crescent phases. We shall return in a few days when it begins to wane.

Be sure to tune in again soon; you won’t be disappointed!

Date: February 5 2018

Time: 00:35UT

Conditions: good, steady conditions, almost totally clear, cold.

Temperature: −1C

I’ve been watching the Super Ball!

No, that’s not a typo!

It’s a lovely winter night here in the glen. The Moon began to rise about 10:30pm local time, but I waited a couple of hours before beginning observations of the waning gibbous Moon. Charging the telescope with the 25mm Explorer eyepiece, I watched in sheer amazement as our wonderful natural satellite rose above the tree line in the east. Even with the 28x eyepiece, there was a wealth of fine detail to be seen. At low altitudes the air roils quite a bit. That’s totally normal. At low altitudes, you are looking through a dense swathe of air, which generates a bit of turbulence. At these low altitudes, you can even make out subtle colour differences in the lunar regolith. Specifically, the Moon takes on a very light, rose tint. This is also to be expected, as at lower altitudes there is more dust which scatters blue light more than red (a phenomenon called Rayleigh scattering). I find it very beautiful! Compare its colour again when it rises a lot higher in the sky. That comely rose tint all but disappears. Only its silvery face presents itself when it rises above the dust line.

Below is an image of how you should see this waning gibbous in the low power field of your 3″ reflector. I simply rotated and inverted a Wiki Commons image of the Moon at this stage in its phase. That said, I perceive the contrast in the telescopic image to be noticeably better than this image.

The waning Gibbous Moon as seen in the low power eyepiece of the telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As the minutes pass, the Moon rises higher and the image becomes steadier. When it reaches a decent height, say 15 degrees or so, remove the low power eyepiece and insert the 10mm ocular, delivering 70x. The image should remain nice and crisp and even more detail should be discernible. Use a Moon map to try to identify some of the sights your eye meets with. As the Moon rises above 30 degrees altitude (so about one third of the way from the horizon to the zenith), use a Barlow lens to boost the power still more. If the optics are working half decently and are properly aligned, you ought to get good sharp images at 150x or higher, if the air remains steady. That the images are crisp and clean even at these high powers testifies to the extraordinary value of this economical little telescope.

Intriguingly, February 2018 will not have a full Moon (it will be almost full though lol); something that hasn’t happened since 1999. And, as if in recompense, March 2018 will have two full Moons; one on the 1st and the other on the 31st. So March 2018 will present another Blue Moon if you’ve missed the apparition in January.

I like to name all my telescopes. This little one is called Oona.

Wee Oona; ready for action.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: February 6 2018

If you follow the phases of the Moon faithfully with the little Space Probe 3 telescope, you’re sure to have an absolute ball. It will serve up beautiful images time and time again. Arguably the best times to observe our natural satellite is between the half−illuminated and crescent phases. You will be astonished at just how much this instrument can reveal!

When taking the telescope and your eyepieces from the cold night air back inside to a warm indoor space, chances are you’ll notice that some condensation may form on the optical surfaces, in much the same way as steam from a kettle fogs up a cold window. This effect of fogging up is more inconvenient than anything else, but you can largely avoid it by capping your eyepieces and the telescope before you bring them back indoors. Under no circumstances are you to rub the lenses or the mirrors while they have dew on them. If you see signs of condensation, just let it evaporate away before capping up the optics. These simple measures will ensure that your equipment will remain in top condition for many years to come.

Observing the Moon is only the first step in enjoying the Orion SpaceProbe 3. As we shall discover, a rich variety of celestial objects are within easy reach of this little telescope. All we need is another clear sky to explore them.

The Ever Changing Sky

The Northern sky on February evenings.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The night sky is constantly changing; minute by minute and hour by hour, as the world turns on its axis and races around the Sun. Consulting the all−sky maps presented on pages 30 and 31 of Ridpath and Tirion’s book, you can see how the February sky appears in the northern hemisphere. Looking south, we see Virgo, Leo, Cancer, Gemini and Taurus, as if in some grand procession, moving from east to west. Concentrating on the constellation of Cancer, the celestial Crab, featured on page 97, I have selected a single object worth investigating with the telescope; The Beehive Cluster (M 44).

The constellation of Gemini in our guide book. M 44 is seen circled near the centre of the consellation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The accompanying notes featured on page 96 give us enough background information in order to make sense of what the telescope will reveal. M 44 is an open cluster, also known as Praesepe (the Manger), the authors inform us. It is large, covering about 1.5 degrees, and consists of some 50 stars ranging in glory from magnitude 6  and fainter. It even tells us how far away the cluster is; a mind−boggling 592 light years according to measurements made by the Hipparcos satellite. It ought to be visible to the naked eye as “misty patch” from a dark country sky, making it easy to track down.

Time: 23:00−23:30 UT

Seeing: Good, clear, cold.

Temperature: −3C

I took the telescope out for a short spell tonight after work. It remained very clear all day, and on into the evening. It was another lovely vigil with a light dusting of fresh snow to brighten up the landscape. So, before the Moon came up, I ventured out when I knew the cluster would be highest in the sky, that is, when it’s due south. Where I live, M44 is a very easy naked eye object. Just like the authors described, it’s a fairly conspicuous “misty patch” that is easily framed in the finder ‘scope and the main telescope proper. Only one eyepiece was used tonight; the 25mm Explorer II, delivering 28x. It framed the cluster perfectly, where dozens of stars of various degrees of glory pepper the field of view. And it’s not at all hard to see why its more popular name, the Beehive Cluster, is alive and well.  With a little concentration, you can make out a soft, yellow colour in the brighter members; a good sign that this cluster is fairly mature in the scheme of things. I made a simple sketch of what it looked like (see below). If you are warm and comfortable, sketching can be a whole lot of fun, even in the cold of winter. I simply try to memorise what the field is like for 10 or 15 minutes, nudging the telescope along with one finger as the Earth rotates beneath my feet. Once I’m indoors I make the sketch. Little Oona frames lots of things in the sky very well.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are, of course, other ways to make a sketch. Many do so while at the telescope. In order to do that, it’s advisable to protect your night vision as much as possible. You see, in the dark, your pupils dilate to take in as much light as possible. This is a natural biological response to low light conditions. Fortunately, red light does not appreciably interfere with this dark adaptation, and so many amateurs choose to make their telescopic sketches of deep sky objects under the illumination of a low intensity red light source. Whatever way you choose to carry out your sketches, I hope you will find the activity both relaxing and rewarding.

Date: February 8 2018

Some Musings on Optics

Anyone who has spent a decent amount of time with this telescope and knows how to keep the optics well aligned will surely tell you that the images are exceptional for its meagre monetary value. The reason for the low cost is the simplicity of the optics. The prmary mirror is spherical rather than a true parabola. Spherical surfaces are much easier to execute well in comparison to their parabolic counterparts, which need further figuring to ‘deepen’ the centre of the mirror. But if its aperture is kept small and the focal length is large in comparison, there is absolutely no need to modify the sphere into a parabolic shape. To get an idea of just how good a 76mm (3″) mirror with a focal length of 700mm can be, take a look at a computation made by OSLO (an optics package);

An OSLO analysis of a perfect 76mm f/9.2 spherical mirror. The reader should concentrate on the red underlined data in the lower box.

 

 

 

 

 

 

 

 

 

 

 

 

If your mirror is a perfect sphere then you have a wavefront rating of 1/12.5 PV. Put another way, a completely error free mirror with these specifications would have a Strehl ratio (seen on the right above) of 1.0. The analysis shows that the actual value is shockingly close to absolute perfection: 0.97!

The conclusion is very simple to interpret: small aperture and long focal length spheres are so close to a parabola it makes little difference.

Of course, we also need to consider the aberrations introduced by the secondary mirror, but suffice it to say that unless the secondary is a complete lemon, it’s very likely that the overall quality of the optics will be very high indeed, good enough to impress anyone who takes the time to spend a few hours with it.

Star testing provides a good way to test how well the optics behave in the field. To do this, make sure the telescope has accurately aligned optics and has had time to cool down outside. Next, select a bright, first magnitude star, situated high up in the sky. For example, Capella is just perfect from my far northerly location. Select a high power; anything between 100x and 150x and carefully focus it. You ought to see a tiny sphere (the so called Airy disk).

The Orion Spaceprobe telescope supports the secondary mirror using a 3 vane spider (b above) and yields six diffraction spikes that are very hard to see except round the brightest stars.

 

Now, if you slowly rack the focuser inward, you will begin to see a set of concentric, Fraunhofer diffraction rings around a dark central spot.The shadow of the three spider vanes will also be seen.

And when you then rack the focuser outward, past the position of precise focus, the diffraction pattern should look identical (or almost so). This is what you want to see in a telescope offering very good to excellent optics. Star testing can provide much information about your telescope, but it’s always best to conduct such tests under the best conditions your local environment will provide, and (preferably) over a few nights. If you don’t get such textbook perfect results, don’t fret. I mean, if you’re already happy with the high power images your telescope is serving up during the day, and again by night, you have a winner and you needn’t worry any more.

Oona star tests very well, showing that her optics are of very high quality. Mass production has clearly come a long way with these little telescopes!

Date: February 9 2018

Time: 19:15 UT

Temperature: 0C

Conditions: good transparency, mostly clear, breezy

Orion is a majestic constellation to explore with a small telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

It was a bright and clear day today and the the sky has remained largely cloudless after dark. The mighty constellation of Orion the Hunter is now approaching its highest point in the sky so is nearly due south. It will present a good opportunity to examine an entirely different kind of deep sky object. Tonight, we will pay a visit to the Great Nebula in Orion. Our guide book on page 197 shows me exactly where to look: immediately beneath the middle star in the Hunter’s belt. The notes of page 198 inform me of some sensational facts about this target; the object, known also as M 42, is a gigantic ball of gas lit up by young stars that are forming inside it. The authors say M 42 lies about 1500 light years away and that it is almost 20 light years across, and much more. Time to set up the telescope once again for another adventure under the stars.

Time: 20:30UT

The Great Nebula in Orion is also easy to spot with the naked eye. A couple of seconds of scrutiny will convince you that it is quite unstarlike; more like another ‘misty patch’ than anything else. Starting with the 25mm Explorer II eyepiece, the telescope clearly reveals its nebular nature in a pretty hinterland of bright stars. If you carefully focus on the nebula, the same eyepiece should allow you to just make out four distinct stars at the centre; this is the famous Trapezium; very young and hots stars that are estimated to be only a few million years old. They formed out of the cool gas that surrounds them. Ordinarily, a gas cloud is not luminous in and of itself. It is only by virtue of the radiation from the stars that form inside it that renders it visible, just like a neon light bulb.

Now switch to the 10mm Explorer II ocular for a better view of this magnificent structure. At 70x, it is much easier to see the four stars making up the Trapezium, as well as much greater detail in the nebula itself. My eyes can clearly discern colour within the nebula; a very pale green. The colour becomes easier to discern as one’s eyes adapt to the darkness. The visual colour of M 42 is quite unlike that produced by a CCD camera however, which picks up vivid blues, pink and red, owing to its greater sensitivity to light. Still, just detecting some colour provides a real visual thrill.

Just to the north of M42, my eye meets with a ‘fuzzy’ star. This is in fact another nebula; M 43.  After several minutes of study, slowly nudging the telescope along as the object moves westwards through the field, I made a quick sketch of my impression of the view as seen through the little 3″ reflector.

M 42 as observed on the evening of February 9 2018 using the 76mm f/9.2 reflector. South is at the top and west is to the left.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Larger telescopes will give even more compelling views. That’s because larger telescopes collect more light and deliver that light to your eyes. A fully dark adapted human eye allows your pupil to dilate to about six or seven millimetres. That is the maximum ‘aperture’ of the human eye. But when you look through the telescope, that 7mm is replaced by a mirror fully 76 mm in diameter! As you can imagine, it collects many times more light than you can with your naked eye because its light collecting area is so much greater; and that allows you to see much fainter objects.

The orion SpaceProbe 3; a wonderful little light cup.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: February 11 2018

Time: 21:10−21:20 UT

Conditions: turbulent, frequent sleet & snow showers, very cold in the wind.

Temperature: −1C

Oona(right, background), accompanied by Octavius, my newly flocked and insulated 8−inch f/6 Newtonian reflector.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I spent Saturday afternoon lining the inside of my 8 inch f/6 Newtonian reflector with cork and then covered it over with flocking paper. This evening, I decided to test drive the 8 inch, which I had planned to use along side the 3 inch reflector, but the frequent interruptions from snow showers forced me to retire the larger instrument after about 15 minutes; I did however gather some useful data on a few tricky double stars.

Because the 3 inch telescope is so lightweight and ultraportable, it was the ideal instrument to use in these very mercurial conditions. And it allowed me to greatly extend my gaze. Everything we have visited thus far with the 3 inch reflector lies entirely within our own galaxy, the Milky Way. Tonight though, I spied the Plough asterism looming large in the northeastern sky and decided to try my hand at tracking down the famous Messier duo, M 81 & M 82; a wonderful pair of galaxies located at a distance nearly four orders of magnitude further away than even the Great Nebula in Orion!

Charting a course.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The pair is easy to track down in a dark, moonless sky. Consulting my guide book on page 251, I was able to chart a course for these fairly easily, by drawing an imaginary line from Phecda through Dubhe, and extending that line about twice as far again until I arrived at my destination. Tucked away in an otherwise fairly barren sector of the firmament, my finder could easily make out 7th magnitude M 81, and, with a wee bit more concentration, M 82 also. Once again, only one eyepiece was used this evening; the trusty 25mm Explorer II eyepiece, which easily framed the duo, separated as they are by about 0.6 angular degrees of sky. M 81 looks fuzzy and elliptical in shape, brightest near its centre and gradually fading towards its edges. M 82 to its north presents as completely different however; more cigar shaped than elliptical. After a while studying the pair, you may come away thinking that M 82 is easier to study, even though it is about four times fainter than M 81. Both galaxies lie at a distance of 12 million light years; an utterly unfathomable scale.

I made a quick sketch, shown below, of M81 and M 82, and its hinterland through the SpaceProbe.

Messier 81 & 82, as seen through the 3″ f/9.2 reflector on the evening of February 11 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are many more galaxes within reach of the little achromatic, and which will take us even further afield. Best to wait ’til better weather sets in though.

Date: February 14 2018

Time: 20:40UT

Temperature: 4C

Conditions: Mostly clear, some cloud interfering with observations, milder than of late, windy.

After enjoying a romantic Valentine’s supper together with my wife, I ventured outside to see how the sky was shaping up, and as luck would have it, it seemed very inviting to continue our adventures under the stars with the Orion SpaceProbe. As promised, we’re going to try our hand at objects significantly farther away than our former targets; specifically,  a trio of galaxies in the constellation of Leo the Celestial Lion, which will be very well placed later this evening. These galaxies are located about three times farther away than either M 81or M 82, so about 35 million light years distant from our galaxy, the Milky Way.

Our targets tonight are located in southern Leo, shown just above the tip of the pencil in this photo.

Consulting my guide book on page 169, I can clearly see the location of these galaxies; M 95, M 96 and M 105; which should be captured in the low power (28x) field of the 3 inch telescope. That said, these ‘island universes’ are considerably fainter than M 81 & M 82 and so will be a bit more challenging to see (my guide book quotes both M 96 and M 105 as having a magnitude +9, whereas M 95 is fainter still at + 10).

I shall report back later to tell you how I got on. Fingers crossed!

Time: 23:45UT

Alas, it has totally clouded over, so I will need to abort this activity tonight and try again another night.

Date: February 15 2018

Time: 14:00 UT

The weather is not always in harmony with human ambition. Meteorology may be a mature science, but it can’t yet be relied on with 100 per cent accuracy. There will always be discrepancies between what the forecast predicts and what you actually experience. It just comes with the territory of any amateur astronomer. That said, such episodes cultivate patience and preparedness; virtues in their own right.

It is a New Moon today, so a thin crescent should appear in the sky over the coming evenings. But once that Moon sets, it will be good and dark enough to ferret out those galaxies in Leo. I will report back again as soon as an opportunity presents itself.

Date: February 16 2018

Time: 00:30UT

Conditions: quite windy, some clear spells, remaining more mild than of late.

Temperature: +4C

I managed a short spell with the SpaceProbe just after midnight. By then, Leo had moved into a favourable position in the south southeast. I centered the finder ‘scope on the star 53 Leonis, which lies just south of the targets in an otherwise rather empty region of sky. Then, charging the 3 inch with the 25mm Explorer II eyepiece, I nudged the telescope about one angular degree to the north norhwest and scrutinised the field for signs of faint fuzzies. Sure enough, both M 95 and M 96 show up well in the little SpaceProbe at 28x. The more easterly M 96 is slightly brighter than M 95. The latter appears rather circular with a noticeable central condensation. To my eye, the fainter M 96 looks a wee bit more elongated along its north−south axis. Both of these objects are classed as barred spiral galaxies. Moving this pair to the southern edge of the field, your eye will pick up the giant elliptical galaxy M 105, appearing as a faint glow.

Although the strong gusts of wind and the constant interruption from clouds prevented me staying out for very long, you can visit another delightful trio of galaxies directly east of these objects; specifically M65, M66 and NGC 3628, also featured on the map above. All shining with magnitudes of about 9, they present as an equally challenging target for the 3 inch reflector. Do give them a visit if your skies permit.

Date: February 20 2018

Time: 14:00 UT

We’ve only just begun to sample the riches of the deep sky with the 3 inch reflector. By studying the maps provided in the guide book, you can explore many more, and all in their due season. The more you use the instrument, the more proficient you will become at finding these objects in the night sky.

I would now like to call your attention to an exceedingly rich cache of double and multiple star systems that can be studied with this little reflector. These objects are a particular favourite of mine, so I hope you will indulge me a little.

The world of double and multiple star systems.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On page 282 & 283 of our guide book, the authors discuss these fascinating objects. Our star, the Sun, is alone, but many stars in the firmanent, perhaps the majority, occur in so−called binary or multiple star systems, where each component is bound up by the gravitational attraction of its other stellar members. A few, as we shall discover, are not true binaries at all. They just happen to be situated very close to each other from our vantage but are not actually physically connected. Such targets are called optical doubles.

Like the many other classes of deep sky objects, double stars come in a variety of levels of difficulty; from the easy to difficult. Fortunately, the easiest double and multiple stars to see through the Orion SpaceProbe are also amongst the most beautiful. If the weather cooperates this evening, we’ll take our first steps into this fascinating sub−discipline of amateur astronomy.

Diviner of double and multiple stars.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 22:45−23:15 UT

Conditions; Cold, partially clouded over, decent clear spells.

Temperature: 0C

I managed a few simple drawings of some double and multiple stars near the north ceslestial pole. I had intended to sketch Castor A & B but was clouded out before getting to it. I will discuss these systems later.

Some simple sketches of double stars in and around the pole.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The above drawings reveal some easy double and multiple star targets near the north celestial pole. Where I live at 56 degrees north latitude, all of these systems are within easy reach, owing to their high altitude. Mizar is the middle star in the Plough handle, now situated high in the eastern sky. Closer naked eye scrutiny reveals that it has a fainter companion, but you’ll get a very pleasant surprise when you examine the system telescopically. For this you will need to use the 10mm eyepiece (70x)  as indicated in the sketch, but you should clearly see that Mizar itself is also double! It is without doubt one of the northern sky’s most celebrated double stars. Curiously, astronomers have discovered that although they appear to be co−located, there is no physical connection between them. Indeed, on page 252 of our guide book, Mizar is found to be 86 light years away and Alcor just 82 light years distant. Thus, we are looking at an optical double here. However, the close−in companion to Mizar is a bona fide companion. This was the first telescopic double ever to be discovered in the history of astronomy, being first sighted by Giovanni Riccioli in 1650.

In my sketch I have also recorded the faint star with a very lofty sounding name, Sidus Ludovicianum, situated between Mizar and Alcor. It is of note only because an intrepid 18th century German stargazer believed it was a new planet and, as was the custom in those days, named it after Ludwig V, his monarch.

Polaris, the pole star, is a completely different animal though. In the low power (25mm) eyepiece, it appears as creamy white star, but if you crank up the power to 70x or higher and closely scrutinise the space in the immediate vicinity of the star you will eventually notice a tiny, faint spark over 250 times fainter than the main star! You might want to increase the power that little bit more with a Barlow lens in order to see it even more distinctly. This is another true member of a gravitationally bound multiple star system, the other constiuents being too difficult to pick up in the little 3 inch reflector. Polaris A and B lie at a distance of 433 light years according to our guide book. Interestingly, Polaris A is a giant pulsating star known to astronomers as a Cepheid Variable. By studying this class of star, astronomers were finally able to elucidate the vast distances to the nearby galaxies beyond the Milky Way in the early decades of the 20th century.

Note: did you notice Polaris moves much more slowly in the telescopic field? Puzzled? Well, that’s because it lies less than one angular degree from the north celestial pole, the rotation axis around which all the stars in the northern hemisphere appear to whirl. This  rather convenient position means it is so much easier to study using the undriven mount of the SpaceProbe 3.

Moving into Canes Venatici (see page 99 of the guide book), yet another showpiece double is ripe for viewing. The brighter member appears white to the eye at 158x and the fainter looks more electric blue to my eye, though reports differ significantly between observers. Indeed, no two observers will report precisely the same colours! This system lies 115 light years away.

 

Date: February 22 2018

Time: 23:18

Temperature: +1C

Conditions: Cold, hazy skies, good seeing.

I had to tie up some loose ends and couldn’t come back to this as early as I had planned, but I made up for it somewhat this evening. Below are two further sketches I made at the eyepiece of the Orion SpaceProbe 3. The first is Castor A & B in Gemini. Using the map on page 153, I was easily able to pinpoint Castor high in the southern sky at 22:00UT. Centring the star in the 25mm eyepiece, I switched to the 10mm and was delighted to see that even at 70x, the components were well split. But you’ll get a much more majestic view if you crank up the power still more, and, like I said before, this telescope takes high power in its stride because its optics are very good indeed. If your sky is good, test it at 210x and I guarantee you’ll be gobsmacked by what you see!

Both Castor A & B appear pure white as the driven snow, and are quite close together; significantly closer than any system we have thus far visited. More on this tomorrow.

An observation of the close double star system Castor A & B, as seen on the evening of February 22 2018 through the 3 inch Orion reflector.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As the night marched on, the skies became steadily more hazy and visibility suffered as a result. But I spied Leo coming into a good position in the southeastern sky. Using the map on 169 of our guide book, I was able to pinpoint the fairly bright star gamma Leonis (or Algieba, in Arabic parlance) and after centring the star in the 28x field, I one again cranked up the power to 70x and was delighted to see that, like Castor A and B, it too was duplicitous. The brighter member (primary) shines with a golden countenance, while the secondary component appears yellow−green to my eye in this telescope. They are exceptionally handsome in the instrument at 210x. The system lies about 110 light years away and our guide book informs us that they orbit their common centre of gravity in just over 500 years!

Wow!

I made a sketch of this system too in the high power field of the 3 inch reflector, pictured below.

An elegant communion of suns, courtesy of your Creator.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Perhaps you noticed that in the high power field of 210x, both Castor A & B and Gamma Leonis appear to be separated by about the same angular distance. Just how close they are will be the subject matter of my next discussion.

See you soon.

Date: February 23 2018

Time: 14:00 UT

A word on the stellar magnitude scale: The stars in our guide book are divided up on a scale of magnitude, first devised by the 2nd century BC Greek astronomer, Hipparchus. He found it convenient to divide up the glory of the stars into six magnitudes, ranging from the brighest stars (magnitude 1) down to the faintest (magnitude 6) stars that could be seen with the naked eye. This rather arbitray assignment of brightness was improved on in the middle of 19th century of the common era, when the English astronomer, Normon Pogson, defined magnitude 1 stars as being precisely 100 times brighter than those of magnitude 6. Roughly speaking, a first magnitude star will be about 2.5 times brighter than a 2nd magnitude star, and these in turn are 2.5 times brighter than stars of the third magnitude, and so on. On this scale, there are stars that are actually brighter than magnitude 1 and are assigned either magnitude zero or a number less than zero. For example, the brightest star in all the heavens is Sirius, shining with a brightness of −1.46! This scale has the advantage of being able to be extended in both directions; brighter objects take on a greater negative magnitude, while stars fainter than magnitude 6 are assigned brightnesses with greater positive values. In this scheme of things, the Sun shines with a dazzling brightness of −26.7! Our guide book depicts stars of varying brightness with different sizes, going from the largest (brightest) to the smallest(faintest).

Angular measurement as it applies to double stars: As mentioned yesterday evening, the Orion Spaceprobe 3 showed us stars that were separated by various amounts of dark space. To see how close these separations are we must first take note of how angles are measured in astronomy. Recall the full Moon in the sky. This conspicuous orb subtends an angle of 0.5 degrees, but when we spied the small list of double stars discussed above, the telescope was able to resolve things separated by much smaller angles. For convenience, one angular degree is further divided into 60 arc minutes, so using this scale, the full Moon spans 30 arc minutes. One arc minute is depicted as 1′. Now each arc minute, in turn, is further divided into 60 arc seconds (depicted as 60″).

So 1.0 degree = 60′ = 3600″.

Using this new scale, we can begin to explore how much the stars in the above sketches are separated by. The companion to Mizar, for example  is separted from its primary by 14″, but the two tightest pairs thus far examined; Gamma Leonis and Castor A & B have much smaller separations; of the order of just 4″ or so. But just how much finer can our little telescope resolve? For double stars, we have a well established rule of thumb devised by the Victorian mateur astronomer, William Rutter Dawes, who suggested that the the limit is given by the simpe formula called the Dawes Limit: 4.56/ D where D is the aperture of the telescope in inches. Thus, for the 3 inch SpaceProbe, we ought to be able to resolve pairs separted by as little as 4.56/3 = 1.5″. The reader will note that as the diameter of the telescope is increased so does its resolving power. A 6 inch aperture ought to resolve pairs roughly half as small again.

There are a few qualifications we have to make with this formula. For one thing, Dawes devised it for two 6th magnitude stars of equal brightness. Things get more difficult as the brighness difference between the components becomes greater. Simply put, the greater the difference in brightness, the greater the angular separation needed to resolve them. What is more, if the stars are blue and equally faint, separations a little smaller than 1.5″ becomes possible. What’s more, the small obstruction made by the telescope’s secondary mirror (which we learn is just 19.9mm as stated on page 8 of the telescope instruction manual) also tends the shift the maximum resolving power a little upwards to more than 1.5″. Finally, these considerations are strictly true only for resolving stellar targets; as we shall see, the telescope will be able to resolve considearbly finer details on extended objects like the Moon and planets.

Small telescopes such as the Orion SpaceProbe 3(laevo) and the Shortube 80 make dapper double star ‘scopes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

These qualifications will help us to gauge how well the little reflector will do in due course. But for now, we have more double stars to visit

A Brief Aside: Return to the Moon

Time: 19:30UT

The Moon is now at first quarter and very high up in the southern sky. This is an ideal opportunity to see just how well the little Orion SpaceProbe 3 can perform. After examining its surface at 28x and 70x, feel free to crank up the power to 150x or 210x and note how well the image bears up. Right now you will see amazing details in the crater fields, the Apennine Mountain range and much much more. It’s at times like this that you will come to appreciate just how good this telescope is. Enjoy the ride!

Date: February 24 2018

Temperature: 0C

Time: 21:45UT

It was a beautiful bright day here in the glen but it remains unusually cold. After a very hazy night last night, transparency improved a great deal today and I set up the little telescope at sunset to enjoy wonderful details on the brightening Moon. Seeing remained exceptionally good, as evidenced by very steady high power views of the Moon and double stars using a couple of  larger telescopes I had also deployed to make the most of the unusually good conditions.

Beginning at about 6:45pm local time, I began to make observations of three rather delicate stellar systems; Rigel (Beta Orionis) easily seen as the exceptionally bright white star in the extreme southwest of the constellation. The SpaceProbe showed its very faint companion just off to the southsouthwest of the primary. Although I caught a glimpse of it at 70x using the 10mm Explorer II eyepiece, I elected to boost the power to 158x using my 2.25x Barlow lens  and was rewarded with an even better view. Although Rigel B is situated about 9″ away from its primary, the enormous brightness differential makes it far more challenging than it looks on paper.

Immediately after that, I moved the telescope east into Monoceros (featured on page 187 of our guide book) by using Orion’s downward sloping belt stars as a pointer. I quickly centred Beta Monocerotis in the low power eyepiece. Then I switched to 210x by inserting the 10mm ocular with my 3x Barlow and was rewarded by a wonderful sight. Here is a magnificent triple star system (sketched below). The reader will note that the B and C components of this system are just 2.9″ apart, so significantly finer than anything we’ve thus far explored. Another triple system can be found in Cassiopeia (see the map on page 109). You can find it by making an imaginary line from Ruchbah through Eta and extending that line about the same distance again until you come to a creamy white magnitude +4.6 star, Iota Cassiopeiae. Using a power of 210x, the 3″ SpaceProbe  showed me an even more beautiful and delicate arrangement of three stars. The C component is easier to see owing to its greater distance from A but the B component is also just under 3″ from the latter.

Below are some simple sketches I made for clarity.

Observations of delicate multiple stars as seen with the 3″ Orion SpaceProbe on the fine evening of Saturday, February 24 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

You can take it from me that these systems are challenging for obervers with significantly larger ‘scopes, so I hope you will agree that the 3″ Spaceprobe is a most capable high resolution instrument.

Date: February 26 2018

Time: 00:10UT

Just as I was about to pack up my 8 inch and 3 inch Newtonians at the end of an excellent vigil under the stars at 23:30UT on Saturday, February 25, I spied a couple of stars in Ursa Major, now very high up in the south southeastern sky, indicated by the position of the pencil tip in the image below (page 251 of our guide book).

On the march.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Specifically, I went in search of a star called Xi Ursae Majoris, also known by the rather charming appellation of Alula Australis. After centring the star in the low power 28x eyepiece, I once again cranked up the magnification on the 3 inch SpaceProbe to 210x, carefully focused and was rewarded with a beautiful, sharp image of a pair of yellow suns, the primary shining at magnitude 4.3 and the secondary, just a half a magnitude fainter at magnitude + 4.8. What is MOST interesting about this system is that they are currently separated by just 2″, so we’re getting awfully close to the double star resolving limit of a 3 inch (76mm) telescope. This pair of stars move fairly rapidly, completing one orbit of their centre of gravity in just under 60 years! The reader will also note that this was the first visual double to have its orbit calculated by Felix Savary back in 1828.

I made a sketch (below) of what I saw in the SpaceProbe. The stars are orientated roughly north to south.

Xi Ursae Majoris; testing the mettle of the little long focus Newtonian.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: February 27 2018

Time: 00:05UT

Temperature: −2C

Seeing: Remaining very good, very bright waxing gibbous Moon, virtually cloudless sky.

We are stuck in very cold, Arctic−like weather which meteorologists have dubbed, “the beast from the east” lol. At this late hour, the eastern sky is now showing the wonderful Spring constellation of Bootes. This constellation is home to a veritable treasure trove of interesting double stars. The other night, I got my first gander through my larger 130mm f/5 Newtonian of one of my all time favourite colour constrast double stars; Epsilon Bootis, or Izar, discussed on pages 90 though 92 in our guide book. Despite the presence of a very bright gibbous Moon, its shines fairly prominently at magnitude + 2.5, so is easy to find even from an urban location.

Bootes is home to some fine double stars, choicest among them being Izar, indicated by the pencil tip in the map on page 91 of our guide book.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shortly after midnight local time, it had a reached a decent altitude above the eastern horizon, so I decided to investigate what was what with the 3 inch telescope. In the low power (28x) field, the star looks singular with a comely orange hue. But when I increased the power to 210x, I was once again delighted to see its greenish companion fairly effortlessly in the fine winter air. Now, while the pair is separated by about 3″, there is a fairly large difference in brightness between the components; the primary being +2.6 and the secondary only +4.8. Thus, there is a 2.2 magnitude differential between the components,  making it more challenging than it looks on paper. The Orion SpaceProbe is turning out to be a most excellent double star telescope that even veteran observers will appreciate!

I made a drawing of what I saw in the eyepiece for reference (shown below).

My sketch of Epsilon Bootis in the high power field of the Orion SpaceProbe 3 telescope.

 

 

 

 

 

 

 

 

 

 

Date: February 28 2018

Time: 17:45 UT

Snowmageddon.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The beast fae the east is here the noo. Shockeroonie!

The elements are arrayed against us.

Cannae see heehaw, ken.

Date: March 1 2018

Time: 14:15 UT

We endured freezing, blizzard conditions (the worst in the country) throughout last night, bringing at least 30cm of snow. The high winds have created dangerous drifts of fine, powdery snow, making the roads all but impossible to travel on. But we have a warm fire, plenty of food and water, and our spirits remain high.

Small telescopes are very popular choices for observing the Sun, the star that sustains all life on Earth. I thought about how I might use the SpaceProbe 3 to do some solar observing when Spring properly arrives. Two methods came to mind: the projection technique and the use of a white light solar filter. The former involves pointing the telescope, fitted with an eyepiece, at the Sun and using some white card to project a focused image of the solar disk in order that I could record the presence of sunspots(regions of high magnetic intensity on the surface of the Sun). But I didn’t want to risk damaging the telescope with excess reflected heat (even a small aperture telescope like this can generate dangerous levels of heat), so I thought about using a white light solar filter as an alternative strategy.

Since I already owned and use an inexpensive white light solar filter with my Shorttube 80 achromat, I wondered whether or not it would fit onto the Spacerobe 3 optical tube.

The white light solar filter used with my Short tube 80 achromat fits snugly on the SpaceProbe 3 telescope!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Well, it was like finding money in the pocket of an old jacket lol! The filter fitted snuggly over the front of the instrument! It was the perfect fit! Now I can observe the glory of our star in perfect safety. The tall tripod upon which the telescope sits is a good height off the ground, allowing any ground thermals to be kept at bay. This should make an excellent little solar telescope but I shall have to wait until this severe weather leaves our shores before more testing can be done.

The filter works by rejecting 99.999 per cent of the incident solar radiation, passing only a tiny fraction of the Sun’s light to the eye.

That being said, it is of paramount importance that the reader heed this warning:

NEVER LOOK AT THE SUN THROUGH ANY OPTICAL INSTRUMENT AS PERMANENT BLINDNESS WILL RESULT!

Date: March 2 2018

Time: 13:15 UT

If you plan to use the SpaceProbe 3 to observe the Sun on a regular baisis, it pays to remember that the most economical way of acquiring a solar filter is to make one yourself. There are many outlets that sell various kinds of polymers specifically designed to reject the vast majority of the Sun’s light and heat. Perhaps the best of all is the very well established Astrosolar Material, marketed by Baader Planetarium. You can purchase a sheath of this material for under £20 UK and use it to make your own, homemade filter. Here is a link to one such DIY project.

22:00UT

A Request:

Attention Experienced Telescopists!

I’d appreciate if someone were to follow up on the reports thus far communicated. It’ll take up a little bit of your free time, but I think you’d get a kick out of it.

 

Date: March 7 2018

Time: 15:20UT

Sol seeker.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Well, after a week long hiatus owing to terrible winter weather, the Sun briefly poked its brilliant rays through the clouds and I was finally able to see if the solar filter worked as advertised. I can report that the Spaceprobe 3 did an admiral job of focusing the solar disk sharply using the 10mm Explorer II eyepiece. Because the Sun’s disk is precisely the same size as the full Moon, it takes up the same area of the field.The reader will note that the small finder ‘scope objective was covered during the observation, so as to prevent any potential accidents! See, you have to think ahead when observing our star!

 

Was there anything to see?

No! Lol!

Though I’m certainly not a diehard solar observer, I’ve never seen it so completely devoid of sunspots! That’s not to say that there are no sunspots on its surface only that they were beyond the detection limits of this small telescope on this occasion. That having been said, there is no reason why a would−be user of the Orion Spaceprobe 3 could not use this as a very effective white light solar telescope; adding to the versatility of the instrument.

Curiously, low sunspot activity is somewhat correlated with cold spells, so in a way, this was not completely unexpected.

Taking stock: By now, I’ve demonstrated just a tiny number of things in the heavens that are accessible to this excellent little telescope. And the sky’s really the limit! By studying the constelattions that are well placed in your local skies, you could spend many happy months and years exploring a host of other deep sky objects, as well as the glories of the Moon and never once feel you’re missing anything. And once you’re done, you can always visit them all over again, each in its proper season. Soon, you’ll find that they become old friends! Such is the atitude of a determined telescopist!

I would like to end this blog by exploring something completely different; a planet dwarfing the Earth in size and majesty, hurtling ’round the Sun beyond the snowline of the solar system. I speak of none other than mighty Jupiter. More on this soon.

 

A Brief Daylight Experiment

Comparing the image sharpness and light gathering power of the Orion SpaceProbe 3 with a stopped down 90mm f/5.5 ED apochromat.

Introduction: On Sunday afternoon, I set up both the Orion SpaceProbe 3 f/9.2 Newtonian alongside a high quality 90mm ED f/5.5 apochromatic refractor during a bright spell in order to estimate the light gathering power of the Newtonian and also to compare and contrast image sharpness in both instruments. Both telescopes were kept out of direct sunlight, so as to miminise thermal effects.

Materials and Methods: I constructed three aperture masks of progressively larger aperture from cardboard. These had diameters of 56mm, 65mm and 73mm, respectively. The masks were affixed using parcel tape, placed ahead of the dew shield of the refractor and carefully centred on the optical train. Starting with the 56mm aperture mask, I compared the images of the denuded branches of a horse chestnut tree about 100 yards in the distance in both telescopes. I charged the ED refractor with a Vixen HR 2.4mm ocular delivering 208x diameters. A 2” Tele Vue Everbrite diagonal (99% reflectivity) was used to maximise image brightness in the refractor. The Orion SpaceProbe 3 reflector was charged with a 7.5mm Parks Gold coupled to a 2.25x Barlow delivering 210x.  The experiment was repeated using the 65mm and 73mm aperture masks on the refractor and the views similarly compared. My wife also volunteered to assess the images and our findings were in good agreement.

Making the aperture masks: left to right: 56mm, 65mm and 73mm, respectively.

 

Results: There was a clear and unequivocal difference between the images when the refractor was fitted with the 56mm aperture mask. The SpaceProbe 3 delivered a noticeably brighter image but image sharpness was quite comparable.

The masks are easily affixed to the front of the refractor using parcel tape.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Using the 65mm aperture mask, the results were much more comparable, with the refractor yielding a slightly brighter image but image sharpness was still quite comparable. Finally, when the 73mm aperture mask was affixed, the refractor produced the brighter image although image sharpness remained quite comparable.

Locked on a stationary target.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Vixen HR 2.4mm ocular with a 2″ Tele Vue Everbrite diagonal.

 

 

Conclusions: The 76mm SpaceProbe reflector has a light gathering power equivalent to a high quality quality 60 to 65mm refractor. Image sharpness is right up there with the apochromat in these daylight tests. That’s a very good result for a telescope that retails for less than £70 delivered to your door. In comparison, a top quality 60 to 65mm Apo (without a diagonal, eyepieces or mount) could set you back between £400 and £800!

Final note: We sent our results to former Sky & Telescope Associate Editor, Tony Flanders, whose opinion I trust, and who has also evaluated the Orion Space Probe 3 in a past review. He agreed with our assessment.

Some readers may legitimately ask why a 76mm reflector would not be as good as the equivalent sized refractor. The answer lies in the way these telescopes are designed. The refractor uses a lens to collect light and its transmission is very efficient. Mirrors are not quite as good though, since they reflect a high percentage of the light which strikes them, though not all. For example, if the mirrors both reflect say, 85 per cent of light incident upon them, then the percentage of light that reaches the eye will only be 85 per cent of 85 per cent; that is 72 per cent. Add in the small amount of light lost by the obstructing effect of the secondary mirror and you can begin to appreciate why it is not as efficient as the same size refractor. Having said all that, the little reflector still collects enough light for you to enjoy many objects in the heavens, as we have discovered.

Date: April 1 2018

Time: 20:45 UT

Temperature: 0C

Conditions: Good clear sky, no wind, steady conditions.

 

An Encounter with Venus

It remains unseasonably cold. Indeed, more snow is forecast for tomorrow. I can’t help but think that this is in part attributed to the solar sunspot minimum that is upon us just now. Nevertheless, the light on the landscape and the lengthening days inform me that April is truly here, lol.

At dusk, I set up the little Orion SpaceProbe 3 reflector at the side of the house to observe Venus, which appeared like an intensely bright star sinking into the western sky. Venus is now an evening ‘star’. Excitedly, I turned the telescope on the planet, charging the instrument with the 10mm Explorer II eyepiece delivering 70 diameters. Well, the strongly gibbous disk of the planet was clearly visible, but it was completely featureless. Increasing the power to 140x didn’t really help things all that much. You see, you can discern very little on the Cytherean disk in any telescope, however large and powerful. But what I could see was the six diffraction spikes emanating outward from the brilliant white planet. I found these very striking and quite beautiful to behold. As mentioned previously, this six−pronged diffraction spike is produced as a consequence of the secondary mirrors three spider vanes. In contrast, the view in my larger Newtonians shows cruciform diffraction spikes owing to the four spider vanes supporting their secondary mirrors.

At present, Venus is at its smallest; just 10 arc seconds in size. It is much larger when it is in its crescent phase and slowly shrinks as more and more of the disk is revealed. Venus, like our Moon, goes through phases!

Venus is covered in quite good detail on pages 348 through 352 of our guide book. And though it looks serene through the telescope, you wouldn’t want to be there. Indeed, it is the nearest thing to a proverbial hell that humans could possibly imagine. Its choking atmosphere of carbon dioxide has generated a massive, run−away greenhouse effect that has raised the temperatures on the surface to about 470C; so hotter than any domestic oven! The atmosphere exerts a pressure in excess of 90 times that found on the Earth at sea level, and then, to add insult to injury, the clouds are not made of cooling water vapour as they are on our world, but instead are composed of droplets of sulphuric acid with a concentration of about 80 per cent. Anyone standing on its surface would be simultaneously crushed, choked, incinerated and corroded to death! Not a pleasant prospect methinks.

But Venus was not created for life, whereas the Earth was.

Thank goodness for small mercies!

I made a drawing of what I saw at the telescope.

Venus as seen through the 3 inch SpaceProbe Newtonian on the evening of April 1 2018.

 

 

 

 

To be continued………………

 

De Fideli.

Pulcherrima!

Beauty and the beast: my 130mm f/5 Newtonian versus a 90mm f/5.5 ED refractor

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: Wednesday March 28 2018

Time: 22:00UT

Temperature: −2C

Seeing: III, bright gibbous Moon, small amounts of cloud cover in an otherwise clear sky.

It is often claimed that refractors give more aesthetically pleasing images of celestial objects than reflectors. But how true is this statement? Last night, I learned yet another instructive lesson that shatters this myth once and for all.

Earlier in the evening, I fielded my 8″ f/6 Newtonian against a very good 90mm f/5.5 ED apochromat. The target was Theta Aurigae, then sinking into the western sky and so past its best position for observing. Seeing was only average. Both telescopes had been fielded about 90 minutes earlier with the optics capped, so both were completely acclimated. I charged the apochromat with a 2.4mm Vixen HR eyepiece yielding 208x. The 8 inch Newtonian was charged with a 6mm Baader orthoscopic ocular delivering 200x.

Examining the system in the 8 inch reflector showed the primary star as a slightly swollen Airy disk but the faint companion was clearly visible. In contrast, the view through the 90mm refractor showed a less disturbed primary but the secondary(for the most part) couldn’t be seen!

Question: How can an image be deemed more aesthetically pleasing when a prime target (the secondary) in that said image can plainly be seen in one instrument and not in the other?

Date: Thursday March 29 2018

Time: 00:05 UT

Temperture:−3C

Seeing; II/III, slight improvement from earlier, otherwise very similar.

Later the same night, I fielded my 130mm F/5 Newtonian along side the 90mm refractor and  turned my attention to a spring favourite; Epsilon Bootis, now rising higher in the eastern sky.

This time, I charged the refractor with a 2.0mm Vixen HR eyepiece yielding 250x. The Newtonian was fitted with a Parks Gold 7.5mm eyepiece coupled to a Meade 3x Barlow lens giving a power of 260x.  Examining the system, I was quite shocked by the difference between the images; the refractor did show a dull, greenish companion but it was entangled in the diffraction gunk from the orange primary. What’s more, the entire system was surrounded by chromatic fog owing to the imperfect colour correction of the refractor (an FPL 51 doublet). In contrast, the 130mm f/5 Newtonian image was far superior in every way; the Airy disks were smaller, tighter and more cleanly separated, and with zero chromatic fog to be seen. The Newtonian image remained just as stable as in the refractor image throughout the observation! The components also displayed their pure colours (as only a reflector can yield); the primary orange and the secondary, blue. In a phrase, the differences between the images was like night and day!

Conclusions: The 130mm Newtonian provided a much more aesthetically pleasing image than the refractor, which was compromised by its smaller aperture and less than perfect colour correction. As a small portable telescope, the Newtonian is far more powerful and is capable of delivering images that are simply in a different league to the refractor.

ED 90 Refractor: Proxime accessit.

130mm f/5 Newtonian(Plotina): Victrix/Pulcherrima!

 

Postscriptum: As always, I would encourage others to test these claims. Truth matters.

 

 

Neil English is author of Grab ‘n’ Go Astronomy.

 

De Fideli.

 

 

My Wonderful Fastnewt 130 F5!

The extraordinary 130mm F/5 super travel ‘scope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A little over two years ago, I first began exploring the potential of a 130mm f/5 Newtonian reflector. As you may recall, I was really quite impressed with what the telescope delivered for its very modest price tag, something I had come to expect after the very positive experiences I had had with a larger 204mm f/6 Newtonian for a whole year. Both telescopes were made by SkyWatcher, and had excellently figured parabolic mirrors with smooth, colour free optics. These collective experiences transformed my opinion of Newtonian reflectors, so much so that I have come to prefer them to my erstwhile favourite type of telescope; refractors.

The 130mm f/5 Newtonian is a very convenient telescope for travel and quick grab ‘n’ go excursions. Indeed, in one form or another, this telescope has travelled the length and breadth of the country with me and has never failed to deliver excellent views on all classes of celestial real estate. Over the 25 months I have owned it, it has clocked up well over 100 hours under the stars. Indeed, it was so easy and comfortable to use that I invested in making an already good ‘scope into a great one. I upgraded the flat to one of higher quality and had both mirrors treated with the best coatings money could buy. In previous blogs, I have described how I re−housed the open tube configuration into a more stable closed tube configuration with a better focuser. I also described how I lined the inside of the tube with cork before covering it with standard flocking material. All of the modifications were very cost−effective and, all in, set me back just a few hundred pounds.

I have enjoyed extraordinary success with the 130mm f/5 in my pursuit of double stars. It has resolved double stars down to 1.0” and elongated 0.9” pairs. And in recent months, I have been able to add a few more strings to my bow, including Iota Leonis and Eta Geminorum to name but two; systems that I found to be very difficult with top quality refractors of 4− and 5−inch pedigree under good, stable skies. Indeed, my notes confirm that on these and other high−resolution targets, the 130mm f/5 was more proficient than a 4−inch f/15 classical achromat, in violation of a tradition that hearkens back to the 19th century, and shattering forever the myth that good Newtonian reflectors cannot serve as first rate double star telescopes.

I can reaffirm the beneficial effects of insulating the tube of my 130mm reflector. My ongoing studies have shown that it significantly reduces tube currents while the ‘scope is acclimating, and in use, I have seen with my own eyes the beautiful, ultra−high magnification views of various tricky double and multiple stars. I would estimate that the insulating material consistently provides text book perfect images at the highest powers I have used with this telescope (over 400x on some objects during spells of good seeing) about 30 per cent more frequently. In addition, and as previously noted, the instrument is also an excellent lunar and planetary telescope for its size, as well as being a very satisfying deep sky instrument.

My success with double stars is particularly noteworthy, and I wanted to communicate another surprising advantage of using a small aperture Newtonian reflector like this. Anyone reasonably well acquainted with optics will tell you that as the f ratio of the primary mirror decreases, so too will the size of the field that is free of coma (an aberration that is particularly important to consider in high resolution double star work). So, conventional wisdom would say that an f/6 ‘scope will have a larger coma free field than an f/5 instrument and so on. But is this true? Surprisingly, the answer is “not exactly.” Let’s do the math to see what I mean.

The coma free field of a Newtonian system in millimetres, scales directly as the cube of focal ratio. Specifically;

The coma free field = 0.022 x f^3.

So, for my f/5 Newtonian we obtain a coma free field = 0.022 x 5^3 = 2.75mm.

Next, consider how this translates into true field.

True field in radians is given by; coma free field/ focal length.

Thus, expressed in radians, the true coma free field in the 650mm Newtonian will be:

(2.75/650) = 0.0042, and converting to angular degrees gives 0.0042 x 360/2pi = 0.24 degrees.

Consider next a typical high−power eyepiece used in double star divination. A popular choice I like to use is a Parks Gold series 7.5mm, coupled to a 3x Barlow lens, with an AFOV of about 50 degrees. This yields a power of 260 diameters in the 130mm f/5, so the coma free field at this enlargement is: 260 x 0.24 = 62.6 degrees!

This means that there is no coma to worry about across the entire field of view using this particular configuration. In contrast, if I were to use a 2.5mm Nagler or some such, offering an AFOV of 82 degrees, the periphery of the field would have some coma.  This observation helps explain why I have done so well using comparatively simple eyepieces!

Favourite double star tools: a Meade 3x Barlow (laevo) and a 7.5mm parks Gold ocular (right).

Curiously, we can do the same calculation for my 8” f/6 Newtonian, which has a focal length of about 1200mm, yielding 0.23 degrees; slightly smaller than offered by the 130mm f/5!

Another consequence of this result is that the coma free field will be proportionally smaller in larger instruments of the same f ratio. Consider my 12” f/5 Newtonian, for example. In comparative terms, a power of 260x will only deliver a coma free field of 26 degrees, which is only about 27 percent of the true field delivered by an ordinary 50 degree AFOV eyepiece.

This agrees with experience; to get the best images at 260x from my 12” f/5 , I have to keep the objects in the centre of the field to derive the best images.

                                                        On the Road

In need of a sturdy case.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I’m a sentimental observer, and I have grown to love my 130mm f/5. I hope to travel further afield with it this coming summer, God willing, when our family will visit the south of Ireland. Here, I’ll hopefully be able to view Jupiter fully 5 degrees higher in the sky than I can at my adopted home here in Scotland. This will be about 8 weeks after it reaches opposition in May, but with the return of truly dark skies for a few hours at this more southerly latitude, I’m hoping that it will make a significant difference to the views. Fingers crossed eh!

For travel, as well as for just general storage of the instrument, I decided it was high time that I invested in a sturdy case for my “Fastnewt 130 F5.” I pulled the trigger earlier today by purchasing a decently priced aluminium flight case, with dimensions of 850 x 295 x 270mm. Here’s the link. I’m hoping this will give me enough room to store the telescope, finderscope, various eyepieces and Barlows, guide and note books etc for hassle free conveyance to our various destinations. As soon as it arrives, I’ll chime in again with news on how I get on with it.

March 9 2018

A fine looking case for my Fastnewt 130 F5.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A great case for a great telescope.

 

Well, the package containing my carry case finally arrived today after a delay of a few days owing to the dreadful weather of late. I’m delighted with it. It’s light weight and sturdy, and should fit the instrument as well as other stuff as I had planned. All I need to do now is cut the foam to size and I’m in business!

After supper I set to cut the foam. Here is the final result. I think it looks dapper!

Snug as a bug in a rug, ken.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

My new case has brought instant domestic dividends! You what mate? It’s got my wife off my case lol. You see, she’s always nagging me about how the Fastnewt 130 F5 clutters up our hallway. It was more or less permanently mounted on my Vixen Porta II from the day I acquired it. Now it has its very own space; a place prepared for it.

I was a bit over ambitious about just how much I expected to pack into the case. My guide and note books didn’t make the cut (excuse the pun lol); they’ll go with the general luggage; no sweat. There’s a silvery (foam) lining though; my home made flexi dew shield just sits ’round the optical tube, and the deep incisions I made to accommodate the finder ‘scope can also carry filters; a variety of kinds; polariser, colour and planetary. Because Jupiter will be low in the sky, colour filters, in particular, will help clean up the images. The polariser will serve me by day, cutting through glare.

March 10 2018

I am lucky enough to have acquired some very nice oculars over the years and have come to appreciate many of them. The f/5 optical system serves up very good images with fairly simple eyepieces, such as orthoscopics, Plossls and even Kellners (on axis). Some of my favourite eyepieces include my 32mm SkyWatcher Plossl, which is my main wide field eyepiece with the Fastnewt F 5, delivering a well corrected 2.5 degree true field; plenty big enough for the vast majority of deep sky objects. For medium power work, I enjoy the widefield options delivered by my Mark III Baader zoom (particularly at the 8 and 10mm settings), but also appreciate the more contrasty views served up by 6mm Baader orthoscopic as well as a 7.5mm Parks Gold eyepiece and a 10mm Orion Explorer II Kellner. For high power work, I am fully sated by amplifying these eyepieces using either a 2.25x or 3x Barlow.

The extra aperture afforded by the 130mm parabolic primary mirror takes grab ‘n’ go to a whole new level of experience; and that’s not a hyperbola! Five years ago, I may have been cajoled by articles like this, but having owned and used many small aperture refractors (including a Zenithstar 66 SD doublet & triplet, SkyWatcher ED 80, Takahashi FS 60C, TeleVue 76, Tele Vue Genesis (original f/5 fluorite model), Tele Vue 102, Skywatcher ED100, and even long (but still small apertured) Skylight 4″ f/15 and Moonraker 80mm f/15 achromats), to name a sizeable fraction, they were all vanities of sorts.

Newtonians alerted me to this rose−tinted, but ultimately delusional state. I just sensed something was wrong.  In contrast, I discovered an honesty in the Newtonian reflector that simply wasn’t there in other telescopes. You do get what you pay for, that’s for sure.  But from a purely visual perspective, you get a whole lot more with the Newtonian! I was seeing more details, capturing more light and extending my target base with the 130mm reflector. Denying or dismissing these facts is a vanity!

Faster, cheaper, better!

As stated in previous blogs, the Fastnewt 130 F5 is truly fast in other regards; most especially cool down. Indeed, (and unlike the Fastmax 180 F4.5) its open tube configuration and small mirrors ensure rapid acclimation without the need for fans and other active cooling systems. The provision of Bob’s Knobs on both the primary and secondary mirrors means I can fine tune collimation in seconds when the most exacting optical ‘syncing’ is called for.

As you may know, I am especially passionate about observing double stars. And the 130 F/5 Newtonian has turned out to be a fine instrument for teasing out pairs down to the theoretical limit imposed by its aperture. I enjoy watching such pairs and triplets moving through the field at ultra high powers. Here are a few sketches of systems I’ve just recently visited.

Iota Leonis: a tricky system in the southeastern quarter of Leo.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A couple of other delicate systems as observed with the telescope.

 

The first drawing shows Iota Leonis, resolved using a 6mm Baader orthoscopic coupled to a Meade 3x Barlow delivering 318 diameters. The second set of drawings are of Mu Bootis(Alkalurops), a most delicate triple system, and Delta Geminorum (Wasat). These were imaged using my 7.5mm Parks Gold and 10mm Kellner, respectively, coupled to the same 3x Barlow. Over the last couple of years, I’ve managed a whole suite of difficult pairs with this telescope and it continues to go from strength to strength.

March 12 2018

I gave up on equatorial mounts after I quit doing CCD imaging and film astrophotography. I felt liberated in being able to find things using muscle power, eye and brain. No wires, battery packs, heavy counterweights and finicky cameras to think about. There is great virtue in such simplicity; it brings peace and joy in equal measure.

The Fastnewt 130 F5 sits pretty astride the Vixen Porta II mount. I have owned this piece of kit for about six years now and it has carried all manner of small and medium sized telescopes. It is an excellent match for this instrument and is gifted with slow motion controls. Over the years I’ve trained myself to use these controls to follow targets, even at very high powers. For example, during a recent excursion, I was following a double star target at 406x fairly comfortably  While looking through the telescope, I grasp both controls and make very gentle adjustments so as to keep the object centred, even in a very narrow field!

Faithful companion; my Vixen Porta II mount.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This kind of work is equally amenable to sitting or standing modes. And it’s made possible by virtue of the close proximity of the focuser to both the azimuth and altitude controls. Such a configuration confers maximum stability for exacting, high power work.

Mechanically it’s been sound; strong, light−weight and modular, breaking down into easily stored and transportable components. It works in all seasons, and here in Scotland you really can experience all four in one day! But like any ole jenny, the Porta can have its moments. The plastic knobs of the slow motion controls have a habit of coming loose…..sometimes during very critical observing moments. That’s why I always check ’em over before beginning a vigil. Having said that, I am now looking into ways of improving these also. That said, there is such a thing as overdoing it; check out what this bloke did with his Porta lol.

The clever design of the Porta enables it to used in spotting ‘scope mode during daylight. I am enjoying my 10mm erecting eyepiece, which delivers a correctly orientated view at 65x with a 2mm exit pupil, but I’m equally enthralled at seeing the details of nature at super high powers, thanks to its superior light gathering power and resolution over a conventional spotter. When you’re using 150x and upwards, it matters little whether an object is upside down or rightside up. This is possible because my climate here does not (as a general rule) endure large diurnal temperature variations and that leads to stable air masses, allowing me to capture wonderful details of nature over distances up to a few hundred yards.

March 14 2018

Pi Day!

Stephen Hawking has gone to meet his Maker. The poor man suffered for so long, trapped in the prison of his wheelchair. May the Lord have mercy on his soul.

Once upon a time, I entertained a dream to have my very own observatory, but now that I’ve matured as an observer, I have little desire to create one. I’ll always have a mancave of sorts though, but not an observatory. My modus operandi is open air observing, using telescopes I can manage; so that confines me to instruments of 12 inches or smaller. I own all the telescopes I could possibly wish for in life. As I get older, I will likely use smaller telescopes more frequently, and the ultraportable Fastnewt 130 F5 will thus remain an important instrument in my arsenal. Right now, I’m in the prime of my life and can enjoy my 8 and 12 inch telescopes just as much as the 130. As good as the latter telescope is, there are many things in the firmament that are beyond its reach. There is a time and a place for them all.

Acquiring a solid tube for the optics at the heart of the 130mm f/5 has proven to be a good move. I can remove the instrument from its case and mount it with little in the way of collimation adjustment. Certainly, it is a great step up from the original Skywatcher Heritage 130P (open tube) in this regard, but with very little additional mass.

Corbie watching.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I am very much enjoying using the telescope as my new spotting ‘scope for nature studies. It’s a pure joy to watch the noisy corbies that make their nests in the conifer trees near my house. The telescope produces beautiful, sharp images and even on a dull day like today its generous light gathering power makes such observations very worthwhile. You don’t miss a trick with a telescope like this! Sometimes they look straight at you and you can see the light in their eyes. I sometimes wonder whether they see me better than I see them!

The telescope also allows me to monitor the buds on the trees as Spring progresses. Horsechestnuts are among the first to bring forth their leaves ’round these parts. I can tell you that they’re well on their way, but will need a few warm, sunny days before we will see their full glory, draped in harlequin green.

Nature waits for no man.

I understand that some folk are reluctant to use Newtonians in terrestrial mode because the tube is open to the elements. But this too is a vanity. As I’ve described in a previous blog, Newtonian optics are easy to clean, and any dust that falls inside the telescope can be easily removed. I find cleaning the optics once or twice a year is plenty often enough. It’s not afraid of pollen, or dust, moisture or even an adventurous spider! Whatever makes its home on the optics or in the tube can be removed; no sweat.

March 15 2018

Well, the weather has taken another down turn. Hoping for some more clear skies, but no go, unfortunately. I do however have a wee treat for you; I found this review of a close kin of my 130mm Newtonian; enter the Vixen R130SF. This lady provided a good review of this telescope on a Porta II mount no less. The reader will note that no mods of any kind were made in this report, but I think you’ll agree that she ticks many of the boxes I have covered in my own exploration of this telescope.

March 17 2018

Lá ‘le Pádraig sona daoibh!

The Fastnewt 130 F5 has been tested in all weathers. I’ve enjoyed it at temperatures as low as minus 10C and as high as +25C. In general, the telescope performs better in milder weather but I have encountered textbook perfect images on many freezing cold nights.

When the weather is settled, I usually bring the instrument out from a warm, indoor environment and let it cool off to ambient temperature. Low powers can be enjoyed pretty much immediately, whereas medium power views (up to 100x say) are fine to explore after about 10 minutes. But for the most critical observations at very high powers, I usually give it at least 30 minutes.

In unsettled spells, such as those we are experiencing just now, I leave the telescope in a dry, unheated outhouse, so that it can be deployed at a moment’s notice. This is a strategy that works well for all kinds of telescopes. That way, I can enjoy the telescopic heavens even during the briefest of clear spells.

Like any other activity, preparation will always be your friend.

Time: 22:10 UT

Observing during a cold snap.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The great French scientist, Louis Pasteur, was fond of saying, “chance favours the prepared mind.” I think this is true. Though the heavens declare that Spring is here; the weather says otherwise. Indeed, this is the coldest St. Patrick’s Day I can remember in many years. A biting easterly wind brought in more snow and temperatures struggled to rise above zero today. But I did get a short half hour spell this evening with the telescope between snow showers, and to my sheer delight I discovered that conditions were excellent. Northerly winds almost invariably bring turbulent air in this location, and quite often, those from the east are little better. But there are always exceptions. Shortly after 9 pm local time, I was able to visit a few of my favourite double stars; Polaris A & B, Theta Aurigae and Iota Cassiopeiae; old friends from the depths of space. Indeed the images served up were so good when the wind died down, I was able to make a recording of what the 130mm f/5 showed me at 183x. A telescope of this size will show a very delicate 1st Fraunhofer diffraction ring ’round Polaris A, a magnitude 2.0 star, together with its tiny spark of a companion. A similar looking system; Theta Aurigae, is significantly fainter; just +2.6. In contrast to brighter Polaris though, the first diffraction ring is much more subdued. It follows that fainter systems will show even less of their diffractive effects; a good thing when it comes to observing these beautiful, delicate wonders of nature.

Below is a pair of drawings I made to show these differences.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

By 9:45 pm, the situation had deteriorated. The clear sky was gone and another snow shower had begun.

Still, it was good to get out, if only for a wee while!

March 23 2018

Time: 18:30 UT

The snow has gone and it’s beginning to look more springlike.

After attending a couple of students, I set up the Fastnewt 130 F5 in my garden near the closing of the day, in anticipation of a wonderfully placed 7 day old Moon. The Moon is especially good to observe in March and April, when we obtain the most magnificent displays of earthshine. It also gains altitude during the earlier points in its cycle. And while it has crossed the meridian by now, it is very high up in the sky and that means the chances are high that I will obtain beautiful images over a range of magnifications.

Moonwatching.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The forecast promises to maintain clear skies well into the night, so I’ll have more opportunities of using the telescope; and not just on the Moon. If conditions are good, I’ll be able to resume my favourite passtime of double star observing. Fingers crossed!

Time:22:00UT

Well, it was a bit of a mixed bag this evening. Conditions were rock steady but the sky became progressively more hazy as the evening went on. That said, the views of the Moon did not disappoint, especially earlier in the evening, when the haze was less obtrusive. As I mentioned in this and ealrier blogs, the Fastnewt 130 F5 delivers excellent views of the Moon and planets, when suitably placed, courtesy of its very decent aperture compared with more ‘traditional’ grab ‘n’ telescopes.. I recall with great fondness the wonderful images the telescope served up on Jupiter during last year’s opposition and even though its positioning in the coming months (it transits low in the sky about 4am at the moment) will be far less favourable than in 2017, I’m still very excited about seeing the giant world again through this telescope.

Hazy conditions often bring excellent, steady images. That much was clear when I visited some of the brighter double stars this eveing; Castor, Theta Aurigae, Algieba, Cor Caroli, Alula Australis, Mizar & Alcor and a few others.Newtonians rock when it comes to double stars and there are very encouraging signs that more and more amateurs are using these telescopes in their pursuit.

By 10:00pm local time, the haze became so dense that only a few of the brighter luminaries dierctly overhead were still visible. But not a bad innings nonetheless!

March 24 2018

I hope to employ the Fastnewt 130 f 5 in all the ways I’ve described for the rest of the spring and will report back after our trip to the Emerald Isle later this summer.

Thanks for keeping up with this blog.

Until then; farewell and best wishes to you all.

Neil.

 

To be continued………..

 

De Fideli.

The Joy of the Maksutov Telescope

The author's superlative 7 inch Maksutov Cassegrain.

The author’s superlative 18cm f/15 Maksutov Cassegrain.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A work began in December 2014.

 

Dedicated to Asbytec.

Among the catadioptrics, the Maksutov Cassegrain has justifiably earned a solid reputation as an excellent high resolution telescope. The Maksutov design combines a spherical mirror with a longer native focal length (slower f/3 relative aperture) than a typical Schmidt Cassegrain (f/2) with a weakly negative meniscus lens in a design that takes advantage of all the surfaces being nearly spherically symmetrical. The negative lens is usually full diameter and placed at the entrance pupil of the telescope (commonly called a corrector plate or meniscus corrector shell). The design corrects the problems of off-axis aberrations such as coma found in reflecting telescopes while also correcting for chromatic aberration. It was patented in 1941 by Russian optician Dmitri Dmitrievich Maksutov after a five year spell of careful ray tracing and prototype building, which culminated in the first working model produced in the autumn of the same year. He based his design on the idea behind the Bernard Schmidt’s camera, which used the spherical errors of a negative lens to correct the opposite errors inherent of a spherical primary mirror. Because the design utilises all-spherical elements, it greatly aids in mass fabrication.

Similar independent meniscus telescope designs were also patented in 1941 by Albert Bouwers (his 1941 concentric meniscus telescope), K. Penning and Dennis Gabor (a catadioptric non-monocentric design).A culture of secrecy during World War II kept these inventors from knowing about each other’s designs, but rightly or wrongly, the design was named after Maksutov and the rest as they say is history.

This design appeared commercially in Lawrence Braymer’s 1954 Questar telescope and in Perkin–Elmer designer John Gregory’s competing patent for a Maksutov–Cassegrain. Commercial use of Gregory’s design was explicitly reserved for Perkin–Elmer but was published as an amateur telescope design in a 1957 issue of Sky and Telescope in both f/15 and f/23 iterations. Most Maksutovs manufactured today are this type of ‘Cassegrain’ design (called either a “Gregory–Maksutov” or “spot-Maksutov”) that use all-spherical surfaces and have, as a secondary, a small aluminized spot on the inner face of the corrector. This has the advantage of simplifying construction. It also has the advantage of fixing the alignment of the secondary and eliminates the need for a ‘spider’ that would cause diffraction spikes. The disadvantage is that, if all spherical surfaces are used, such systems have to have focal ratios above f/15 to avoid aberrations. Also, a degree of freedom in correcting the optical system by changing the radius of curvature of the secondary is lost, since that radius is the same as that of the rear meniscus face. Gregory himself, in a second, faster (f/15) design, resorted to aspherization of the front corrector surface (or the primary mirror) in order to reduce aberrations. This has led to other designs with aspheric or additional elements to further reduce off-axis aberration. This type of Maksutov-Cassegrain’s high focal ratio and narrower field of view makes them more suitable for lunar and planetary imaging and any other type of observing where a narrow field high power view is just fine for resolving tightly packed globular clusters and double stars.

The elegant Questar 3.5

The elegant Questar 3.5

The Rumak
The Rutten Maksutov–Cassegrain (also called a Rumak or Sigler Maksutov) has a separate secondary mirror mounted on the back of the meniscus corrector, sometimes similar to the corrector/mirror holder configurations found in commercial Schmidt–Cassegrains. This provides an extra degree of freedom in correcting aberration by changing the curvature of the corrector and the secondary independently. Specifically it allows the designer to aspherize the secondary to provide a flatter field and slightly better colour correction than traditional spot Maksutovs, with less off-axis coma. Mounting the secondary on the corrector also limits diffraction spikes. This version is named after the work of the Dutch optical designer, Harrie Rutten.

Are Rumaks something to aspire to over the Gregory Mak? That’s something you’ll have to decide for yourself. To my way of thinking, a Gregory Mak is more than up to the task.

Some Historical Models

Perhaps the most iconic of modern telescopes is the beautiful Questar 3.5, a classic all metal, 90mm Gergory Maksutov that has changed very little in over half a century. While expensive, it is a great work of art and is still highly favoured by telescopists in the 21st century. The company also make larger Maksutovs (the Questar 7, for example) at (you’ve guessed it) much higher prices. Celestron was the first to respond to the high cost of the superlative Questar and marketed their orange tube C90 Maksutov in the late 1970’s for less than $500.

Optically, these were said to be quite variable, from mediocre to excellent. The big game changer came in the 1990s when Meade revolutionized amateur astronomy by introducing the ETX, first in the form of the RA, which had a built in clock drive and then shortly afterwards with the ETX EMC which featured full go-to capability. As an owner of the original ETX 90 RA, I can vouch for the excellent optics – on par with that of the far more expensive Questar 3.5. And though my unit is approaching twenty years of age, the mirror is in excellent condition, as are the coatings on the front corrector plate.

The venerable C90. Image credit; Celestron.

The venerable C90. Image credit; Celestron.

Shortly after the launch of the ETX 90, Meade introduced two larger instruments from the same family – the ETX 105 and the ETX 125. I spent a considerable time looking through the 125 and can vouch for the razor sharp optics on these units when conditions allow.
Meade also produced a 7inch (178mm) f/15 Gregory Mak as part of their highly successful LX-200 series of computerised telescopes which received very high praise from discriminating lunar and planetary observers who raved about their apo-like optics. These telescopes are now considered highly collectible classics from the late 20th century.

Celestron has recently revamped their venerable C90 in a neat black-tubed spotting scope. Costing less than $200, it provides excellent optics in an ergonomic package, eminently suitable for general nature studies and astronomy. It has to be one of the best bargains in the hobby today.

Cheap as Chips: the all new C90 spotting scope from Celestron.

Cheap as Chips: the all new C90 spotting scope from Celestron.

Despite these innovations it is arguably the range produced by Orion (USA) and SkyWatcher that has made most heads turn in the Maksutov camp in recent years. Following fast on the heels of the better established small companies, Synta churned out an exciting suite of Gregory Maks in the 90mm – 180mm range which could be purchased as complete packages including a mount or as optical tube assemblies. Over the last six months or so, I have been carefully evaluating an Orion re-branded version of Synta’s 180mm model – the telescope that has really opened my eyes to the tremendous versatility of the Maksutov design as a visual instrument.

She sure is purdy: the ETX 90 RA.

She sure is purdy: the ETX 90 RA.

 

 

 

 

 

 

 

 

 

 

Fit ’n’ Finish
The Orion 180mm Mak is no Questar 7 that’s for sure. But it’s got a few things going for it that makes it an exciting prospect even in comparison to the legendary Questar. For one thing, the corrector plate is made from the highest quality Schott optical glass and has the very latest in multi-layer anti-reflection coatings. The primary spherical mirror is over-coated too which will ensure its longevity over many decades if properly looked after. As a result, it may surprise you that it will yield slightly brighter images than older Questar 7s what with their more primitive magnesium fluoride based anti-reflection coatings.

The instrument is focused in a completely different way to a refractor and involves moving the primary mirror either closer or further away from the front corrector plate. I received the unit in perfect collimation after a long road trip and all of the components have remained in perfect alignment despite me taking the entire instrument apart to flock the inside tube as well as the long, slender baffle tube leading to the eyepiece. There is not many telescopes on God’s Earth that would allow such license. Remarkable!

The telescope equipped with tube rings and a 50mm finder tips the scales at under 20 pounds and is less than half a metre long, so it can be used on a light weight mount so saving quite a considerable cost to the user. This makes the instrument super portable, much more so than the equivalent refractor.

Maksutovs and Acclimation
Large catadioptrics can take some time to acclimate, especially if taken from a warm indoor environment to a chilly night outside. But this is not unique to this telescope genre; all large telescopes will struggle for a while before they stabilise in their new environment. Thankfully there are ways to ameliorate this. I’ve often taken my 17cm Orion Maksutov out from the warmth of my living room into my dry, unheated shed and after just a few hours it was delivering pinpoint stars in temperatures just a few degrees above zero. I’ve also had it working perfectly well in sub-zero temperatures.

The same instrument can be made permanently grab ‘n’ go by keeping it in the same environment while not in use. Others resort to active cooling using fans that blow cool air across the optical components. Some have suggested using cheap ice packs to create strong thermal gradients to draw heat out of the instrument. All these measures will accelerate the process of thermal acclimation. That being said, there are a few individuals (the ‘poodle pushers’), who have persisted in wilful scaremongering about these telescopes by asserting that they won’t acclimate in many locations. I was alerted to this after discovering that a seasoned observer located in La Union in the Philippines, who has done great work with a 6–inch Maksutov, over many years, enjoys diurnal temperature changes of ~10 degrees Celsius. This prompted me to do research into diurnal temperature variations and what I discovered was quite revealing; the vast majority (pick a location, any location LOL) of locations where humans live and observe enjoy annual diurnal temperature variations of the order of 10C, so telescopes of most any design will acclimate. At my location, these variations amount to little more than a few degrees (check out Glasgow climate and its average high and low temperatures throughout the year) and I have never had any significant issues with my 18cm f/15 Maksutov. The worst places, which exhibit diurnal temperature swings of the order of 20C or more, are located in deserts and at high altitude.

Maksutovs will work nearly anywhere on Earth. Laziness and ill-preparedness have prevented many from discovering this. Others have been led to believe that they won’t acclimate. But I wonder if this is the result of cultivating an elaborate lie; a  bad meme spread on tinternet. I remember a well known American astronomy couple who boldly wore T-shirts emblazoned with a  ‘No to Catadioptrics’ logo. How myopic is that? How misleading is that?

Recurring interest in the Maksutov Design over the Decades
There seems to be a recurring interest in this design, its elegance of form, extreme portability for its aperture, rigidity of the various components in the optical train and so on and so forth. It’s interesting that three of the leading amateur ‘scope makers in the USA; TEC, Astrophysics and D&G have offered Maksutov or classical cassegrains to their customers. The leading UK telescope manufacturer, Orion Optics, Newcastle under Lyme, England, also produce their own versions – the OMC series;

Zeiss too seem to have offered Maksutovs for amateur astronomers back in the day. And then there are the various incarnations from Intes and Lomo etc etc.

Why do you suppose the Maksutov Cassegrain has garnered such interest from these opticians of skill? The reasons are clear to me. The extreme portability and ergonomics of the design is a major plus of course, and the not too inconsiderable fact that they serve up images midway between an SCT and a fine refractor, has led leading telescope makers to maintain an interest in building them and bringing them to market.

Having said that, in independent bench tests, the mass market Maksutov fairs very well in comparison to custom designed units made by leading telescope makers.

I found one test on Mr. Rohr’s website, where he evaluated the 6 inch SkyWatcher model;

Herr Rohr also evaluated a 8-inch TEC Mak.

You can see two further  tests on the SkyWatcher 180 Maksutov here and here.

Not bad quality from the mass market Chinese Mak eh?

That kind of quality is more than enough to achieve  superlative visual results as is showcased in the next section.

A Case Study; Asbytec’s Work with a 6 inch Orion Maksutov

As mentioned previously, dedicated observers using the Maksutov have produced some very high quality work. Based in La Union in the Philippines, Asbytec has faithfully used his 6 inch Orion Mak over several years to produce an excellent portfolio. Many of his drawings have appeared on the online telescope site Cloudynights. His work highlights the high resolution capabilities of the Maksutov under good seeing conditions and his trained eyes have really pushed the envelope in terms of what can be seen. My own but less extensive work with its larger Orion sibling dovetails very nicely with his.

Jupiter

Jupiter. Image Credit: Asbytec

 

Mars

Mars. Image credit: Asbytec

 

 

 

 

 

 

 

 

Saturn

Saturn. Image credit: Asbytec

The Eskimo Nebula

The Eskimo Nebula. Image credit: Asbytec

 

Elongation in 72 Pegasi. Note the angular separation!

Elongation in 72 Pegasi. Note the angular separation! Image credit: Asbytec.

 

 

 

 

 

 

 

 

 

 

 

 

 

 Imaging with the Maksutov

The long focal length of the Maksutov makes it especially suited to lunar and planetary imaging. The majority of other instruments require powerful Barlow lenses or Powermates to boost the f ratio to about f/20 ( generally considered to be the sweet spot for imagers) but with many Maks having relative apertures of 15 or so, little in the way of auxiliary amplifiers are needed to get to that optimal imaging speed. Richard Garrad, an imager from Utah, USA, has used his Orion 180mm Mak to great effect capturing detailed images of the bright planets and the vast lunar regolith. You can see examples of his work and gain an appreciation of the excellent resolution and light gathering power of the same instrument here.

Notes from the field

To get the best performance out of the telescope, I flocked its main tube as well as the long baffle tube connected to the primary mirror. This resulted in a small increase in the contrast of daylight images (which can ‘flood’ the tube with off axis light) as well as on bright objects like the Moon and bright planets. After testing a few different types of diagonals, I came to the conclusion that a good quality prism diagonal was preferable to its dielectric mirror based counterpart. Well made prism diagonals seem to do a better job curtailing stray light and improve contrast. That said, the model used was not one of the expensive prism diagonals but a no frills 1.25” Celestron model # 94115-A, which I consider an excellent value in today’s market.

Like the classical refractor, one of the great joys of the Maksutov telescope is that it can be used with fairly inexpensive eyepieces owing to its high f ratio. Simple Plossl and orthoscopic  eyepieces give excellent edge to edge performance in this telescope so the user will not incur a large monetary sacrifice in using the instrument. For low power work,  I elected to use a SkyWatcher 32mm Plossl delivering a power of 84x and a half a degree field. For higher power applications I employ a 24-8mm Mark III Baader Hyperion zoom, the performance of which is excellent.

One might think that such a large aperture telescope would be unsuitable for nature studies but I found it to be excellent in this capacity. What makes it so versatile in this respect is its low mass and tremendous back focus. You can focus on flowers just a few metres away and examine their glory at powers up to 300x. I found this to be quite an enjoyable pastime during the summer months. Without the addition of various extenders etc, you simply can’t do that with a refractor of the same size.

Comparing its double star efficacy with that of my fine 5” f/12 achromatic refractor, I found the Orion Maksutov to be noticeably superior at ferreting out sub arc second pairs such as the 0.9” Lambda Cygni and on one occasion, a big surprise from the star O Sigma 507 (RA 23h 49 min, Dec +64 degrees 54 min). The A/C components (mag 6.8/8.6), separated by about a Jupiter diameter and arranged roughly north-south, were easy pickings at low power but I was more interested to see what happened to the primary as I cranked up the magnification to 340x. So I swung the system to the east end of the field and let the vibrations settle down. To my sheer amazement, I glimpsed (often for several moments at a time) the secondary (A/B; mag 6.8/7.8) just (and only just) touching the primary, and extending away to the northwest! I repeated this several times within a few minutes to make sure I wasn’t seeing a diffraction artifact. As I have described elsewhere in my double star surveys, it looked for all the world like a “a tiny little snowman in the sky” morphed time and again by the vagaries of the atmosphere. Now, my records show that A/B is currently of the order of 0.7 arc seconds apart! This is truly an extraordinary result, as the components were not merely elongated but very nearly separated to my average eye. Clearly, the Maksutov was operating real close to its theoretical limits (so far as is known conventionally). Let me tell you you’ll struggle to get this kind of performance out of  the finest 6 inch refractor money can buy!

This is a new ‘personal best’ for me. If anything, it shows that I can go beyond the 0.9 arc second barrier under the best conditions which were clearly on offer at this location (Torphins in Northeast Scotland) on this evening. That said, my notes show that I already enjoyed excellent seeing here before, albeit using smaller instruments.

In other tests, I turned both the Orion Maksutov and my high quality 5″ refractor on Psi Cassiopeiae. The primary is a 5th magnitude K spectral class star and just east of it lies the faint magnitude 9.1 and 10.0 (C & D components) separated by 2.3”. Looking first through the large Maksutov, I could see the exceedingly faint pair at 170x. The challenge here is that the C and D components are both very close and very faint and the bright orange glow from the primary right next door doesn’t help. In comparison, the 5 inch refractor really struggled. I convinced myself that it was doable – but only just! Thus, there was a clear performance difference between the instruments here.

The faint companions to Psi Cassiopeiae as sketched by the author.

The faint companions to Psi Cassiopeiae as sketched by the author.

The same is true of its lunar and planetary performance. If fully acclimated and under good conditions, the Orion Maksutov will comfortably outperform the 5 inch refractor. This was made apparent by studying the craterlets on the floor of Plato. The largest – A, B and C – can be seen in the 5-inch refractor but are better defined in the larger Maksutov. The D craterlet, which was distinctly seen in the Maksutov, was invisible in the refractor under the same conditions.

Preliminary tests comparing the views of the 5 inch refractor with the Orion Maksutov confirms that the latter can also resolve significantly finer atmospheric details on Jupiter than the former. The brighter image of the 170mm Maksutov allows greater magnifications to be pressed into service and under good conditions shows the true colour of ovals and barges.

Though opinions differ, like many larger aperture telescopes, I believe the Maksutov does benefit from the use of filters to bring out very subtle planetary details on the precipice of visibility. Blue filters (the 80A and 82A) are excellent for bringing out belt details, while the Baader Neodymium, Contrast Booster and TeleVue Bandmate planetary filters show great promise in enhancing low contrast details on the Jovian disk.

Some amateur astronomers consider the Maksutov to be a rather specialised, high power, high resolution instrument, but that does not mean it can’t be put to good use as an effective instrument on deep sky objects. Truth be told, the vast majority of these objects are well framed within the smaller field of view of the Maksutov. In this capacity, I enjoyed many evenings studying the glories of the late summer Milky Way through Cygnus and Cassiopeia. Small open clusters are excellent targets for this telescope, as are globular clusters, owing to the telescope’s extra light grasp over a mid-sized refractor. The finest 5-6 inch refractor money can buy will not give you an image of M13 like this economical Maksutov. Everything is easier to see and better resolved. The Orion 18cm Maksutov is also a wonderful telescope for studying planetary nebulae. The views I had of M57, M27 and NGC 6826 were simply spell binding, exploiting the natural, high magnifications achieved by this instrument.

There is nothing preventing a determined observer from sketching larger swathes of sky than can be captured in the small field of view of the Maksutov. Here is a modest sketch I made of the Double Cluster (Caldwell 14) in Perseus. Because the maximum field of view presented by the 32mm Plossl is only of the order of 0.5 degrees, it cannot wholly capture both clusters in the same field of view. Both NGC 869 and NGC 884 individually span some 18’ of sky and are separated by about a Moon diameter (25’). Nevertheless I wanted to include both in the sketch, so I took to ‘stitching’ them together by moving the telescope slowly eastward from the core of NGC 869 towards NGC 884.

In this way the traditional limitations of the Maksutov’s small field can be overcome; in just the same way that imagers have done with their CCD cameras.

The Double Cluster in Peeus as drw by the authorr using his 17cm Orion Mak and a 32mm Plossl eyepiece.

The Double Cluster in Perseus,  as drawn by the author using his 18cm Orion Mak and a 32mm Plossl eyepiece.

Conclusions
The Orion 180mm Maksutov Cassegrain represents an excellent alternative to a medium aperture apochromatic refractor but is more closely akin to what you would expect from a long focal length classical refractor of the highest quality. The telescope will need some time to acclimate in winter, especially if taken from a heated inside room to the cool of the night air, but storing it in a dry unheated outhouse should alleviate any problems in this regard. Its ultra-compactness and relatively light weight for its aperture will allow you to transport the instrument safely in the back of your car to a dark sky site. In today’s market, where some amateurs obsess over high quality refractors costing a second mortgage to acquire, this magnificent, ergonomic telescope represents an exciting breath of fresh air! A telescope like this would have astounded an observer in my father’s time and he would have needed the wealth of a Sultan to acquire one of this quality. To think that one can get this kind of performance out of a telescope that cost just a few hundred pounds, is only half a metre long and weighs a mere 20 pounds, is a joyous revelation.

Why would anyone want anything more from a lightweight, ultraportable visual ‘scope?

Update: March 19, 2015

Having spent a fairly cold winter with this instrument, I am delighted to report that it has earned my deep admiration. Out of curiosity, a second time: I deliberately unscrewed the back, removed the flocking from the long baffle tube on the primary and reapplied fresh stuff LOL. When I put it back together, it still held perfect collimation as judged by a high power star test on two separate nights! This telescope is amazingly resilient to mis-collimation! Try it out for yourself! I think the rigidity of the aluminised spot on the secondary helps make this magic happen.

I have managed its ‘alleged’ thermal problems throughout this time and never once have I needed to resort to some kind of active cooling. I will re-state what I said previously; if the telescope is kept in a dry unheated shed, it is effectively in a permanent ‘grab n’ go’ state. Only the local seeing conditions will curtail its efficacy.

My family and friends have enjoyed some positively charming views of Jupiter, the Moon and a variety of deep sky objects with the telescope.

Here is a drawing of Jupiter I made on the evening of March 24 during a spell of fine weather.

Jupiter, as it appeared in the telescope at 190x on the evening of March 24, 2015.

Jupiter, as it appeared in the telescope at 190x on the evening of March 24, 2015.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In addition, the telescope has continued to provide excellent views of tricky double stars. Challenging pairs such as Eta Geminorum (Propus), Iota Leonis and Eta Orionis have been successfully split under good seeing conditions.

Since first beginning my assessment of this large Gregory Maksutov, I have been made aware of two independent tests, both of which suggest that the optical quality of this telescope is very high.

You can see one such test here and another here.

I have had many opportunities to compare the views of Jupiter through my fine 5-inch f/12 achromat the 17cm Maksutov during bouts of fine seeing. The latter shows a good bit more detail than the long glass. My conclusions mirror this gentleman’s findings when he compared a 5″ f/15 refractor and a 7″ f/15 Intes Mak on the Moon and planets.

Cornelia Africana, my 180mm f/15 Maksutov Cassegrain.

Cornelia Africana.

 

 

 

 

 

 

 

 

 

I have named this telescope ‘Cornelia’ and she will remain in my stable, serving as a powerful and ultra-portable telescope.**

My Initial Exchange with the Public

And its Follow Up

Update: April 23, 2015

More Mak varieties have now hit the market.

Meade Instruments and Explore Scientific announce exciting new 6 inch Maksutov telescopes which were showcased at NEAF. Explore Scientific plan to shortly launch an even larger 8-inch model.

This is an exciting time for the Maksutov Cassegrain!

** The instrument was eventually sold on and the funds raised were given to a charity supporting the earthquake victims of Nepal in mid-2015. These days the author makes do with an excellent Skywatcher 8-inch f/6 Dobsonian.

 

Update: March 7 2018

An interesting test report comparing a SkyWatcher 180 Maksutov versus a Takahashi Mewlon 180.

 

De Fideli.

Changing Culture V: Using Newtonians in a Terrestrial Setting.

See the difference.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In a previous blog, I described, in considerable detail, my enthusiasm for the lightweight but powerful 130mm f/5 Newtonian reflector. This modest instrument beat the codpiece off a way overpriced 90mm ED apochromat which retailed for about £1,000 (and is now discontinued) on every test object. This little Newtonian has an excellent SkyWatcher parabolic mirror and the secondary was upgraded to an Orion Optics UK sourced unit, with a semimajor diameter of 35mm, thus delivering a moderate 27 per cent linear obstruction (so considerably smaller than a similarsized SCT or Maksutov). Both mirrors were also treated with Orion UK’s proprietary HiLux coatings, providing an overall reflectivity of 94 per cent. Further testing showed that it provided images that were effectively equal in brightness to a fine 127mm f/12 refractor (which has now been retired). The interior of the tube was lined with cork for improved insulation and then covered with standard flocking paper, maximising contrast and reducing stray light to near zero.

Such an instrument has provided excellent views of the heavens, from 20x in a 2.5 degree true field, to over 400x on very tricky double stars down to 1.0″ separation. During last year’s apparition of Jupiter, the 130mm f/5 Newtonian also proved its worth as a very capable planetary telescope. The instrument was also fitted with easytouse Bob’s Knobs on both the primary and secondary for ultraprecise collimation that takes just seconds to execute.

Newtonians need to be very well flocked to serve as effective terrestrial telescopes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

It may come as a surprise to some readers to learn that this author spends as much time looking through telescopes by day as by night, and over the past few months, he has been using the 130 as a ‘super’ spotting ‘scope, where it has dlivered crisp, colourtrue images of a range of terrestrial targets, including, birds, trees and various manmade landmarks. This has led him to openly question the dominance of more conventional spotting ‘scopes (usually small refractors and catadioptrics). The only reservation I had while using the Newtonian for nature studies was that it delivered an image which was upside down and rightleft reversed. And while this ought not to bother a determined telescopist, some have dismissed the small Newtonian as a daytime spotting ‘scope precisely because of the orientation of its images. Yet, there are ways to produce correct orientation views through Newtonians and it doesn’t require expensive prism diagonals and the like; enter the Newtonian erecting eyepiece.

The SkyWatcher 10mm Newtonian erecting eyepiece.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I was able to get hold of a 10mm focal length ocular marketed by SkyWatcher for less than £30. It has basic but effective antireflection coatings and appears to consist of a simple Kellner design with an extra lens inserted so as to invert the image at the focal plane and, unlike conventional refractor diagonals, it flips the image so that left and right are correctly presented.

The 10mm SkyWatcher erecting eyepiece has basic anti–reflection coatings.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The eyepiece delivers a power of 65x, with a near 2mm exit pupil, which closely matches the diameter of my pupil during bright daylight. Optically, the unit delivers good, sharp images, with a welldefined field stop, although critical tests did reveal a small amount of lateral colour. Contrast is good but not quite in the same league as a dedicated astronomical eyepiece endowed with fully multicoated optics. Yet, it is more than adequate for casual nature studies.

The instrument can be focused on objects as near as 25 yards without adjusting the position of the ocular, but by moving the eyepiece further up the barrel, or using the supplied extension tube (pictured below),objects even closer to the telescope can be brought to a good focus.

The extender tube supplied with the 10mm SkyWatcher erecting eyepiece.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Doing an internet search, I have also become aware of a 20mm model (supplied by Celestron with some of their smaller Newtonians), which would produce a power of 33x or so with the 130. This would be a useful addition for those wishing to extend the range of magnifications achievable with the telescope during daylight hours, and I will report back on this if I am lucky enough to find one.

Using the supplied extension tube allows the 130mm spotter to focus on objects as close as ten yards.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

So to summarise, there is absolutely no reason why observers possessing small Newtonian reflectors cannot use them in a variety of terrestrial applications. Their increased light grasp and resolution over conventional spotting ‘scopes and small refractors will both surprise and delight their users. The range of terrestrial eyepiece options available are quite limited at the moment (as far as I can tell) though, but I would warmly welcome the introduction of more models offering a greater range of magnifications, as well as improving the optical quality of these designs. But one thing is clear; using erecting eyepieces increases the verstaility of what is, already, a great, allround ‘scope.

 

Neil English is the author of Grab ‘n’ Go Astronomy.

 

 

 

 

De Fideli.