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, USA), 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 mass 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.

 

My personal experience has been that my dirt-cheap 10″ GSO Dob produces better planetary images than my 4″ Apo that cost well over 10 times the price. Yes there is some diffraction, but the increased resolution, brightness and higher possible magnification compensate for this.

There is definitely a point where a good reflector (probably Newtonian) must overtake any practical Apo (i.e. <=6″ for most mortals). I suspect this point is probably achieved with premium reflectors >9″-10″ aperture.

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

As of last night I now have some direct experience relevant to the question at hand . . .

A seller had got together the parts to build an 8″ F7, had sold it to a second guy who was more of an imager and decided not to go ahead with the build. I was the third in line, and I finally got it put together.

Parts are an 8″ F7 Zambuto quartz mirror (made in 2016), a 1.3″ 1/30th wave astrosystems secondary with holder and four vane spider, 10″ x 60″ parallax instruments tube, and a moonlite single speed focuser. It also came with a Meade cell that I upgraded to a Aurora precision cell, and I had to get flocking, rings (parallax), and a dovetail plate.

After two days of drilling, filing, screwing, sticking, and flocking (and probably several other ‘ings’) I now have a fan-bleeding-tastic 8″ F7 Newtonian for something in the neighborhood of $1600.

I made mistakes along the way. I miscalculated the placement of the spider/secondary, and so had to source a longer bolt for the secondary. I got lucky with some old plumbing parts that serve as a ball joint at the end to pivot the mirror for collimation. I messed up a measurement on locating a hole for the spider, and my flocking job doesn’t look completely pretty, but it works.

First light was yesterday afternoon on the moon. Seeing was so-so. High frequency fuzz that makes it seem that the focus is always out interspersed with brief moments of stability. Jupiter finally got high enough for a look around 10:30 PM . . . poor to moderate seeing, but WOW! Exactly what you’d expect from these optics. GRS was bang in the middle of the planet, and very obviously off-pink colored. Numerous bands and a big blue barge visible. Brief moments of very good seeing and I was up to ~300x.

So how does it compare . . . well, it blows my Televue 101 out of the water on Jupiter and the moon. In fact, it blows my old 6″ F8 triplet apo out of the water, and provides nicer contrast by far than I ever saw in my 11″ Edgehd, albeit with less illumination. And compared with my 12.5″ F5 (Zambuto again) Portaball, well not quite as good as that, but the Portaball would still be thinking about cooling when the 8″ was throwing up great views.

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

Bigger Newts will always beat out smaller APO’s on cost and image detail on planets if they are built good. Now compare a 8″ APO to a 8″ Newt and the APO is gonna win, but at 20 to 30 times the cost of the Newt.

CHASLX200(Tampa, Florida); from an online thread entitled; SW MAK 180.

 

Others will advise a moderate-sized reflector as affording wonderfully fine views of the Moon and planets. The question of cost is greatly in favour of the latter construction, and, all things considered, it may claim an unquestionable advantage. A man who has decided to spend a small sum for the purpose not merely of gratifying his curiosity but of doing really serviceable work, must adopt the reflector, because refractors of, say, 5 inches and upwards are far too costly, and become enormously expensive as the diameter increases. This is not the case with reflectors; which come within the reach of all, and may indeed be constructed by the observer himself with a little patience and ingenuity.

*My 10-inch reflector by With-Browning was persistently used for four years without being resilvered or once getting out of adjustment.

William F. Denning, Telescopic Work for Starlight Evenings (1891) pp 38-39

An amateur who really wants a competent instrument, and has to consider cost, will do well to purchase a Newtonian reflector. A 4 1/2-inch refractor will cost about as much as a 10-inch reflector, but, as a working tool, the latter will possess a great advantage. A small refractor, if a good one, will do wonders, and is a very handy appliance, but it will not have sufficient grasp of light for it to be thoroughly serviceable on faint objects. Anyone hesitating in his choice should look at the cluster about χ Persei through instruments such as alluded to, and he will be astonished at the vast difference in favour of the reflector….. When high magnifications are employed on a refractor of small aperture, the images of planets become very faint and dusky, so that details are lost.

William F. Denning, Telescopic Work for Starlight Evenings (1891) pp 41-42

Perhaps it may be advisable here to add a word of caution to observers not to be hastily drawn to believe the spots are visible in very small glasses. Accounts are sometimes published of very dark and definite markings seen with only 2 or 3 inches aperture. Such assertions are usually unreliable. Could the authors of such statements survey the planet through a good 10- or 12-inch telescope, they would see at once they had been deceived. Some years ago I made a number of observations of Venus with 2-, 3- and 41/2 inch refractors and 4- and 10-inch reflectors, and could readily detect with the small instruments what certainly appeared to be spots of a pronounced nature, but on appealing to the 10-inch reflector, in which the view became immensely improved, the spots quite disappeared, and there remained scarcely more than a suspicion of the faint condensations which usually constitute the only visible markings on the surface.

 

Concerning Venus: William F. Denning, Telescopic Work for Starlight Evenings (1891), pp 151

 

Coma is essentially negligible at F/8. It’s there, and can be seen in my 2″ widefield eyepieces, but it’s very muted, even compared to my F/6.24 8″ GSO, to say nothing of the multitude of F/5 and faster mirrors out there. The SkyWatcher 6″ traditional dobsonian makes a nice lightweight alternative when I want something quick to setup, but with enough aperture to wow people on the planets and such. The SW6 makes owning a 5″ refractor obsolete, in my opinion, all while providing the great dobsonian stability that handles the West Texas winds so much better than anybody’s refractor that’s not in an observatory, or using a mount that’s ridiculously heavy and expensive (to say nothing of the accompanying 120mm+ ED glass tube). Yes, it will have less thermal stability, like all reflectors compared to refractors, but that’s a problem one might resolve with a cross-mirror fan, and would be a whole lot cheaper to implement than a big mount, ED glass, etc, without affecting general portability very much.

I like reflectors, and especially dobsonians, for their ease of setup and use. I have always preferred the eyepiece-at-the-top-&-angled kind of design ergonomically, and the general dobsonian design, with the weight at the bottom of the tube, cannot be emphasized enough how wind resistant it is compared to a refractor’s flying in the air like a flag setup. This comparative difference was demonstrated to me Saturday night, when I had out my SW6″ for its maiden sky-voyage and an often-used Kunming 102mm F/7 refractor on the GSO SkyView Deluxe Alt-Az mount. Although it wasn’t very windy that evening, we still had some, and every wind produced a light dance in the refractor, and only a little wiggle in the dobsonian, which dissipated much, much more quickly than the spasmodic gyrations of the image in the refractor.

I will have to decide if I want to sell my most excellent Z8 and replace it with a GSO-10″-dob-and-Coma-Corrector or not. That’s a different story, and would involve comparing dobsonian performance to 6″+plus refractors, which are, to my line of thinking, insane and off the table, cost and mount options considered. But I believe the stories I’ve read here on CN, that a 6″ reflector can keep up, visually, with 5″ ED refractors. I’ve seen for myself how much better Saturn appeared one evening long, long ago, in a LB8″ dob compared to an Orion 120mm ED scope. No comparison, really, the 8″-er was that much better, so I’m sure one would have to move into the refractor stratosphere to continue competing with dobsonians above 6″, and why I’d never own such a refractor. But the SW6, especially if I can upgrade the rather inferior Synta 2″ rack and pinion it comes with, puts all the performance of a 120-127mm refractor into an easier to manage, more stable package, at a fraction of the cost.

CollinofAlabama (Texas, USA), from an online thread entitled; Of coma & 120mm ED refractor.

The best telescopes known to amateur astronomers have a thin aluminum coating supported by glass, diameters considerably exceeding the largest apochromats, and are at their best under dark, steady skies.

Alan French (Upstate New York, USA), from an online thread entitled, Comparing FPL-53 and CaF2

 

It is worth remembering that Stanley Williams and Elmer J. Reese, whose names stand very high in the list of students of the planets, did most of the work for which they are remembered with reflectors of less than 20cm aperture. One of the authors(W.S), while at home from college in March 1978, made an independent discovery of a new SEB disturbance with a 20cm reflector. There was nothing extraordinary in the feat; it was simply a matter of looking at the right time and knowing enough to recognize the significance of what was seen.

William Sheehan & Thomas Hockey, Jupiter, Reaktion Books, 2018, pp 161

Well after sitting in my living room corner for several weeks after purchase I managed to get out last night with an Orion XT6 dob, now this is the basic one, 1.25″ focuser, no eyepiece rack and just the one eyepiece, lots of eyepieces already so its not needed anyway. I bought this on a whim new for less than what I have paid for a mid range single eyepiece, $300 Canadian taxes included, free shipping. I,m older and weight was an issue so the 6″ made more sense than the 8″ which I owned many years ago so I was aware of the weight and bulk of it, also the 6″ will live in a small upright tool shed I have for gardening stuff. Just lift it out and use it.

Lots of light pollution where I live so I tend to observe the moon and planets so after adjusting the secondary (it was way too far towards the primary) I turned it onto the moon.

Well it looks like I got a good one and I came in at 1:30 pm when both it and Jupiter fell behind the trees, tremendous detail on the moon and sharp crisp views, I like a lot of others have over the years got wrapped up in complex and expensive gear so have a night like this for a modest outlay was a delight, I found it really worked well with some of my lower cost eyepieces, higher grade ones made a difference but not that much.

Binojunky, from an online thread entitled Cheap small Dob Delight.

+1

The XT6i was my default recommendation to newcomers who were confident they would enjoy the hobby. Alas, Orion no longer offers the 6″ with IntelliScope. As Binojunky said, enough aperture to open the door to DSO, can handle magnifications I like to use on planets (200x-300x), light, easily carried, etc., etc. It’s also the perfect size for kids who are old enough to “drive” by themselves. My son and I used one when he was ten. He liked that he could collimate it himself, use the IntelliScope computer himself and point the scope himself. He just wished it tracked.

macdonjh, from an online thread entitled Cheap small Dob Delight.

I have owned three of each and still have one of each, both Orion. 6”f8 weighs 34#. 8”f6 weighs 41#. 7# doesn’t sound like much, but it’s a major difference for me at this site that requires a lot of tree dodging; 6” is very easy to use here; 8” is almost unusable, which is why I own the 6. Be aware that 6 and 8 weigh about the same with some brands, SW for example.

Focal lengths are identical, 1,200mm. 6s cools a little faster. All three 6s had a poor a quality 1.25” focuser. It can be adjusted well enough to be serviceable, but requires frequent tuneups. 8s come with an OK 2” focuser. Both are equally easy to colimate to the required tolerances using laser or collimation cap; theory suggests the collimation tolerances are more forgiving on the 6”, but I haven’t noticed a practical difference.

Optical quality (figure) of all of them were about equal, good to very good, no advantage to 6 or 8. 6” might be easier on inexpensive eyepieces, but I only use expensive EP, so can’t say from experience, but it’s consistent with optical theory.

With the same LP EP in both scopes, the 6” has a smaller exit pupil, which is a bit more compatible with the astigmatism in my eyes, so star fields seem a bit sharper to me. At the same exit pupil stars are equal[ly]sharp to me in both scopes. I doubt a person without astigmatic eyes would notice a difference.

The larger 8” is a noticeably better optical performer an all targets, but especially DSOs. Noticeable, but not wow! I also believe the 8s have slightly better motions, but it’s subtle, and most people probably won’t notice the difference if they don’t have the opportunity to use bith scopes side-by-side. For sites where I can carry the scope out in two pieces and leave it in one place all night, I prefer the 8.

gwlee(California), from an online thread entitled Cheap small Dob Delight.

 

I was quite lucky when I bought my 6″F8 Synta(Orion) xt6. Its optics are so good that I don’t really need a premium mirror maker to make me anything better since my Xt6 shows a textbook star test and has been lab tested to be of excellent quality. Perhaps the Chinese have really gotten the 6″F8 optics to a very high level of performance and Zambuto knows this which is why he doesn’t make anything smaller than an 8″. Perhaps not, I don’t know for sure but all I can say is that my 6″f8 shows me fantastic views of the planets rivaling those of my apo refractor [100mm f/9 ED], but with a little more light grasp for deep sky objects. About 20 years ago, I had a Bushnell 6″F8 Dob and it was just o.k. Fast forward to the present and my current 6″F8 dob, the difference is like night and day in optical performance and mechanics so I would say the Chinese have improved by “light-years”, at least when it comes to making 6″F8 mirrors.

Barbie; from an inline thread entitled;Why won’t Zambuto make 6″ f/8 mirrors.Truth Please

Did a public star gaze on the beach last Friday and Sat night. Took my 6 inch f8 home built dob out there.

Haven’t done any such gazes in years and back when I did I was hauling out the 10 f5.6 “big dob”.

Turns out the 6 inch f 8 is the perfect outreach scope as well !

There was a C8 celestron. A 9.25 something or other cat. A 4 inch relatively fast ED refractor. Some other guy with another C8 ish type scope set up with a display screen and astrophotography.

Then, off to one side was my little 6 inch F8 Dob.

A fair fraction of the folks that looked through my scope made a point of saying that they were attracted to the scope and wanted to check it out.

And I can think of several reasons why. First obviously home built. Not nearly as impossing as the other scopes. Even the 4 inch frac had a serious looking mount. Not complicated looking. Those other scopes with all those fiddly bits and hand controllers and whirling motors are fairly intimidating to the general public I think. And needless to say the astrophoto/display screen scope took that to the next level.

Not only did it look simple…folks could see it was simple in use. Look at Jupiter say. Then swing around, sight along the side of the tube or use the laser pointer on the tube and bammmm….now we have Saturn….swing around again….Venus….swing around again…Alberio…swing around again…the moon…and so on and so on.

Need to move the scope to get an unobstructed view of X? Pick it up….move over…plop it back down….bam….done.

Most people expressed awe that I could “just find” things. But I explained things…simple landmarks in the sky. Albierio….end star of the easy to see Cygnus. M4…sorta between Antares and that other star. M22…forms a parallelogram with the handle and top of Scorpious the Tea Pot. M57….right between those two easy to find stars near easy to find Vega. Explained how Mars, Jupiter, and Venus are fairly obvious targets once you know what you are looking for. And even Saturn with a little care.

Then a fair number got fairly interested in the home built aspect. Hey, I just bought the optics and built a wooden box ! The side bearings are PCV flanges…look here the focuser is made of plumbing parts….you can do this too…especially with all the info and help on the internet these day….

Hey, how much does this cost? Ohhh, you can get something like this for around $300. A bit more and you can get an 8 incher ! The 4 inch frac cost about twice that (the tripod alone was $300). The other scope…well, more like $3000 rather than $300. They probably didn’t wanna know what the imager guy had invested.

As for views? The 9.25 showed a little bit more detail on Jupiter…but it was all a bit washed out to me (probably that large secondary mirror doing that). The six f/8 dob beat everything else IMO. And this is just some random mirror I bought 25 years ago with a bog standard diagonal. Have never even star tested it. And the eyepieces….my $10 Vite 3 element/plastic lens 10 and 23mm plossls.

End of the night. Put the tube under one arm…grab the handle on the rocker box and walk to the car in the parking lot. Easy peasy.

I think a lot of people came away less intimidated about telescopes and costs and finding things in the night sky after seeing the little dob in action.

Starcanoe; from an online thread entitled; Cheap small Dob delight.

***

I built and enjoyed this 6-inch F/7.3 before I even knew what a Dobsonian was. But it’s really close to that concept. Enjoyed that for a long time, added setting circles and wroth my own calculator program to point at things. Used that for years on planets, clusters, nebulae, etc. It was wonderful! I would take it in my compact car to star parties. Very convenient. Sure, I eventually went bigger… but your point is a good one. There is a LOT to be said for starting out with this size and doing visual.

TOMDEY( Springater, New York, USA): from an online article entitled: Versatility of a 6″ Newt.

 

A 6″ f/8 holds a special place in the hearts of us older amateurs. The classic RV-6 Criterion is the poster child for the 6″ f/8s. Many had exquisite optics and the planetary views were quite memorable. I was interfaced with an RV-6 in high school (I graduated in 1970) – the school owned one and it was superb.

Yeah – yeah, that’s the nostalgia talking.

Today, with the Dobs, I would say that the modern equivalent is the 8″ f/6. It’s not that 6″ f/8 is any less worthy a telescope than it was 50 years ago – it is still a wonderful telescope to own. But nowadays the 8″ f/6 has such a small differential in price to the 6″ f/8 that it makes sense to get that instead for most folks. Both telescopes share the same 48″ focal length. So both are manageable as far as size is concerned.

Siriusandthepup(Central Texas, USA): from an online article entitled: Versatility of a 6″ Newt.

 

I agree with siriusandthepup that while a 6-inch f/8 Dob is a great scope for beginners — and for experienced observers as well — an 8-inch f/6 Dob is even better. The 8-incher is very nearly the same size as the 6-incher due to its shorter focal ratio, and is quite a bit more capable. The only real advantages of the 6-incher are that it’s somewhat lighter and cheaper and significantly more forgiving of poor collimation. But once you learn how to do it, collimating an f/6 scope should take well under a minute in most cases.

As it happens, my own scope is halfway in between — a 7-inch f/5.4 Dob. It’s a total joy to use, in every way. I can carry it easily in a single trip and set it up in a matter of seconds. Its ergonomics are miraculous — completely stress-free observing while sitting in a standard chair for objects almost from the zenith down to 20 degrees above the horizon. With a 2-inch focuser, it has an amazing widefield capability, fitting and framing objects like the Pleiades beautifully.

On 90% of all nights it shows almost as much planetary detail as my 12.5-inch Dob. Under dark skies, it shows hundreds of deep-sky objects with ease, resolves at least a dozen globular clusters, and shows a great deal of detail in nearby spiral galaxies such as M33, M51, and M101.

 

Tony Flanders (Cambridge, MA, USA): from an online thread entitled: Versatility of a 6″ Newt.

 

I have been using a celestron c102 4″ f/10 refractor for weeknight hour-long observing outings. With the planets well placed they have been getting much more time lately. However, I find the CA quite bothersome (perhaps spoilt with my other scopes Nexstar 8 GPS and 12 inch dob – naturally color-free but more cumbersome to set up than the 4 inch frac).

I have been eyeing the At102ed as the natural solution to my problem, and a while back was able to compare the views between the two scopes. Another person present at the club outing had a 6-inch f5 reflector with 2 inch focuser and type 1 paracorr.

The reflector provided best views of saturn and jupiter – bright, sharp and color-free. It was slightly better on globs like M13 (obviously due to the slightly better light grasp). With the paracorr it was also an amazing wide-field instrument. Just a slight step behind the At102 in FOV department, the paracorr-corrected views were brighter and more engaging to me than the At102ed. It displayed all the portability advantages of At102ed, had better color correction, and provided slightly better wide-field performance but with a slightly smaller wide-field FOV.

Going by memory (as I had not set up the C8 side-by-side that night) I’d rate the views of the 6″ reflector far closer to the C8 than to 4″ refractor.

I was about to pull the trigger on At102ed, but I found the 6 inch f5 more satisfying. Although a 4″ ed better compliments my existing line-up, the 6″ f5 is a better stand-alone scope.

eklf (Carrboro, North Carolina, USA) from an online thread entitled: Versatility of a 6″ Newt.

I am all about aperture most of the time.That being said, my 6″ is a keeperI have seen spiral arms of M51 in it and fanstastic planetary observing as well. Under dark skies it is a very capablle little scope.Even after getting a 15″ I have sometimes used it for conveniece or neccesity and it has not been ” too bad I can’t use the 15″ scenario.It satisfies.Easy forgiving collimation, very quick cool down and super easy to transport.Odds are you will have good to great optics as well. Outside of Quasars it shows all of the types of objects out there.

aatt (Connecticut, USA), form an online thread entitled: Versatility of a 6″ Newt.

 

Definite pros and cons to different sizes. Mass produced costs less, though. With 8″ f6 vs 10″ f5, both should be moved in 2 pieces. But the 8″ can moved in one piece if you really need to dodge a tree. Still, you will want more aperture.

6″ is enough to get interesting views. M13 starts to break up. Planets start to get beef that the 4″ can’t muster. The view is wider. And the scope is portable. But 6″ is mainly a grab n go. If you drive way out some place dark, you will want a 10″ to enjoy the night. Even at home, the 10″ will be much better on planets.

Stargazer193857(Southern Idaho, USA), from an online thread entitled: Versatility of a 6″ Newt.

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.

Justice, truth, fairness.

Mr. Hardglass.

 

Neil English is author of Chronicling the Golden Age of Astronomy, due out late in 2018.

 

De Fideli.

 

Going from Strength to Strength: the 130mm f/5 Newtonian.

Plotina: queen of grab ‘n’ go ‘scopes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I’ve spoken quite extensively on the considerable virtues of my modified 130mm (5.1- inch) f/5 Newtonian with a 27 per cent obstruction. In contrast to the prognostications of fake theorists and arm-chair amateur astronomers, it has proven to be a fantastic all-round ‘scope, easily trouncing smaller grab ‘n’ go refractors and equivalent sized Maksutovs costing significantly more. It provides very pleasing wide field views at low magnification and excellent performance at high magnifications, especially on a suite of double stars, the Moon and bright planets.

As a double star enthusiast, I have managed to split systems down to one second of arc with this telescope during the winter months but in theory it ought to do a little better. Specifically, the classic Dawes limit for this aperture is given by 4.57/5.1= 0.89″ but is confined to pairs which are reasonably matched in terms of brightness. In this capacity, I was curious to see whether I could resolve the very challenging Lambda Cygni, with a current separation of 0.92″, the components of which differing only by 0.4 stellar magnitudes(5.4 and 5.8).

Taking full advantage of the hot, settled spell (Scorchio lol!) that is currently being enjoyed by residents of the British Isles, I eagerly sought out a system I’ve visited many times before, but mainly with my larger instruments (8″ f/6 and 12″ f/5 Newtonians). I speak of course, of that easily accessible system riding high in my summer sky after midnight during June evenings; Lambda Cygni.

This magnitude 4.5 system is easy to track down, even in twilight, and in preprartion, I have been monitoring an easier system; Pi Aquilae, located much lower down in the east south east at this time. My reasoning was simple; if this lowly system was well presented at high powers in the 130mm instrument, there would be a decent chance that Lambda Cygni would also bear fruit. But that proved to be easier said than done. Over several nights, both this week and last week, I have carefully studied the system but invariably recorded strong elongation. Yet in double star observing, as in so many other arenas of human enquiry, it pays to persevere; and finally in the wee small hours of June 27 2018, I won my prize!

At half past midnight, I noted an exceptionally stable and well resolved Pi Aquilae at powers of 260x and 406x and excitedly turned my telescope on Lambda hoping for a better result. And at 2 minutes past 1am local time, it yielded. Letting the system drift through the field several times over a period of a few minutes I could make out two distinct Airy disks intermittently separated by a delicate sliver of dark sky using a power of 406 diameters!

To put this in context, I have previously just resolved this system using a fine 127mm f/12 achromatic refractor at very high magnifications. And though my recollections show that it was that little bit better at ferreting out the pair, it was always very challenging and only possible under similarly clement conditions. So a most satisfactory result, but not at all violating the rules of classical optics. If something is possible, it will happen; you just have to be there to experience it!

I made a drawing of what I observed at the eyepiece( shown below);

Shumbody stop me!

I’ve been thinking about the eyepieces I wish to bring on our summer vacation and decided to treat myself to an upgrade to my trusty 32mm Plossl. To that end, I gravitated toward the Explore Scientific 24mm 68 degree ocular, which would provide a power of 27x in a 2.5 degree field (the maximum possible for a 1.25″ focuser). So I ordered one up for the princely sum of £142 plus shipping. I had very high expectations about this eyepiece judging by the excellent performance of two other 68 degree Maxvision oculars ((34mm and 40mm also marketed by Explore Scientific) I have already field tested. Both of these provide very highly corrected fields across a very expansive field and provide excellent eye relief for maximum viewing comfort. The eyepiece was ordered on Monday June 25 and it arrived in the early evening of June 27.

The Explore Scientific 24mm 68 degree ocular.

As soon as it was getting dark, I fielded the 130mm f/5 Newtonian once again in order to test the new eyepiece out. Centring Vega in the field, I focused the image and to my chagrin, I noted pretty harsh field curvature and coma in the outer part of the field. When Vega was sharply focused at the edge of the field, the stars in the periphery of the field were quite badly out of focus. This was patently not the result I expected for such a pricey eyepiece. What is more, the eye relief was pretty poor too. I had to bring my eyeglasses right up to the field lens, with the ruuber eyecup pushed down, to try to take in the entire field but it was barely possible and far from comfortable. “As tight as a knat’s chuff” is an expression that immediately sprang to mind lol!

When I compared it to my 32mm, the eye relief was far more comfortable (being about 0.73 times the focal length in millimetres, so ~ 23mm) and though the magnification was slightly lower (20x) the Plossl proved significantly better corrected at the edge of the field!

Was I disappointed? You bet I was! I don’t know if I received a lemon or not but on the morning of June 28 2018, I phoned the dealer and explained that the eyepiece did not perform as advertised and that the 32mm Plossl I tested alongside it delivered better performance. Thankfully, they gave me the go ahead to send the eyepiece back so they could test the unit out. I expect a full refund in due course.

What a palaver!

Anyway, while thinking about my next move on the low power eyepiece front, I intend to bring my trusty 32mm Plossl on my vacation, together with my old Mark III 8-24mm Baader Hyperion zoom. This will provide all the medium power viewing I will likely do, and the 2.25x Baader Barlow will enable me to increase the power to 183x; good enough to study quite a few double stars under dark, Hibernian skies.

Travelling light ( from left to right); my 32mm SkyWatcher Plossl, 8-24mm Baader Hyperion zoom and dedicated 2.25x shorty Barlow.

 

After several more nights of observation with the 130mm f/5 Newtonian, I managed yet another sighting of the companion to Lambda Cygni. Specifically, on June 30 at 23:20 UT, using the same power of 406x, the stars were seen cleanly separated on and off during several minutes of observations. With the fine weather continuing for UK observers, I would warmly encourage others with instruments of 5 inches and over to have a go at this system at high powers. It’s very accessible with an 8″ f/6 Newtonian (confirmed once more around local midnight on July 1/2)

The Explore Scientific eyepiece arrived safely back at the dealers this afternoon (July 2 2018). I am now considering the Celestron 25mm X-Cel LX, which is purported to work well in f/5 optical systems and with a 60 degree AFOV should give nice, expansive views, well over 2 degrees in extent.

 

July 4th 2018: A Very Happy Independence Day to all my viewers in the Colonies!

We leave for Ireland on Monday next, July 9. I’m very excited about sampling the skies of my youth with my 130mm f/5. Of course, I’ve had other telescopes over there, back when my folks were still in the land of the living; a 90mm f/10 achromat (which is still at my sister’s home), and when the ETX 90 was all the rage in the late 1990s, I astounded my late father with its go-to capability and almost magical ability to centre and track down the planet Jupiter in the field of view one chilly Christmas Eve.

Plotina being readied for another night of sky gazing.

 

Bringing a Newtonian is a big change for me. It was always a small refractor or Mak that made it, but this time ’round, I can think of no better telescope to enjoy my vacation with. My wife got a bit of shock when I told her I’d be lugging the 130 in its case, but she has since come round to the idea of having me put all my astro junk in one neat place lol..

I’m relatvely new to Newtonians you see. I pretty much overlooked them, owing to the rise of refractor mania and catadioptrc telescopes in the last few decades. I did have one in my youth however; my second telescope, a Tasco 114mm (4.5-inch), f = 900mm or some such that came in a big yellow box decorated with fabulous photos of planets and deep sky objects. Back then though, I knew next to nothing about the rigours of fine collimation, or how to precisely align its equatorial mount(non-motorised). I bought it second hand from a jeweller that lived near me. It cost me £100; an enormous sum of money for a young teenager in the early 1980s. I eventually sold it on to raise some funds for University a few years later.

Still, the 130mm is far superior in many ways to that old Tasco; greater aperture, light gathering power and sharper optics owing to its nicely figured parabolic mirror. No fooling around with complex mounts either; just stick it on the Vixen Porta II and I’m off to the races! Eyepieces have improved vastly as well; the Tasco came with two cheap Huygenians and a junk Barlow lens.

Mars’ fiery red mien graces my horizon after midnight and Jupiter is quite a bit past opposition, but I hope to get a better view of both worlds as they will rise a few degrees higher in the sky than they do here in rural central Scotland. And having the chance to explore the vast skyscape within the confines of the Summer Triangle (marked by Vega, Deneb and Altair) from a truly dark sky will be an enjoyable experience. That said, last night I lingered a while on a reasonable view of the Ring Nebula in Lyra with my 34mm widefield and 8-inch reflector in summer twilight. How much better will the views be under true July darkness?

I decided to pull the trigger on a Celestron X-Cel 25mm LX eyepiece, which should arrive here by Friday. Fingers crossed for reasonable performance in the f/5 optical system!

The sky is darkening more now as the days and weeks have flown by the Solstice. The stars of Delphinus are beginning to show in the deep twilight and so a chance to visit another summer favourite; the delightful colour contrast pair, Gamma Delphini.

After midnight on July 5 2018, I began searching for two systems; Gamma Delphini and Mu Cygni. The latter proved much more challenging to track down, even with the Celestial Swan now having gained a considerable altitude. Gamma is widely spaced and presents with an aureal primary and lemon-white secondary. Mu is much more challenging though, especially at this time of year; the secondary is situated right up next to the primary but the great light gathering power and resolution of this grab ‘n’ go telesope on steroids made light work of it at 260x but the view was even more compelling at 318x. It’s such a delicate system to study telescopically; like budding yeast seen through a powerful microscope. I made a couple of drawings of what I saw (shown below):

Two gems of the summer twilight: Gamma Delphini & the challenging Mu Cygni, as seen through the 5.1″ f/5 Newtonian in the wee small hours of July 5 2018.

 

July 6 2018

The Celestron 25mm X-Cel LX 60 degree eyepiece.

 

Well, the new 25mm Celestron X-Cel LX eyepiece arrived late this evening. It was packaged well and a quick inspection revealed no internal dust in the optical train. It is very light, considerably less so than the 24mm Explore Scientific (ES) 68 ocular I sent back to the dealer and that’s a bonus, given the low mass of the optical tube. Like the Baader zoom, this eyepiece has a twist-up eyecup which allows the user to adjust the distance between the large eye lens and the eye. Testing it on the telescope in the bright evening sunshine revealed some very good things; the image of a distant rooftop was very sharp. Constrast was excellent. It showed a very small amount of field curvature and/or distortion at the edge of the field but best of all the eye relief was just right; that is, I was able to comfortably view the entire field with my eyeglasses on, in sharp contradistinction to the ES 68. Things were indeed looking good.

The Celestron 25mm X-Cel eyepiece has a large eye lens and twist-up eye cup for optimal viewing pleasure.

Around local midnight, I was able to test the new eyepiece on the stars. I am happy to report that it produced very sharp images of Vega and its hinterland, with good contrast and, to my relief, off axis performance was much better than I had experienced with the 24mm ES 68. Nor did I detect any internal reflections. There was a liitle distortion at the edge of the field but it was more than acceptable, certainly a notch up from the 32mm Plossl I have used for so long with the instrument. And like my daylight experiences, the eye relief was more than adequate when used with my eye glasses(which corrects for the natural astigmatism in my viewing eye).  This improved perfomance may at least in part be attributed to the smaller AFOV of this eyepiece (60 degrees as opposed to 68 degrees with the 24mm ES) but maybe also to its design differences. Nevertheless, I am more than content with its optical performance as a low-power, wide-field scanning ocular, delivering a power of 26x in a true field of 2.3 degrees. And in consideration of the fact that it set me back just half the price of the 24mm ES 68 (£70), I think it represents a really good bargain.

Technology has come a really long way since the days of my youth.

A happy camper am I.

 

At 00:45 local time on Saturday July 7, I turned the telescope toward Cassiopeia, now low in the northern sky and washed out quite a bit by the presence of twilight. I used my 6 x 30mm finder on the 130 to track down the creamy white magnitude +4.6 star, Iota Cassiopeaie. Ordinarily, I wouldn’t go near such a system at this time of year owing to how bright the sky is, but the persistant good weather here inspired me to give it a go. From memory, this star is annexed to a triangular configuration of three fainter stars so it was easy to identify. This is a famous triple system and its delicate cast under good conditions never fails to impress. I was pleasantly surprised with how well it presented at 260x, with all three members showing up clearly and distinctly. I made a quick sketch of what I recorded in the small Newtonian telescope, and is shown below. This is well worth a try at high northern latitudes in small telescopes with easy access to the northern horizon.

 

Iota Cassiopeiae as seen at 23:45 UT on the night of July 7th 2018 using the 130mm F/5 Newtonian at 260x. Note that the date should read July 7 and not July 10. Mea culpa.

 

I spent the afternoon of July 7 2018 deliberating about which eyepieces to bring and which to leave behind. The new 25mm Celestron is definitely coming on the trip. Further daylight tests showed that it Barlows real well with the 2.25x Baader shorty Barlow giving a nice medium power of 59x in a one degree true field. I have had second thoughts about the Baader zoom though, as it’s a bit on the heavy side and even with the same Barlow would only yield 183x, grand for most systems but since the telescope can very comfortably accommodate 50x per inch of aperture, I wished to coax that little bit more power out of the instrument. Racking my brains, I pulled out an older eyepiece which I had boxed away under my bed; a Meade Series 5000 5.5mm Ultra-Wide Angle (82 degree field). As I’ve said in a previous blog, I’m not overly enamoured by 82+ degree AFOV oculars, preferring 60 to 70 degree units in my field work, but upon testing it out in the 130mm f/5 Newtonian on a bright sunny day, I was quite impressed with what it delivered. A high-end eyepiece like this has very good edge-of-field correction and yields a power of 118x in a field of 0.7 degrees. Coupled to the 2.25x Barlow I can squeeze a high power of 266x out of it; perfect for the most challenging doube stars should they present themselves!

So, in the end, two eyepieces, both significantly lighter than the Baader zoom, will be coming on the trip with me, together with a single, 2.25x shorty Barlow. That combination will tick all the boxes!

Final choice (left to right): the Celestron 25mm X-Cel LX, the Meade 5.5mm Ultra Wide Angle and the 2.25x Baader short Barlow lens.

 

This is a good place to wrap up this blog. Take care and see you all when we get back in a couple of weeks.

 

All the best,

 

Neil.

 

 

 

De Fideli.

Spectrum

Take a Closer Look.

 

 

In this blog, I’ll be exploring subjects of general interest/concern to me and wider society:

The Dark Side of Transgender Medicine

 

How the Media Manipulates Truth

 

Cogito ergo sum

 

The Secular Case Against Homosexuality

 

Duelling Worldviews

 

Our Fragile Home

 

Discernment

 

The Anti-Social Network

 

A Form of Child Abuse

 

Cool stuff you never hear in Church

 

The Rise of Homeschooling

 

A Debate: Has the Church Replaced Israel?

 

James Clerk Maxwell: a Great Life Lived

 

Reasonable Faith: An Interview with Professor Alvin Plantinga

 

Doubting Dodgy Science

 

Evaluating World Views

 

Depraved Minds

 

The Beauty of the Creation

 

The Preciousness of Free Speech

 

Walking your Way to Good Health

 

Did the Eye Really Evolve?

 

Teilhard de Chardin: Heretic

 

Unholy Alliance: when Dodgy Science Merges with Theology

 

Tour de Force: Why we are Fearfully and Wonderfully Created

 

The Humanist Delusion

 

RTB Classic: The Truth about UFOs

 

RTB Classic: The Bible Code Myth

 

The Rise of Neo-Paganism

 

The Brute Logic of Exclusivism

 

Can a Christian Accept Evolution as a Theory of Origins? Computer says No!

 

Observing in Twilight.

A great ‘scope to use in twilight; the author’s 130mm f/5 Newtonian which combines light weight with good optical power.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

At my northerly latitude (56 degrees north) every year from about the middle of May to the first week in August, the sky fails to get properly dark and twilight dominates the northern horizon. As a result, the glory of the summer night sky greatly diminishes, with only the brightest luminaries being visible to the naked eye. But despite these setbacks, one can still enjoy a great deal of observing. In this article, I wish to outline some of the activities I get up to during this season.

Observing in twilight makes observing faint deep sky objects very difficult, so my attention is drawn to the Moon, brighter stars and the planets. Although a telescope of any size can be used during twilight observing, I find it most productive to field a telescope that has decent aperture and so I generally reach for my larger telescopes. Arguably my most used instrument during these times is a simple 130mm f/5 Newtonian, which offers good light grasp and resolution but I am also very much at home with my larger 8 and 12 inch reflectors for more specialised work. The 130mm has the advantage of being light and ultraportable and so I can move the instrument around to get better views of low lying targets.

The bright planets are very accessible during twilight and I find it fun to observe them with a variety of instruments. Venus is generally uninspiring, showing only an intensely white partial disk, but I find Jupiter much more exciting owing to its constantly changing atmospheric features and satellite configurations. But because of its low altitude in my sky, I employ colour filters to bring out the most details on the planetary disk. This is where larger apertures have their advantages, as some filters can absorb a significant amount of light and dim the images too much. The sketch below was made during twilight using my 130mm f/5 and a Tele Vue Bandmate planetary filter, power 108x, which imparts a lively colour tone to the planet, enhancing the colour differences between the dark belts and light zones. It’s also an ideal filter for enhancing the visibility of the Great Red Spot(GRS).

Jupiter as observed durng twilight at 22:55 to 23:05 UT on the evening of May 28 2018 using a 130mm f/5 Newtonian, magnification 108x and a Televue BPL filter.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Twilight nights are also excellent for double star work and summer often brings prolonged periods of excellent seeing at my location. Larger apertures allow higher magnifications to be pressed into service, which also helps to darken the sky making the views more aesthetically pleasing. As in all other aspects of amateur astronomy, you can be as ambitious as you want. The most demanding systems are difficult, sub arc second pairs. As a case in point, I recently trained my 8 inch f/6 Newtonian on 78 Ursae Majoris (78UMa), conveniently located near the bright star, Alioth, in the handle of the Ploughshare. Conditions were near ideal on this evening (details provided in the sketch below) and I was able to push the magnification to 600x to splice the very faint and tight secondary star from the brighter primary.

The sub arc second pair 78 Ursae Majoris 78 as seen in twilight on the morning of May 30 2018 at 23:20UT using an 8″ f/6 Newtonian reflector (no fan).

Another system that I like to re–visit in summer twilight is Lambda Cygni (0.9″), which is easier to resolve than 78UMa, as the components are more closely matched in terms of their brightness and are slightly farther apart. Because it rises very high in my summer sky, it is ideally placed for high magnification work.

Conducting sub–arcsecond work with an undriven Dob mount is certainly not for the faint hearted but does bring its unique challenges, and I for one get a buzz out of doing this kind of work. But there are many easy and visually stunning systems that can be enjoyed at lower powers and it is to some of these that I will turn my attention to in the coming nights.

Last night (the early hours of June 2 2018) my wonderful little 130mm f/5 Newtonian was used to visit a number of easy to find and visually engaging binary and multiple star systems. During warm, settled weather, and with high pressure in charge, the twilight conditions proved near ideal for studying these fascinating objects;

Some binary systems visited in twilight using a 5.1″ f/5 Newtonian.

 

 

 

 

The celebrated Double Double in Lyra as seen through the 5.1 inch reflector at 260x.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The very fetching Epsilon Bootis as seen in the 130mm f/5 Newtonian at 260x.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

These observations were conducted between 23:00UT and 00:00 UT.

Indeed, of all my Newtonians, it is the 130mm f/5 that provides the most aesthetically pleasing views of double stars. Colours are always faithful and images are invariably calm owing to its moderate aperture and rapid acclimation. Contrast is excellent too. It just delivers time after time after time…..

The sky as experienced 15 minutes before local midnight on the evening of June 12 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As May turns to June, the twilight becomes ever brighter, with more and more stars becoming invisible to the naked eye. But this greater sky brightness should never deter a determined observer. On the evening of June 12 2018, I set about visiting a score of  double and multiple stars with my 130mm f/5 Newtonian, as is my custom. I turned the telescope toward Polaris at 22:45 UT  and was deligted to be able to pick up the faint 8th magnitude companion to the 2nd magnitude Cepheid primary. Looking for something more challenging, I waited another half an hour to allow the sky to darken maximally but also to allow a summer favourite to gain a little altitude but still several hours away from culmination in the south. I speak of that wonderful binary system, Pi Aquilae( Aql), a pair of yellow white stars of near equal brightness and separated by about 1.5 seconds of arc.

From extensive, previous experience, I know it is possible to split this pair in smaller telescopes than the 5.1 inch reflector, particularly a suite of refractors ranging in aperture from 80mm to 102mm. But under these June conditions, the advantages of decent aperture become readily apparent; smaller telescopes simpy run out of light too quickly when the high powers needed to splice this pair are pressed into action. Locating the 6th magnitude pair at a fairly low altitude under bright June twilight  is even a challenge for the 6 x 30mm finder astride the main instrument. To my delight though, I was able to track it down and once centred, I cranked up the power to 325x ( using a 2mm Vixen HR ocular) to obtain a marvellous view of this close binary system, the components aligned roughly east to west with clear dark space between them. Adopting these powers with smaller apertures is problematical to say the least. Why strain one’s eyes when one can view it in much greater comfort using the generous aperture of this trusty 130mm grab ‘n’ go ‘scope?

I made sketeches of both Polaris A & B and Pi Aql as I recorded them at the eyepiece (see below).

Polaris A & B and the tricky, near equal magnitude pair, Pi Aql, as seen in the 130mm f/5 Newtonian reflector on the evening of June 12 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As the June solstice approaches, the twilight continues to brghten the sky, but there’s still lots to see. Beginning about 10pm local time, I began observing a pretty crescent Moon sinking into the western sky. The instrument I chose this evening was a very inexpensive but optically excellent 76mm f/9.3 Newtonian reflector, which I described at length in previous blogs such as this one. Because our natural satellite is so big and bright, a small telescope like this one is ideal for casual observing. Because the sky is still quite bright at this time, I found it helpful to employ either a neutral density or variable polarising filter to increase the contrast between the lunar regolith and the background sky.

An amazing performer in June twilight: the Orion Space Probe 3 altazimuth reflector.

Observing the Moon in June twilight is fun at all magnifications, but I have discovered this little telescope can provide razor sharp images up to about 210x. You’ll not get this information from the telescope forums though; it still seems beneath them to test it and spread the word, but I digress!

On the evening of June 18 2018, I visited a suite of summer double and multiple stars with the same instrument.

At about 11.30pm local time, the sky was dark enough to track down some pretty tight double stars, as well as a variety of easier but just as comely systems. Conditions were good enough for the little Spaceprobe reflector to nicely resolve Epsilon Bootis, Epsilon 1 & 2 Lyrae and Delta Cygni (210x in each case). My study of the Lyra Double Double in particular with this telescope shows that it is significantly better than any 60mm refractor in terms of raw resolving power. As I have reported earlier this year, the same telescope was able to resolve Xi Ursae Majoris, Porrima, Eta Orionis, and the wonderful triple system, Iota Cassiopeiae. Sadly, the latter system, which is still present low in the northern sky in June, was hopelessly lost in the summer twilight. Bootes always presents a nice playground for easy and pretty double stars, including Kappa, Pi, Xi and Nu 1 & 2 Bootis, which were all easily split at 116x.

June is also high season for the beautiful, ghostly whisps that meteorologists refer to as noctilucent clouds. These thin, high altitude formations are lit up by the Sun while still below the northern horizon, creating quite surreal visual delights to the naked eye. I took a couple of low resolution images with my iphone (shown below).

Noctilucent clouds captured outside my house at local midnight on the evening of June 18 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Another view captured at local midnight on the evening of June 18 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I shall endeavour to capture some higher resolution shots of these wonderful meteorological structures in due course.

Plotina, the author’s amazing 130mm f/5 Newtonian reflector as seen at 11.10pm on the evening of June 21 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On the June Solstice of 2018, I  walked through the garden in the cool of the evening, fetching my trusty Vixen Porta II mount to field my 130mm f/5 Newtonian. A gentle westerly breeze was blowing and the sky was resolutely clear, but I have learned on many past occasions that these conditions often bring very good seeing conditions for high resolution double star work. And my efforts were rewarded with text book perfect images of a suite of difficult double stars, some of which I have mentioned earlier in this report. I also ended my year long evaluation of a variety of eyepieces and Barlow lenses,varying quite considerably in price range. These studies have led to some firm conclusions regarding the effects of moving air upon Newtonian optics, as well as some very surprising results concerning the efficacy of certain oculars in regard to resolving double stars. Do you always get what you pay for? Most certainly not!

Insofar as artificiallly blowing air on a Newtonian mirror has been shown to scrub off the so-called boundary layer immediately above the reflective surface, my field testing over many nights shows that natural wind can also improve the images in exactly the same way. For this reason, I invariably point the telescope into any prevailing wind while the telescope cools and this works especially well for my larger Newtonian reflectors (8- and 12 inches). Furthermore, I am not aware of any historical precedent for this; the work of some notable telescopic ancestors of the ilk of W.F. Denning, T.H.E.C. Espin, T.E.R. Philips, A.S. Williams, T.W Webb and N.E. Green ( the selected work of which I will feature in my up-and-coming historical work) all of whom used Newtonian reflectors to great effect do not explicitly give mention to this result, though there is no doubt it is generally true.

The Vixen HR series of oculars; nice but totally overkill for high resolution double star work in medium and large aperture aperture Newtonian reflectors.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On many fine evenings using a variety of Newtonian telescopes, I have compared the views through top-of-the-range eyepieces, such as the new Vixen HR series of ultra-short focal length oculars(1.4mm, 2.0mm and 2.4mm) and those derived from much more modest (but still very good) Plossls and orthoscopics coupled to decent Barlow lenses and my conclusions are that the much more expensive eyepieces do not confer any real advantages over the latter.

Ordinary eyepieces and Barlows work perfectly well with Newtonian reflectors for high-resolution double star work. Left to right; a 3x Meade achromatic Barlow, a 7.5mm Parks Gold and Baader 6mm classic orthoscopic.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Yes, the HR series do display slighly better contrast and reduced light scatter compared to Plossls and orthoscopics but the differences were never enough to count. i.e. There was never an occasion where I could not see a tight companion in one over the other at comparable magnifications. Indeed, the HR series of eyepieces have very restrictive fields (42 degrees), even compared with the modest 50 degree fields offered up by a Plossl and/or the Baader classics (which have a larger 50 degree field) when Barlowed allow for significantly larger fields to be exploited. There is thus a distinct advantage to the using the far less expensive Plossl and orthoscopic type eyepieces over the HR series (the three of which will set the consumer back a hefty £750 UK), especially when employing a non-motorised altazimuth mount such as my Vixen Porta II.

Don’t believe the hype; binary stars are very simple, just tight little Airy disks. Save your money and use it more productively on other things.

Well, I hope you enjoyed this blog and that you don’t become discouraged observing throughout the twilight season wherever you live.

Thanks for reading.

 

Neil English’s new book, Tales from the Golden Age, uses history to debunk a few myths that have crept into modern amateur astronomy. Available in late 2018.

 

 

De Rerum Natura

Hubble deep Field Image. Credit: Wiki Commons.

 

However, the Most High does not dwell in temples made with hands, as the prophet says:

 ‘Heaven is My throne,
And earth is My footstool.
What house will you build for Me? says the Lord,
Or what is the place of My rest?
Has My hand not made all these things?’

                                                                                         Acts 7:48-50

 

A new paper by a team of Oxford University scientists, submitted to the Royal Society, London:

Dissolving the Fermi Paradox

(Submitted on 6 Jun 2018)

The Fermi paradox is the conflict between an expectation of a high {\em ex ante} probability of intelligent life elsewhere in the universe and the apparently lifeless universe we in fact observe. The expectation that the universe should be teeming with intelligent life is linked to models like the Drake equation, which suggest that even if the probability of intelligent life developing at a given site is small, the sheer multitude of possible sites should nonetheless yield a large number of potentially observable civilizations. We show that this conflict arises from the use of Drake-like equations, which implicitly assume certainty regarding highly uncertain parameters. We examine these parameters, incorporating models of chemical and genetic transitions on paths to the origin of life, and show that extant scientific knowledge corresponds to uncertainties that span multiple orders of magnitude. This makes a stark difference. When the model is recast to represent realistic distributions of uncertainty, we find a substantial {\em ex ante} probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it. This result dissolves the Fermi paradox, and in doing so removes any need to invoke speculative mechanisms by which civilizations would inevitably fail to have observable effects upon the universe.

Full Paper here

 

 

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 giving a 23 per cent central obstruction) 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.

Date: May 8 2018

Well, the primary arrived back safely from the coaters this morning. I was busy with a few other things so only did a quick check to see that all was well. It was exceptionally well packed for transit. Later on, I gave it a good look over and can say that the firm did another excellent job applying the high reflectivity coating to the 30.3cm mirror, and they centre spotted it, as requested.

The recoated 12 inch primary mirror arrives back home in perfect nick.

 

 

 

 

 

 

 

 

 

 

 

 

Side view.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

It was then carefully placed back inside its cell, making extra sure that the clips holding it in place were not overly tightened to avoid pinching of the optics.

Mirror now back in its cell for remounting onto the optical tube.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After putting the mirror back inside the tube, I left it outside to cool in the bright evening sunshine.

The innards of the foot ‘scope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Following a few hours of rain, it cleared up in the late afternoon and stayed that way well into the evening. So, all I need to do is align the optical train before sunset and I can take it for a spin under the stars.

Awaiting darkness in a race against time.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Yeehaw!

Date: May 9 2018

Time: 00:00UT

What a glorious night! Telescope performed flawlessly!

Boys oh Boys!

Will tell you about it later today.

Starting at about 11:30pm local time, as the twilight had all but abated, the fully acclimated and carefully collimated telescope rendered excellent star tests on a few third magnitude stars, with a very high degree of symmetry in the intra- and extra-focal images at 250x. I could however detect a trace of under-correction, as I reported before, but it was not enough to bother the image in any significant way. In focus, the same stellar targets rendered hard, round Airy disks with no astigmatism or coma at the centre of the field at powers up to 450x (the highest tested this evening). No evidence of pinched optics was manifest.

My first proper target was Izar(Epsilon Bootis) now sitauted high up the southeast. At 250x, the image was remarkable! Both the primary and the secondary were beautifully resolved and intensely bright! Bright targets like this would actually benefit from filtering in this large telescope with a neutral density filter or polariser. As the sky darkened further, I turned the telescope on two stellar targets with very faint companions in comparison to their primaries. Keeping the magnification at 250x, Polaris B stood out wonderfully well; far more ‘in your face’ than the images garnered by even the 8 inch f/6 Newtonian. Even more striking was the very faint and close-in companion to Alula Borealis. The ruddy primary here shines at magnitude +3.5, and the secondary, a feeble +10.1. The 12 inch cleanly resolved the pair separated by about 7.4″ of dark sky, with the companion very obvious and much more easily seen than with any of my smaller telescopes. Where even the 8 inch requires some degree of concentration to pick off the secondary, the 12 inch made it very easy to see at a glance. Indeed, I can’t recall seeing it so well and so easily!

As the sky became maximally dark between midnight and 1 am local time, I turned my attention to a variety of deep sky objects to assess both the light gathering and defining power of the 12″ f/5. And here again, I was not disappointed!

I first turned the telescope on M 51 in Canes Venatici, now very well placed high overhead. Even with the 32mm Plossl I used to centre the galaxy in the field, it was strikingly bright and obvious in the expansive, low power portal. Inserting my 7.5mm Park Gold ocular delivering 200x, I was able to discern far more of the spiral structural details in the galaxy’s spiral arms of this amazing target. Indeed, it was in a completely different league to the views I have recently been enjoying with my 8″ f/6 Newtonian. A very enjoyable experience!

Next, I moved into Hercules, which by this time was well placed high in the eastern sky. Excitedly, I turned the 12″ on its deep sky jewel; Messier 13, the great globular cluster some 23,000 light years away. The instrument served up an amazing image at 200x( 7.5mm Parks Gold), but it was even better at 250x (6mm Baader ortho). The storm of stars resolved in this large aperture telescope was simpy mesmerising and again in a completely different league to that rendered in any of my smaller instruments. For kicks, I cranked up the power to 450x (Parks Gold 7.5mm with a 2.25x Baader shorty Barlow), refocused and sat back to enjoy a field of view littered with innumerable faint, round stars, all finely resolved right down to the core. Lesser instruments just run out of light at these very high powers but not so with the 12″!

Not too far away and significantly higher up in the sky was Messier 92, and once the telescope was centred on it, it produced a wonderfully sharp and well resolved globular cluster, with many hundreds of individual stars clearly seen at 250x (Baader 6mm ortho). As before, while the view in my 8″ f/6  was rewarding, the 12 inch takes you to a whole new level of visual experience!

My final targets were located in Lyra, which I visted shortly before 1am local time. First I turned the telescope on the famous Double Double (Epsilon 1 & 2 Lyrae). At 250x, all four components were beautifully resolved and intensely bright, more like distant coach lamps etched onto the sky than anything else. Slightly lower in altitude was M57, the famous Ring Nebula. At 250x, the image of this planetary nebula, more like a luminous smoke ring, was big and bright and easy to study. Generous amounts of structure were delineated at 450x along its southern border, with many gradations of brightness, mottling etc observed in the brighter outer annulus. Central star not seen (of course!) but many more stars observed in its immediate hinterland than that presented in the 8 inch instrument.

Conclusions: The telescope delivered great images, fully in keeping with its large, high quality optics. I am adequately convinced that the 12″ gains that extra (approximately) one magnitude over the 8 inch telescope, allowing many deep sky objects and faint stellar companions to be more easily studied.  Throughout last night’s vigil, the stellar images at very powers remained tight and calm, suggesting that the insulating cork lining was doing its job (no fan used). All images were presented with very good contrast and with little in the way of stray light drowning out the faintest details. If anything, the experience in the field induced strong desires for even more aperture. But it is reassuring to realise that in order to gain yet another magnitude in light grasp, I’d have to move up to an 18 inch!

I am over the Moon with the performance of this telescope, which was purchased for just a few hundred pounds. And even with the additional costs of the modifications, the overall financial outlay came in at about half the price of my most expensive telescope; a diminutive but very fine 5″ f/12 refractor. Heck, that telescope would make a good finder on the 12 inch behemoth lol.

Date: May 10 2018

Time: 20:15 UT

The foot ‘scope passively cooling.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The forecast looks good again this evening and so I can spend more time with the foot ‘scope. I leave it set up in my back garden with the optics capped and let it cool naturally to ambient temperature for a couple of hours before commencing observations. That way I can return to my writing committments and/or other things. Although one can have the instrument set up permanently in a cool outhouse, I want the coatings I invested in to last as long as possible. Water vapour and its condensations are the enemies of all optical coatings, so that’s why I store all of my Newtonians indoors when not in active use. My Newtonians are all long term committments; parts of my family, as it were. And like everything else that is valuable in life, it pays to give your instruments a bit of TLC if they are to deliver top perfomance time and time again.

Date: May 11 2018

Time: 23:00 to 00:30 UT

I enjoyed another hour or so of good dark skies last night, visiting a whole suite of double stars in Coma Berenices and Bootes, which were well placed near the meridian at this time. Conditions were a little hazier this evening though, reducing transparency.

There are two lovely doubles in Coma worth visiting; 24 Com, which consists of a gorgeous colour contrast double, the primary shines with a ruddy complexion at magnitude 5 while the ‘secondary’ has a gorgeous blue white hue some 1.3 magnitudes fainter. The system is orientated roughly east to west and very nicely framed at 200x.  I say ‘secondary’ as it is unknown whether this is a true binary system and at this time, the consensus appears that they are unrelated. The second system visited was 35 Coma, with the telescope easily resolving this tight duo of yellow and yellow white components with a striking 9th magnitude outlier. I believe this system is a little over 1 arc second at the present time but is slowly converging over the next few decades. A power of 450x was found to be optimal to splice this puppy, the components of which are 5.1 and 7.1. The orbital period of this system is about three and a half centuries.

Then into Bootes; Iota, Epsilon,Kappa, Mu, Pi  and Xi were beautifully rendered at 200x to 250x. With the generous aperture of this telescope, the stellar members of these systems were very brilliant and colour faithful. Seeing was not as good last night as on the previous night, but I was extremely impressed at how the instrument maintained high quality images over periods of a few minutes, as each system in turn was studied at leisure.

Yet again, I was very impressed with the optical prowess of this large telescope. It holds collimation well (I checked it at various times and in various orientations throughout the vigil), perhaps a tad better than my other Newtonians. It also appears to be behaving itself thermally, which is a great relief. Again, no active cooling was employed.

As I was packing up my gear, I realised that I had not named this telescope properly. I can’t just call it the ‘foot ‘scope’ forever now can I?  But what shall I call it?  Not ‘Alexa’ to be sure; far too creepy for my liking. I need to spend more time with the instrument before I decide.

Time: 13:15 UT

A quality focuser.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I am thoroughly enjoying the sturdy dual speed focuser on the 12″ f/5. All my other Newtonians have simple, singe speed focusers but having the ability to very finely adjust the focus position during high power applications is a great bonus. Frankly I’m amazed that the manufacturers were able to offer this feature as standard equipment with the telescope. A super nice touch!

Well, though the morning was quite cloudy, with the rain arrving on schedule this afternoon, the forecast says that it will quickly pass through, leaving the evening clear once again. I would like to return to the realm of the globular clusters; but not in Hercules. There can’t be many dark nights left what with summer twilight knocking on the door.

Time: 23:00UT

The sky has not yet cleared up. Up early tomorrow so need to call it a night anyway.

Date: May 14 2018.

Time: 23:00 UT

 

The light bucket.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After a cloudy and wet morning, the skies cleared to give a beautiful sunny afternoon. Those conditions gave way to a good clear night, but even at midnight local time, the twilight has noticeably brightened in the last few days, especially towards the north. I set the foot ‘scope out about 10pm local time to fully acclimate prior to resuming observations. Tonight I wish to begin with another celebrated globular cluster, Messier 3, conveniently located almost exactly half way between Arcturus and Cor Caroli.

Time: 00:15UT

Another great night, although the seeing was a bit rough. Nonetheless, some great sights captured in the foot ‘scope. Will tell you about what I got up to later today. Nite nite.

Starting about local midnight, I trained the 12 inch Dob on Messier 3 in Canes Venatici. Centring the object in the low power (47x), approximately 1 degree field of my 32mm SkyWatcher Plossl, I noted a fairly bright field star just west of M3 which provided a means to carefully focus the image. Messier 3 has a very condensed core with quite a few stars being resolved at its periphery. Both my 5.1″ and 8″ Newtonians are well able to resolve the outer parts of this globular cluster but the core remains stubbornly unresolved even at higher powers. Not so with the 12″ instrument, which opened up this globular at powers of 200x and 250x, showing many more stars resolved to its core. The instrument works well with simple, short focal length eyepieces. Indeed, my 4mm Revelation Plossl, which delivers a power of 375x, produced a truly wonderful view, where its constituent stars filled the 0.14 degree field of view. Tracking the instrument was never a problem owing to the smooth azimuth and altitude bearings on the Lazy Susan mount, which enables me to nudge the telescope along as the object drifts through the field from east to west.

M 3 is noticeably smaller than M 13. But it is also located some 10,000 light years further away from the solar system than the latter, explaining its smaller angular size at equivalent magnifications.

This telescope is worth every penny spent on it just for the quality of the views of globular clusters alone. The foot ‘scope is a veritable “glob buster.”

I recorded 4 bright telescopic meteors during my 75 minute vigil.

Keen to get a look at some other showpieces before the worst of the twilight returns, I turned the telescope on the bright galaxy pair, Messier 81 & 82 in Ursa Major, and my trusty 32mm Plossl framed both galaxies in the same field of view. Even at this low power, the generous light gathering power and resolution of the telescope displayed these galaxies extraordinarily well, with prominent mottling in M82 evident at a glance along its major axis. Cranking up the power to 200x using my 7.5mm Parks Gold, clear spiral structure in M81 could be made out without much effort. Again, the level of detail seen in these galaxies is a very significant increase over my next most powerful telescope; the 8″ f/6 Newtonian.

Time: 21:15 UT

Another clear night beckons, so more tests can be made on the foot ‘scope.

Date: May 15 2018

Time: 00:20 UT

Tonight I enjoyed a stellar extravaganza, cruising at 200x through a wilderness of light and colour. More info later today.

Last night’s spell with the telescope took me to a variety of colour contrast double stars. First came 30 and 31 Cygni, arguably one of the most comely binocular doubles in the entire sky, the brilliancy of the stars and their colours; orange and turquoise were beautifully framed in the 0.25 degree field of my 7.5mm Parks Gold eyepiece delivering 200x (a rather pedestrian magnification for this large telescope). While smaller ‘scopes certainly present this vista well, the view is truly transformational in this large aperture telescope owing to its superior light grasp and defining power. I then moved south to Beta Cygni (Albireo) and enjoyed a wonderful view of the marmalade orange primary and blue –green secondary at the same power. It was just a joy to see them so faithfully rendered in their true colours and shining so intensely in the telescope.

Following this, I ventured into the large and sprawling constellation of Hercules, starting with Rasalgethi(Alpha Herculis) with its red giant primary and bluish companion perfectly framed in the eyepiece. Then I threw caution to the wind and moved higher up the sky visting each star brighter than 5th magnitude within the constellation, examining their hinterland in the 200x portal. As I moved from star to star using the 8 x 50mm finder, I was amazed at the sheer light gathering power of this telescope and the number of extremely faint stellar ‘companions’ which attended many of the brighter stars. Where my smaller telescopes only revealed the brighter members or none at all, the 12″ f/5 pulled in many more! I was reminded of the work of the English amateur astronomer, the Reverend T.H.E.C Espin of Tow Law, Northumbria, who used a 17.25 inch equatorially mounted Calver reflector at the turn of the 19th century to discover a sizeable tally of these faint and wide companions strewn all across the northern sky. It seems that good reflecting telescopes are ideally suited for such work. Indeed, they can hardly be beaten in these pursuits!

With every increase in magnitude, there is a corresponding increase in stellar number, but there is no fixed power law that might enable us to compute how many more stars there might be as the magnitude is increased. The distinguished 19th century German astronomer, F. W. Argelander, estimated that each magnitude exhibits a rise of about 300 per cent. Indeed, in data presented on page 294 of W.F. Denning’s masterful tome, Telescopic Work for Starlight Evenings (1891), he provides these figures, collated from a survey between 2 degrees south of the equator all the way to the north pole:

 

1st: 20

 

2nd: 65

 

3rd: 190

 

4th: 425

 

5th: 1100

 

6th: 3200

 

7th: 13,000

Having spent some time traversing the stars of Hercules, I can definitely see that Denning was on the right track. Indeed, I would say that the 12 inch instrument does yield an approximately three fold (maybe more) increase in star numbers over my optically excellent 8 inch f/6 Newtonian; and in many cases that is sufficient to change the visual perspective of each telescopic field by a considerable degree. In small telescopes, many star fields can present as rather bland and uninteresting. Patently not so with the 12″ f/5!

Although the sky is clearing up as I speak, I have decided to take a break tonight as I’m knackered and need to recharge the ‘batteries’. More to come soon.

Date: May 16 2018

Time: 18:00UT

I love the low tech approach of the Dobsonian. No electronics to fiddle with, no star alignments to perform. Just mount it on its lazy suzan and you’re off to the races. But this simple approach doesn’t suit everyone. In particular, many prefer driven mounts that keep objects centred in the field while making observations. If that’s your forte then there’s a solution; enter the driven Dob mount. Many such equatorial platforms are available for purchase today and they vary quite a bit in price, but these days you don’t have to spend a fortune acquiring one. Have a look at this one, for example. All you need to do is adjust the inclination of the platform to coincide with your latitude(in my case it’s 56 degrees North), power it up and you can enjoy an hour of active tracking before you have to reset it. If you do decide on one, you need to ensure it can be adjusted to your latitude angle. That’s why a variety of them can be purchased to suit your precise location, either south or north of the equator.

The good Lord has granted us a spell of settled weather here and tonight looks very good to go. Where will my foot ‘scope carry me off to this evening?

Date: May 17 2018

Time: 00:30UT

The Wide field experience.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tonight I stuck mainly to low power, wide–field viewing. When coupled to a good 2 inch wide–angle eyepiece, the foot ‘scope serves up some spectacular views! More later.

Time: 20:00UT

Last night the foot ‘scope did experience some thermal issues as it struggled to follow the rather large temperature differential between daytime highs and night time lows. This time of year, we tend to experience larger temperature swings than in other months where it is not especially unusual for the diurnal temperature variation to exceed 15C (as opposed to about 5 or 6 degrees which is normal). As a result, high magnification images of stars were quite swollen and, in the absence of any breeze,  I considered using the battery–powered fan. In the end, I changed strategy and decided to explore the wide field sky around Lyra and Cygnus.

Beast of an eyepiece: the Explore Scientific Maxvision 40mm wide angle ocular.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The telescope came with two eyepieces from the former owner; a Revelation 30mm 70 degree Superview 2 inch ocular, as well as a 9mm Revelation Plossl. The former unit was quickly found to be adequate on axis but rather poor off axis, with coma, distortion and astigmatism being in evidence. To enjoy a much more immersive view, one needs to invest in a higher quality wide angle ocular. The 32mm Plossl gives a significantly smaller true field but off axis aberrations are still manifest. To this end, I removed the 1.25″ adapter on the focuser and reached for my 40mm Explore Scientific Maxvision 68 degree eyepiece, which has been used extensively over the last few years with my 8 inch f/6 Newtonian.

While the exit pupil was pushing 8mm on the 12″ f/5, I was delighted with how well it performed. Yes, there was some minor light loss but otherwise it served up excellent, bright and sharp images of star fields out to about 90 per cent of the way to the field stop. And even then, the distortions were more than tolerable. The Maxvision eyepieces are clones of the longer established Meade Super Wide Angle(SWA) and Tele Vue Panoptic oculars, but are offered at significantly lower prices.

To best match the faster f/5 system of the foot ‘scope with my 49–year–old eyes, I ordered up the 34mm unit, which will deliver an excellent 1.5 degree true field, a magnification of 44x and sub–7mm exit pupil. This will be an excellent eyepiece for sweeping the heavens for comets, faint nebulae and open clusters on the precipice of visibility. A large, high–quality telescope like this deserves a good, wide angle eyepiece. The Maxvision range offer this quality at very attractive price points (£114 plus postage). I’m hoping to receive the unit by the middle or end of next week. Of course, there are other options for money conscious amateurs; the second hand market is likely to have something suitable come up from time to time and with patience and discernment, good deals can be had.

This evening looks good to go again, but I would like to take a break from the foot ‘scope for a few days and feed some starlight to my smaller instruments. More soon.

Date: May 18 2018

Moon watching.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 21:30UT

Last night I enjoyed a wonderful evening of double star observing with my 130mm f/5 Newtonian.The sky was very tranquil, allowing almost textbook perfect images to be generated on a variety of systems. The good weather remains with us again today and this evening I noticed a beautiful crescent Moon hanging in the western sky. I just couldn’t resist the chance to observe it in the 12″ f/5. My 32mm SkyWatcher Plossl delivered a jaw dropping view of the crescent at 47x in a one degree field and the wondrous earthshine enveloping its darkside. Reaching for my 7.5mm Parks Gold delivering 200x, I was delighted with the razor sharp views of the lunar regolith, especially considering its fairly low altitude at the time of observation. Though not a lunar observer per se, I look forward to observing this magnificent world with the foot ‘scope as it rises higher in the sky in the coming days.

Date: May 21 2018

The new 34mm 68 degree Maxvision eyepiece arrives tomorrow, so not as long a wait as I anticipated.

Date: May 22 2018

Time: 21:30UT

The foot ‘scope fighting the Spring haar.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I set the foot ‘scope out late this evening so that I could get a quick look at a fairly well placed first quarter Moon, with the express intention of testing the high magnification images garnered by the telescope. In the end, it proved an exercise in frustration more than anything else, as the haar (low altitude cloud and mist) came rolling in off the North Sea from the east as soon as the Sun’s rays became weakened by its falling altitude in the northwestern sky. I did however manage to get some quick peeks at the lunar surface at powers of 250x (6mm Baader ortho) and at 375x (4mm Revelation Plossl). I can report that both ‘high power’ oculars delivered very sharp and detailed images of the lunar regolith in twilight, demonstrating that these powers can be productively used on extended objects like the Moon and the planets in the foot ‘scope. That said, I’ve used nearly double these powers on sub–arc second double stars in work conducted during the summer and autumn of last year.

Alas, the courier never showed up today with the eyepiece……ho hum.

Maybe tomorrow lol!

Date: May 23 2018.

Time: 12:20 UT

The Explore Scientific 34mm 68 degree Maxvision eyepiece.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Well, the new 34mm eyepiece has finally arrived.

Schmokin’!

It’s a scaled down version of the venerable 40mm.

The 34mm Maxvision ocular(left) in comparison to its 40mm counterpart(right).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What I especially like about this series of wide angle eyepiece is that they provide excellent performance in a no–frills package. It came in a plain box with no colourful logos and no advertising brochures. Compare them to the now discontunued Meade SWA incarnations;

The now discontinued Meade Series 5000 Superwide Angle eyepiece family.

 

 

 

 

 

 

 

 

I seem to recall that the Meade 34mm SWA retailed for £249, but were reduced in price for clearance after they were discontinued. Many retailers do not offer the Maxvision series but appear to be selling a hermetically sealed (argon purged) product with a re–designed body for £219.

So, I was able to purchase essentially the same eyepiece for a little over half the price of the latter. That’s what I call a bargain!

You might need to shop around to get your hands on these eyepieces, but I was able to secure this one from Rother Valley Optics.

Of course, I could have gone for some 82 degree wide angle eyepieces which would provide a slightly larger true field (approximately 1.6/7 degrees), but my eyes seem to prefer 68 to 70 degree fields.I appreciate that this is a highly personal choice though.

The Maxvisions seem to be enjoyed by many amateurs. See this thread, for example. Some amateurs prefer to de–cloak them for some reason, perhaps to pare down their weight or to make them look more appealing, but I have never seen the need to do so.

The stubborn haar is still with us and though my skies are currently blue, it will likely roll in off the North Sea later this evening.

No matter, I’ve done good!

Time: 14:05UT

Gaius, the author’s beloved 80mm f/5 ShortTube refractor fitted with the 34mm eyepiece.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I couldn’t wait to see how it performed, so I mustered my 80mm f/5 achromatic telescope and inserted my Televue 2 inch Everbrite diagonal and in went the 34mm Maxvision.

Wow!

The eyepiece delivers a wonderful, wide field at 12x giving a 5.75 degree true field. The field stop is hard and well defined and contrast appears to be excellent. With these eyepieces one can readily adjust the distance of the large eye lens by rotating the upper section to provide the optimal level of viewing comfort.

I’m currently writing a book that is wholly dedicated to the ShortTube 80 achromat and one of those chapters will de devoted to choosing eyepieces for use with it. I hope to perform more critical tests on the night sky in due course.

The 34mm will also serve Octavius, my 8 inch f/6 Newtonian, by delivering a power of 35x in a field just under 2 degrees in extent.

Carrying on the work with the foot ‘scope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 21:45 UT

Contrary to what I expected, the haar did not roll in in the late evening, and it is still clear just now. I set the foot ‘scope out again at 19:00UT and was able to continue my high magnification testing of the early gibbous Moon. I began observing at about 20:40 UT when the Moon had past the meridian and was located at an estimated altitude of about 37 degrees. This was a good altitude to test the defining power of the 12 inch. On fine days like this, the air can be very tranquil in the minutes immediately after sunset and so I began with 200x (Parks Gold 7.5mm). Eventhough the sky was far from dark at this time, the lunar regolith presented with razor sharpness and very good steadiness. Ditto at 250x. Then I attached my Baader 2.25x Barlow to the 7.5mm Paks ocular which delivered a power of 450x. Carefully focusing, I was delighted to obtain a wonderfully sharp and (still) fairly stable image. Having the facility to use the microfocuser proved very useful.  Looking at the ragged crater walls, I could see details which I do not recall observing in my 8 inch at high powers.

This was a most satisfying result! This instrument is indeed capable of very high powers on extended objects like the Moon and a solid indicator that the optics are of high quality, but I am also fortunate enough to live in a place where the seeing will allow a 12 inch to work beyond the remit of my 8 inch telescope.

I’m away out again to conduct some further observatons and to test the 34mm Maxvision ocular. Shall report back later.

Time: 22:45 UT

Well, the haar has come back lol. It was rolling in as I was writing the last section of the blog. But there was a few suckerholes in the sky and I naturally took advantage of them. My first target was Capella now located quite low down in the north northwest. Charging the foot ‘scope with the 34mm Maxvision I can report excellent results. The bright first magnitude star remained pinpoint sharp across the vast majority of the field while wearing my eyeglasses (which correct for the astigmatism in my eyes). Only at the extreme edge of the relatively massive field did the star show signs of field curvature, coma and astigmatism. The same was true of Polaris located at an altitude of 56 degrees above my northern horizon.

Intriguigingly, I also tested the same eyepiece on my 80mm f/5 achromat. The results were broadly the same but I would say that there was slightly less aberration at the extreme edge of the field of view! It had field curvature and astigmatism but not much in the way of coma. Thinking about this for a few moments, I figured that this slightly better result is due to the fact that even at f/5 an achromatic doublet has very little coma inherent in the design. This is a relatively unsung virtue of modern refractor optics.

So a very good result, which left me very satisfied indeed. The eyepiece does exactly what it says on the tin. No hyperbole; just great performance at an excellent price!

Happy camper.

Need to pack up all the toys now and return to barracks.

Date: May 25 2018

Time: 00:05 UT

Just a quick report from tonight. I only fielded Octavius, my 8 inch f/6 Newtonian this evening to test out the 34mm Maxvision ocular. True to form, it delivered fantastic views and just that little bit better correction right at the edge of the field. I’m going to have an absolute ball with this when dark skies return later in the summer!

My main high resolution target was 78 UMa, conveniently located very near Alioth (Epsilon UMa), one of the stars that form the handle of the Ploughshare. My notes inform me that I’ve not revisited this system for close on three years. And it’s got tougher! The separation was about 0.84″ in 2015 but judging by observations conducted tonight using a power of 500x in good seeing conditions (II) at its currently high altitude above the horizon, I would say that the companion is nearer 0.7″. It was spotted roughly east of the primary and pretty much kissing it but I need to make more observations, especially with the foot ‘scope. The primary is magnitude +5.02 and the secondary +7.88.

More on this later.

Time: 10:25 UT

Setting up the 8 inch is easier on the back than doing the same with the 12 inch. There is quite a step up in mass and bulk volume as the image below suggests;

A 12 inch Dob(right) is considerably bigger than the 8 inch(left).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Still, I am more confident than ever that this will also be matched in terms of performance.

I found out that the companion to 78 UMa orbits the primary in just over a century and it’s currently rapidly closing, reaching its minimum separation in 2026 with a separation of 0.48.” Dynamically, this will be an excellent subarcsecond system to study over the next few years and both the 8 inch and 12 inch Newtonians will be pressed into service monitoring its movements. More details here.

This is just one of many fascinating high resolution targets that you can study using telescopes of this size.

Right folks, that’s your lot for this blog. I hope you have enjoyed its content and that it gives you some encouragement to get out there and enjoy the glories of the night sky.

Update: June 4 2018

Since I intend to get a lot of use out of the foot ‘scope, I invested in a small trolley that can help lighten the load of carrying the large optical tube from idoors to the outdoors and back. All I have to do is place the optical tube on the platform and secure it in place using two ropes (supplied with the trolley). It is thereby easily moved from place to place using a couple of small ramps.

I attach a couple of pictures of the ‘scope on the trolley, for interest;

The foot ‘scope on its trolley.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The tube is kept in place by two flexi ropes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The trolley can also be folded down to a neat size for easy storage.

The trolley collapses for easy storage.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

 

 

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 separated 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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An Encounter with Jupiter:

Studying Jupiter from the guide book.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: April 28 2018

Time: 01:30am

Temperature: 3C

Conditions: mostly clear, bright gibbous Moon now sinking into the southwestern sky, rather cool.

This morning, I enjoyed my very first telescopic observation of the giant planet Jupiter in 2018 as it approached the meridian. I very much wanted to begin this season of observations using the Orion SpaceProbe 3 reflector. And boy was I not disappointed! To see it well, I had to move the telescope(on its mount) across the road to the children’s play park so that I could get a good view of the planet as it hung over the trees like a distant coach lamp. But that was never an issue, as the set up is so lightweight that transporting it over the 80 yards of so was not an issue.

Charging the telescope with the 10mm Explorer II eyepiece, the telescope delivered an excellent panoramic view of the planet at 70x with its four large satellites; Io, Europa, Ganymede and Callisto. Even at this power, I was able to see that the planet was flattened at its poles. This is caused by the planet’s rapid rotation on its axis, taking less than 10 hours to complete one revolution. As a result, its equator bulges owing to fierce centrifugal forces, which also somewhat flattens the poles. Jupiter’s shape is thus best described as an oblate spheroid.

Using the 2.25x Barlow with the 10mm eyepiece yielded a power of 158x, but while this gave a sharp image, I found that a better image was obtained by backing down on the magnification in order to optimise resolution, contrast and image scale. I reached for my 1.6x Barlow with the 10mm Explorer giving a power of 112x. This  gave a wondeful image! I was able to make out the tan coloured equatorial belts and also a few other belts at more northerly and southern latitudes (maybe 5 bands in all?). I could also make out significant detail within the equatorial belts. Studying the image from minute to minute, I tracked the planet simply by nudging the telescope along, applying gentle, finger pressure to the optical tube.

Having observed and enjoyed the Giant Planet in many small telescopes over the years, I can report that the 3″ f/9.2 Newtonian provided an image that was significantlty more detailed than a classic, long focus 60mm refractor and was more reminiscent of the details garnered by a very high quality 66mm William Optics triplet apochromatic refractor I had the pleasure of owning many years ago. The SpaceProbe 3 will definitely allow you to study this planet, and with some practice, you will be able to make out other features, such as the famous Great Red Spot(GRS), an enormous, terracotta brick−coloured storm that has persisted on the planet for at least the last few centuries. Such tempests last much longer on this world owing to its lack of a solid surface, which causes terrestrial storms to abate quickly as they get drained of energy when they fall over land. Every now and then (but not on this occasion), one or more of the satellites crosses in front of the planet allowing you to see a disk shaped shadow of the same moon projected onto the cloud tops of this giant world. When you see such an event, it will most assuredly take your breath away!

A light blue Wratten no 82 filter is a good tool to enhance belt detail on Jupiter.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I watched the planet until it culminated in the south after 2:00 am local time, when it reached the same altitude as Rigel (so not very high) does in my local skies, and was delighted by the high quality images this simple, inexpensive telescope served up. As an experiment, I screwed on a light blue Wratten filter to the same eyepiece/Barlow combination and found that this filter improved the contrast between the dark belts and brighter zones of Jovian atmosphere. I would advise other observers to try this filter (which can be picked up for just a few pounds).The planetary image in the telescope was quite stable and relatively devoid of turbulence in comparison to larger aperture instruments. That’s because small aperture ‘scopes such as the SpaceProbe 3 are relatively insensitive to the vagaries of the atmosphere and are quite well suited to low altitude planetary observations.

I left the field tired but genuinely impressed with how well the telescope showed this fascinating target. I even made a quick sketch of the panormaic view at 70x but hope to make a full disk drawing of Jupiter in due course.

You can find out much more about Jupiter and its satellite system by consulting pages 362 through 367 of our guide book.

The mighty planet Jupiter, as it appeared in the Orion Spaceprobe 3 telescope in the wee small hours of April 28 2018.

 

Date: May 19 2018

Time: 23:45UT

This evening I set up the Orion Spaceprobe 3 reflector to have a look at Jupiter and was delighted to see that the Great Red Spot was prominent near the central meridian (the planet’s north−south line). I made a quick sketch (shown below) of what I saw using the 10mm Explorer II ocular supplied with the telescope coupled to a 1.6x Barlow yielding a power of 112x and a Wratten no 82A light blue filter. Having a hoot with this charming little telescope!

Jupiter with its main belts and zones and the Great Red Spot(GRS) near the planet’s central meridian, as seen through the 76mm f/9.2 Orion Spaceprobe reflector. Local time: 23:4o UT.

 

 

 

 

 

Spotting the GRS proved rather easy for this telescope even without the filter, its distinctive colour being readily detected.This is an instrument that will certainly allow you to study the constantly changing aspects of this fascinating world. And with more practice, you will become adept at recording its subtle features.

Conclusions

Three cheers for Oona.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

We have now come to the end of this journey with the Orion Spaceprobe 3 altazimuth reflector. As I’ve demonstrated, you can accomplish a great deal with the instrument on the Moon, bright planets, the Sun and into the depths of the deep sky. I feel very privileged to have acquired this simple little telescope and it will remain in my stable.

I hope you have enjoyed this blog.

Keep looking up!

Neil.

Neil English is author of several books on amateur telescopes.

 

De Fideli.

‘Scope Testing: What the MTF Graphs Reveal.

MTF graph comparing a perfect 5 inch triplet Apo(blue line) with that of an 8 inch Newtonian with a 24 per cent obstruction(worst case scenario)  shown with a dotted red line, as well as a sensibly perfect 8 inch Newtonian(<20% obstruction) shown as a solid red line). Image credit: Ed Moreno.

 

 

 

 

Over the last few years, I’ve been conducting extensive field tests comparing Newtonian reflectors to refractors. Those conclusions can be found elsewhere on my website for both my 130mm and 203mm reflectors and a variety of refractors from 90mm to 160mm in aperture. In this blog, we’ll explore what Modulation Transfer Function(MTF) graphs have to say about the conclusions reached.

 

Tune in soon for more details……..

 

De Fideli.

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.