The ‘Foot’ ‘Scope Project

Fintry, July 2017.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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.

Larger than life: the Revelation 12″ f/5 Dobsonian dwarfs Plotina, my ultraportable 5.1 inch f/5 reflector (shown on the left).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 primary mirror as received. Note the milky appearance due to a thin layer of fine dust on its surface.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A sudsy mirror.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There we go; a nice clean mirror ready to reinstall 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.

The Revelation dual speed focuser; an excellent addition to an economical telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

The oversized knobs on the primary make precise adjustments child’s play. The previous owner installed stronger springs to better hold the cell in place.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

The 12″ f/5 Newtonian awaiting maximal darkness on the evening of July 8 2017.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

Temperature: 10C

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)

Plotina(left) and the 12″ f/5 field tested side by side.

 

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!

General Commentary:

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(18931958).

pp 86

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.

Bob’s Knobs replacing the generic screws on the secondary.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Looking good tonight for clear spells.Fingers crossed!

The 12 inch awaiting darkness.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 23:20 BST

Temperature: +15C

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!

14:50 BST

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.

pp 57

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.

Temperature: 14C

 

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.)

pp 135

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.

00:48BST

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

Doing the night shift ken

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 23:18 BST

Seeing; Ant II, partially cloudy, brisk westerly wind

Temperature: 13C

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 original flat elliptical mirror in its plastic housing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

My dream ‘scope: Octavius, a simple 8″ f/6 Newtonian reflector.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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!

Time: 23:00BST

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

Octavius; carrying on the subarcsecond project.

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.

A rather specialised ocular: the 2mm Vixen HR.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

Proverbs 6:6

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;

  1. What is really meant by a subarcsecond night?
  2. Are the results obtained thus far the result of special seeing conditions?
  3. Is the complete lack of such sustained observations of this kind on the various double star fora attributed to good old fashioned laziness?

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

Gaius(laevo) et Octavius: fratres aeterni.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

Tiberius (laevo) et Octavius: fratres aeterni.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

Temperature: 12C

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

Temperature: 13C

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.

Dream machine, ken.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 22:30UT

Seeing: II/III. Almost a carbon copy of last night but with no cloud.

Instrument: 20.4cm f/6 Newtonian

Temperature: 12C

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.

Time: 22:48UT

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

Champion ‘scope; Octavius.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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!

Temperature: 12C

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

Temperature: 12C

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!

 

The newly coated and edge blackened secondary on the new supporting structure.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

Temperature: 13C

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

Temperature: 13C

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.

Temperature: 12C

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

Say, that’s a bonnie lightbucket oot me back gairden, ken.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

Temperature: 15C

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.

Time: 22:00UT

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.

Time: 22:45UT

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

Lone Ranger….ken

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

Satis.

 

De Fideli.

 

6 thoughts on “The ‘Foot’ ‘Scope Project

  1. Dear Neil,

    Again a very interersting work! Looking forward to read the next steps.

    May I afford two questions:

    – how convenient are the GSO alt az movments compared with your 8″ dob?
    – you wrote that the dual speed focuser is really appreciated on your 12″ ; do you feel it will be an asset on a 8″ too (or the f6 ratio makes it less necessary) ?

    After having intensely used a 130 newtonian and having carefully read your articles, I plan to buy a 8″ Dob actually. Cheap astronomy has never been so fun!

    Many thanks,

    Sas

  2. Good evening Sas,

    Thanks for your post.

    Yep, having piles of fun with a good but inexpensive ‘scope!
    I don’t think you could go wrong with the 8 inch Dob. It’s the perfect all round telescope since it does everything very well indeed.
    The 12 inch was a real bargain though but it’s much heavier to haul about. Truth be told, unless it were a truss tube design, it’s the largest telescope I’d be comfortable working with, but I’ve already been shown how larger aperture trumps smaller aperture when conditions allow. I would like to know how often those conditions come about.
    The bearings appear very similar and the gentleman who had it before me has clearly adjusted the azimuth tensions to make the motion very smooth. High powers are quite easy to handle. The Skywatcher altitude bearings are a wee bit easier to move but there really isn’t much in it.
    The 10:1 focuser is a great addition. It’s not essential but nice to have nonentheless. At f/6 it’s not really necessary (and I have no plans to upgrade it) but as the ‘scope gets faster (< f/5), it becomes a very desirable attribute. It's just great fun being able to tweak the focus ever so slightly before letting the image settle down as it moves across the field. Away out for another gander. Best wishes, Neil.

  3. Hello Neil,

    Lovely to read your reports of your 12″ F/5 dobsonian. You are certainly pushing the high powers with the scope and it seems to be responding very well indeed !

    I have had my 12″ Orion Optics F/5.3 dobsonian for a couple of years now and find it my most used scope despite the others being rather nice refractors.

    I do tend to use the refractors more than the dob for double star viewing but spurred on by your writing, I’ll be sure to remedy that over the coming months.

    Best wishes,

    John

  4. Good afternoon John,

    Thanks for your message. My experience with big Dobs is much more limited than yours. I tended to dismiss them for double star work. But there’s a lot going on at the moment. There’s a guy in the CN double star forum called ‘Nucleophile’ ( Mark McPhee), who is doing extraordinary work with his 8 and 15 inch Dobs. I think it’s a very exciting time and I’m hoping more folk will take up the challenge and see the results for themselves.

    Best wishes,

    Neil.

  5. Hi Neil,

    I’ll have a look at what Mark McPhee is up to – sounds interesting !

    Nice skies here tonight (for a change !) so I’ve been trying my 12″ dob on some doubles and the results are very good. I’ve found the Baader Classic Orthoscopic 10mm and 6mm very good eyepieces for this purpose with low scatter and crisp views. Pi Aqulliae (one of my favourites this time of year) is really well defined and even the normally challenging Lambda Cygni shows a clear split.

    Hope you get some good observing where you are as well !

    Regards,

    John

  6. Evening John,

    Thanks for giving this a try. You don’t know how much it means to me for others to give this a go! Would be very interested to see how regularly you can split Lambda Cygni with your 12 incher.
    You know, my favourite eyepiece is a 6mm Baader classic ortho too, which delivers 200x with the 8 inch. I like the slightly larger field of view compared with the original incarnation. With the 2.25x screw on Barlow, it gives 450x, which I have been using but found that switching to the 2mm Vixen HR (which has a built in Barlow) gives the greater power of 600x. But these eyepieces have issues; the field of view is tiny (only 42 degrees; that’s tough at 600x) and they don’t accommodate filters. I’m thinking of switching to a good 3x Barlow to allow me to use the 6mm ortho again.That’ll create a significantly wider field at the same power, making manual traking that little bit easier.

    It’s a great night up here; absolutely rock steady. I’m away again to cruise the summer Milky Way at 30x.

    Thanks again for your report and I hope the skies continue to cooperate with you.

    Best wishes,

    Neil.

    Ps. Mark McPhee’s work is truly inspirational. Living, breathing proof of concept I’d say!

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