The venerable 80mm f/5 achromat continues to inspire. Tune in soon to find out how I’ve been learning how to maximise its potential for use under varied conditions, both by day and by night……………….
The venerable 80mm f/5 achromat continues to inspire. Tune in soon to find out how I’ve been learning how to maximise its potential for use under varied conditions, both by day and by night……………….
Chapter 1: Thomas Harriot; England’s First Telescopist.
Chapter 2: The Legacy of Galileo
Chapter 3: The Chequered Career of Simon Marius
Chapter 4: The Era of Long Telescopes
Chapter 5: Workers of Speculum
Chapter 6: Charles Messier: “The Ferret of Comets”
Chapter 7: Thomas Jefferson and his Telescopic Forays
Chapter 8: The Herschel Legacy
Chapter 9: The Pioneers of Parsonstown
Chapter 10: Thinking Big: The Astronomical Adventures of William Lassell
Pause for Thought: Achievements of the Classical Refractor
Chapter 11: Friedrich W. Bessel; the Man who Dared to Measure.
Chapter 12: The Admirable Admiral
Chapter 13: The Stellar Contributions of Wilhelm von Struve (1793-1864)
Chapter 14: The Reverend William Rutter Dawes: The Eagle Eyed.
Chapter 15: The Telescopes of the Reverend Thomas William Webb
Chapter 16: Artist of the Creation: The Astronomical Adventures of Nathaniel Everett Green.
Chapter 17: Edward Emerson Barnard; The Early Years
Chapter 18: William F. Denning: A Biographical Sketch
Chapter 19: A Modern Commentary on W.F. Denning’s, “Telescopic Work for Starlight Evenings (1891).
Chapter 20: The Astronomical Legacy of Asaph Hall
Chapter 21: The Dubious Career of Leo Brenner
Chapter 22: The Life & Work of Charles Grover (1842-1921).
Chapter 23: Angelo Secchi: Father of Modern Astrophysics.
Chapter 24: Hunters of the Red Stars.
Chapter 25: A Historic Clark Telescope Receives a New Lease of Life
Chapter 26: A Short Commentary on Percival Lowell’s “Mars as the Abode of Life.”
Chapter 27: The Great Meudon Refractor
Chapter 28: A Short Commentary on R.G Aitken’s “The Binary Stars.”
Chapter 29: S.W. Burnham- a Life Behind the Eyepiece
Chapter 30: Explorer of the Planets: The Contributions of the Reverend T.E.R Philips
Chapter 31: Excerpts from the Life of Leslie C. Peltier.
Chapter 32: Clyde W. Tombaugh; Discoverer of Pluto.
Chapter 33: A Short Commentary on Walter Scott Houston’s, “Deep Sky Wonders.”
Chapter 34: A Short Commentary on David H. Levy’s, “The Quest for Comets.”
Chapter 35: Restoring the Alcock Telescope
Chapter 36: What Ever Happened to Robert Burnham Junior?
Chapter 37: The Impact of Mount Wilson’s 60 inch Reflector.
Chapter 38: Seeing Saturnian Spots
Chapter 39: John Dobson and his Revolution
Chapter 40: Barbara Wilson: Queen of the Deep Sky
Chapter 41: Einstein’s Personal Telescopes
Chapter 42: The Telescopes of Sir Patrick Moore (1923-2012)
Chapter 43: A Personal Tribute to the 20cm Schmidt Cassegrain Telescope
Chapter 44: A Gift of a Telescope: The Japan 400 Project
Appendix: Why a Parabolic Reflective Surface Fully Corrects for Spherical Aberration.
Bibliography & Useful Links
Saturday July 8 2017
I took a chance on a large reflecting telescope; a Dobsonian with a 305mm (12”) mirror and focal length of 1525mm (so f/5 relative aperture). The price was just too good to pass on so I contacted the seller and it transpired that he was a professor of optics from a Welsh University. I asked him about the telescope and in particular, about its optics. He assured me that they were good from his limited use of it, a tad over corrected but otherwise fine. When I enquired as to why he was selling the telescope he simply admitted that he didn’t have much time to use it and would rather see it collecting starlight than sitting in his garden shed. Although based near Chester, England, the owner kindly agreed to drop off the instrument in person (with an appropriate reimbursement for pertrol) and so early on Saturday morning, he and his wife set out on the road north to my home here in rural central Scotland. The day was bright and sunny, good for a car trip and they arrived in the mid afternoon.
Branded as a ‘Revelation’ 12” f/5, the instrument is fitted with GSO mirrors, which, as I have shown in previous blogs, has now established itself as a manufacturer of high quality optics at very reasonable prices. A few years back, I had actually tested one of these units but, unfortunately, found the mirror to be astigmatic; a real show stopper for me as I like to push my instruments on high resolution targets.
The instrument came with all the usual accessories; a 9mm Plossl (1.25” fitting), a 30mm wideangle ocular (2” format), an extension tube and a ‘straight through’ 8 x 50mm achromatic finder ‘scope. And while the original instrument came with a built in fan, the owner apologised that he had taken it off whilst installing a set of stronger springs to support the primary mirror and had forgotten to reinstall it. He was relieved to see that I wasn’t in the least bit bothered about it and reminded him that many of the great observers of yesteryear never used fans on their reflectors and that this didn’t seem to hinder their fine work in any significant way. He gave me a wide smile. I handed over the cash and treated the couple to high tea, where we discussed, among other things, the many virtues of the Newtonian telescope. Suitably refreshed, my wife and I bid them farewell and they began their long car journey south of the border.
No sooner as they hit the road, I visually inspected the primary mirror and found that it had accumulated quite a bit of dust, which imparted a milky appearance to its surface. There was no evidence of coating deterioration on the primary mirror, but it would require a good cleaning, so I removed it from the tube, gave it a ‘finger tip’ cleaning, described previously in this short blog, using a few drops of washing up liquid added to a bowl of lukewarm water, before hosing it down with my garden hose, whereafter it was dried out indoors and reinstalled in the tube.
The mirror was centre spotted (which came as a relief) and I noted its thickness to be about an inch Thus, it is acceptably thin and should cool off in a reasonable amount of time.
The telescope came with a very smooth dual speed (10:1) Crayford style focuser, a feature I was to learn to greatly appreciate, as the reader will discover shortly.
Collimation was very easy to perform using the oversized knobs on the rear of the primary cell, as well as using a small Philips screwdriver to make the appropriate adjustments to the secondary.
An inexpensive SkyWatcher laser collimator whipped the optics into line in a matter of seconds. Later I removed the secondary mirror for inspection and noted no coating issues with it either. I measured its minor axis to be approximately 70mm so a very respectable linear obstruction of the order of 23 per cent. Not bad at all!
Movements on the lazy suzan mount were smooth and easy to execute, both in azimuth and altitude; certainly adequate to the intended purposes I wish to use the telescope for.
I fitted the instrument with my right angled 8 x 50mm finder borrowwed from ‘Octavius’, my 8 ” f/6 Newtonian reflector. Whatever others claim concerning the curse of acquiring a new telescope to play with, the weather remained fair for me that evening, with the promise of a clear sky, albeit in summer twilight. So I readied the instrument and set it outside to acclimate as sunset slowly approached.
At 23:00 BST, I managed to track down the bright summer luminary, Vega, in bright twilight and excitedly aimed the telescope at it, using a power of about 190x initially. To my great relief, the star focused down to a very tight disk with intense diffraction spikes from the secondary support. The image was remarkably calm and I then racked the eyepiece inside and outside focus. Again, I was very impressed at how the defocused Fraunhofer diffraction pattern presented itself. The optics looked nice and smooth, being virtually identical inside and outside focus. Inserting a quality, 6mm orthoscopic yielding 254x, I re-examined the star in the same way. Again, I was very impressed at how the star test was shaping up. I noted a touch of overcorrection; but it was very minor. There was no visible sign of astigmatism (phew!) or ugly zones. This was indeed a good, large, mirror; no, a very good mirror; in fact, as I recall, absolutely astonishing for the low price I paid for it!
As the sky grew a bit darker, I swung the telescope over to Epsilon 1 & 2 Lyrae, which the finder was just able to pick up in the bright, twlit sky. Leaving the 6mm orthoscopic in situ, I was delighted to see that it rendered a textbook perfect split of all four components. From there, I moved the instrument westward into Bootes and centred Epsilon Bootis (Izar) in the field. Refocusing slightly (it has a lower altitude afterall), I was again rewarded with an excellent image. This tricky, colour contrast binary system can elude telescopes if the seeing is not up to scratch. It was around this time that I reached for my trusty Baader single polarising filter, which imparts a slight darkening of the twilit sky and increased the contrast of the stellar components without imparting a colour shift. The filter improved the image still further by reducing irradiance, I thought. Indeed, I recalled that the previous owner had also learned this trick whilst observing Jupiter with the telescope, so he was a convert to using filters on bright objects too!
Feeling more ambitious, I turned the 12” reflector on Pi Aquilae now positioned low in the south southeast; an interesting binary system with roughly equal magnitude components separated by about 1.5”. Well, the instrument made light work of the system; both stars focusing down to beautiful, round buttons at 254x. Finally, at around 00:15 BST (Sunday), I swung the telescope up the sky once again, where the difficult Delta Cygni was now showing in a darker sky. Again: astonishing! The telescope made very light work of picking off the faint companion set beside the comparatively bright primary. The image was wonderful and calm; a fine night to begin my adventures with this large telescope. Alas, there it had to end, as I had to rise early the next morning, but I retired from the field confident that I had an excellent telescope and one that would assuredly be put to good use in the coming days.
Monday July 10 2017
Time: 16:30 BST
After an afternoon of drizzly rain, it stopped for a wee while allowing me to perform a high power daylight test to the telescope. With a very overcast sky, the temperatures had stablished so I was assured of a good image of a relatively nearby terrestrial target. Coupling a 2.25x Barlow lens to the 6mm ortho yielding 570 diameters, I focused on the topmost boughs of a horse chestnut tree adorned in its full summer foliage and located approximately 80 yards distant. Focusing carefully with the fine focuser of the telescope, I was greeted with a beautifully sharp image of the leaves, with all their minute imperfections being made manifest before my eye. 570x is very close on 50 x per inch of aperture and it passed this daylight test with flying colours. Still, I was quite unprepared for what I experienced the following evening.
Tuesday, July 11 2017
Time: 22:50 BST
Seeing: very good (II), partially clouded over again after a rather clear evening.
I began the evening with a star test on Vega as before at 254x, the result of which was as good (if not better) than the results obtained on Saturday last. Very slight overcorrection noted. Nothing else to report. Polariser used to darken the sky a bit.
23:15 BST: Epsilon 1 & 2 Lyrae perfectly split at 253x. Cranking up the power to 570x yielded similar results. Stars tiny and round; very well corrected optics.
23:20: Ditto for Epsilon Bootis at 570x. Excellent split. Beautiful stellar diffraction images at these uber high powers. Amazing!
23:40: Delta Cygni. Wonderful split at 570x. More turbulence witnessed at this power but the image was mighty impressive. Stars remaining, tiny and round.
Wednesday July 12 2017
Time: 00:10 to 00:20 BST
Seeing: remaining excellent (I/II)
Moved the telescope over to Lambda Cygni, a 0.9” pairing of white stars well positioned very high in the sky. At 254x, the system was well resolved. Then the power was increased to 570x and the image rexamined. Wow! I had never seen the system so clearly and so easily at a glance. The stars are orientated north to south, effectively perpendicular to the direction of drift!
The experience affirms the superiority of aperture under good seeing conditions. What a magnificent telescope I have in my possession!
The following evening was also clear. Details below:
Time: 23:45 to 00:15 BST (July 14)
Temperature: 13C easily noted as the midgees were more numerous tonight than the cooler night of last night.
Seeing: III/IV much more turbulent than the perfection of last night
Instruments: 130mm f/5 Newtonian & 305mm f/5 Newtonian
Targets: Epsilon 1 and 2 Lyrae: split in both instruments but aesthetically more pleasing in the smaller instrument (powers employed 185x and 253x, respectively)
Epsilon Bootis: Not reliably seen in the larger instrument at 250x. Only a swollen seeing disk with maybe a hint of a companion under brief moments of improved seeing.
Companion was clearly seen in the 130mm instrument and aesthetically more pleasing at 185x
All absolutely normal.
What a difference a night maketh!
After a week’s vacation to the southwest of Scotland, I was able to resume my testing at home.
Sunday July 23 2017
Time: 23:45 BST
Instrument: 12″ f/5 Newtonian
Seeing: Appears excellent once again (I/II), quite a bit of cloud, clearing slowly.
00:00 BST (local midnight July 24)
Had a quick look at 78 UMa at 570x but failed to resolve this 0.8″ system now about half way up the northwestern sky. It is considerably lower in altitude than Lambda Cygni though. Will stick to Lambda Cygni.
00:18: Finally cleared up, but still quite hazy. Managed another excellent split of this system this evening. Execllent definition at 570x. System followed through several fields. The addition of the fine focuser is a godsend. Very useful addition!
This is the second time in 12 days that I’ve managed this subarcsecond pair!
Therein lies a project; to ascertain, through actual observation, the frequency of such nights that are available for the 12 ” to do this kind of high resolution work at this location.
00:50; went out to reexamine the system and still very well resolved!
As it so happens, Lambda Cygni is Astronomy Now magazine’s Double Star of the Month (August 2017 issue pp 86). This is what astronomer, Bob Argyle, says about the system;
In 1842, using the new 15 inch refractor at Pulkowa, Russia, Otto Struve noted that the star was a close and very unequal double star. The companion (B), some 1.5 magnitudes fainter than the primary, was found in position angle (PA) 107 degrees (east southeast) and at a distance of 0.7 arcsecond. Since then, the companion has moved retrograde to PA 5 degrees (almost due north) and the separation is near one arcsecond………B is easily seen though not so easily measured with the 20cm refractor at Cambridge; a measurement last year put B about 5 degrees behind the ephemeris, which is derived from the 391 year orbit of Wilhelm F. Rabe(1893–1958).
My observations match Argyle’s very well. That it can be monitored with a 12 inch f/5 Newtonian shouldn’t surprise those who have followed my work over the years. Having enjoyed tremendous success with both a 20.4cm f/6 Dob (which has split this system but not nearly as convincingly) and a smaller, 13cm f/5 ultraportable Newtonian (pictured above), I was never in any doubt that the larger instrument would deliver. But to my knowledge no one has addressed the frequency with which this observation can be made with a 30cm aperture at this location. My hypothesis is that it is significantly more frequent than is commonly reported in the literature(or on forums). I do not, however, consider my location to be special in any particular way.
While I would concede that a large aperture classical refractor, mounted on a good equatorial mount, would be the ideal instrument for measuring this system, my observations suggest that the 12 inch reflector shows it more easily, supporting my previously stated maxim: ‘eye seeth afore I measureth.’
Monday, July 24 2017
A set of Bob Knob’s was fitted to the secondary of the 12 inch, thus facilitating quicker collimation in the field.
Looking good tonight for clear spells.Fingers crossed!
Time: 23:20 BST
Seeing: A notch or two down on last night. (Ant III), Clear sky, very little cloud.Midgees legion.
Marginal split reported at 570x (with polariser) but seeing disks swollen due to atmospheric turbulence. To get some perspective on this, Ant III seeing allows a good split of Epsilon 1 & 2 Lyrae in the 12 inch, but less aesthetically pleasing splits of Delta Cygni and Epsilon Bootis; again with slightly swollen seeing disks.
Will have another look shortly after midnight.
Tuesday July 25 2017
Time: 00:10 BST
System slightly better resolved; certainly to be counted as a split at 570x. Very impressive!
An Aside: 00:30BST
Had my first look at M13 with the telescope. Sky not fully dark yet but boy is it impressive at 254x! Easily superior to the best dark sky images with the 8 inch. Physics is physics afterall!
Some Implications of the ‘Foot’ ‘Scope Project
One of the most important things a tester of telescopes must do is to work in an environment that allows such instruments to be properly assessed. For example, if one lives where the seeing is continually lousy, or at best, mediocre, one will consistently report that small, high quality optics beats everything else, especially on planets and double stars. This is, of course, the mantra of the refractor nut, and it is true only insofar as what their local seeing can establish. Having said that, find out where your favourite telescope tester does his/her observing, and what the seeing is generally like there. Chances are you’ll see a pattern in their reports. It is anomalies like these that lead to much heated (and needless) debates on forums, where the sincere convictions of one individual conflicts with others, only because the air under which they live puts a ceiling on what can be achieved.
For example, a long time reviewer of telescopes provided an in depth review of the Discovery 12.5 inch f/5 Dob in the November 2003 issue of Sky and Telescope Magazine. In that review he states that big Dobs are not always the best choice for double star observing. He writes:
A large Dobsonian is not always the first choice for double star observing; the scope is often too bulky to track at the high powers necessary to split close doubles. Nevertheless, I ran some tests with the 12.5 inch PDHQ. The well known stars Mizar and Polaris were easy, as were the Double Double in Lyra. I was also able to split Alpha Herculis, which has a relatively easy separation of 4.6 arcseconds but is made somewhat difficult by the mgnitude difference (3.5 and 5.4) between its components. But despite repeated tries, I never did split Delta Cygni, an even tougher target with 2.2 arcseconds separating its 2.9 and 6.3 magnitude components.
While there is no other indication from the same review that there was anything untoward about the optics in this telescope, what does seem odd is that he never managed to split the relatively easy pair, Delta Cygni. This would indicate to me that his seeing conditions were just not up to scratch for this task. The 12.5 inch ought to have done far better if his conditions were in any way decent. Thus, and with all due respect to the tester, reports like this must be taken with a pinch of salt.
Time: 22:45 BST: Looking promising again tonight! Yeehaw! I have just come in from a quick test on Epsilon Bootis with the 12 inch telescope and managed an excellent split at 254x. Midgees biting like mad though. More cloud tonight but some good clear spells presenting themselves.
I spent some time earlier dipping into the interesting chapter 11 of the 2nd edition of Observing and Measuring Double Stars (Argyle R.W, ed). I have mentioned the author’s work before; a one Christopher Taylor, who has been observing ultra tight binary stars from central England since the 1960s using a 12.5 inch F/7.04 Calver reflector. On page 135 Taylor mentions something of great interest to me;
It is probably in part the lack of such training and consequent failure to distinguish the seeing blur( the gross image outline) from the still visible Airy nucleus which is responsible for the persistent myth that seeing limits ground level resolution to 1 arc second at best, and is certainly the origin of some of the more spectacularly absurd figures one sees quoted for alleged image size.This author’s experience of typical conditions at a very typical lowland site may be of some interest in this context: using a 12.5 in Newtonian at 400 feet elevation (130m) in central England, an equal 0.75 arc second pair (such as η CrB in May 2000) is steadily separated by a clear space of dark sky at 238x in seeing of only III to II (Ant.)
You don’t say!
Time: 23:41 BST: After waiting for a suckerhole to appear in the clouds, I finally got a glimpse of the system (it’s dead easy to find!) for about 90 seconds, but enough to witness yet another clean split of the stars. Power 570x. Much better than last night. Steady image with plenty of dark sky separating them.
n = 4
I believe Taylor is telling the truth. My observations so far match his.
I would warmly encourage others to participate in this high resolution experiment. A 10 or 12 inch Dob should do the trick, and don’t worry about how much the instrument set you back. As far as I’m concerned the cheaper the better!
Vere dignum et iustum est.
If you’ve been following my blogs, you’ll be well aware that I’ve been chasing Lambda Cygni for a few years now. The 8 inch f/6 Newtonian has resolved the pair well, but only on the best nights (Ant I), but the 12 inch f/5 seems to show this spectacle of nature routinely at Ant III or better. I think Taylor is on to something here. Allow me to couch what I think he’s saying in the simplest possible terms:
With a modest gain in aperture, separating these stars is easier because there will always be moments in fair to average seeing conditions for the larger aperture to split them. It’s pretty much analogous to the idea that a larger aperture shows planetary details better even in fairly rough seeing because nature provides opportunities to let those details pop into view, if only for a few fleeting moments. Shimples!
Wednesday July 26 2017
Time: 23:18 BST
Seeing; Ant II, partially cloudy, brisk westerly wind
Comments: If a job’s worth doing, it’s worth doing fully and completely.
n = 5. Good split at 570x. Image breaks up momentarily but comes back together often enough to see both components clearly. Making more observations in the next half hour or so.
Time: 23:41 BST
System revisited and easily resolved under tonight’s conditions.
Thursday, July 27 2017
The results that I have obtained thus far can’t be exceptional. They must be part of a broader aspect of natural behaviour Thus, there must exist many such places where larger aperture Newtonian telescopes have done the same thing. And since this blog is about the performance of Newtonian reflectors in particular, I contacted Mark McPhee, an amateur astronomer based in Austin, Texas, USA. Mark has been observing and imaging subarcsecond pairs with both his 8″ f/6 Orion (XT8i) Newtonian and a 15 inch f/4.5 Newtonian and produced this amazing post back in December of 2016.
Quite clearly, Mark has provided powerful evidence that subarcsecond pairs cannot just be observed but they can also be effectively imaged. Many of Mark’s targets, of course, go considerably deeper than anything I’ve done in this blog. I asked Mark to provide an overview of what his typical conditions are under which he performs his work. This is what he said:
I gather that my seeing is very good here compared to that for most. In the warmer months (which is most of the year here) I can get a good number of very good seeing days in. I often rate the seeing as at least a 3 out of 5 with a good sprinkling of 3+, 4- and bone fide 4’s in the mix. So, the images I presented are fairly representative of what I see and match a 3+ out of 5 on average. A seeing of 2 or less would likely not be feasible for imaging (or splitting) these challenging systems.
This agrees with the observations I have made thus far regarding Lambda Cygni. But he thinks his conditions might be a wee bit special. I respectfully disagree (n=?). I also believe that if other amateurs tested their large Dobsonians (up to about 15 inches), many more would discover their power to resolve such pairs.
Mark has since gone from strength to strength. He writes:
I am in the process of compiling about 30 double star measures of rather difficult pairs for my first solo JDSO submission–this will contain a detailed description of my methodology.
Fondest congratulations Mark! I hope it will the first of many such submissions!
Nota bene: Mark has also posted work done with his XT8i. You can see some of this work here.
Further thoughts on the Newtonian in respect of high resolution, double star astronomy
Taylor’s essay in chapter 11 of the aforementioned book states that he has done all his subarcsecond double star work in the open air, that is, there is no observatory. My work is also conducted entirely in the open air.
Taylor’s analysis, reproduced in my blog here, advises that this kind of work is unlikely to be successful at < f/5 relative apertures. This author’s work is in disagreement with that conclusion, as is McPhee’s phenomenal results highlighted earlier. My own work utilises only a Barlow lens (2.25x) boosting the geometrical optical train from f/5 to approximately f/11.3. Furthermore, the use of a Paracorr (or other coma correcting optics) would also help correct the field of view for this type of exacting work. Taylor’s analysis never took any of these considerations into account and so his f ratio restrictions can be somewhat relaxed. Thus, I can see no theoretical barriers to owner’s of f/4 Newtonian systems with good, properly collimated optics. Why not give it a go?
Friday, July 28 2017
Well, I’ve reached my first milestone with this telescope; I have (very probably) used it more than the previous owner has lol!
Am I happy with it so far? You bet! To be honest I’m rather in awe of how good the optics are. As I have said previously, I have always suspected that the chances of acquiring a good, mass produced telescope in this aperture class is rather less than for smaller telescopes, such as an 8 inch. The reason I believe this is the case is that the amount of effort needed to get a good mirror must scale with the area of the surface to be worked. And there is plenty of anecdotal evidence to support that claim. How many times have we heard of individuals purchasing a telescope of this size only to be disappointed with the star test it serves up? And there is no shortage of folk who decided to have the primary mirror refigured or some such. From the observations I have made, I am relieved to say that I have absolutely no intention of upgrading the primary. I do however plan to do what I did with my smaller Newtonians, namely to get the mirrors coated with HiLux enhanced coatings, as I have been very pleased with how the others have turned out.
After talking with Orion Optics UK, I decided on replacing the secondary mirror with a slightly smaller unit; in this case a 63mm minor axis diameter. That’s a little bit smaller than the existing 70mm flat but not enough to require a lower profile focuser or some such. The new flat will give a 20.6 per cent linear obstruction, so very respectable indeed for all round work. I intend to get the primary recoated later in the autumn.
The replacement dovetails nicely with a turn in the weather. After a longish spell of fair evenings, we are now sat under a big, ugly low pressure system delivering torrential downpours; so not good for hauling out a large telescope like this.
What a roller coaster ride it’s been so far. Going forward, I determine to accept nothing on faith, or received wisdom, but only to see everything with my own eyes.
Newtonians have been so very kind to me, helping me to take my observing to new heights of sophistication. For many years I dismissed their powers largely for trivial reasons. Sure, they don’t look quite as fetching as a pretty refractor or compact catadioptric, but it’s the views that count. My environment clearly permits me to exploit telescopic aperture in a productive way, unencumbered by physical, geographical or psychological boundaries. And should I get an opportunity to observe while the new flat is being fitted, I’ll be reaching for Octavius, my wonderful 8″ f/6 Newtonian, the instrument that most powerfully catalysed my transition from small refractor culture. For more than a decade I succumbed to the charms of the object glass, being exceedingly zealous to promote their various attributes. Indeed, it is all too easy to engineer a scenario where the little ‘peashooter’ ‘scopes always win. Try comparing a 4 inch refractor to a 12 inch reflector say, while the latter is still acclimating and you’ll see what I mean. Newtonians teach you to be patient with telescopes, to figure out how best to tame them. And when you do that, a whole new Universe is set before you.
Saturday, July 29 2017
There will be a slight change of plan regarding the secondary mirror. I have decided just to have it recoated. Afterall, the existing mirror works perfectly well and the central obstruction is already acceptably small. The better coatings will increase light transmission to the eye and help increase overall contrast in the image by scattering less light/lowering irradiance. The primary will follow suit later this year.
Monday, July 31 2017
Secondary despatched to Orion Optics UK.
Haste ye hame!
Seeing: very good but not perfect (Ant II), slight westerly breeze, some breaks in the cloud.
Instrument: 20.4cm f/6 Newtonian reflector, 450x, polariser
Comments: Continuing this project with Octavius, I was delighted to get a convincing split of Lambda Cygni again this evening under conditions which I did not think would be favourable enough for the 8 inch instrument to pull off. Perhaps it was my recent training with the 12 inch or my lack of diligence in following up this system with the smaller instrument under less than ideal conditions that led me to conclude that it can only be seen in Ant I. Clearly it can be resolved in Ant II. Thus, using inductive reasoning we have n = 6.
Time: 23:50 BST
With a good clear spell now developing, I decided to have another look at the system with the 8 inch. 450x is a good magnification for this kind of work, but even at this power, the system remains small and tight, so I had the idea of boosting the power still more; to 600 diameters using a not too frequently used Vixen 2mm HR ocular.
Well, it certainly improved the situation! The pair were more convincingly separated at this power than at 450x.
Ocatvius certainly has excellent optics for an 8 inch ‘scope! 600 represents 75x per inch of aperture; very good indeed under field conditions.
Thus, in all future observations of well placed subarcsecond pairs with this instrument, I will utilise this ocular as it has clearly proven its worth tonight.
System reobserved just after local midnight at 600x. Split once again confrmed.
Tuesday July 2017
Time: 22:45 BST
Instrument: 20.4cm f/6 Newtonian
Seeing: III, more turbulent than last night, good transparency.
Comments: After a day of torrential downpours with some sunny spells thrown in for good measure, the sky cleared at sunset and I was able to perform another observation. Tests on both Epsilon Bootis and Delta Cygni both revealed their companions at 200x but not as well as last night. Applying 600x to the instrument on Lambda Cygni revealed a very complex diffraction pattern. One can easily discern that the system is duplicitous but no clean split was forthcoming. Out again for another look.
NB. The Vixen HR series are not threaded to accommodate filters. What a bummer. Such an expensive ocular without this basic provision!
Time: 23:07 BST
More cloud encroaching unfortunately. Time to pack up methinks!
Time: 23:17 BST
Hold your horses! Had another look; seeing improved and a split recorded at 600x so n = 7
Comments: Not that unusual for seeing to improve during a vigil. Both stars steadily held on and off through a couple of fields.
Explanations: slight gain in altitude or more thorough passive cooling of the optical train; more likely the former as the system was first examined earlier tonight than last night.
Heavy dew now; so need to pack up.
Time: 23:27 BST
Couldn’t resist one more gander lol. Both stars cleanly resolved between intervals of turbulence, where the image breaks up. This is so cool!
n = 7 stands.
Note tae sel’: Will attempt to refrain from making observations before 23:00 local time (22:00 UT) at least for the next few weeks.
Thursday, August 3 2017
Go to the ant, thou sluggard; consider her ways, and be wise
I was reading through my Bible this morning and the proverb above just jumped out of the page. It’s amazing how Scripture does that eh?
What an extraordinary run of results so far! It appears I can manage a decent split of this pair any time the seeing is fair to good and as long as I use decent telescopic aperture.
All sorts of questions popped into my head, such as;
Like I said, I strongly suspect question 2 is false, as I don’t really think that my location is an isolated system.
But what about question 3? How many folk really understand the nature of the environments in which they regularly observe? Would more people report the same had they enough diligence to do the necessary work? I dare say they would!
The newly coated secondary should be with me towards the end of next week so I’ll be able to resume testing with the foot ‘scope.
Time: 23: 25 BST
The forecast predicted a mostly overcast evening, but as I’ve explained many times before, there will always be the odd break now and then. I decided I’d be ready early this evening, fielding both Gaius, my trusty 80mm f/5 achromatic, as well as Octavius (20.4cm f/6 Newtonian) from about 20:30UT.
I enjoyed a few favourite double star targets with Gaius as I waited for time to pass after 22:00 UT and at 22:25UT I finally got my chance to examine Lambda Cygni at 600x with Octavius. I can report yet another clean split so n = 8.
By 22:37 UT it had totally clouded over, so no further tests could be made.
I suppose the old adage is true: good things come to those who wait. Or how about, chance favours the prepared mind?
The system is very well placed now for far northern observers so if you have a good medium sized Dob, give it a go. Chances are you’ll see it regularly too!
For those further south, why not pick another candidate system just below the 1″ threshold. What have you got to lose? It’d be fun discovering new stuff eh?
Or do you have something to hide? I wonder!!
Friday, August 4 2017
I am hoping as many people as possible will participate in this project to get to know their local conditions better. Surely such knowledge is valuable! Of course, there will be places here and there that won’t yield these results (or at least nearly as often), yet in truth, of all the places I’ve observed from for any length of time here in Scotland, only two locations proved poor quite a bit of the time (and one of them includes my previous abode in the village of Kippen just 7 miles away).
Nor do I claim any credit for myself. This was Christopher Taylor’s revelation and therefore his ‘discovery.’
Away for a short weekend vacation. See you guys n’ gals next week.
Monday, August 7 2017
Time: 20:20 UT
Another night of tests coming up. Good clear evening, ken. I felt like Hulk Hogan fielding Tiberius, my 5 inch f/12 refractor, a top quality long focus instrument. Weighing in at 40 pounds (OTA only), it’s a beast of a ‘scope. Accompanying it is Octavius.
Time: 22:15 UT
Seeing: Very good (II), some light cloud moved in but large swathes of sky remaining clear. Moon low in the south southeast.
Lambda Cygni examined in both instruments.
5″ f/12 refractor: Unresolved but strongly notched at 429x and 572x
8″ f/6 Newtonian: Easily resolved at 600x, so n = 9.
The limited aperture of the refractor is plainly on display. The 8 inch reflector is far more suitable to this kind of work than a 5 or 6 inch refractor.
Ye cannae change the laws o’ physics captain.
Don’t you just love debunking myths.
Tuesday, August 8, 2017
Time: 23:25 UT
System reexamined and once again split at 600x.
Also studied Delta Cygni (now at zenith) at 200x with the 8 inch reflector both with and without the Baader single polariser. I can report that the filtered image gives a more aesthetically pleasing image of the companion. The stars are tighter pinpoints. Very refractor like! This is a marvellous (and relatively inexpensive) little tool for the reflecting telescope.
Wednesday, August 9 2017
Time: 23:17 UT
Seeing: A notch down on last night, slightly more turbulence (II/III). Some rather stubborn cloud moved in, dousing the instrument in a light shower of misty rain lol. Thankfully all optics were covered! Once the cloud moved away, another observation was made.
Instrument: 20.4 cm f/6 Newtonian
Comments: Rather late to the table this evening, owing to considerably more than expected cloud cover. Lambda Cygni resolved unstably this evening at 600x. Diffraction pattern more messy, but the image does settle down frequently enough for its full duplicity (i.e. two non contacting stars) to be plainly discerned.
n = 10
Time: 00:03 UT
System reobserved and split confirmed in the same manner as earlier. n = 10
Time: 20:45 UT
I can hardly believe it’s only been a month since I started this blog. Seems a lot longer than that!
I received news today that the secondary for the the 12 inch will be with me early next week, so slightly later than I previously envisaged. But Octavius is doing rather a good job don’t you think?
Yet another clear night this evening and the 8 inch has been set up to do another night’s work. Looking good.
Seeing: II/III. Almost a carbon copy of last night but with no cloud.
Instrument: 20.4cm f/6 Newtonian
Comments: Started observing the star at 22:00UT but was unsuccessful for quite a few minutes. I found it hard to focus tonight and checked collimation of the optical train, making a slight adjustment (which probably would not have made much difference). After a few more unsuccessful tries, I finally gave it a go at 22:30 UT and did manage a split of the components at 600x, so n = 11.
Out again for another observation.
Another successful split at 600x. No problem, easier this time. n = 11
Thursday, August 10 2017
Time: 23:13 UT
So another good night of work. Clearly, it’s generally beneficial to wait until the system rises as much in altitude as possible, so my earlier attempts might be reflecting this to some degree.
I am missing the sheer aperture advantage of the 12 inch instrument. My notes and mental recollections showed me how much easier it is to see the components of this sub arc second pair. They are easier to see at a glance in the larger telescope, no question about it. I just wish I had the secondary back, but I know I’m just being impatient. Silly me.
Saturday August 12 2017
Time: 20:30 UT
After a couple of cloudy and wet days, we have another clear sky here this evening.The glorius 12th! So, once again, I have fielded Octavius to continue the work until the 12 inch is ready.
Time: 22:03 UT
Instrument: 20.4cm f/6 Newtonian
Seeing: Very good (II), wonderful transparency. no cloud; a beautiful evening!
Comments: System split at 600x. No problems tonight. n = 12. A telescopic meteor darted across the field while the observation was being made; a Perseid of sorts!
Away to briefly watch for more meteors.
Tuesday, August 15 2017
Time: 20: 22 UT
After another couple of overcast nights with no prospect of getting an observation in, the sky looks good again this evening. Alas, the secondary has not yet arrived back, but I have been assured that it will be with me tomorrow. So, I call upon the services of Octavius for a last time.
I have been reflecting a little on the results I have thus far obtained. In essence they demonstrate a very basic tenet of telescopic astronomy; a tenet accepted by all previous generations of amateur astronomer but less so in this one for reasons I am acutely aware of; that aperture rules provided the conditions are good enough to exploit those apertures. Indeed, this work fits seamlessly with all of my other work. For example, a 130mm f/5 Newtonian proved superior on all targets to a 90mm apochromatic refractor (which was very embarrassing). The 8 inch reflector proved crushingly superior to a very high quality 5 inch refractor on all targets. Indeed, the former will outperform any refractor up to at least 6 inches (I’ve actually tested it against a 160mm triplet and found the Newtonian better in some respects and at least its equal in others). These are true and expected results because my environment can clearly handle moderate apertures very well. Indeed, I am more than happy to test any refractor in the aforementioned size range against my 8 inch f/6 Newtonian if the reader is interested in delivering a unit to my home. I suspect though that I’ll not have many offers lol. Denial and hubris, no doubt, are key factors here. But the offer is there should any one of you wish to take me up on it.
Will the 12 inch do likewise to my 8 inch? Judging on what I’ve observed so far, I can’t think of a single reason why it wouldn’t, but those tests will continue in due course.
True darkness is upon us once again! And what an autumn it will be for the 12 inch reflector!
Time: 21:33 UT
Seeing: Excellent ( I/1.5), beautiful clear sky, very gentle southerly breeze
Instrument: 20.4cm f/6 Newtonian
Comments: Lambda Cygni easily split once again at 600x. Indeed, it was so easy this early on that I had a go at 78 UMa (easily found in the Ploughshare), which has a 0.8″ companion. At 21:40UT I managed to see this companion at 600x on and off as it drifted through the field! That’s very encouraging to say the least! Though considerably lower in the northwestern sky at this time, the excellent seeing allowed me to glimpse it!
n = 13.
Away to have some fun with the deep sky now. Talk again soon.
Wednesday, August 16 2017
Time: 19:48 UT
Well, the recoated secondary arrived here safely this afternoon, as promised. They did a great job on the mirror. Looks flawless. There was a slight hiccup with the original mirror holder though. If you look at the image posted Friday, July 28, you will notice that the original mirror was held inside a plastic holder. The technician at Orion Optics informed me that while he was prizing the flat out of the plastic(read cheap) structure it actually fractured!
Shockeroonie ken !
All was well though when he kindly offered to mount the flat on one of their own secondary structures (with no additional charge). And naturally, I accepted!
That was a nice gesture on their part.
Like all the other secondaries I’ve handled, I gave the edge of the mirror a coat of matt black paint before remounting it inside the telescope tube. Optics were then accurately realigned and now the instrument sits ready to sample star light once again.
The accurately measured flat minor axis is exactly 70mm, so that translates to a very respectable linear central obstruction of just 22.9 per cent.
The heavens opened in the early morning and continued all day. Still cloudy and dreich as I write.
Thursday, August 17 2017
Time: 21:34 UT
Seeing: Very good, II, sky cleared at sunset after another day of torrential rain.
Comments: A race against time this evening, as more heavy showers are forecast overnight. But I had the 12 inch f/5 Newtonian maintained near ambient temperature in my dry, unheated shed. I can report a very good split of Lambda Cygni at 570x (6mm Baader classic Orthoscopic with 2.25x screw in Barlow). As reported previously, the pair of white stars are easier to see in the 12 inch than in the 8 inch. Very impressive sight! n= 14
Now retiring the ‘scope before the next downpour is upon us.
An aside: As well as the other observing blogs I’ve done over the last several years in the peaceful surroundings of my home, I left it a few times in order to engage with the public on other(mainly) double star projects establishing the efficacy of other telescopes for the interested amateur. See here and here for examples. One can gauge the frequency of fair to good skies I enjoyed in recent years, which I believe strengthen the central tenets of Taylor’s hypothesis, at least at my observing location.
Friday, August 18, 2017
Time: 22:50 UT
Seeing: IV, below average, good transparency, little cloud
Instruments: 20.4 cm f/6 Newtonian & 12″ f/5 Newtonian
Comments: companions unresolved in both instruments (600x and 570x, respectively). Turbulent, swollen and disjointed diffraction pattern.
Saturday August 19, 2017
Time: 21:15 UT
Seeing: III, blustery winds, some clear spells.
Instruments: 20.4cm F/6 Newtonian & 12″ f/5 Newtonian
Comments: After another unsettled day, we got a reprieve in the late evening, so I decided to field both instruments again. Lambda Cygni pair just resolved in both instruments (same magnifications as last night) but it was that little bit easier to discern in the larger instrument, despite the choppiness of the atmosphere. n = 15.
Wednesday August 23 2017
Time: 20:25 UT
After another brief vacation and a few days of inclement weather, it’s back to work again tonight. Good chance of making another observation a little later on. Fingers crossed eh!
Time: 21:45 UT
Instrument: 12″ f/5 Newtonian
Seeing: very good, II, light westerly breeze, mostly overcast with the occasional clear spell.
Comments: A braw evening. Target beautifully split with the 12 inch at 570x. The combination of the 6mm classic Baader orthoscopic and 2.25x screw in Barlow proved much more comfortable to use in the field than one of those fancy schmancy Vixen HR thingmies.
n = 16.
Target examined once more and full duplicity easily discerned at 570x.
This is a verifiably real phenomenon. How many times must I repeat it to demonstrate its veracity? This high resolution target is accessible in the foot ‘scope any time the seeing is fair to good. Why should my observing location be privileged?
I dinnae ken.
Overall Conclusions: The Taylor hypothesis appears to be correct. I got this from the essay he wrote in the aforementioned book and not from anyone on the internet. Taylor could state this as real because he made the observations to demonstrate its validity, as did I. I am astonished and a little upset that this has not been reported by those who claim to have the most experience.
This is where the blog ends. But I will come back to this occassionally with updates.
I would encourage others in possession of moderate aperture Dobsonians to test this work for themselves. Make sure your optics are accurately collimated and thoroughly acclimated before conducting such tests. Good luck and thanks for reading!
Update: August 29 2017
Two more sightings made on August 26 and August 29 (consecutive observations). Both with 12″ f/5 instrument at 570x.
n = 18.
Update: August 31 2017
Two more good nights of observations made (30th and 31st August) and two more clean splits to report with the 12 ” f/5 reflector at 570x.
n = 20
Update: September 5 2017
Two further consecutive positive observations to report with the 12″ f/5 Newtonian made at 570x on Friday and Saturday, September 1 and 2.
Thus n = 22.
A Work Dedicated to Brian Carter
The cure for unobtanium is a good dose of speculum!
Here I shall provide an in-depth evaluation of the SkyWatcher Skyliner 200P; an 8 inch ( 203mm) f/6 Newtonian reflector.
Friday, January 30 2015: The telescope was ordered from Rother Valley Optics, UK. The complete telescope was purchased for £288, inclusive of delivery to my door. I chose this telescope owing to its almost universal acclaim by amateur astronomers of all levels of experience, from novices through to seasoned veterans. I was interested in getting something larger and more powerful than the most excellent 6″ (152mm) f/8 model but not something that would be too large and cumbersome. Many literary sources discussing Newtonian optics recommended as slow a mirror as one could get away with. As a purely visual observer, I was pleased to hear that SkyWatcher were offering their 8-inch Dob at a respectable f/6 relative aperture; a good compromise between portability, functionality and performance with a modest eyepiece collection.
An inexpensive Skywatcher laser collimator was purchased at the same time.
Monday, February 2: The telescope arrives in two boxes; one containing the telescope and various accessories and the other containing the flat-packed Dobsonian base. The telescope was presented in excellent condition, as were the accessories, but it was quickly discovered that the lazy Suzan rocker box supplied with the telescope was actually for the smaller 6 inch model. Oh dear; never mind!
A quick phone call to the retailer was enough to arrange for the delivery of the correct size base and the collection of the 6 inch base.
23:00h: A set of tube rings and a dovetail plate were found for the telescope and I was able to attach the instrument to my heavy duty SkyTee Alt-Azimuth mount. Turning to Jupiter, it was easy to see the optics were quite a bit out of alignment but I was taken at the sheer brightness of the planetary image. Star testing confirmed that the optics were mis-collimated.
The simple but sturdy focuser on the telescope can accommodate both 1.25 and 2″ oculars. The package came supplied with an 8x50mm straight through finder- always an impressive addition in my opinion.
The innards of the optical tube were painted matt black and the parabolic primary mirror looked immaculate with no sleeks or flecks of dust/paint. Very nice indeed! Two eyepieces were supplied with the instrument; a ‘wide field’ 25mm focal length ocular delivering 48x and a higher power unit giving enlargements of 120 diameters.
Tuesday, February 3: The laser collimator arrived this morning and I quickly got to work aligning the optics. This device makes very light work out of precisely aligning the optical components. After placing the device firmly in the focuser, the secondary mirror was precisely aligned with the central spot of the primary and then the primary was adjusted slightly to complete the collimation. This only took a few minutes to do but should make a huge difference to the images garnered by the telescope.
23:30h: Seeing fair to good(Ant II-III).
With the telescope fully acclimated in -6C temperatures, I conducted a quick star test using my trusty 24-8mm Baader Hyperion zoom to confirm that the optics were properly aligned. The full Moon was easily framed with lots of room to spare at the 24mm (50x) setting of the zoom, the image being razor sharp and blindingly bright at the same time. Aiming at Polaris, I was very pleased indeed with the beautiful concentric diffraction rings either side of best focus at 150x. No astigmatism was noted with no signs of significant zones. This is a good, smooth mirror by most anyone’s standards. In focus Polaris A was pinpoint sharp with delicate diffraction spikes consonant with a good Newtonian image. Its faint companion was easily picked off wide away.
Comparing the views of Jupiter with my 17cm f/16 Maksutov Cassegrain at~ 150x, I was very impressed how well the 8 inch Newtonian was performing. At a glance I could see finer detail than in the smaller aperture Maksutov, although the sky background in the latter was considerably darker.This could be attributed to stray light from off axis moonlight though and will require further investigation. I could also see the faint impression of the slender spider vanes superimposed on the in focus image, though after a few seconds, one could effectively ignore them and get on with enjoying the images.The brightness of the planet in the Newtonian at 150x will call for higher optimal magnifications to be pressed into service in due course.
Turning the telescope on Iota Cassiopeiae, the instrument was able to cleanly resolve the three components fairly easily. Almach, now fairly low in the northwestern sky was beautifully rendered, the golden and blue colours of the components coming through easily. The faint diffraction spikes around the stars were quite fetching to my eye. I don’t know what to make of them as yet.
All in all, an impressive first light for the econo-Dob.
Thursday, February 5: The replacement base arrived safely today and the 6 inch base collected. Assembly took about a half an hour. All tools were supplied with the package.
18:30h: Seeing II, temperature -0.5C, clear, tranquil sky after dusk. Telescope kept outside all afternoon with optics covered. Little chance of dew as the air is still very cold and dry.
Theta Aurigae: companion easily picked off from the bright primary at 150x.
22:30h: Some low altitude cloud rolled into the valley for much of the evening while I was teaching. The telescope remained on duty throughout. Also fielded my 17cm Maksutov (acclimated) for comparison. Only a few targets visible at any one time. Seeing improved and now excellent, as judged on a very near perfect rendition of Castor A and B through the Maksutov at 343x. I turned the instruments to Jupiter and studied the images delivered.
The winner: without a shadow of a doubt- the 8 inch f/6 Newtonian.
Both served up very fine views but the extra resolution and light gathering power of the Newtonian in these braw conditions put it comfortably ahead. An incredible amount of ultra-fine fine detail could be made out all across the planet but my eye was drawn to the high latitudes of the southern hemisphere, where a few curious white spots and a riot of linear structures quite literally jumped out at me! Where the smaller Maksutov suggested, the larger Newtonian plainly revealed.
The above was based on unfiltered observations, but I felt the icing on the cake was delivered with the addition of Al Nagler’s latest technical innovation: the Televue Bandmate BPL. It diminishes the glare around the planet, darkens the background sky and brings out all kinds of reds, oranges, yellows and whites within its enormous atmosphere. To my eye, the image at 170x with the filter was truly magnificent! I didn’t try any higher powers as there was no need to do so.
I would invite others to pull out their GSO/Synta 8 inch Dobs, spend a few minutes lining up its optics, letting it fully acclimate (I didn’t use a fan) with its cap on and comparing its views with a more ‘revered ‘scope of similar aperture.
To the rich man I speak: the man who has ‘seen’ it all in the cold light of day.
Maybe you could buy one in for a while at least? Nothing to lose, right??
But be prepared to be shocked!
SkyWatcher Skyliner 200P: planet killer extraordinaire!
Sic transit gloria mundi!
Friday, February 6: I am still somewhat in awe of what I saw last night and no one can take that away from me. It only takes one good night to reveal the truth about any telescope, whatever preconceptions one may have had about it. Would I have been better off with a larger mirror; a 10- or 12-inch maybe? I believe that the difficulty in producing a fine mirror scales with the square of aperture. A 12 inch reflector takes four times more effort to make well compared with a 6 inch. Larger apertures may have some advantage over the 8 inch but my previous experiences with these larger Dobs suggest that I would not get as many nights where everything comes together like it did last night. Mileage counts for me. No, the right choice was the 8 incher since I now know that it will play ball with the environment in which I reside.
I spent some time this morning mulling over old books on planetary astronomy. One choice example is Bertrand M. Peek’s tome on Jove; The Planet Jupiter: The Observers Handbook (1981 edition) in which he states categorically that “An 8 inch [reflector] is probably adequate for all purposes.”
Fred W. Price and a host of other authorities I respect, say much the same thing.
Fortune continues to smile my way, as the settled conditions look to last at least another night.
Thank goodness for small mercies!
18:50h temperature -1C, seeing II
Had the ‘scope out for a couple of hours while I was teaching. Before the Moon rose above the horizon, I managed a very competent split of Eta Orionis (1,6″) at 225x. The Great Nebula in Orion (M42) was jaw-droppingly fine; a great heaving mass of ‘chlorescent’ gas at 120x. The Trapezium stars, including the more elusive E and F components, were easily sighted.
19:30h In a race against time, I assessed its wide field capability with two of my eyepieces; a Mark III 24-8mm Baader Hyperion zoom and 40mm Erfle. Both eyepieces performed extremely well in the very forgiving f/6 Newtonian. Cruising through central Orion at 30x in a 2+ field is a joyous experience, with stars staying acceptably sharp over the majority of the field with only the extreme edges showing coma and field curvature. I noted identical behaviour with the zoom eyepiece at the 24mm ( x50) setting.
Caldwell 14, the Great Spiral in Andromeda (M31), the Auriga open clusters and M35 were simply spellbinding in the telescope. I have a 8 inch f/6 doublet achromat awaiting return to its manufacturer but I can tell you this Skyliner 200P package – costing 11 times less and weighing half as much – is a much superior telescope in almost every conceivable way!
Oh vanity of vanities!
Later tonight it’s Jupiter watching time. Away in to watch the rugger the noo.
23:30h:Smashing opening performance by England against Wales in the Six Nations championship.
Low waning gibbous Moon in the southeast. No clouds.
Seeing deteriorated a little this evening (Ant III), as judged by the appearance of slightly swollen seeing disks in Castor A and B in the acclimated Maksutov. I decided to test how fast it would take the 8 incher to come to temperature by taking it directly out from a warm indoor room to the cold of pre-midnight air at -3C ( so ~ 25 degree C swing). The optics were left covered throughout. When I returned to the telescope an hour later, the images had stabilised. That’s no surprise though, at 8.6 kilos (19 pounds) fitted with its finder, the Newtonian actually weighs less than the 20 pound Mak and enjoys a much greater area over which to rapidly radiate heat.
I again compared the views of Jupiter served up by the Maksutov (17cm) with the 20.3cm Newtonian and the result was the same; the Newtonian shows finer details than the compound, confirming that aperture wins.
I’m not really known for having great affection for Newts, but this dapper telescope has got my pulse racing.
Saturday, February 7: This afternoon I leafed through my old observing notebooks from the years 1996 through 1997. Back then I was living in the city of Aberdeen, Northeast Scotland, and enjoying my first salaried job as a lecturer at the local university. In the summer of 1996, I purchased a Celestron 8″ f/6 Star Hopper Dob and at a much higher relative cost than today. “Wolfgang,” was big and awkward, with a cheap, oversized sonotube OTA. I observed Jupiter throughout the summer and autumn of 1996 with this telescope and my drawings reveal a good amount of detail; rather similar to the details I have recorded in more recent years with my 5″ f/12 achromatic. I was very pleased with the images Wolfgang served up – it was the base that failed first – but the planetary detail revealed by my new Skyliner 200P is easily better (on all but the worst nights) than any five incher can deliver. I was puzzled by this, and it got me digging a little deeper into my notes. Turns out Jupiter was fairly low in my sky during those years, sprinting through Capricorn (1996) and then Aquarius(1997). Now, Jupiter is considerably higher in the sky and the differences between these instruments are much more apparent. That’s one theory. Here’s another one: Maybe the SkyWatcher mirror is truly better than the one I got with Wolfgang? Can technology improve in 20 years? It is not unreasonable to think that it could.
Man and his technology!
22:15h: Sky clearing of clouds, -2C, good seeing (Ant II): One final comparison between the 17cm Maksutov and the Skyliner 200P. Target: Jove: Both telescopes serving up super fine images. The 8 inch image is more detailed though. GRS approaching the planetary limb…..cool.
23:00h: Since the conditions were quite good, I decided to push the telescope by examining the diffraction images of stars at very high powers. Using the 2.25x Barlow with the zoom, I dialed in a maximum power of 338x and examined the brilliant white pair Castor A & B. In this cold weather, the heat from your body can affect the image, especially when you place your warm hand in front of the optical train to reach for the handle. This quickly dissipates though and when you are wrapped up warm and well insulated the effects are minimised.
I was really quite impressed at how clean and together the morphology of the Airy disks presented at these high powers. The diffraction spikes are quite charming and have an aesthetic grace all of their own. I have a very good mirror; a mirror that will surely see a lot of use over the months ahead.
Monday, February 9: With the moon now out of the evening sky, I spent a few minutes yesterday evening enjoying some dark, transparent skies with the Skyliner 200P. Using the low power (50x) setting on my zoom, I turned the telescope towards Cassiopeia now nearly overhead, and spent a few minutes drinking up the views of a few favourite open clusters including NGC 457 (with its ET eyes staring back at you), M103, M52 and a real corker: NGC 7789 which, at higher powers (75x), resolves into a plethora of faint stars. The traction on the mount is quite good and it’s easy to find the ‘sweet spot’ for most any application, from low power scanning to tracking planets and smaller deep sky objects at higher powers.
The SkyWatcher model in my possession probably has a similar mirror to the US branded Orion XT8 Dobsonian. US-based telescope reviewer, Ed Ting, has very interesting things to say about it here:
“It’s not a Zambuto,” he says, but it’s “shockingly good!”
These telescopes have been used to great effect by very well established observers on both sides of the pond. Dr Paul G. Abel, a professional astronomer and BBC Sky at Night presenter, uses the same model as my own – albeit on a motorised equatorial platform – to make all his detailed observations of the planets. I contacted Paul to enquire about whether he had any modifications done to the optics. He told me he had not and saw absolutely no need to do so. A true draftsman, his portfolio of work is of the highest quality.
Arizona based astronomical artist, Jeremy Perez, needs no introduction in amateur astronomy circles. Using only an XT6 and XT8, Perez provides first rate illustrations to all the major astronomy magazines including Sky & Telescope, Astronomy and Astronomy Now,and has contributed to several major books on the subject of astronomical sketching. In addition, Jeremy maintains an excellent website where his versatile work with the XT8 is clearly demonstrated. Worth checking out I’d say.
What inspirational blokes we have here!
21:45h After enjoying some gorgeous views of M36, M37 and M38 at low and moderate powers, I turned the telescope to Jupiter, not yet at an optimal altitude, and was delighted to see that a satellite transit is currently underway. Will report back again later.
Seeing wasn’t great tonight (Ant III mostly) and it was a bit on the breezy side, which made the image shake a wee bit. Fairly mild (+5C) though. I decided to keep magnifications down at 150 diameters. I followed the eclipse until it reached the middle of the disk and then noticed the GRS had reappeared. A fantastic experience!
Thursday, February 12: On family vacation until next week.
Monday, February 16: My short time away from this telescope got me thinking about its enormous potential. As it is, the Skyliner 200P is an excellent general purpose instrument; a veritable ‘diamond in the rough’. Yet, it can be improved still more and with only a modest additional investment. The reflectivity of the mirrors(worst case scenario) is ~87 per cent, so combined produce an overall light gathering power of 0.87^2 or 76 per cent. Light loss due to the area of the secondary mirror reduces this by just a few more per cent. That’s not bad at all:- still significantly more light gathering power than a 6 inch refractor but with greater resolving power.
Curiously, there are services available to increase the overall reflectivity of both mirrors to 97 per cent. For example, Orion Optics UK offer their Hilux coating which would bring its light gathering power into line with a similar sized refractor and maintain this ultra-high reflectivity for two or three decades!
The secondary mirror in the Skyliner 200P has a diameter of about 50mm, giving a 25 per cent central obstruction. This provides full illumination over ~ 25mm of the central region of the 46mm diameter field of view; a good compromise for all round use. Yet, Orion Optics UK also offer the amateur the opportunity to buy a smaller secondary with a diameter of 36mm, thus reducing the central obstruction to just 18 per cent, in order to optimise the instrument for planetary and double star work. Heck, one could keep both flats and inter change them as and when required!
Man and his technology!
Small modifications to the existing secondary, such as thoroughly blackening the sides of the mirror and the supporting structure would cut down on glare from bright objects. Flocking the tube with low reflection material, especially opposite the focuser, would also improve the overall contrast of the image reaching the eye.
What exciting telescopes these 8-inch Dobs are; lucis in caelo!
23:00h: With all the moving about the ‘scope has thus far endured, I decided to check collimation of the Newtonian, discovering that it was a wee bit off perfection. That’s how accurate the laser collimator is! Set it upon my kitchen table and tweaked collimation until it was spot on again and then set it out to cool.
Tuesday, February 17:
Ambient: +1C, blustery northwesterly sleet showers coming and going all evening.
Seeing quite poor (Ant III-IV). En passant, neither the fully acclimated 17cm Maksutov or the Skyliner 200P were giving good stellar images this evening. Only the easier doubles were resolved; Gamma Leonis was pretty at 150x and Mizar & Alcor lovely at 120x, their seeing discs large and ‘boiling’ in both instruments, but sightly more so in the bigger Newtonian. I attribute the latter to its greater sensitivity to atmospheric turbulence
Jupiter looked rough even at 150x but I was still able to watch the GRS whirl across its disk in both telescopes, the slightly larger Newtonian showing it that little bit more easily throughout.
Thursday, February 19: Having discussed the tremendous value of the Skyliner 200P with my editor, I decided to embark on a project to make the aforementioned modifications to the instrument in order to maximise its potential. The project will be featured in an up-and-coming issue of Astronomy Now and, at some later stage, on this website too.
Thanks for reading my story so far.
I leave you now with a short video on Sir Isaac Newton’s original reflecting telescope, its speculum mirror and the ingenious design of the tube and mount.
Man and his technology!
Wednesday, April 1, 2015:
I got both mirrors re-coated but in the end decided on just one secondary of 44mm diameter, and not two as I considered previously. This secondary provides a very decent 22 per cent obstruction – less than my Maksutov and a good compromise between a smaller secondary and a larger one. This still provides excellent illumination even towards the edges of the field with a low-power 2-inch eyepiece. I bought a water butt that perfectly fits the mushroom knobs under the base of the lazy suzan mount and provides both a stable and more elevated platform for more comfortable, seated visual use. I have undertaken all the modifications to the tube mentioned previously.
After putting the whole thing back together this afternoon, I set the telescope outside with its caps on about an hour before my teaching finished. As luck would have it; the sky was both clear and tranquil (seeing I-II) and I trained the instrument on Jupiter. Wow! Incredible detail such as I’ve never seen in the smaller Maksutov! I watched a beautiful shadow transit of one of the Galilean satellites. The GRS was near the centre of the disk and the satellite shadow was directly north of it.
I made a sketch to record those moments.
Time: 20:40-50h UT
Seeing: Ant I-II
CM II: 236 degrees
By 22:00 BST, I had successfully split Theta Aurigae and the magnificent triple system, Iota Cassiopeiae.
This is my best telescope, no doubt about it, but it’s also considerably less (even with the mods) expensive than the 180mm Mak and my 5 inch refractor.
In time, it will become my most used telescope.
Aperture wins. Period!
Don’t let any wooly thinking cloud your judgement!
And so, it only remains for me to bestow a name on my powerful speculum; eight inches of Newtonian bliss.
Only one appellation trips off the tongue: Octavius!
Saturday, April 4, 2015
An Evening with Octavius & Cornelia
Time: 22:00 BST
After a beautiful bright and reasonably warm day, I set up both my 17cm Maksutov and Octavius side by side and allowed them to fully acclimate over a couple of hours with the optics capped. I watched the Moon rising in the East and brilliant Venus in early gibbous phase setting in the West. When dusk arrived, I discovered that the seeing was near perfect! Hardly a quiver on Theta Aurigae at 340x in the Maksutov. Comparing the Jovian images one more time, I got the same result; two lovely instruments capable of rendering excellent images but one clear winner; the 8″ f/6!
The images are more stable in the Maksutov, owing to its greater insensitivity to atmospheric turbulence but that said, when the images settle down in the Newtonian, it easily shows its superiority to an attentive telescopist.
I would welcome people to test this claim and report it to as many astro folk as possible.
The biggest surprise though was the efficacy of the reflector in resolving the tricky binary system Iota Leonis. At magnifications of 225x, the 8 inch speculum showed me the clearest view of its elusive secondary that I have yet seen in any telescope. It’s raw resolving power is a law unto itself!
This is very encouraging as it means that there will be nights where I can push the 8 inch on pairs that are deemed very tough for my smaller instruments.
There is something very sweet and pure about this telescope; it’s understated power and charm shine through when just a little care and attention is afforded it.
A Triumph for Octavius!
For the defeat of badness with goodness!
For reason over darkness.
For diligence over laziness.
For vanquishing bluff with truth!
For heart filled humility!
And the ostrasization of hubris.
A Triumph for Octavius!
Go in Peace Octavius!
Tuesday, April 7, 2015
Continuing to learn from Octavius in good seeing. Started a blog on my adventures on CN to save some space on my site. Thank you CN!
I am eternally grateful to Cornelia for teaching me the ways of Octavius.
On vacation until next week.
Wednesday, April 15 2015
Work on CN aborted owing to account suspension.
After a rather grotty few days compared with what our neighbours south of the wall have enjoyed, the clouds cleared in the late afternoon here and it stayed that way for the rest of the evening. After work, I set Octavius outside to cool for about 40 minutes from my heated office. That was enough time to get it serving up excellent images of Jupiter in very good to excellent seeing (I-II). My favourite magnifications are about 170x with the Televue BPL filter in place. Though less than 50 degrees altitude at this time, the 8 inch speculum rendered some really fine details within the planet’s vast belt system. The NEB was a heaving mess and the SEB distinctly bifurcated. When I began my observations at dusk at 20:30UT, the GRS was just coming round the eastern limb of the planet and over the next half hour I watched it grow more and more distinct as it edged its way into the disk.
I made a sketch of my impressions at 20:45-55 UT CM II 182 degrees.
It is hard to describe the image of the planet in the Newtonian. It ‘flits’ back and forth between slightly blurry and magnificently sharp over the seconds and minutes. I have learned to completely ignore the spider vein shadows superimposed on the planet’s disk. They are largely cosmetic in nature and have little or no impact on the resolution of fine detail.
I have not encountered much in the way of the ‘tube currents’ that other observers have reported. Indeed, I have had the instrument long enough now to judge that I do not need a cooling fan. The mirror is relatively small and of low mass and cools very quickly, even if taken out of a warm room. I am mindful also of many distinguished observers from yesteryear (Philips, Webb, Browning etc), who produced some very fine work over many years using nothing more than passive cooling to the night air. Fans did not exist during their lifetimes.
Friday, April 17, 2015
Time: 21: 20h UT
Seeing: II-III, fully clear sky.
I set up my fine 5″ f/12 achromatic refractor (Tiberius) as well as Octavius to again compare the views in each telescope when I pointed them toward Jupiter. I also compared the views of Theta Aurigae in both telescopes.
Will report back; a shadow transit has now commenced on the eastern limb of the planet.
Saturday, April 18, 2015.
Time 23:25 UT
Both telescopes easily split Theta Aurigae at about 150x. The refractor view had a darker sky background and the pair more stably presented. The Newtonian showed the pair more easily but less stably. The explanation is probably complex; the smaller aperture of the refractor and its greater thermal stability were probably at play here. But if I were not measuring the system, the Newtonian would be the better choice; simply because everything is brighter and better resolved.
I enjoyed a wonderful shadow transit and recorded my impressions of the event at 22:45h CM II 192 degrees.
Both the 5 inch glass and the Newtonian revealed the event well but the superior resolution of the Newtonian made it far more compelling. ‘Perfect’ linear features in the 5-inch come alive in the 8 inch speculum and were transformed into a sea of ‘imperfections,’ as a feast of micro-contrast details – entirely invisible in the refractor – popped in and out of view. And all the while, the image always flits in the Newtonian and I did experience a minor tube current that lasted for about ten minutes before it vanished.
A 8-inch f/6 Newtonian has not received much acclaim as a double star telescope but I wonder if this is yet another urban myth. I am very encouraged by the ability of the instrument to split some tricky double stars – I added Epsilon Lyrae (observed just after local midnight) and Izar to my tally this evening. I would like to flesh this interesting topic out further after I have performed more tests, but in the meantime I encourage you to look at Jeremy Perez’s website to see how well an 8-inch Newtonian can perform on binary star systems. I am also mindful of the work of the English amateur astronomer,Thomas Teague, who has measured many double stars with a quality 8″ f/5 Newtonian and a Celestron Astrometric Eyepiece.
I would now like to quantify the overall quality of the 8″ f/6 reflector in light of the modifications I have made to the instrument.
Here are some pictures of the modifications made.
Upgrading of the reflective coatings on both mirrors to 97 per cent. These should remain durable for at least 25 years, even in our rather damp climate.
Replacement of the secondary by a smaller one of semi-major diameter 44mm. Mirror edges blackened.
The interior of the tube opposite the focuser was flocked as well as the drawtube of the focuser itself.
These modifications give the instrument the contrast transfer of a 204* – 44 = 160mm unobstructed aperture – so a little better than a 6 inch refractor. Light gathering power will be significantly better than a 6 inch refractor though. ( *The diameter of the primary mirror as measured by Orion Optics UK)
The central obstruction does reduce the system Strehl in a quantifiable way (see below).
Taking a 22 per cent central obstruction and reading off the graph we get a Strehl of ~0.9.
All in all, I have a very fine telescope in my possession, as experience at the eyepiece testifies.
The Skyliner 200P: £288 delivered.
Water Butt: £20.00
Flocking paper: £9.00 (including post and packaging)
Secondary mirror replacement with enhanced Hilux coatings ( including optical work to check surface flatness, post and packaging): £81.40
Primary mirror re-coating with Hilux (including post and packaging): £147.20
Total Cost: £550.60
Is it any wonder why I like to wax lyrical about Octavius!
My sister in law came to visit yesterday and my wife and I treated her to a view of Jupiter at sunset. At this precise time, the Great Red Spot was prominently on display and had just moved into the eastern hemisphere of the planet but the image was beautifully sharp. “Wow!” she explained, ” I have never seen the planet so well!
The superior coatings on the mirrors seem to have reduced light scattering in the image, improving the overall view.
When I ventured out later the same evening, I obtained a great and easy split of Iota Leonis at 339x. My first attempt at Delta Cygni was unsuccessful at 22:00 UT but it was rather low in the east at this time. When I tried again at 22:30 UT, the companion as well resolved at 225x.
Sunday, April 19, 2015
Yet another clear night tonight (remember you can always check my weather!) and time to explore some of the glories of the deep sky with Octavius.
I will report back on those activities later but for now I wish to share other user testimonies of the unmodified SkyWatcher Newtonian. I do not trust the judgement of those who express unbridled enthusiasm for apochromats. I believe their judgement in these matters is ‘coloured’.
In addition, I would like readers to compare and contrast the Jupiter drawings of Dr. Paul Abel (mentioned earlier) – a highly experienced planetary observer – who regularly uses the same telescope (albeit entirely unmodified!) as my own.
You can see a drawing of Jupiter he made with his 8″ f/6 in good seeing here.
Now, compare that drawing to one he made with the venerable 6″ f/15 Cooke refractor at Hampstead Observatory, London, just a few days afterwards (also in good British seeing).
Would you concede that the drawings reveal similar amounts of detail?
Tuesday, April 21, 2015
21: 40 UT
The Lyriads have been dandy this year! Hoping for the best of them tomorrow evening!
I have been very busy preparing my students for their science and mathematics exams, which are starting in just a few short weeks. But Octavius is so easy to set up and get working that I can put him to good use more or less immediately after I finish with them. The key is preparation; leave the telescope out with its caps on for about an hour and you’re cooking with gas.
Sunday evening presented near ideal conditions and I set the telescope to work showing me many deep sky objects. As dark skies will only remain for a few more weeks, time is against me and so I will refrain from providing that report until I have visited all the targets on my list.
Last night was interesting. At 21:10 UT, I had both the five inch refractor and the 8″ speculum out in the open air and fully acclimated. The seeing was unexpectedly grotty though (Ant IV), as I discovered while looking first through the refractor. I had to look very hard to see the GRS in the long glass; the details having been smeared out by the turbulent air. Remarkably though, while the image in the Newtonian was roiling in the bad seeing, I could much more easily pick it out on the Jovian disk. A modest aperture advantage is a boon on planets like Jupiter even in rough seeing. A good lesson learned!
Beginning at 20:10UT this very evening, I uncapped Octavius, turned him toward Jove and was delighted to see that the seeing had once again improved. The telescope was placed on its Lazy Susan mount an hour earlier and I gave Ciaran, my final student this evening, his first ever telescopic gander at a beautiful crescent moon dominating the lower western sky and Venus to its upper right. But first, I turned the telescope on Jupiter, dialled up 170x in the Baader Hyperion zoom (with TV filter attached) and focused the planet in the centre of the field. Ciaran peered in and after just a moment of eye-brain coordination shouted out, ” That’s so amazing! It looks like a spacecraft image!”
And it was! No GRS this time but plenty of palpable activity across its vast globe. The planet literally comes alive in the large aperture Newtonian.
He asked to look at Venus and I obliged. “This will look different,” I explained, as I unscrewed the filter. Choosing a power of 150x or so, I centred the planet and invited him to take a look.
” Wow!, he exclaimed, ” its dazzlingly bright! What’s that cross spread over the disk?
“Ah, that’ll be the shadow of the telescope’s spider veins on the planet,” I explained, turning the telescope to show him the secondary assembly.
” Oh I see!”, he said.
We ended by taking a quick look at the Crescent Moon and though quite low down, was wonderfully sharp and filled with astonishingly fine details (magnification about 80 diameters).
“Oh my God!” Ciaran said, ” that’s so beautiful!”
They say that what goes into a person cannot defile them, but what comes out, can. Ciaran spoke from the heart and revealed the truth about this telescope. And he did not defile himself.
Wednesday, April 22, 2015
The spell of fine weather continues and the telescope performed flawlessly all night. Jupiter was magnificent. The Crescent moon was eye-wateringly beautiful! I was able to effortlessly push the magnification to 340x without any degradation of the image.
Collimation has held remarkably well thus far; f/6 is clearly a good place to be in this regard.
I visited a suite of double stars to assess the efficacy of the Newtonian. Eta Geminorum Iota Cassopeiae, Alula Borealis & Australis, Iota Leonis and later Izar. All of these are repeat observations – routine but important work in the true assessment of any instrument. All were easily split with the 8 inch speculum. I was most impressed at the calm and well resolved images of Iota Leonis at powers up to 500x. Out of curiosity, I threaded a neutral density filter onto the eyepiece and studied the images of Iota Leonis at 340x. The filter cuts off quite a bit of the glare and attenuates the bleeding of light from the brighter primary. The background sky was also darkened producing images that were incredibly refractor like!
The attenuation of light was modest though, as judged by my ability to easily detect (with the same filter in place) the light from the exceedingly faint (magnitude 10.1) companion to Alula Borealis. I tried this trick because of what I learned from reading the works of skilled observers from a by gone age – vis-a-vis on the large American refractors – and I believe it will be an exceedingly good and inexpensive way to help ferret out faint and tight companions to a legion of double stars within reach of my modern 8 inch reflecting telescope.
The air was so dry here that even though the telescope was left out for several hours, it did not dew up and even after I brought the instrument in shortly after local midnight, only the merest veneer of moisture settled on the outside of the tube; the mirrors being entirely dew free! That doesn’t happen very often round these parts.
My growing scepticism of many of those who have dismissed the Newtonian as a capable double star ‘scope impelled me to, once again, seek the knowledge of my ancestors. Though regrettably, their work has been summarily ignored by many of my contemporaries – I have ‘discovered’ for myself that truly dedicated observers achieved some mighty impressive results with instruments not too dissimilar to my own.
I speak especially of the work of the great British Victorian astronomer, Thomas William Webb (Anno Domini 1806-85), who resolved many sub arc second pairs with a Newtonian reflector – and had no reason to mislead others. Earlier this afternoon, I received a copy of a book chronicling his life and work.
Webb owned many smaller refractors in his early days – a 3.7 inch Tulley refractor, a similar sized Dollond and even a fine 5.5 inch Clark refractor – but eventually he settled on a 9.3 inch With-Berthon silver-on-glass reflector, which he used with great enthusiam for the last 20 years of his life. It is especially noteworthy that despite having the privilege of observing through similar sized refractors on magnificent equatorial mounts (owned by fellow astronomers in England, including those of Dawes and Huggins), he expressed no desire to acquire one of his own.
In the words of Robert A. Marriot, author of Chapter 8 of the book, The Stargazer of Hardwicke: the Life and Work of Thomas William Webb;
Having observed with these large telescopes, with which he was obviously impressed, Webb must have had at least some desire to own such an instrument himself, and yet for the last two decades of his life he was perfectly content to use his 9.3 inch With-Berthon reflector, which, although beyond his definition of a ‘common telescope,’ always served his needs ’till the dappled dawn doth rise’.
Believe me when I tell you that I know exactly how the Reverend Webb felt!
Saturday, April 25, 2015
Seeing III, excellent transparency, cool northerly airflow.
I am thoroughly enjoying the views of Jupiter with Octavius but the planet is now well past the meridian when full darkness falls upon the landscape. I can locate the planet just before sunset and with the TV filter in place can still make out some very fine details. The GRS is now in full view on the eastern hemisphere and can be very clearly made out with the generous aperture. Soon, I will show my boys the wonders of the first quarter Moon.
The boys were blown away by the clean, crisp images delivered by the Newtonian. They had great fun zooming from 50x to 150x with the Baader zoom.
I returned to Venus and enjoyed looking at its marble white, slightly gibbous form. 150x is about as high as I’d like to go on this planet. It’s hard to imagine that a world that looks so comely from our clement vantage is the most hellish place that one can conceive of.
I find the diffraction spikes on Venus to be a source of endless fascination. Like the presence of modest levels of secondary spectrum in achromatic telescopes, they have a singular beauty all of their own.
Sunday, April 26, 2015
Time 22:25h UT
Ambient: Seeing poor (IV), transparency excellent, temperature -2C, light north-northwesterly winds bringing in frigid polar air.
We had all four seasons in one day today. A freak Arctic blast of cold air brought hail and a light dusting of snow which quickly dissipated in the bright April sunshine.
Northerly air flows generally bring poor seeing to this valley and I could only manage 150x at the most on a handful of objects visited. Jupiter was poor this evening, the Moon reasonable at the lower powers. Caught a brief glimpse of Theta Aurigae’s faint companion though at 150x, which gave me a lift. All four components of Epsilon Lyrae also reasonably well (though still low down in the north east) resolved but the swollen seeing disks made the sight far less compelling. Ditto with Castor A & B and Gamma Leonis.
Called it an early night; glad to embrace the simple comfort of an open fire.
Thursday, April 30 2015
With every passing hour, my admiration for the Newtonian grows. Myths cultivated in refractor forums have served to steer people away from them too long and my contempt for those who advocate apochromatic refractors in the larger sizes grows stronger day by day.
Disillusioned by contemporary telescopic culture, I am finding myself spending more and more time reading the literature of older, accomplished observers. Just this morning, I spent some time leafing through Fred W. Price’s book, The Planet’s Observing Handbook. Like every other author of his generation (and many before him), he recommends – for sound, practical reasons – the Newtonian as the instrument of choice in the long term study of planets. The book is filled with beautiful drawings made with his own 8-inch reflector. There is something very pure and uncorrupted about his work that very much appeals to me.
In recent years, there has been a movement in the direction of ultra fast Newtonians, mainly to maximise aperture and portability. But not so long ago, opticians were making Newtonians with slower f ratios – in the f/7-12 range. With their very small central obstructions (CO) and amazing resolution and light gathering power, they would have beaten the pants off those pretentious large aperture Apos being offered to the unwary today.
Those who want that little bit more from a Newtonian would do well to consider models produced by smaller firms such as Mag1 Instruments, Orion Optics UK, and R.F Royce, to name but a few. Though more expensive than mass produced products, they are still far less pricey than their refractor equivalents and deliver excellent results that will serve you for a lifetime.
Personally, I am entirely sated by the performance of my 8 f/6 speculum, but I would love to see Synta or some such come out with a 8 inch f/7 or 10″ f/6 Newtonian models with enhanced coatings and a ~20% CO at a reasonable price. A big optics house like that should be able to pull this off without much alteration to its existing manufacturing ethos.
Check out this thread for encouraging signs of cultural change within the hobby.
Another very cold and clear night, 2C, bright gibbous Moon in the south, light northerly airflow. Seeing lower than average (Ant III-IV).
Conducted some more observations of Jupiter and a drawing made at dusk as it appeared at 20:45h.
CM II 271 degrees. Altitude ~45 degrees.
I hope milder weather will come soon and with it the return of better seeing. Then I can begin investigating some sub-arc pairs.
Friday, May 1, 2015
Cornelia, my large Maksutov, has been put up for sale to raise funds to donate to the Nepal emergency appeal.
Saturday, May 2, 2015
Playing with numbers: Last night, the seeing improved quite a bit and I was treated to a beautiful image of Jupiter with the Newtonian at 170x despite its lower altitude. Later, I visited some of the show piece doubles in Bootes and Lyra. The Newtonian has thus far proven to be very powerful in this regard. All in all, I’m very impressed with its efficacy; quick cool down, excellent performance on the full panoply of celestial targets and relative insensitivity (compared with larger specula I’ve owned) to the vagaries of the atmosphere.
That got me thinking about an old chestnut oft pondered upon by amateur astronomers; is there, in any objective sense, an ‘optimum’ sized telescope for the pursuit of my double star adventures? Then I re-visited knowledge garnered by my diligent forebears.
According to the work of John Sidgwick in his Amateur Astronomer’s Handbook, the maximum useful magnifcation (M) is given by M = 28D^0.5 where D is expressed in millimetres. Setting D= 200mm gives M = 396x, so about 50 per inch of aperture for my 8″ speculum. This seems like a reasonable upper limit for most applications conducted by amateurs and over quite a wide range of fielded apertures.
The late professional double star astronomer, Paul Couteau, considered the minimum magnification needed to best see and measure doubles to be M~ > D, where D is again expressed in millimetres.
Since magnification M is F/f, where F is the focal length of the telescope and f is the focal length of the eyepiece we have:
F/f > D, so F/D > f. F/D is the focal ratio (relative aperture) of the telescope and the formula predicts that this minimal magnification will be achieved with an eyepiece of focal length approximately equal to the the f ratio of the telescope you use; an observation born out well in my field experiences over the years with many kinds of telescopes.
But over what range of apertures does this hold true? It stands to reason that Couteau’s minimum magnification ought to be less than Sidgwick’s maximum magnification. This can be expressed mathematically as an inequation:
D < 28D^0.5
Squaring both sides yields;
D^2 < 748 D
Thus, one solution yields D < 748mm.
That is a most interesting result, as 748mm translates into an aperture of the order of 30 inches! Bigger sizes are (presumably) too perturbed by the atmosphere to be used( without modern technology).
Can it be a coincidence that virtually all double star work has been conducted with instruments of this size and smaller?
I think not!
But, we may go still further. Is there in any sense an optimum sized telescope between zero and 748mm? Interestingly, we may also express this mathematically.
Specifically, what aperture, D, provides the biggest difference between the maximum and minimum magnifications employed, that is, what is the optimum value of D for the function arbitrarily defined as f(D)= 28D^0.5 – D?
Differentiating the function with respect to D and setting the result equal to zero yields:
f'(D) = 14D^-0.5 -1 = 0
Solving for D yields D = 14^2 = 196mm.
Thus, in this simple analysis, the optimum aperture turns out to be 8 inches!
Bigger is better, of course, but not nearly as often!
References: Argyle, R (ed.) Observing and Measuring Visual Double Stars (2012).
Tuesday, May 5, 2015
A spell of unsettled weather has befallen us. All day long, sullen rainclouds drenched the landscape with life sustaining moisture. It was good, proper rain.
I’ve become much more curious about the potential of the Newtonian to explore hitherto uncharted territories in my observing experience. One of the posters on this thread was kind enough to share his experience with me regarding his success with the sub-arc second pairs; Eta Coronae Borealis and Zeta Bootis, using a 8″ f/6 speculum.
Literature describing those kinds of activities conducted with Newtonian reflectors is well nigh scarce in comparison with the documented achievements of astronomers who have used the classical refractor. But I did find one interesting contemporary reference: Observing and Measuring Visual Double Stars (2nd Edition), 2012. In Chapter 11, written by Christopher Taylor, he crystallizes his thoughts on that very subject – The Newtonian Reflector in Double Star Astronomy.
Good with numbers, Taylor presents a proper (and I mean proper!) theoretical consideration of the Newtonian telescope in the pursuit of double star astronomy. Though he rightly acknowledges the superior stability of the images in long focus refractors, he nonetheless concludes that, given f/6 or slower relative apertures, “All the supposed optical defects of the reflector are removable or fictitious“, and further reminds us that, “a good 0.3m reflecting telescope is a far less expensive item than an equally good 0.3m refractor!“
But there’s more. Taylor, rather admirably, backs up his conclusions with the results of his own observational experience using a ‘disembodied’ (my choice of word) old 12.5 inch f/7 Calver reflector with a 16.3 per cent central obstruction, erected in a “good spot” in his garden in rural Oxfordshire. There is no tube; the mirror is completely exposed to the night air and, perched seven or so feet above it, sits the secondary assembly. The mount, massive though it is, turns out to be an altazimuth! LOL!
The magnificent apparatus weighs in at an incredible 1500 pounds (680 kilos)!
On page 140, he describes his achievements with this mirror with which he employs a power of 825x on nights of excellent seeing. Though he does not mention the frequency with which he enjoys such nights, Taylor presents tables and sketches of drawings he made of exceedingly close pairs like Delta Equulei and Beta Delphini (and many others); pairs that have orbital periods of just a few years or decades! Taylor describes the essence of why these investigations are so invigorating:
An unforgettable demonstration of this was provided by the 2005 periastron passage of the famous 169-year pair gamma Virgini…. In May of that year, gamma Vir swept through 0.3 arc seconds approach of the two stars with an apparent rate of revolution which briefly peaked at 2 degrees per week! This superb phenomena was closely followed by the author’s 12.5 inch right through closest approach, at which it was still found possible to make formal measures of p.a., yet it appears that sadly, few observers equally well equipped saw much of this spectacular double star event of the century.
His enthusiasm has rubbed off on me. I understand why he felt so passionate about seeing these things; for like ships passing in the night, it is only in the sub-arcsecond realm that amateurs can truly hope to enjoy a ‘ringside seat’ on the dynamics of distant suns sailing far beyond the Solar System.
We cannot perceive what we cannot conceive.
Friday, May 8, 2015
Even though I have quite an extensive library on astronomical topics, of which I am very proud of, I came to realise that it was heavily biased towards the classical refractor. But I have become much more interested in the work of historical figures who used the power of the speculum mirror to advance the cause of astronomy. Accordingly, I have began to redress that imbalance by buying up several books – old and new – chronicling the lives of the Herschels who brought the reflecting telescope to the fore.
Saturday, May 16, 2015
I have not had much time to use Octavius of late owing to my teaching commitments. But I hope to redress that soon. I have examined quite a few deep sky objects on and off over the last month and will report back on my findings in due course. The length of true darkness at this latitude is now very short, heralding the onset of summer twilight which will persist until late July.
I have been reading some of the articles of Sky & Telescope associate editor, Gary Seronik, who is a long-time Newtonian enthusiast. In particular, I found Gary’s article on his 6 inch optimised Newtonian to be a good read. Seronik shows us how to get top quality views from a Newtonian at a fraction the cost of a refractor of the same aperture. And he derives even greater pleasure from the fact that the telescope is entirely home built.
Perhaps most importantly though,Seronik reminds us of the importance of aperture, noting at the end of that article that despite building and using a super duper 6 inch f/9 Newtonian, a 8 inch f/6 is, in his own words, “crushingly superior” on all targets.
No matter how much you mollycoddle a telescope, increasing its aperture is a better way to go.
Monday, May 18, 2015
CN account un-suspended but I will not be contributing there any more for personal reasons.
Friday, May 22, 2015
More musings on numbers: This thread has alerted me to the joy of establishing a theoretical basis for my experiences with Octavius. ‘Aperture’, you have heard, ‘wins’. Many know this to be true, as I do, within certain limits. But is there a physical basis for believing this? Why does resolving power scale inversely with aperture?
This leads us to Airy’s result for a circular aperture where he showed that the resolving angle, theta = 1.22 lambda/D, where lambda is the wavelength and D is the diameter of the aperture.
The derivation of the Airy formula is really quite involved but an email from a gentleman in the States (thanks Jim!) prompted me to look at a simpler approximation based on one rendition of Heisenberg’s Uncertainty Principle. Airy himself did not have knowledge of such physics, as this was only developed in the early 20th century. What follows is an elaboration of the approach of Dick Suiter, in his book, Star Testing Astronomical Telescopes.
Starting with the momentum/ position inequality.
delta p x delta y~ h where delta p is the ‘fuzziness’ in the momentum in the y direction and delta y is the fuzziness in position y. h is Planck’s constant.
The momentum of the photon can be expressed as E/c and since E = hf where f= c/lambda we get E = hc/lambda (wavelength). Delta y can be considered to be the diameter of the circular aperture, D.
so delta p/ p ~ h/ (p x delta y) ~ hc/fhD and since c/f = lambda the formula reduces to lambda/D.
It is interesting that this approximation is very close to Airy’s result of 1.22 lambda/D!
Octavius has eight inches of aperture; Tiberius, only five!
Wednesday, May 27, 2015
With the chemistry examinations taking place tomorrow, my academic work has come to an end for another year, so I have more time to finish this particular blog.
So, let us reason again, you and I.
I have already stated that I believe Octavius would give very similar planetary views to a 6- inch refractor and have a light gathering power at least equivalent to, or better than, a 7-inch refractor.
One other way to establish the veracity of these claims is by comparing CCD images of a tough target like Jupiter.
In this capacity, I searched tinternet for comparison images taken with a 8″ f/6 Newtonian and a refractor that has garnered quite a bit of prestige in the amateur world; the TEC 140 (a 5.5 inch triplet refractor).
Here is the best sequence of images of mighty Jove I could find taken with the TEC 140.
Now, please compare these images with those taken with an unmodified 8″ f/5 SkyWatcher Newtonian. You can see some good ones here.
I have no reason to suspect any foul play, as both imagers would have striven to show off the best attributes of their instruments. After all, ’tis only human nature to do so!
Would you say that they are broadly equivalent?
I think the TEC images are a bit over processed and were probably (that’s a hunch, I can’t prove it however), captured using a more sophisticated CCD camera than that used by the owner of the Newtonian. The f/5 SkyWatcher Dob was completely unmodified though; so it will have a (larger) central obstruction and standard mirror coatings than my own telescope.
And yet it produces similar or even greater amounts of detail than the prestigious TEC!
But let’s now factor in the cost of these telescopes;
Suppose I were to order up a 8″ f/6 Dob from this retailer.
And then buy the TEC 140 (optical tube assembly only) from the same retailer.
The price differential is 20x!
Is there something I’m missing here?
Mein Gott im Himmel, ich verstehe nicht!
The ‘majesty factor’ perhaps?
A more ‘transcendent’ image maybe?
I can’t quantify either of those things, unfortunately, but I’m sceptical, as I know, having owned my speculum for a few months now and having personally tested many refractors of similar or larger size over several years, that both types of telescopes produce beautiful images of planets.
Octavius, with its 22 per cent central obstruction and light gathering power broadly equivalent to a refractor of the same size, must be a better all-round telescope than the famous TEC 140. Not just because I want it to (I do admit to disliking these telescopes for logical reasons); but because it has to!
Octavius the Meritorius!
Sunday, May 31, 2015
A note on further experiments
The primary mirror of the 8-inch SkyWatcher is very good. Very smooth optics with no astigmatism. I have experimented with removing the mirror from the cell a few times now to explore the effects of tightening the three clips that hold the mirror in its cell. A word of caution:-
Over-tightening the mirror will induce marked pinching in the optics that can ruin high power images.
I have found that they should be tightened just enough so as to hold the mirror rigidly in place but only so tight as the clips can still wiggle a little. The difference between getting it right and over doing it is like night and day!
Is your primary over tightened?
I have not thought much more on improving the thermal properties of Octavius because I could possibly be blissfully happy with its native performance without a fan. But I have learned that in days gone by some reflector enthusiasts have lined their tubes with cork or, more recently, with polystyrene flocking.
Will I give this a go?
Maybees aye, maybees naw!
Some notes on low power eyepieces:
I’m not one to fuss about eyepieces, especially these days when even inexpensive stuff is so good. Of all the astronomical kit discussed by amateurs, it is arguably eyepiece discussions that produce the most heat and the least light. Don’t get sucked down that black hole what ever you do LoL!
Since Octavius is destined to become my most used telescope in the coming years, I have thought some more about getting the best bang-for-buck, low power ocular for Milky Way sweeps and for framing the largest deep sky objects. At f/6, the 65 degree AFOV Erfle gives good performance but my attention was piqued by a new eyepiece marketed by Explore Scientific. As part of their Maxvision range, the company offer a 40mm model with improved coatings and eye relief, an adjustable eye cup and a larger 68 degree AFOV.
After testing the unit for a review (you can see that in Astronomy Now magazine) I decided to buy one as it offers enough of a performance boost to justify the switch, eventhough it weighs in at nearly three times that of the Erfle (1.25 kilos LoL)! And at £117 plus shipping, it wasn’t an extravagant splurge. Now I can play with a 2.25 angular degree field with my 8-inch speculum. M31 here I come!
Man and his improving technology!
Tuesday, June 2, 2015
As I briefly touched on previously, some amateurs have found that using a fan which blows air over the primary to be a useful tool in bringing the optics to thermal equilibrium with the outside air. Where I live though, there are never great temperature swings at any time of the year and my months of testing suggest that it would not really be necessary.
I’m a very lucky man!
Besides, I am not overly enamoured about the prospect of having some electrical appendage grafted onto Octavius. It just wouldn’t feel right to me.
Wednesday, June 3, 2015
I would like to give you more.
I would like to describe my deep sky experiences with Octavius over the last few months.
Thursday, June 4, 2015
Octavius is a very impressive deep sky telescope. With a good 40mm wide angle eyepiece, I can coax fields of view in excess of two angular degrees out of it. On the evening of Sunday, April 19, I caught sight of the Pleaides (M45) just above the north-western horizon, where it seemed to hover above a distant rooftop. Excitedly, I trained my 8 inch speculum and focused the stars down to tiny, crisp pinpoints. I was delighted to see that the entire cluster fitted neatly into the field of my six element Erfle! I have since replaced this unit with a significantly better Explore Scientific Maxvision ocular offering a larger field of view (~2.25 degree) with slightly better contrast and edge-of-field correction. From a dark and transparent sky, my 8-inch speculum provides lovely, contrast-rich views with only a slight drop off of light at the extreme edges of the field. This edge-of-field vignetting is entirely acceptable though.
The improved coatings on both mirrors came into play when I visited the great globular cluster, M13 in Hercules. I could push the telescope to 200x before the image became too dim. The view was spectacular though, more reminiscent of what you would get with a standard 10-inch Dob. The cluster was beautifully resolved with hundreds of stars cleanly resolved to the core. The widely reported ‘propeller’ streams curving out from its main body were very obvious with a direct gaze. When I swung the telescope over to M92, I wasn’t disappointed either; a veritable swarm of white stars at 200x, more condensed than M13 but still well resolved almost to the centre.
Spring galaxies also benefited from the improved coatings. The celebrated M81 and M82 were easy pickings for this telescope, with both ‘Island Universes’ revealing excellent structural detail at powers of 150x or so. The improvement was obvious compared to a 17cm Maksutov set up along side it.
More exciting still, I could more easily trace out the spiral arms of the Whirlpool Galaxy, M51, in the constellation of the Hunting Dogs. The difference between the views in the smaller Maksutov and the larger Dob was subtle but quite obvious. The same result was observed when I swung the telescopes down to the Sombrero Galaxy (M104) in Virgo. The greater light grasp and resolving power both came into play to deliver a noticeably superior view in the Newtonian than in the Maksutov, where it was easier to see the prominent dust lane bifurcating this classic edge-on spiral at powers of 150x or so.
Open clusters are a pure joy to observe with Octavius. The Double Cluster (C14) in Perseus was beautifully framed at 30x. I spent a good twenty minutes in the wee small hours of Monday, April 20, in sheer awe observing this spectacular communion of stars. The superior light grasp of the reflector over either my 17cm Maksutov (now gone) or 127mm refractor was painfully obvious, my eye being able to differentiate white, blue-white, creamy, orange and downright ruddy constituents at moderate powers (100x or so).
Having become intimately familiar with the appearance of the three bright Messier clusters in Auriga in my 5-inch refractor, I was simply stunned at the difference manifested in the 8 inch speculum. While they are beautiful in the 5 inch glass, the view of M36, M37 and M38 in the larger speculum are quite simply in a completely different league!
The same was true when I compared and contrasted the views of the famous planetary – the Eskimo Nebula (NGC 2392) in Gemini – using the 8-inch speculum to my smaller Maksutov and refractor telescopes. The superior light grasp and resolution of the Newtonian allowed me to push the magnification to significantly higher powers. I found 250x presented the best views, with the bright, 10th magnitude central star being clearly differentiated from not one, but two diffuse, concentric shells of luminous matter. In contrast, the smaller ‘scopes maxed out at powers at or slightly below 200x. Shell detail was also a notch down in these smaller instruments.
All in all, I am positively delighted with the deep sky views served up by my 8-inch light bucket. From my relatively dark country sky, it will provide a lifetime of wonderful sights to visit, some for the first time, but many to be returned to again and again with the passage of the seasons, like faithful old friends.
Haste ye back the dark skies of August!
Friday, June 5, 2015
Having sold off some gear that I no longer need, I raised some more funds to purchase a better finder for Octavius. Nothing fancy; a SkyWatcher 9 x 50 right angled model, which can be bought new in the UK for a very reasonable price (£59). Such an upgrade will enhance my observing experiences by reducing neck strain and should make finding objects that little bit easier.
With June now upon us, the skies never get truly dark here. At such times, I turn my attention to double stars since they are little affected by twilight. Summer can present quite excellent seeing here (as revealed in many previous blogs), especially if its settles down for any length of time. I am very excited about examining progressively tighter pairs to see how much I can push my 8 inch speculum. Once this study is completed I shall bring my public telescope reviewing to an end. I pray that the weather will be kind to me in the coming weeks.
Saturday, June 6, 2015
Time : 00:05h BST
Ambient: 10C, brisk westerly wind, good transparency. Seeing fair to good (Ant II-III).
I got off to a solid start this evening. Octavius was placed outside and left to completely equalize with the night air. No dew as the wind is too strong.
Izar ( Epsilon Bootis) beautifully split at 225x. Faithful colours – yellow and blue.
Epsilon Lyrae 1 & 2 easy at all powers above 100 but best seen at 225x
Alula Australis: lovely near equal magnitude split at 225x
Delta Cygni; easy pickings at 225x
Zeta Herculis – unsuccessful, strongly elongated at 225x and 340x. Will need calmer conditions to bag this puppy.
00:30h: The bonnie triple system, Iota Cassiopeiae, beautifully resolved at 225x, despite its fairly low altitude in the northern sky.
No’ bad ken.
Telescope put away. Time tae hit the hay.
21:00h BST: Heehaw else tae report today.
Dreich weather ken.
Sunday, June 7, 2015
Time: 19:50h BST
The Lord works in mysterious ways. After a day of downright rotten weather, today has been much better and this evening promises more clear skies! I have no idea how good they will be but at least I’ll get a chance to field my best telescope once again.
In addition, it occurred to me that I have another witness to my own weather conditions, someone impartial, who lives near me, and has been a contributor to this blog. He can vouch for my blue skies.
Indeed, maybe the same gentleman can vouch for most, or even all the observing-related weather entries I have made on this blog/review since its inception at the end of January last?
Hey, how lucky am I?
Just a few hours to go before my next adventure.
Fingers crossed eh!!
Ambient; westerly wind has all but abated at ground level but with some isolated cloud patches moving swiftly across the sky at high altitudes. The cursed wee midgees came out earlier but now the temperature has fallen to 7C, so not likely to pose a problem going forward. Some good images of Arcturus.
More cloud encroaching, seeing a notch or two down on last night (Ant III). But still managed a clean split of Izar at 170x. Seeing disks more turbulent tonight though. Ditto for Epsilon 1 & 2 Lyrae. The quartet were fairly stably held at 340x but with frequent morphing of the image in and out of focus as the stars swept through the field. Don’t see much point in continuing higher resolution targets tonight. Need to wait for better nights.
Monday, June 8, 2015
A Note on Collimation:
As anyone who uses a Newtonian regularly will tell you, alignment of the primary and secondary mirrors is absolutely critical to gaining the best possible images. Some folk get in a right guddle with this procedure though, while others border on being OCD, checking it two or three times per night. LOL!
As briefly touched on earlier, collimating a f/6 Newtonian is fairly straightforward and is rendered almost completely pain free using an inexpensive laser collimator (I use an inexpensive SkyWatcher unit). F/6 or slower systems can be accurately aligned during the day but I tend to always back this up with a star test before beginning serious observations.
You can find a very good demonstration of how to quickly collimate your Newtonian here.
I would say however that it is better to do the collimating on a horizontal bench/table so as to avoid the small risk of one of the Allen keys falling down the tube and hitting that all-important primary mirror – yikes!
Looks like the weather is good again for tonight, so perhaps some better opportunities to split some tougher pairs.
New finder should be with me tomorrow- yeehaw!
At last, a fairly warm and bright day. And the day has given way to what looks to be a clear and tranquil night.
I walked through the garden in the cool of the evening. With a song on my heart and a spring in my step, I retrieved Octavius from my office and set it out to cool.
The warmer temperatures have brought out more insects. The swallows feast on them high in the sky – a good sign that fair weather is here for a while. Nearer ground level, the bats are busy too. No wind. Only the sound of a distant cuckoo breaks the silence.
Will report back later.
Ambient: 8C, twilit sky, clear and calm, seeing appears very good (Ant II).
I have just come in from examining the images of my first two targets.
Epsilon 1&2 Lyrae: Magnificent tonight! Much greater stability to the images, four tiny Airy disks surrounded by well structured diffraction rings at 340x.
Delta Cygni: Companion very easily seen and perfectly formed at 340x!
Just waiting for the sky to get that little bit darker……
Tuesday, June 9, 2015
Lambda Cygni resolved tonight! Couldn’t see anything except the primary at 340x but the image was calm and very well defined. I ran to the office to get my 1.6x Barlow. This yielded a power of 544 diameters. Swung the star to the eastern edge of the field, refocused until it was at its best at the centre of the field – both members (0.9 arc seconds) well resolved! Mirror holding up really well at these very high powers!
8-inch Newt owners please give this system a try, and, if successful, post it where everyone can see it!
Will talk more about it in the morning.
My new finder arrived today. Looks cool!
I had to get up early and leave for the city this morning, so was not able to make any more observations last night. But that’s beside the point; my modified 8 inch f/6 Newtonian resolved a sub arc second pair – Lambda Cygni – and with relative ease!
Why was I astonished by this result? Well, for one thing, being used to the domination of this arena of observational astronomy by the classical refractor, it was quite a reality check to see that a Newtonian could perform so well in this regard. But there is absolutely nothing in this observation that violates any known principle of physics; I mean, according to the Dawes limit (4.56/D) my Newtonian ought to do considerably better – down to 0.57 arc seconds.
I know from previous experience with a 17cm Maksutov that in some locations I can split pairs as low as 0.7 seconds of arc. And if I can do that with a Maksutov, I can also do it with a Newtonian. Let’s just say I have faith in Octavius; not a blind faith but one that is based on reason and experience.
The fine weather is continuing but this would be a suitable place to finish.
I commend this economical telescope to you and invite you to test everything I have said about it.
It is, by some considerable margin, the best bang for buck in the entire hobby! It is a most excellent, all-round performer, an instrument that will serve up a lifetime of wonderful views and require little in the way of maintenance.
Three Cheers for Octavius: the People’s Telescope!
Update: September 27 2017
It is exceedingly rare that an individual will openly admit the true performance of a 8″ f/6 reflector compared to a ‘premium’ medium aperture apochromatic refractor. But I found one such assessment here. You will note that the gentleman in question compares the performance of his 8″ f/6 Newtonian with a TEC 140. This is what he said (I assume English isn’t his first language) about a comparison between the two instruments on Jupiter;
There is similarity with my 200mm Newton: both instruments encourage using high magnifications. For these average conditions, if my Newton allows more megnification ( about 285x) and makes detection of little contours of faint contrast easier, then there is no major difference between both scopes……..By exceptional conditions (no turbulence) I remember my 200mm going further in magnification (400x) and detection of colours and contrasts….
Then speaking of deep sky objects such as M13, the gentleman admits the 200mm Newtonian offers better resolution than the TEC 140:
M13: Splendid and perfectly contrasted. Periphery resolved but core remains ‘milky’ or granulous. Newton 200mm allows more resolution.
All in all, I feel this is an honest and realistic assessment of both instruments compared to the hyperbolic and emotionally charged statements of the somewhat blinkered (or blinded?) opinions of refractor only fanatics. This author is only too happy to test any similar sized premium refractor against his own superlative 20.4cm f/6 Newtonian.
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Wednesday, February 3 2016: SkyWatcher has established a solid international reputation for producing high quality Newtonian optics for the modern amateur astronomer, and at prices that won’t break the bank. Having been thoroughly satisfied with a 8″ f/6 Skyliner Dob, I became very curious about a smaller, model – the Heritage 130P (a 5.1″ f/5 Newtonian with a parabolic primary) tabletop Dobsonian – which promises to provide decent light grasp and resolution in an ultra-portable package for take anywhere travel and short grab ‘n’ go excursions to the back garden.
The telescope was purchased new from Rother Valley Optics on Tuesday morning, February 2, and arrived in the mid-afternoon today. The price, inclusive of postage, was £129.
The telescope came double-boxed and involved no assembly. The optics looked clean and streak-free. A neat instruction manual accompanied the instrument.
The ‘scope, weighing about 6 kilos with the mount, has a built-in carrying handle for swift transport into and out of the house.
Following along the same lines as their extremely successful flextube line of larger Dobs, the Heritage 130P can be extended to reveal the upper tube assembly, lengthening the tube from just 38cm to about 61cm. The lower assembly is adorned with the names of time-honoured astronomers, celebrating four centuries of telescopic astronomy. While some folk might find this ‘tacky,’ I rather liked it.
Remarkably, the telescope was almost perfectly collimated out of the box, as evidenced by the just slightly offset red dot from the centre-marked spot on the primary mirror. That’s a nice touch, as one can imagine the reaction of a complete novice were he/she to discover that the optics were delivering iffy views as a result of mis-aligned optical components. It might be enough to put someone off the hobby for good.
Once the collimation was tweaked, I investigated retracting and extending the tube assembly several times to investigate the rigidity of the structure. I am pleased to report that the collimation held quite well but might still require last-minute tweaking for more demanding tasks, such as obtaining the best lunar and planetary views, as well as double star work. Overall though, this is a very well thought out piece of kit and certainly better than I had anticipated.
The telescope primary and secondary mirrors are fully adjustable and can be aligned in a matter of minutes. Unlike the three ultra-thin spider vanes on larger models, the secondary mirror on the Heritage 130P is affixed to a single vane, which is a good bit thicker than the latter; a necessary design compromise to maintain that little bit more stability to the optical train.
The focuser is unusual. Unlike standard rack and pinion or Crayford type focusing mechanisms, the Heritage 130P employs a simple helical focuser which involves rotating the eyepiece either clockwise or ant-clockwise to bring objects to a sharp focus. In addition, the length of the upper tube can also be adjusted to accommodate cameras and other equipment. In short, any eyepiece will reach focus using a combination of these procedures. Only 1.25″ oculars can be used with the instrument, however.
Some observers may find reaching precise focus a little fiddly, but with a bit of practice, it works smoothly and accurately.
The Heritage 130P also came with a simple red dot finder (RDF) to aid in locating objects quickly under a dark sky.
A particularly attractive feature of the instrument as received is the dovetail mounting of the optical tube assembly which enables one to remove the tube assembly from the mount proper for even easier storage.
In addition, the dovetail plate allows the user to mount the instrument separately on other types of mounts such as this author’s ergonomical Vixen Porta II alt-azimuth for an alternative style of observing. What a nice touch!
Optical testing: Although the instrument suffers from the introduction of considerable amounts of stray light during daylight use without employing some sort of light shroud, I set the instrument up in the late afternoon, aiming the instrument at a roof top about 100 yards distant. I didn’t wait around to use the supplied oculars (which are adequate but not great for testing) but instead decided to push the ‘scope as hard as I could. To that end, I ran inside and affixed a good quality 6mm orthoscopic to a 2.25x Baader shorty Barlow lens, which would deliver a power of 244 diameters. Inserting these into the helical focuser, I carefully rotated it until best focus was achieved. Although the view was a bit drowned out with extraneous light, I am happy to report that the image of the terracotta roof tiles came into very sharp focus; a great initial sign that the optics were of potentially high quality.
After dark, more cloud encroached, but I waited for the odd sucker hole and was rewarded by a clear spot corresponding to Auriga, then high in the eastern sky. Relocating the instrument in a dark spot in the garden, I centred the bright star, Capella, using my multi-coated 32mm SkyWatcher Plossl in the field (yielding a true field of 2.5 degrees!) and was delighted to observe (with my eye glasses on) a beautifully sharp vista, with pinpoint stars across most of the field. Then, I investigated the high power view of Capella at 244x and after refocusing, was thrilled to see a tight white Airy disk with diffraction rings a shade more prominent than what I have observed in my work horse telescope, a larger 8″ f/6 Dobsonian. This could be explained by the larger central obstruction of the Heritage telescope (~29 per cent by aperture) as compared with 22 per cent for the larger 8 inch.
On a whim, I moved the instrument north-eastward from Capella and centred the star, theta Aurigae. Focusing as accurately as I could, I was able to steadily hold its very faint companion at 244x, some 4 arc seconds away from the primary. Very encouraging to say the least!
It wasn’t long before the skies completely clouded over, and the drizzle came back, ending my first light vigil under the stars. Needless to say, the instrument performed surprisingly well under admittedly dodgy observing conditions.
More testing in the pipeline though.
Thursday, February 4, 2016
Having collimated the telescope in situ and placed a makeshift light shround around the upper telescope assembly (UTA), I am happy to reaffirm that the telescope delivers tack sharp images of distant willow tree branches at 244x.
Friday, February 5, 2016
The Heritage 130P has a parabolic primary mirror, that is, it is figured into the shape of a parabola. Why is a parabolic shape responsible for such sharp images in a Newtonian reflector? It’s an interesting question, yet many amateurs accept it as a given. But we can do considerably better than that. We can analyse the properties of the parabola, one of the conic sections beloved to the mathematicians of classical antiquity, and thereby gain a deeper appreciation of why this shape, over all others, is chosen by opticians in the fashioning of high quality primary mirrors. Our analysis will borrow from the approach of the great French mathematician, Rene Descartes (1596-1650), who developed a way of investigating geometry using algebra.
A parabola is the set of all points which are equidistant from a given point called the focus and a given line known as the directrix.
The image below outlines the basic features of a parabola drawn on a x-y axis.
Let the focus be the point S( a,0) and the directrix be the line x=-a, as shown in the diagram. Consider any point on the parabola, P(x,y).
Thus, by definition, the length of SP = length of PM
So [(x-a)^2 + y^2]^0.5 = x + a
Therefore, (x-a)^2 + y^2 = (x+a)^2
Thus, x^2 -2ax +a^2 + y^2 = x^2 + 2ax + a^2
From which y^2 = 4ax ( Eq 1)
This is the standard form of the equation of a parabola.
Consider next the parametric equations x = at^2 and y = 2at.
Substituting the expression for x into equation 1 we obtain;
y^2 = 4a^2t^2 = 4a(at^2) = 4ax
So, x = at^2 and y = 2at represents the parametric coordinates of any point on the parabola y^2 = 4ax.
We can use this to derive two more equations that will enable us to arrive at the result we want. Consider the diagram drawn below.
y^2 = 4ax
Differentiating implicitly with respect to x we obtain;
so f'(x) = 2a/y, which is the gradient of the tangent at any point.
Now since y = 2at, the gradient becomes 2a/2at = 1/t
And so the equation of the tangent to the parabola at the point P is given by:
y – 2at = 1/t(x-at^2)
Multiplying across by t gives;
ty – 2at^2 = x-at^2
or x – ty + at^2 =0 ( Eq 2)
Also, the gradient of the normal at P = -t and so the equation of the normal will be:
y – 2at = -t(x-at^2)
or tx + y – 2at – at^3 = 0 ( Eq 3)
Now we are ready to obtain further information from the parabola under discussion.
Let the tangent at P intersect the x-axis at R and the y-axis at U, and let the normal to the parabola at P intersect the x-axis at V, as shown in the diagram below:
The coordinates of R are obtained by setting y = 0 in equation 2
x – ty + at^2 =0 and so if y = 0 then x = -at^2 and so the coordinates of R are (-at^2, 0)
The coordinates of U are obtained from setting x = 0 into equation 2, from which it is easily shown that y = at i.e. U(0, at).
The x-coordinate of V can be obtained by setting y = 0 in equation 3;
tx + y – 2at – at^3 = 0 and when y = 0 we obtain:
t(x- 2a – at^2) =0,and since t cannot equal zero we have
x = 2a + at^2 and so the coordinates of V are given by (2a + at, 0).
From these results it is possible to verify the following:
(i) U is the midpoint of PR
(ii) length of SR = length of SV = length of SP
(iii) US is parallel with PV and that PU is perpendicular with SU
I will leave these as exercises for the interested reader.
Now, to the meat of the analysis. Consider a line PZ drawn parallel to the axis of the parabola as shown in the diagram below:
Since length SP = length SV so too must angle SPV = angle SVP
But angle SVP = angle VPZ since PZ is parallel with RV
So angle SPV = angle VPZ
But ZPV is the angle of incidence of a ray of light incident upon a reflective parabolic surface and so the law of reflection requires that the angle of reflection be the same i.e. angle VPS.
But since P is independent of S, the result implies that any ray of light parallel to the axis will be reflected through the focus, S.
This is the reason why parabolic mirrors work so well, as they completely avoid a phenomenon known as spherical aberration, which can can plague other kinds of optical designs.
That’s enough math for one evening eh.
After a day of more or less constant rain, the sky appears to be clearing up and so I’ll get some more time under the starry heavens using my little parabolic Newtonian.
Thank goodness for small mercies!
Saturday, February 6 2016
The telescope was collimated perfectly before use and left to cool in a dry, unheated shed. Initially, I had intended to use my Baader zoom and dedicated 2.25x Barlow to observe Jupiter, now 31 degrees above the horizon. To my chagrin, I discovered that this combination failed to reach focus. Due to the constant interruptions from clouds and with the rain never far away, I did not want to retract the UTA enough to get it to focus. Instead I chose a 7.5mm Parks Gold ocular and 2.25x Barlow yielding 195x.
Though the helical focuser is a bit fiddly and takes some getting used to, I am happy to report that the Jupiter images were wonderful in this telescope, with lots of nice detail showing up under moderate scrutiny. The planet’s enormous equatorial belts were seen in their faithful colours and many shades of tan were observed. A Baader Neodymium filter took away a little bit of glare surrounding the planet, helping to bring out more subtle details. Although I felt 195x was a little too high, and would have been happier with 160x, I was most impressed by what this inexpensive Newtonian was delivering.
Turning then to some brighter stars appearing from behind the clouds, I was equally impressed by how well the instrument focused them down to tight round Airy disks at the highest powers pressed into service (244x). The telescope seems quite immune to atmospheric turbulence as judged by the calmness of the images. Returning to a 32mm Plossl, I enjoyed a spell binding few minutes drinking up the famous Double Cluster (Caldwell 14) in Perseus. The 20x delivered by this eyepiece provided a very generous field of view, allowing both star clusters to be easily framed in a most beautiful portal.
This is certainly not a toy telescope! It is impressively powerful with high quality optics. Indeed my initial impressions were very similar to this assessment made by Ralph Bell back in 2009.
Monday, February 8 2016
Time: 18:30-45 UT
I enjoyed another brief vigil under the stars with the Heritage 130P Newtonian. Charging the telescope with a 32mm Plossl (20x), I first visited the Pleiades, now high in the southern sky. Its constituent stellar components focused to fine points of light, pure white as the driven snow, with excellent contrast. Though I did not do a side by side comparison with my 80mm f/5 shorttube refractor, I was immediately aware of the Heritage’s significant advantages in light gathering power, with many more fainter members coming through at a glance. Then, I moved the instrument southwards, where majestic Orion was just about to culminate. The view of M42, the Great Nebula, was a sight for sore eyes. Cranking up the magnification to 81x with my Baader Zoom, I enjoyed a sumptuous field of view dominated by the emission nebula and Trapezium stars at its heart. The hinterland of the nebula was jewel encrusted with brilliant white stars set against a jet black sky.
Before packing up, I examined three higher resolution targets; first Rigel, just a few degrees to the southwest of M42. Using a power of 108 diameters, I was delighted to see the faint companion to this brilliant giant star cleanly and steadily. Then I swung the telescope over to Cassiopeia, now high in the northwestern sky. First I centred eta Cassiopieae and keeping the power at 108x I was able to easily split this pair, consisting of a beautiful yellow primary of magnitude +3.5 and its ochre companion some 13 arc seconds away, shining considerably more faintly at magnitude 7.4. Finally, I moved the Heritage 130P over to iota Cassiopeiae and could make out two of the three components of this system at a glance at 108x. The third member remained somewhat more elusive though, so I attached the Baader 2.25x Barlow yielding a higher magnification of 244x, refocused, and was overjoyed to see all three components clearly and precisely!
The imminent arrival of another student meant that I had to end the short vigil there, but it was very rewarding nonetheless. The telescope has great potential as a deep sky instrument and appears to be no slouch on moderately difficult double stars.
Tuesday, February 9 2016
Time: 19:00-30 UT
After a cool but crisp day, I continued my Newtonian education by fielding two telescopes; the Heritage 130P and a high quality 90mm f/5.5 ED doublet on loan for a a magazine review. Both instruments were given plenty of time to thermally acclimate and placed in the darkest spot in my garden to minimise stray light flooding into the open tubed reflector.
The sky after sunset was clear but the stars were corruscating fairly wildly. Transparency was excellent though, so I decided to assess the seeing conditions some more by turning the 130P on Castor, now quite high in the eastern sky. Charging the telescope with a power of 195x, both the A and B components were resolved but there was quite a bit of turbulence which made the stars bloat significantly from their calmer appearances under better seeing conditions. Comparing the same target in the ED90 charged with a power of 188x, both components were also resolved but there was still noticeable turbulence. It was not quite as unsettled in the refractor though, a consequence I suppose of its smaller aperture. This demonstrated to me that poor seeing can (though thankfully rarely at my location) adversely affect small telescopes. I judged the image in the refractor to be slightly more aesthetically pleasing under these conditions.
The reader will also note that the refractor comes equipped with a state-of-the-art 11:1 dual speed micro-focuser and so was considerably easier to focus finely than with the comparatively crude helical focuser on the Heritage 130P. This may also have contributed to my conclusions regarding Castor A & B. Accurately focusing f/5-ish instruments is never a walk in the park.
Turning to M42 once again, I compared and contrasted the images in both telescopes matching their image scales as best I could (~100x). Both telescopes delivered good images but the superior light gathering power of the reflector gave it a distinct edge. More nebulosity was seen and the stellar images were noticeably brighter in the reflector. This was despite the fact that the refractor had superior contrast, with a blacker sky background.
I am hoping that conditions will improve by the time Jupiter rises in the sky in a few hours from now.
The sky has completely clouded out and the forecast predicts that it won’t clear again until the wee small hours. I am very tired though, so will leave further testing for another night.
Thursday, February 11 2016
I fielded the same two instruments tonight as last night; the 130P reflector and the ED90 refractor. I finally found a good eyepiece to optimise the 130P’s capabilities on Jupiter; a 4mm Plossl delivering a power of 165x.The ED90 was charged with a power of 150 diameters.
Seeing was only marginally improved over last night (Antoniadi III-IV) but it was nonetheless a good test of what both instruments could deliver on Jupiter under these sub-par conditions (we have a north westerly air flow here which almost invariably brings more turbulent conditions but with excellent transparency).
I fitted a Baader Neodymium filter (with very high light transmission and virtually no colour shift, more a moon and skyglow filter than anything else) to the 130P to reduce the glare a little.
Comparing the images in both telescopes over a period of about half an hour, I gathered my thoughts.
Both showed some nice details in the equatorial belts. The ED90 image revealed hints of more subtle details at higher and lower latitudes but in the end I felt the 130P showed that little bit more. In particular, it was easier to see those details at temperate latitudes, as well as the more delicate polar shadings. One very striking difference was the colour of the Jovian disk presented in the telescopes. The ED90 was noticeably yellower in overall hue – a consequence of its imperfect achromaticity in comparison to the perfectly achromatic reflector. The latter presented a brighter disk in its true colour; much more creamy white than yellow. The Neodymium filter showed that the colour in the ED90 remained the same but with a little more light loss.
In retrospect, this should not have come as a surprise; while the refractor has a low dispersion element, which improves colour correction, it still can’t deliver perfectly achromatic images. Yes, it’s a sizeable improvement over the traditional achromat but still not perfect. Only a reflector image – which brings all wavelengths of light to the same focus – could really reveal this. In addition, a brighter image can also help the eye see finer details. You need light to see such details.
That being said, I do know the ED90 is capable of showing more on better evenings ( data not communicated) but so must the 130P, as they were both compared under the same conditions. I am eager to conduct further tests in this capacity as soon as the seeing conditions return to normal.
This was an instructive vigil. The 130P should give very decent images of Jove when the seeing is fair to good.
SkyWatcher has also brought to market a related telescope called the 130PD-S, which, as far as I can tell, features the exact same optics as those possessed by the Heritage 130P but retails for about £30 more. The optics are housed in a closed tube and the spider vanes are akin to what is seen on a traditional Newtonian. It also features a low profile 2-inch dual speed focuser for precise focusing and the secure mating of a CCD camera to the instrument. The 130P-DS has proven a huge hit with astro-imagers who have used it to good effect to capture stunning views of the night sky. Featured on this link is a plethora of deep sky objects captured by this modest telescope, but the reader will also take note of the lunar and planetary images captured by the same instrument.
Although not a visual assessment, I hope you will agree that the unlying camera shows just how good the optics are in these telescopes.
Friday, February 12 2016
The seeing was vastly improved tonight, frosty but no wind. I only had time for one target; Jupiter. Like last night I fielded the same telescopes and employed the same magnifications etc.
Both telescopes served up some excellent images, but this time there was a clear winner – the 130P.
Though the image flitted somewhat between perfect focus and slightly out of focus in both telescopes, both instruments revealed excellent details in the equatorial and temperate belts. Details in the more prominent NEB were more finely resolved in the Newtonian than in the ED90. But what clinched it for me was the sighting of the Great Red Spot (GRS) near the western limb of the planet (at 00:01UT) that was picked off in the 130P but was not seen clearly in the ED90.
As always, I would be very grateful if someone could repeat these observations if you have the 130P and a good 90mm refractor.
The 130P is turning out to be a fabulous little telescope and I am overjoyed to have made its acquaintance!
I have noticed that the price of the ED90 has been bumped up by £48 in the short time since I acquired it for review. It now retails for £868?! I don’t know why this was done (it was £820 just last week, remember?), but I can tell you I do not consider these telescopes good value for money and do not understand some people’s obsession with them. Under good conditions the Heritage 130P will outperform it and for 1/6th of the price. And if the classical achromat is the prince of telescopes, Newtonians are the ruling monarchs.
I would like to keep this telescope and learn how best to maximise its potential. I have bestowed a name on her; Plotina.
After another beautiful, crisp day, the firmament was glorious after sunset, with a gorgeous crescent Moon adorning the western sky. I set up Plotina at the side of the house and trained her on our life-sustaining satellite. She cools super quick, faster perhaps than the ED refractor that now sits in its case. The view of Luna at 20x was simply breathtaking, with razor sharp crater fields and the most wonderful earthshine from its dark side. Cranking up the power to 165x, the image remained razor sharp with excellent contrast and without a trace of chromatic aberration.
After that, I headed over to eta Orionis, a fairly tricky double star and was rewarded by a good clean split of the A and B components, the primary shining about a magnitude brighter than the secondary (3.8 and 4.8, respectively) and separated by a mere 1.7 arc seconds. Because of its f/5 relative aperture, it is very important to examine such high resolution targets at the centre of the field. This can be achieved by placing the system at the eastern edge of the field and letting it drift into the centre. The procedure is repeated several times until one is certain that the duplicity has been unveiled.
Some haar moved in a short time ago but hopefully it will clear later. I hope to field my most powerful telescope, Octavius, to continue my study of the Giant Planet.
Saturday, February 13 2016
My luck ran night overnight, as instead of clear skies, we got a fall of snow.
The final step in keeping anything in my family is to get my wife’s approval. For that, I had to get all my facts together to make a convincing case lol:
The optical tube assembly weighs just 3.2 kilos
The little lazy Susan weighs 2.8 kilos
The telescope can be collapsed to half its length.
The tube assembly can be used with a variety of other mounts.
The telescope is easy to tweak; involving a couple of minutes with a laser collimator.
The telescope is easy to carry about using one hand, so even when I’m feeling lazy it will not overtax me.
The telescope cools rapidly, so no waiting around or extensive pre-planning involved. Just set it out 15 or 20 minutes before use and you’re cooking with gas.
Because the tube is open, the optics can be accessed to remove dust and other grime easily.
The telescope gathers a very decent amount of light to go that little deeper than my short-tube refractor; very good for deep sky viewing.
The telescope takes high magnification well; images remain sharp and well defined up 244x (higher powers not yet tested) when conditions are average to good, so will perform well on lunar, planetary and double star targets.
The telescope can be improved in a number of ways; for example, the mirrors could be re-coated to give both higher reflectivity and increased durability, the secondary size re-assessed, ways could be found to refine the helical focuser, a permanent light shroud can be installed etc. Any amount of tomfoolery is permissible!
The instrument exudes charm and is popular with the kids.
The entire package cost only £129.
I think these points will be enough to win her over. Fingers crossed eh!
Improving the Focuser:
As mentioned earlier, the focuser on the Heritage 130P is of the simple, helical variety. One simply twists it one way or another to attain a good focus. But in the field at night, it can be a little frustrating to focus precisely, especially when using high magnifications. Manhandling the focuser almost always causes the telescope to move a little, necessitating re-centering of the object under study.
Fortunately, I was able to find a very simple solution; about six inches of string!
The string is tied in a single knot around the focuser, gripping the top thread, and leaving two overhanging ends which can be pulled in either direction causing the focuser to move inward or outward, as desired. This enables both course and fine focusing with much less vibration or annoying image shift. I tested it out during the day on a variety of targets at various distances from about 40 yards to infinity and it worked really well! This will allow more quality time observing and more precise focusing from moment to moment.
I’m well happy with the improvement!
Sunday, February 14 2016
St. Valentine’s Day and the first Sunday of Lent.
Last night I fielded Plotina just before midnight. After snowing for much of the day, the late evening sky cleared up to reveal the hosts of the second heaven. Seeing was very good but bitterly cold(-4C), but I was rewarded by quite an extraordinary view of Jupiter and its magnificent satellite system. I watched the planet for about 40 minutes, beginning at 23:50UT and ending at about 00:35UT.
This instrument continues to humble me in many ways. The optics are unreasonably excellent in this telescope; something I was not really prepared for, but hand on heart, it has thus far given me the finest views of Jupiter in any small telescope that has passed through these parts. I made a quick sketch depicting the planet’s appearance at 23:50UT (CM II 217 degrees), when it was 33 degrees above the horizon. The Great Red Spot (GRS) was plainly seen in the eastern hemisphere of the planet. The magnification employed was 165x and a Baader Neodymium filter threaded to the 4mm Plossl.
Indeed, I was able to use this telescope to establish the most accurate longitude of the GRS during this apparition. The GRS was observed transiting the centre of the planet at 00:32 UT where the system II longitude was 243 degrees. Not bad eh?
In the immortal words of Alexander Pope;
Nature and nature’s laws lay hid in night;
God said “Let Newton be” and all was light.
Monday, February 15 2016
I subjected the 130P to a high magnification test on the first quarter Moon, at an ambient temperature of -1C. I am very happy to confirm that it handled 244x without flinching, with the craters, mountain ranges, maria and valleys remaining tack sharp and colour free throughout. This is about as high as one would like to go with this telescope in the vast majority of applications and a testament to the quality of the underlying optics.
I would warmly encourage other individuals to test each and every one of the claims I have made about this telescope. Test everything; hold fast to that which is good.
Sound Biblical advice that!
Way hay! I found me an online thread about the same telescope; Enter the One Sky Newtonian from Astronomy Without Borders .
200K+ hits ……..Crikey!
Seems like I don’t need to say anymore, eh.
Tuesday, February 16 2016
What a thread! The things they say about this telescope warms my heart.
That thread has saved me months of blogging; Laudate Dominum!
Gary Seronik of S&T also found the telescope a joy to use; see here.
And yet another independent review can be read here.
Here my story ends.
Thank you for viewing.
Thursday, February 18, 2016
Having just acquired the latest issue(March 2016) of Astronomy Now (pp 63), I read with interest that the current longitude (system II) of the GRS is 238 degrees. That’s just 5 degrees shy of my best estimate made with the 130P shortly after midnight on Sunday February 14 (see above). I’m thrilled to bits to have gotten so close with this nifty little travel Newtonian.
Monday March 14, 2016
I have found that the Televue bandmate planetary filter is a great match for the 130P whilst studying Jupiter.This filter will be used in all future observations of the planet with this telescope.
The primary and secondary mirrors of the Heritage 130P have been despatched to Orion Optics UK. Both mirrors will be re-coated with Hilux enhanced aluminium reflectivity coatings and a slightly smaller secondary (35mm @27% linear obstruction) is to replace the original flat.
Will report back on progress.
Tuesday, March 22 2016
The mirrors arrived back from Orion Optics UK this afternoon and I immediately set to work putting it all back together again.
Out came the matt black paint to darken the periphery of the new secondary mirror to further reduce stray light and increase contrast.
The primary mirror had to be re-spotted at its centre but this can easily be done by placing the mirror shiny side down on a sheet of paper and tracing round its circumference. Next, the 130mm diameter circle was carefully cut out and folded first in half, and then once again into quarters. When the paper is unfolded the centre is marked by the intersection of the two crease lines. A scalpel (lol!)was used to excise a very small hole at the centre of the unfolded paper and then it was placed over the mirror, being secured in position with some cellotape. Finally, a doughnut shaped sticker was placed on the spot exposed by the hole. Job done!
The optics were then rehoused in the tube, collimated using an inexpensive laser collimator (SkyWatcher) and briefly tested with an eyepiece. Everything looked dandy!The telescope should now deliver brighter, more contrasty images on all celestial targets. And those special coatings will last at least a quarter of a century!
Surely now Plotina will be as durable as any high quality refractor nay?
All I have to do is wait for a decent clear spell to see how well she performs under the starry heaven.
Wednesday, March 23, 2016
Beginning about 20:30 UT this evening, I took advantage of a clear spell after a few hours of light rain. Jupiter was about 34 degrees above the horizon and rising, and I continued observations through to 21:15 UT before more cloud rolled in. I captured some beautiful detail on the Jovian disk, including the appearance of the GRS at the planet’s eastern limb. As the minutes passed, the view of Jupiter got ever better as it gained in altitude. The 130mm f/5 performed flawlessly. The planet was brighter, crisper and cleaner than I had ever seen it before with this instrument under these conditions (Ant II). To say that I’m pleased with the modifications would be an understatement, but we’ll leave it at that.
I heartily recommend this telescope to my amateur friends across the world.
Wishing you all a very blessed Easter.
March 31, 2016
I enjoyed a half hour with the Heritage 130P this evening after I had observed Jupiter. After spending some time in Leo hunting down some spring galaxies, I started looking at some double stars. Gamma Leonis was easy, Castor A and B just as easy, iota Cassiopeiae triple lovely and all three components resolved. Mizar & Alcor were glorious at 150x as was Polaris A & B. Izar (epsilon Bootis), a summer favourite, was high enough in the east for me to split it. These were all seen at 183x save for Mizar & Alcor. I then decided to try a pair of stars I haven’t visited in a while; Alula Borealis and Alula Australis in Ursa Major. They are high overhead this time of year. Aiming is quite difficult using just the RDF but with my 32 mm Plossl delivering 20x, I was able to frame them both in the same field. Starting with the orange star Alula Borealis, I employed 183x using my most comfortable ocular; the Mark III Baader Hyperion zoom set to 8mm with its 2.25x Barlow. Although this does not show the highest contrast views (but only by a surprisingly small margin!!), I was able to see the very faint spark of its companion. The primary is magnitude 3.5 but the secondary shines at magnitude +10.1 and only 7.4″ separating them! I was chuffed to see this in such a humble little reflector. Then came the icing on the cake; I moved south to Alula Australis (Xi UMa) and could see that the star looked ‘entangled’ but I knew I needed a little more power to get a clearer view. So I ran in and fetched by 6mm orthoscopic and coupled it to the little 2.25x Barlow yielding 244x, centred and focused carefully: Voila! The pair (1.6″ split) were beautifully resolved (magnitudes 4.3 and 4.8), the components round as buttons, with a kind of diffraction halo encircling them; kind of like an ‘aura’ encasing two luminous eggs in a wafer thin handkerchief lol.
If no one bothers, how can one ever discover the truth? The Heritage 130P is unreasonably excellent on everything; a great little bundle of joy!
April 7, 2016
Mr. Adam Blake from Pennsylvannia USA, was kind enough to share some video footage of Jupiter he captured with his One Sky Newtonian, as seen on the evening of April 5, 2016 during a spell of good seeing. He used an inexpensive 5X GSO Barlow and standard UV/IR filter on the camera at prime focus to capture the images, which have only been very lightly processed to show the telescope’s potential. See below.
I aimed the Heritage 130P at iota Leonis, now high in the south. Using 244x I was able to quite easily resolve A-B. The primary shines with magnitude +4.06 and the secondary +6.71 with 2.1″ separating the components. I would warmly encourage others to try this system, as well as the aforementioned star systems with this telescope.
A Portable Dew Buster: Are you concerned about dew building up on the open tube of the Heritage 130P? Nae worries! I never let any heating devices within a country mile of my telescopes, just like my forebears. I bought a portable three-speed fan for about £10 that zaps dew in seconds from the secondary and primary using cold air. Now you can enjoy the telescope under the stars for as long as you like!
April 28, 2016
At an ambient temperature of -1C, the Skywatcher Heritage 130P worked flawlessly to bag epsilon 1 and 2 Lyrae, eta Bootis (with its 10th magnitude companion), pi Bootis ( AB: 4.9, 5.8 separation 5.4″ and AC: 4.9,10.6, separation 127″), alpha Herculis ( AB:3.5, 5.4, separation 4.6″ and a corker, AD: 3.5, 11.1, separation 79″)
For lunar and planetary studies, I can also recommend the Baader single polarising filter to use with this adorable little telescope. Retailing for £32.00, it significantly enhances belt detail on Jupiter, reduces glare and presents the planet in its natural colours.
Sunday, May 15, 2016.
During a relaxing weekend away with a group of old friends in the picturesque and historic village of Luss, on the western bank of Loch Lomond, I took the little SkyWatcher Heritage 130P along with me, as it was so easy to transport and set up. After long sunny days outdoors, I set the instrument (on its Dob mount) up on the garden table for a look at Jupiter and the first quarter Moon, which were perfectly positioned in the evening sky.
As this was an annual event away, the crew were expecting me to bring along a telescope, but it is usually of the short refractor variety. I got some odd looks from the gang as I extended the upper stage of the ‘strange’ reflecting telescope, but I was sure glad I made the effort; they were all mightily impressed by the images the little portable reflector served up:- and even more gobsmacked when I told them how relatively inexpensive an instrument of this quality cost to acquire!
July 21, 2016
My collegaue at Astronomy Now, Steve Ringwood, has independently reviewed the New Meade Light Bridge 130 Mini Dob for the August 2016 issue of Astronomy Now (now in the shops) on page 108-10. Although a slightly different design to the Heritage 130P featured in this blog, the optics are essentially the same but features a solid tube and a more traditional four spider-vane secondary support for even more rigid collimation maintenance in the field. Steve found that the optics were very good indeed, being capable of powers in excess of 200x, in agreement with my findings. At $200, it is priced at the same as the One Sky Newtonian from Astronomy Without Borders, discussed above.
So more choice for the discerning amateur.
Brian Schultz, from his YouTube channel Cool Space, describes how the One Sky Newtonian can be fitted to an inexpensive go-to mount for added versatility. See here for a video clip.
August 8-9 2016
Our family ventured to the remote Isle of Skye, a place of outstanding natural beauty, for our summer vacation. My trusty 130mm f/5 Heritage Newtonian travelled with us. Though the weather was mostly damp and windy, I did enjoy a bout of observing with the instrument during brief clear spells on the evenings of August 8 and 9. The sky is truly glorious at this location, presenting some of the darkest and most transparent skies in all of Europe. And the (not so) little 130mm did not disappoint, serving up jaw-dropping views of the northern Milky Way high overhead, once the crescent Moon fell out of the sky. Deep sky objects were a joy to behold, including M31,Caldwell 14, M57, M13 and M92. The North American Nebula in Cygnus was as plain as the nose on the your face, as were the eastern and western Veil nebulae nearby.
I can also report that high resolution targets – including a batch of close test double stars – presented very well indeed. Images of systems such as Izar, delta Cygni etc, were calm and well resolved at high powers (243x), showing that this island has good seeing conditions for such work. Scotland has many such places(as I continue to discover) if one is intrepid enough to find them out!
September 30, 2016
My experiments with the Skywwatcher Heritage130P continue apace. A while back a kindly gentleman from the USA alerted me to a potential issue with the instrument; the loss of precise collimation as the instrument is pointed to different parts of the sky. In a series of experiments conducted over the last six weeks or so, I discovered that while tightening the shaft that holds the secondary mirror in place seems to solve this problem for lightweight eyepieces, it doesn’t always hold collimation for heavier oculars such as the rather bulky, Baader Hyperion zoom.
As a consequence, I have reassessed the suite of oculars I use with the instrument and have switched entirely to smaller, more lightweight units. Below is an image of my current experimental set up; a 32mm Plossl, delivering a power of 20x and a 2.5 degree true field. Using the tiny, screw-on 2.25x Baader Barlow, I can couple the 32mm ocular to give a power of 45x and a true field of ~1.1 degrees – just large enough to frame the entire Double Cluster in the field!
For higher power work, I use a Parks Gold 7.5mm delivering 87x, a 6mm Baader classic orthoscopic yielding 108x, and a 4mm Revelation Plossl (fully multicoated) giving 163x. Finally, using the 2.25x Barlow I can achieve 243x and even 366x when mated with the 6mm and 4mm oculars, respectively. I also have an old 1.6x screw-on Barlow made by UK Astro Engineering, which gives me still more options to play with.The Barlows will increase the eye relief of the short focal length of the short focal length eyepieces too.
Over the winter I hope to fine tune this set up some more, but I am very happy with the range of powers available to me and the relatively low cost of its operation.
I also intend purchasing some Bob’s Knobs collimating screws to fit to the secondary assembly in order to make collimation even more easy to achieve.
I will report back later in the year to tell you how I got on!
The instrument continues to inspire in so many ways and needless to say I have grown very fond of using it.
Thursday, October 13, 2016
Plotina received her new set of Bob’s Knobs secondary screws to make fine adjustments to collimation easier. I consider these to be a quality acquisition going forward.
Monday, October 17, 2016
Upon further investigation, I have been able to tighten up the stalk holding the secondary mirror in place by inserting a small washer, as shown below.
This increased rigidity allows the instrument to maintain precise collimation even after moving the telescope wildly in altitude and azimuth. This was verified using a laser collimator. The telescope can now use larger oculars once again, including the Baader zoom.
Monday & Tuesday, October 18 and 19, 2016
A break in the wet autumnal weather over the last two nights has allowed me to conduct further tests with the SkyWatcher 130mm f/5 Newtonian. I fielded a 90mm apochromat (retained for further testing) side by side with the instrument and studied how both performed on a variety of high resolution targets located in different parts of the sky.
Yesterday evening, shortly before midnight, I compared and contrasted both instruments in respect of their ability to maintain crisp, bright images of a waning gibbous Moon. Once our satellite achieved a decent altitude, I cranked up the magnifications on both instruments and examined the cratered terrain along the day-night terminator. Both instruments performed well but the larger aperture of the Newtonian allowed me to employ significantly higher magnifications (in excess of 300x) before the image became unsatisfactorily dim for my liking. The 90mm refractor, in contrast, maxed out about 200x.
Tonight, with better seeing but in colder(+4C) and hazier conditions, I ran the two telescopes to a variety of double star targets at various altitudes; gamma Delphini, theta Aurigae, Iota Cassiopeiae and delta Cygni; these systems were deliberately chosen so as to test how the 130mm Newtonian would hold collimation as it was adjusted in altitude and azimuth. My results show that the insertion of the washer in the stalk supporting the secondary mirror (described above) worked perfectly well, the stellar images remaining crisp, round and tiny. In every case, the Newtonian produced brighter, more convincing splits of these systems under equivalent magnification regimes – 200 to 250x.
These results show that the Newtonian is a wonderful, cost-effective and versatile instrument for all celestial targets and is noticeably superior to a much more expensive 90mm refractor, which quickly runs out of both light and resolving power in comparison.
I continue to highly recommend this instrument to those who are looking for excellent performance on a limited budget.
Nothing more to say really.
Thanks for following this blog.
Update: February 15 2017
My colleague at Astronomy Now, Ade Ashford, is helping to change culture by writing an excellent four page article on how to tune up the SkyWatcher Explorer 130PDS, mentioned in the blog above, and essentially the same telescope optically as the Heritage 130P (but with a closed tube) for better visual and photographic use. You can read this VERY interesting article in the March 2017 issue (page 98 through 102), out now.
Update: July 17 2017
Time: 00:09 BST
Location: Wigtown, Southwest Scotland.
Seeing: ( I to II): generally excellent, very calm
Instrument: 130mm f/5 Newtonian
Comments: A fabulous bout of double star observing. See notes below.
Update: July 18 2017
Time: 00:45 BST
Comments: Just in from another excellent session with the 130mm Newtonian. Highlight of the night was tracking down and resolving the lovely Mu Cygni. Tight pair, even at 244x and a fainter ‘companion’ wide away making it seem more like a triple system. Generous aperture and solidly good optics made very light work of this system. Like I said, this is arguably the best grab ‘n’ go ‘scope on the market today. Details below;
Update: July 21 2017
Time: 00:35 BST
Instrument: 130mm f/5 Newtonian, aka ‘Plotina’
Seeing: Excellent (I); very clear before midnight. Some cloud moved in after midnight.
Comments: Still in Wigtown. Third night where conditions have been excellent.
Some very tricky systems resolved once again this evening with this modest telescope. Textbook perfect results!
Monday, December 19, 2016
As described in a previous blog, I have come to learn the many virtues of the powerful yet relatively inexpensive SkyWatcher Heritage 130P, a 5.1 inch f/5 tabletop Newtonian. I described various modifications I made to the telescope in order to optimise its performance. These included replacing the existing secondary with a smaller unit, giving a secondary obstruction of just 27 per cent. Both the primary and secondary mirrors were also treated with Orion Optics’ HiLux super high reflecting coating, providing brighter, more contrasty views of celestial targets. I also described some modifications which involved tightening up the secondary stalk holding the secondary mirror in place, which helped maintain precise collimation while the telescope was being slewed to different parts of the sky.
I can report that the telescope is still performing excellently, so much so that I now question the wisdom of using a small aperture refractor (or catadioptric) for grab ‘n’ go excursions. As explained in my blog, this telescope is very lightweight, fits on a variety of ergonomic mounts owing to the included Vixen style mounting plate, and cools super quick due to its relatively small, thin primary mirror and open tube configuration. But on the evening of December 19, I learned yet more of its secrets.
The night was cold (near zero Celsius) but the sky remained steadfastly clear from sunset to near sunrise the next day. I felt rather tired that evening, having gone through several hours of maths teaching, but I still wanted to venture out under the wintry sky before the waning gibbous Moon got up. So I turned to the 130P, mounting it on a lightweight Vixen II Porta altazimuth to get some observing in. Seeing conditions were not fantastic but perfectly adequate for most targets. The instrument was precisely collimated using an inexpensive laser collimator, as described previously, and made even easier since I installed some Bob’s Knobs secondary adjustment screws. This operation takes only a couple of minutes to execute accurately and I was then ready to reach for my Baader Hyperion zoom, an eyepiece I have grown very fond of owing to its excellent quality for its modest price. Indeed, it really is only slightly inferior to high quality oculars of fixed focal lengths. Thankfully, this is now being openly acknowledged by many amateurs on the forums. See this interesting link comparing this zoom to a much more expensive Leica zoom covering more or less the same focal length range.
In previous excursions, I reported that the zoom was rather heavy and I was concerned that it might be throwing off the collimation as the telescope was aimed at targets of varying altitude. But I can report that the addition of a single washer to the stalk holding the secondary mirror greatly increased the rigidity of the system and I felt I could chance using this large (and bulky) eyepiece as my only portal on the Universe on this frosty evening. So, how did it perform? In a word; magnificently!
But to elaborate, I discovered that the zoom keeps one’s body a few inches further back, away from the optical train, and more effectively attenuates the thermal heat plumes issuing from my body. An open tube like the Heritage 130P is significantly more sensitive to thermals introduced into the optical train, especially on cold nights like that experienced on the evening of December 19. I was actually quite shocked at how calm the images appeared in the eyepiece, examing as I did, several fairly tricky double and multiple stars, including some of my seasonal favourites, like beta Monocerotis (at a fairly low altitude), and much higher up: theta Aurigae, iota Cassiopeiae and (the less challenging) Castor A & B. All were well resolved. The native zoom provides a very useful range of magnifications from 27 to 81x, and can be further extended to a greater range of powers up to 182x (and thereby further extending the distance from the optical train). The images of all these systems were remarkably calm!
Furthermore, comparing the views through the zoom and a much lower profile 7.5mm Parks Gold ocular and Barlow, I could see that the images remained calmer for longer using the zoom. The images were quite simply less affected by anthropogenic turbulence. This is going to make a very significant difference while conducting high resolution work with this telescope during the many cold nights we experience here in Scotland. Nor did the zoom cause any miscollimation issues throughout the vigil. The stars always focused down to small, tight and round seeing disks.
Moving back to the native zoom, I visited M31, riding high in the winter sky, followed by the beautiful trio of Messier star clusters adorning the heart of Auriga (M36, M37 & M38), and from there I visited to my favourite Messier open cluster, M35, in Northern Gemini. I experienced nothing but pure joy experimenting with the right magnifications to frame these clusters using the zoom and the Barlow. I especially like the way the zoom ‘opens up’ at the lower focal length settings (to a very generous 72 degrees indeed) allowing one to soak up the beautiful hinterland around the Auriga clusters.
From there, I panned the telescope down to M42, the Great Nebula in Orion, which had, by now, all but reached meridian passage, and I ‘dialled in’ the optimum viewing magnification (about 150x as it turned out), drinking up the beautiful, crisp nebulosity surrounding the theta Orionis complex (Trapezium).
My adventure under the winter sky was a wonderful experience and only ended once I saw the vault of light emerging in the eastern sky from a rising Moon. The telescope is well able to handle this extraordinary eyepiece, enabling me to effortlessly cruise from low to high power. As I already reported, it is significantly more powerful than a 90mm apochromatic refractor (tested extensively along side the 130P over several months). It can do things no 127mm Maksutov can do, especially on low power, wide field targets, and its smaller central obstruction ensures crisper lunar and planetary views.
This grab ‘n’ go system will take your short, backyard excursions to new heights, thanks to its very generous aperture. Can I recommend this telescope and zoom eyepiece combination highly enough?
Neil English is the author of several books on amateur telescopes.
Please check out this ongoing thread on a related telescope, The One Sky Newtonian, which is still going from strength to strength.
I’ve noticed that one issue that seems to give folk concern about investing in a good Newtonian pertains to having to clean the optics every now and again. I’ve never really understood this mindset though. Having had my closed-tube 8-inch Newtonian for about 18 months now, and having clocked up a few hundred hours of observations with it, I felt it was time to give the mirrors a cleaning. Here’s how I do it:
The mirrors are removed from the tube.
First I make sure that all the loose dust and debris has been blown off using an air brush. Next, I run some cold tap water into a sink and add a drop or two of washing up liquid. The water we use here is very soft; indeed we are graced with some of the softest water in the British Isles, which also makes drinking tea especially pleasant! If your local water source is hard, I’d definitely recommend using de-ionised/distilled water.
Starting with the secondary mirror, I dip my fingers into the water and apply some of it onto the mirror surface with my finger tips, gently cleaning it using vertical strokes. Did you know that your finger tips are softer than any man-made cloth and are thus ideal for cleaning delicate surfaces like telescope mirrors?
Next, the mirror reflective surface is rinsed under some cold, running tap water.
The procedure is repeated for the primary mirror;
The mirrors are then supported on their sides to allow them to drain excess water, and then left to dry in a warm, kitchen environment. Stubborn water droplets nucleating on the mirrors are removed using some absorbent tissue.
Finally, the mirrors are placed back in the telescope tube, making sure not to over-tighten the screws which hold the primary in place inside its cell. All that remains then is to accurately align the optical train, as described previously.
There we are! Not so difficult after all; and all done in about 40 minutes! The soft water doesn’t show up any significant spots after cleaning unlike hard water sources and now the optics are as clean as the day they were produced.
With a busy season of optical testing and planetary observing ahead, I know that my 8-inch will be operating as well as it possibly can. And that’s surely good to know!
I feel a nice, hot cuppa is in order!
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
Eye seeth afore I measureth.
Introduction: Having spent several years enjoying the views of double stars of varying degrees of difficulty with a variety of classical achromatic and apochromatic refractors of various apertures (60mm-150mm), this author has dedicated the last 15 months investigating the prowess of Newtonian reflectors in regard to their efficacy in splitting double stars. Surprisingly, a 8″ f/6 Newtonian with traditional spider vanes and a 22 per cent central obstruction was found to be noticeably superior to a first rate 5″ f/12 glass, as well as a 180mm f/15 Maksutov Cassegrain, on all targets, including double stars.
These experiences have collectively led to a deep seated scepticism concerning the traditional claims of self appointed ‘authorities’ who have tended to downplay the Newtonian reflector as a worthy double star instrument. But as the quote from Mr. Denning’s book states above, this prejudice is not derived from sustained field experience. Instead, it is cultivated by, at best, tenuous theoretical considerations. And yet theory counts for nothing if contradictions are found by experimentation, and must be revised in light of new evidences brought to the fore by active observers.
In this capacity, this author has spent several months investigating the performance of a very modest 5.1 inch (130mm) f/5 Newtonian reflector on an undriven alt-azimuth mount. The instrument was modified in two principal ways:
The instrument has a single stalk supporting the secondary mirror which produces greatly reduced diffraction effects compared with more traditional Newtonians, yet was found to be sufficiently rigid to deliver very sharp and detailed views of the Moon, planets and deep sky objects.
The optical train can be accurately aligned in minutes by means of fully adjustable screws on both the primary and secondary mirrors and an inexpensive laser collimator.
Preliminary field testing has shown that the telescope provides very fine high power views of stellar targets under fair to good conditions. Even at powers beyond 50 per inch of aperture, stars remain round, free of astigmatism and perfectly achromatic. Furthermore, the diffraction spikes attributed to Newtonians are much subdued in this instrument owing to its single vane secondary support. The diagram below shows the relative intensity of diffraction spikes manifesting from various secondary mounting configurations and the reader will note the minimal effects of a single support (seen on far left).
Materials & Methods: The telescope was mounted on an ergonomic but sturdy Vixen Porta II alt-azimuth mount equipped with slow motion controls on both axes. the instrument was carefully collimated prior to the commencement of observations using a laser collimator. No cooling fans were employed. A red dot finder was used to aim the instrument and various oculars and barlows were used to resolve pairs. For fainter stellar targets, the system was centred first using a 32mm SkyWatcher Plossl which delivers 20x and an expansive 2.5 degree true field.
Time: 00:00-00:30 UT
Seeing: Antoniadi II-III
Epsilon Lyrae: x 271; all four components cleanly resolved, stars round, white and undistorted. No diffraction effects noted.
Pi Bootis: Easy at 150x. Components appearing white and blue-white.
Mu Bootis (Alkalurops): Wonderful triple system; fainter pair (magnitudes 7 and 7.6) separated by 2.2″ and perfectly presented at 271x. This pair has an orbital period of just 260 years!
Epsilon Bootis: Primary (magnitude 2.5) presenting in a lovely ochre hue and its fainter companion (magnitude 4.7) easily picked off at 271x.
Delta Cygni: Magnitudes: 2.89, 6.27, separation: 2.7″
Well split at 271x, although conditions a little turbulent and not yet at an optimal altitude for observation.
Time: 00:00-00:30 UT
Seeing: II. Indifferent seeing at sunset (III-IV), improving as the night advanced (II).
Xi UMa: beautiful clean split of this 1.6″ pair (magnitudes 4.3 and 4.8) at 271x
Epsilon Bootis: textbook perfect split @ 271x
Delta Cygni: Child’s play this evening, separation 2.7″. Companion presented as a perfectly round, steely grey orb @271x.
Beta Lyrae: remarkable multiple star system. Four white/blue white stars framed in the same field at 271x.
O^1 Cygni: a corker at 20x, but more fetching at 81x. Orange and turquoise stars, with the former showing its blue magnitude 7 companion.
Time: 22:30 UT
Seeing: II-III, clear, brightening moon, twilit
Iota Cassiopeiae: Just one entry tonight. More challenging to locate owing to its relatively low altitude above the northern horizon and the encroach of twilight. All thee components well resolved at 271x. This is the third successful split of this attractive multiple star system with the same instrument.
Time: 22:10 UT
Seeing: II, partially cloudy, twilit.
Epsilon Bootis: Another lovely split this evening @271x. Primary(magnitude +2.5) orange and the secondary a regal blue (magnitude 4.9) separated by 2.8″.
Xi Bootis: Striking yellow and orange components (magnitudes 4.7 and 7, respectively), separated by ~6.5″ and beautifully framed @ 150X.
Rho Herculis: A comely pair of blue-white stars shining at magnitudes +4.5 and +5.4. Easily resolved (4.0″)@271X.
Epsilon 1 & 2 Lyrae: textbook perfect split of all four components @271x. Subtle colour differences noted between the stars.
Delta Cygni: Perfectly resolved at 271x. Magnitudes: 2.89, 6.27, separation: 2.7″
Seeing: II, very good, mostly clear, twilit, bright Moon low in south.
Marfik(Lambda Ophiuchi): Quite hard to track down owing to an unusual amount of glare in the southern sky. System split at 271x. The components ( magnitudes 4.2 & 5.2), well resolved. Tightest system so far resolved with this instrument: 1.4″. Both stars appeared creamy white and orientated roughly northeast to southwest. Superficially, very much like Xi UMa but slightly more challenging.
No’ bad ken.
Time: 00:10 UT
Seeing: I-II, excellent steady atmosphere, no cloud, twilit, cool.
Pi Aquilae: Another good target affirmatively resolved this evening. Separation 1.5″ with magnitudes of 6.3 and 6.8. Power of 271x applied. First hint of duplicity seen shortly after local midnight when the system was quite low down in the east, but much better presented at 23:45 UT when it rose a little higher.
Delta Cygni: Another textbook perfect split! This system is child’s play with this telescope, but remains a good indicator of local seeing.
I would warmly encourage others using this telescope, or its closed tubed counterpart, to confirm these findings.
Time: 22:45 UT
Seeing: II, good stable air for double star work, cloudless sky, twilit.
Epsilon 1 & 2 Lyrae: beautiful easy and dazzling split of all four components @271x
Delta Cygni: Another textbook perfect split of this very unequal magnitude pair @271x
Mu Cygni: difficult to find as it is currently lower down in the east under twilit conditions. Excellent multiple star system, A-B well split @271x, colours white and yellow (+4.8/6.2 magnitudes, respectively), separation ~1.66″. Another tight, unequal magnitude pairing. C component too faint to pick off in the twilight. D component (+6.9) seen about 3′ off to the northeast.
Doing well so far don’t you think?
Ps. Interesting findings from a few guys here.
Time: 23:10 UT
Seeing: II, almost a carbon copy of last night. Twilit.
Just two targets this evening.
Epsilon Bootis: a good ‘warm up’ system. The telescope showed a textbook perfect split during the finest moments at 271X. I have found that wearing a good heat-insulating jacket and hat gives noticeably better results on cooler nights, as thermal energy from the body can sometimes distort the image at least for a wee while.
From there I moved to my target system for the evening.
Sigma 1932 AaB: a very challenging system in Corona Borealis. It is located about 3.67 degrees directly west of Alphecca (alpha CrB) which is easily seen even in twilight. My 32mm SkyWatcher Plossl, which yields a field of view of 2.5 angular degrees was used, together with my star atlas, to finally track down this magnitude 7 system. After a few false starts, I eventually centred the target system, cranked up the power to 271x and, with a concentrated gaze, obtained a good split! This binary system consists of a pair of yellowish stars with equal magnitudes (7.3 and 7.4, respectively) oriented roughly east to west and separated by 1.6″.
Time: 23:00-23:30 UT
Seeing: A fine and mild night, remaining very good (II), high pressure bubble stabilised over Scotland, some intermittent cloud, twilit. Midge flies back.
Tonight, I wanted to compare and contrast two very different telescopes in respect to their ability to split a few of the tougher pairs visited thus far; a 90mm f/5.5 doublet Apo (retail price now £912 UK) and the 130mm f/5 Newtonian (~£200 UK with the modifications).
90mm glass; difficult split @208x
130mm speculum: much more cleanly resolved@271x
System: Pi Aquilae*
90mm glass: very dim, touching @208x
130mm speculum: cleanly resolved/brighter @271x
90mm glass: dim, elongated @208x
130mm speculum: fully resolved /brighter @271x
You cannae change the laws o’ physics captain!
And ignorance of the law is no excuse.
Oh vanity of vanities!
Self-evidently, an unfair comparison: the 130mm f/5 Newtonian is clearly the superior double star instrument.
The words of the prophet, Isaiah, come to mind;
For fools speak folly,
their hearts are bent on evil:
They practice ungodliness
and spread error concerning the Lord;
the hungry they leave empty
and from the thirsty they withhold water.
Scoundrels use wicked methods, they make up evil schemes
to destroy the poor with lies,
even when the plea of the needy is just.
But the noble make noble plans,
and by noble deeds they stand.
Time: 23:05 UT
Seeing: III; significantly more turbulent than last night. Twilit.
This evening I had intended to concentrate my observations on one target; the very difficult sub-arc second companion to Lambda Cygni, using my best instrument; a 8-inch f/6 Newtonian, in order that I might train my eyes to see this companion (separated by 0.9″) in my smaller 130mm instrument.
Using the 130mm as a seeing gauge; I found Epsilon 1 & 2 Lyrae to be resolved well but nearby Delta Cygni was poorly resolved. This was also found to be the case in the 8-inch aperture.
Project shelved for a better night.
Time: 23:30 UT
No opportunities afforded this evening owing to the encroach of haar after sunset.
Let us consider some of the optical principles relevant to splitting such a tight pair.
Diffraction theory states that the position of the first bright ring (between 1st and 2nd minima) is located at a linear radius of 1.63 lambda x F where lambda (wavelength) is quoted in microns and F is the focal ratio of the scope. By dividing this quantity by the focal length we obtain the angular radius of the 1st minimum (in radians) and this yields (1.63 x lambda)/D where D is the aperture of the scope in metres.
Now, there are 57.3 angular degrees in a radian and 3600 arc seconds in each angular degree, so if we multiply the above expression by 57.3 x 3600 = 206280 and so we arrive at 206280 x (1.63 x lambda)/D.
Setting D = 0.1m for example, and lambda = 0.55 microns (green) yields 1849300 micro arc seconds, which is 1.85”.
Or more generally, the locus of the first diffraction ring is 185/D where D is the aperture of the telescope expressed in mm.
Applying this formula to the 200mm and 130 mm reflectors, the position of the first diffraction ring is 0.9” and 1.4”, respectively. Thus, the companion to Lambda Cygni will be located on the first diffraction ring in the 8-inch instrument, and inside the ring in the case of the 130mm telescope.
The primary has a magnitude of +4.5 and the secondary, + 6.3, so there is a magnitude differential of 1.8. The significant brightness differential makes this system more difficult to crack.
The Dawes limit for a 130mm (5.1 inches) ‘scope is given by 4.57/D in inches, which is ~0.9”.
Time: 23:30 UT
Seeing: III-IV, very turbulent
Conditions clear but remaining very turbulent. A light, northeasterly air flow is likely the culprit(see my local weather; Stirling, Scotland).
My notes show that I have glimpsed the companion to the primary on a few occasions over the last few summers with my 5″ f/12 achromatic. But I have seen it much more clearly – and also on a few occasions – with the 8″ f/6 Newtonian.
In order to maximise my chances with Lambda Cygni, I have decided to wait until August at the earliest, when the system will be high overhead here, in a dark sky. Patience is a virtue is it not? And I can afford to be patient with this one, as it is a very slow moving binary and so will remain very challenging for a good few years to come. So no hurry.
The capabilities of the 130mm f/5 on double stars have already well exceeded my expectations. My experiences with the smaller, 90mm refractor especially, have reinforced the notion that aperture is a vital commodity when it comes to seeing objects clearly and distinctly. It pays to remember that resolution scales with aperture. That’s why it is easier to see things in the 130mm than the 90mm, irrespective of how fancy its optics and mechanics are. And this can be tested, again and again and again…..ad nauseam.
This is factual knowledge, and facts are stubborn and immutable things!
Over the next few months I would like to return to the many beautiful and easy systems within reach of this remarkable telescope; even in heavy twilight.
Time: 23:00-59 UT
Seeing: II, good, a little hazy, twilit.
I walked through the garden in the cool of the evening, after a very warm and sunny day. I set up the 130mm f/5 as usual and began to explore some of the nicer double stars of the sky.
Mizar & Alcor: A perennial favourite, high overhead this time of year, dazzlingly bright, the light from these stars fills the field and induces instant joy. Well framed at 81x in my trusty Baader mark III zoom.
Cor Caroli (Alpha CVn): Easy to find under the handle of the Ploughshare. Both components appearing white to the eye with magnitudes 2.9 & 5.6.
Alpha Herculis (Rasalgethi): A corker! At 108x, this pair presents as marmalade orange and blue-green, which orbit their common centre of gravity every 3600 years.
Albireo (Beta Cygni): A stunning sight in the little reflector at 81x. Glorious contrast of colour; orange (magnitude 3.1) primary, blue-green secondary (5.1).
61 Cygni: historically very significant as the first star system to have its distance measured in 1838 by F.W.Bessel. Only 10.4 light years away. Both stars are cool, orange dwarfs with magnitudes 5.2 and 6.1.
Eta Cassiopeiae: A bit more challenging to locate in the strongest twilight coming from low in the northeast. Easily split at 81x, presenting as orange and red (magnitudes 3.5 & 7.5, respectively). These constitute a true binary system, with a period of about 480 years.
A quick peek at a more difficult pair:
Pi Aquilae: Once again, beautiful and easy to resolve in the 5.1” reflector at 243x. I have been observing this system for five years now, with various instruments. My notes from the end of July 2011 showed that it was very difficult with a high-quality 4” f/15 classical refractor, the twilight making it challenging. Observations made with variety of 5” refractors over the same period – and also in summer twilight – show that it is not difficult in these sized instruments (only anomaly recorded in an optically so-so 6” f/8 speculum used for outreach also from 2011, where it was relatively poorly seen). In the absence of a good 4” refractor at present, this provides good evidence that the 130mm reflector is indeed operating closer to the performance of a 5” glass than a 4” glass, which is very encouraging.
Before leaving the field, I spotted Saturn below the tree line in the south, so I decided to uplift the telescope on its Porta II mount and walk about a hundred yards to a grassy spot at the local primary school grounds, where I could better aim the telescope. Despite its very low altitude, it was a beautiful sight at ~150x, it glorious ring system now wide open for business. Cassini Division seen, as well as some banding on the Saturnian globe.
Vicious midge flies making any further observations uncomfortable, the vigil was aborted shortly before 1 AM local time.
Time: 23:00-30 UT
Seeing: II, good and stable, variable amounts of thin cloud, twilit.
Polaris: Always a lovely system to study, even in the twilight. In the telescope at 108x, the 2nd magnitude primary (Polaris A) presents as a beautiful creamy white, the secondary a haunting bluish grey some 6 magnitudes fainter seen in the 10 o’ clock position in the 130mm Newtonian. A third companion lies much closer to Polaris A but is woefully beyond the powers of any backyard telescope to resolve. Interestingly, all three stars in this system, located about 430 light years away, are of the F spectral class, and thus should present with the same colours. This is readily seen with Polaris A but the exceeding faintness of the Polaris B hides its true colour. Polaris B orbits A at a distance of about 2400 further out than the Earth-Sun distance, taking over 400 centuries to complete a single lap. Polaris A is a giant, pulsating star, part of a class known as Cepheids. With such stars, humans have been able to extend the plumbline of their reach into the realm of the galaxies. Stars like Polaris A have helped us gain a truer sense of the vastness of the Universe in which we miraculously inhabit. These are some of the things I like to ponder on, whilst spying the Pole Star.
16 Cygni: A fourth magnitude system a little to the northeast of the lovely red variable star R Cygni. In the 130mm f/5 at 81x, the decent light gathering power of the instrument presents the pair in their natural colours: a yellow primary (magnitude 4) and golden secondary (magnitude 6), separated by about 40 arc seconds of sky.
Eta Lyrae: Located a few telescopic fields east of Vega, this is normally a very easy system to crack at low powers (~40x) with a magnitude 4.4 blue-white primary and 9th magnitude secondary wide away. In the twilight, I find a higher power of 108x is needed to see the faint secondary well, and is even better presented again at 150x. Much more gloriously presented from a truly dark sky.
Time: 22:30-59 UT
Seeing: II-III, clear, twilit, bright waxing gibbous Moon culminating in the south. Evening made especially pleasant by the absence of midge flies, which don’t like temperatures below 10C.
After over a week long hiatus in the weather, which brought endless cloud and some rain, the sky finally cleared up this evening, allowing me to resume my adventures with my 130mm f/5 Newtonian.
Two reasonably challenging doubles to start with:
Epsilon Bootis: beautifully sharp and well resolved at 195x
Delta Cygni: Ditto @195x; always a joy to observe this system so well.
Iota Bootis: A wonderful low power system, located about 4 degrees northeast of Alkaid (at the tip of the handle of the Ploughshare). At 81x, the system was beautifully framed and showed a yellowish primary(magnitude +4.8) well separated from a bluish secondary, some three magnitudes fainter (+7.5). Very fetching colour contrast in the Newtonian!
95 Herculis: Found by panning some 10 degrees east of Delta Herculis. To my eyes, this nearly equal magnitude pairing(4.9/5.2) has a very subtle colour contrast: one appears silvery, the other creamy white. Easily resolved at 81x. Consulting my old Burnham’s Celestial Handbook Vol 2, there is an interesting discussion on the historical colour presentation of this pair, especially from some eccentric 19th century observers!
What colours do you see?
How wonderful it is to get outside on this beautiful mid-summer evening!
Time: 22:30 UT
Seeing: II, some hazy cloud, bright Moon in south.
Epsilon 1 & 2 Lyrae: Textbook perfect split of all four components at 243x
Delta 1 & 2 Lyrae: Easily found in the low power (20x) field of my 32mm SkyWatcher Plossl, just a few degrees to the east of Vega. No need for higher power with this system; lovely colour contrast – red and blue-white. Stars physically unrelated i.e an optical double.
SHJ 282: Seen in the same lower power field of Beta Lyrae, some 1 degree to its northeast. Under darker skies, it forms a wonderful sight in the 2.5 degree field of the 32mm Plossl, together with the celebrated Ring Nebula (M57). At 41x, this comely system (actually triple) looks like a copy of Albireo; an aureal primary well separated from its pale blue secondary.
Seeing: II, very good, partially clear, beautiful noctilucent clouds in the northeast, fresh westerly breeze, nae midgees.
The weather has been quite unsettled of late, with little in the way of clear skies, but this evening I grabbed an opportunity with both hands and fielded my bonnie 130mm Newtonian.
A number of systems visited this evening including:
Delta Cygni: wonderful split and (as usual) easily resolved at 243x. Lovely round stars well separated in the twilight.
Epsilon 1 & 2 Lyrae: Textbook perfect at 243x
Epsilon Bootis: Very easy for this telescope, as I have found on many occasions now. Lovely colour contrast at 243x
Pi Aquilae: Better positioned these days. Easily split at 243x
11 Aquilae: Found by centering Zeta Aquilae in the low power (20x) field. 6th magnitude 11 Aq lies just one degree or so to its west. At powers up to 100x or so, only the white 6th magnitude primary is visible, but when the power is cranked up beyond about 150x, the much fainter 9th magnitude companion was observed wide away. Reasonable concentration is required to tease this out of the twilight. Once picked off, the greyish companion was better seen at higher powers (243x). This system is far more glorious in a fully dark sky, and I shall look forward to visiting it again in August.
All in all, a grand half hour under a Scottish summer sky. My little Newtonian reflector is most assuredly a proficient double star telescope. The unbridled joy of discovery!
Time: 22:45-23:20 UT
Seeing: Excellent, I-II, gentle breeze, very little cloud, twilit.
After assessing the seeing in the 130mm Newtonian and judging it fine ( as evidenced by cleanly splitting Delta Cygni at 243x), I fielded my 8-inch f/6 Newtonian and turned it on Lambda Cygni, now considerably higher in the sky and applied a power of 450x. I also employed a Baader single polarising filter, which helped to reduce glare and darken the sky. I could indeed see the companion to the primary star intermittently and oriented north to south. And during the better moments I could see that it was clearly disembodied from the primary. I then turned the 130mm on the same system, employing a power of 365x with the polarising filter. Letting the image settle down as it moved across the field, I observed good elongation in the same orientation, but no separation.
This was a most exciting and encouraging vigil, the first of many more I hope.
Seeing: II, good clear spells, some cloud, westerly gusts, cold, twilit.
After a day of heavy and frequent rain showers, I enjoyed a short clear spell around midnight.
Iota Cassiopeiae: Fairly tricky to track down in twilight, but was rewarded with a lovely clean split of this picturesque triple star system at 243x.
Eta Cassiopeiae: Picturesque colour contrast pair (A/B orange and yellow). Easy to split at powers at ~100x.
Sigma Cassiopeiaie: located a few degrees southwest of the easternmost star in the constellation ( Beta), this is a wonderful target for small telescopes. It consists of two blue-white stars separated by about 3.2″. The primary shines with magnitude 5.0 and the secondary, 7.2. Best seen at magnifications > 150x.
Delta Cephei: Beautiful and easy with the 130mm Newtonian. The stars appeared pure white and easily resolved even at low power but nicely framed at 81x. The primary is actually another Cepheid variable (described above in relation to Polaris).
Two tighter test systems visited:
Delta Cygni: good clean split at 243x
Epsilon Bootis: ditto at 243x
Seeing: III-IV, below average seeing, partially cloudy.
Fairly choppy seeing this evening, as evidenced by somewhat bloated stellar seeing disks observed with the 130mm f/5 Newtonian.
Delta Cygni: barely resolved at 243x
Epsilon Bootis: split but not cleanly at 180x
Xi Bootis: yellow and orange pairing, easily resolved (6.4″) at 150x
Pi Bootis: Blue and yellow components, easily resolved (5.6″) at 150x
Zeta Coronae Borealis: Lovely yellow and blue-green components easily resolved (6″) at 150x
Mu Bootis (Alkalurops): All three components resolved easily with the 130mm Newtonian at 243x. System previously visited on May 12 last. The two seventh magnitude stars (B/C) were surprisingly well split (~2″), a consequence I suppose of their low brightness which curtails the size of their seeing disks. Fainter pairs seem less susceptible to seeing conditions.
Time: 22:40-23:00 UT
Seeing: III-IV, remaining turbulent, mostly cloudy.
Further trials with the 130mm f/5 Newtonian.
Delta Cygni : unresolved at 183x
Epsilon 1&2 Lyrae: resolved at 183x
Cor Caroli: very pretty at 63x
Time: 22:45- 23:00 UT
Seeing: III-IV, very turbulent mostly cloudy, a few suckerholes appearing here and there.
Two instruments fielded this evening; a 130mm f/5 Newtonian and a 90mm f/5.5 apochromatic refractor (price now hiked up to £1017?! i.e. fourth successive hike since review)
Epsilon Bootis (Izar): Companion resolved reasonably well with 130mm reflector but very poorly (if at all) with 90mm refractor at comparable magnifications i.e.~180x. Quite revealing really!
Mission aborted owing to light drizzle.
Time: 22:30-23:00 UT
Seeing: III, partially clear, cool, twilit.
The conditions were slightly improved over last night. I fielded the 130mm f/5 Newtonian again and examined the following systems. I employed a single polarising filter which does a very good job removing some glare and improving the aesthetic of the stellar images, especially in twilight.
Epsilon 1&2 Lyrae: easily split at 181x.
Epsilon Bootis: well split at 180x
Delta Cygni: good split at 180x and 243x
Low down in the east, I visited Delphinus for the first time this season.
Gamma Delphini: A corker at 181x! Located some 100 light years from the Solar System, the primary(magnitude +4.4) shines with a lovely marmalade orange hue, while the secondary (magnitude 5.0) shows up as lime-like. 9 arc seconds separates them.
Struve 2725: Seen in the same high power field as Gamma Delphini, this fainter system can be seen a little to the southwest of Gamma. This pair is a bit more challenging to spot, the primary and secondary having magnitudes of 7.5 and 8.4 respectively and orientated north to south. To my eye they both look white and are separated by 6″.
No’ bad innings for an average July evening, ken.
Time: 22:30-23:00 UT
Seeing: II-III, an improving picture, though not where I would like it to be. Partially cloudy, twilit.
Systems visited this evening with the 130mm f/5 Newtonian (with single polarising filter) included:
Delta Cygni: well split at 181x
Iota Cassiopeiae: A beautiful, delicate triple system, well resolved at 181x but more compelling to behold at 243x
After spending about five minutes admiring the comely, sanguine Garnet Star (Mu Cephei), I move the instrument a little to its southwest until I arrived at a field of view containing two other stellar systems of interest:
Struve 2816: A magnificent triple system (actually quadruple). All three stars are arranged in a line running roughly northwest to southeast. A/B looks yellow to the eye (magnitude +5.6) with two equally bright stars (C and D), located 12″ and ~20″ away from the primary, respectively. A grand sight at 181x.
Struve: 2819: Just off to the northwest of Struve 2816, this is a fainter system requiring high powers to see well. Both stars appear white to the eye. The primary is magnitude + 7.4 and has a fainter companion (magnitude +8.5) ~13″ off to its northeast. Best seen at 243x.
Very much looking forward to darker and more stable skies coming back in a few more weeks.
Time: 22:20-30 UT
Seeing: sultry, clouded out, midge flies by the legion, twilit.
I was hoping to get some observing done this evening, as the forecast looked reasonably promising after a long spell of very unseasonal weather (The Open at Troon sure wasn’t pretty lol). I have not been able to make any additional progress beyond what I’ve recorded but having been at this a few months now and having seen what I’ve seen, my conclusions are as follows;
The modified 130mm f/5 appears to be an excellent double star instrument! This came as a quite a surprise to me, as I was not entirely prepared for what it could deliver given its very modest cost. All of this can be tested, of course, and I’d warmly encourage you to have a go.
The instrument will comfortably outperform any 90-100mm refractor given a fair trial (proper acclimation, optical train alignment, reasonable to good seeing conditions, etc.). It is especially adept at resolving close, fainter pairs of roughly equal brightness.
Millimetre for millimetre, its performance in comparison to a refractor of equal aperture is much closer than is commonly reported (or commonly believed), though I would concede that the refractor will have an edge when pushed to the limits*.
*Valid only over the aperture ranges studied.
My conclusions are fully in agreement with the comments made by W.F. Denning (1891), reproduced above.
I will continue to monitor these and other double stars, God willing, in the coming months and years and will report back in due course.
It has been an absolute pleasure discovering the many charms of this little Newtonian. As telescopes go, there is something very endearing about their ingenious simplicity, and given half a chance, they can show you remarkable things.
As I write this, there are more encouraging signs that the prejudice traditionally attributed to Newtonians for this kind of work is being lifted and that is great to see! Just have a look at the CN Double Star forum to see some examples. I believe much of this prejudice is/has been due to the usual suspects: laziness, lack of interest, somewhat irrational, material attachment to other kinds of telescopes, and the like. You see, you don’t need a big vainglorious refractor (I should know, I’ve got one lol) to do this kind of work, and dare I say, one can actually derive a greater level of satisfaction achieving goals with these modest instruments over more traditional ones. You begin to see the hobby in a whole new light.
Thank you for following this blog.
Date: August 17, 2016
Time: 00:05h BST
Seeing: Excellent: I, excellent definition, fairly bright sky owing to very late gibbous Moon low in the south, gentle westerly breeze.
Instruments: 203mm f/6 & 130mm f/5 Newtonians, Baader single polariser.
Observation: The 8-inch reflector easily resolved Lambda Cygni B (0.9″), clearly seen at 450x and orientated at right angles to the direction of drift (E-W). Both components presenting as perfectly round and clean white. Deeply impressive!
The 130mm f/5 showed the system as plainly and strongly elongated N-S, power employed x325. Careful attention to accurate collimation necessary. Best evidence for the appearance of duplicity thus far recorded with this instrument.
Date: August 28 2016
Time: 23:10 BST
Seeing: Excellent (I), a bonnie evening, very steady, no clouds, no Moon, cool.
Instruments: 203mm f/6 and 130mm f/5 Newtonian reflectors, Baader single polariser.
After obtaining an excellent high power split of delta Cygni & pi Aquilae with both instruments, I turned the telescopes toward lambda Cygni. The 8-inch served up another clear split of the 0.9″ B component at 450 diameters, just like the evening of August 17. The 130mm, once again showed strong elongation (north to south orientation) at 325x and 406x, but was not split.
One of the ABCs of telescopic optics is that resolving power scales linearly with aperture and light gathering power with the square of aperture. These are fundamental facts that are demonstrably true and have been used productively over two centuries of scientific applications. And yet, all the while, there has been a consistent drive in the last few decades within a section of the amateur community that somewhat erroneously links performance to absolute monetary value. This largely corrupt movement is most ostensibly seen in the refractor market, where amateurs are apparently willing to shell out relatively large sums of money for telescopes that, in terms of performance, are severely limited by their small apertures. This is a worrying trend indeed, and has led many astray within the hobby.
In this capacity, I decided to highlight the anomaly by devising a simple test which exposes this ‘peashooter’ mentality for what it is; a gross misrepresentation of basic optical principles.
Materials & Methods:
Two telescopes were set up in my back garden; a 90mm apochromatic refractor retailing at £1017 (tube assembly only) and a 203mm f/6 Dobsonian, with a retail price of £289, but with some basic modifications (97% reflectivity coatings and a smaller secondary giving a linear obstruction of just 22 per cent) which increased its cost to approximately half that of the smaller telescope. The Newtonian was carefully collimated before use.
The telescopes were left out in the open air during a dry and bright evening when the temperatures had stabilised and were fully acclimated. Both instruments were kept out of direct sunlight. The refractor had an extendable dew shield to cut down on ambient glare, while the Newtonian was fitted with a flexible dew shield to serve the same purpose. To remove the complicating effects of atmospheric seeing, the telescopes were targeted on the leaves of the topmost boughs of a horse chestnut tree, located about 100 yards away.
Both telescopes were charged with approximately the same magnifications, in this case, a very high power was deliberately chosen; 320x. Next, the images of the leaves were examined visually, being especially careful to achieve the best possible focus, and the results noted.
The 203mm Newtonian images of the leaves were crisp, bright and full of high contrast detail. In comparison, the image served up by the refractor was much dimmer and a great deal of fine detail seen in the larger instrument was either ill-discerned or completely invisible in the smaller instrument. Though less dramatic, the same results were obtained when a larger refractor (127mm f/12) was compared with the 203mm f/6 Newtonian under similar conditions, with the latter delivering brighter, crisper images with finer detail.
This simple experiment, requiring nothing more than a few minutes of one’s time and no complicated formulae or optical testing devices, clearly showed the considerable benefits of larger aperture. The images served up by the Newtonian were brighter and easier to see than those served up by the smaller instrument. Resolving power and light gathering power work hand in hand; you need decent light grasp to discern fine details and vice versa.These results were largely independent of the surrounding atmospheric conditions, as the targets were located at close proximity to the telescopes and thus had to travel through a short column of air.
These experiments were repeated with larger instruments; a 127mm f/12 refractor and the same 203mm Newtonian, with the same results, that is, the smaller instrument runs out of light faster than the larger and shows less fine detail in the images served up.
These results confirm that larger aperture is superior to smaller aperture. No amount of claptrap can change the result either. Complications may arise when the same tests are performed on celestial targets, especially during bouts of turbulent atmospheric seeing, when the larger instrument will be commensurately more sensitive. In such instances, it is the environment that introduces anomalies. But when conditions are good, the benefits of larger aperture will be seen, clearly and unambiguously. Absolute monetary value has little or nothing to do with the end result, in direct contradistinction to what is claimed by those who promote small aperture refractors in an unscientific way.
See here for further reading.
As I have commented on in previous communications, an urban myth has been cultivated over the years regarding the unsuitability of Newtonian reflectors in the pursuit of double stars. In the last six months or so, there are encouraging signs that more people are bucking this trend using Newtonian optics of various f ratios and in the examination of pairs of various difficulty, including the sub-arc second realm;
These are but a few examples, and I can only hope that the changes will continue so that more people can enjoy this wonderful pass-time.