Jump to content

  •  



Search Articles


- - - - -

Taming a Tiger - My Experiences with a Tal 125R achromat.


Voice your opinion about this subject in our forums

Taming a Tiger - My Experiences with a Tal 125R achromat.

By Neil English

http://www.youtube.com/watch?v=1lyu1KKwC74

“Do not lay up for yourselves treasures on earth, where moth and rust destroy and where thieves break in and steal; but lay up for yourselves treasures in heaven, where neither moth nor rust destroys and where thieves do not break in and steal. For where your treasure is, there your heart will be also.

Matthew 6: 19-21

The Greatest Generation got to save old tires, dig a Victory Garden and forgo sugar. The Richest Generation is being asked to shop.

Margaret Carlson

My Siberian Tiger: the Tal 125R.

I hold a candle for achromatic refractors. I grew up with them, learned to see with them, used them faithfully through my twenties and thirties, and now in my early forties, I find them more appealing than ever. Indeed, there is something deeply compelling about well figured, durable, hard glass. That trusted combination of crown & flint served our telescopic forebears with distinction for nearly two centuries. From the balmy tropical climes of Brazil to the frigid wastes of the Russian Steppes, these telescopes have revealed all of the celestial treasures we amateurs keenly seek out today.

My experiences in the field lend me to believe that achromats are desirable in and of themselves. To my eye, they present uniquely beautiful images, faithful renditions of the cosmos that were actually experienced by our telescopic ancestors in ways that the modern apochromat user often fails to appreciate. Achromats are thus singularly qualified ‘time-machines’ that make a palpable connection with the telescopic heroes of the past in ways that are quite simply absent from the ‘garish beauty’ of the apochromatic image. Rare is the amateur who cannot learn a great deal from their colourful images.

But these sentiments are not just born from some sort of fatalistic (some have even said ‘delusional’) nostalgia. You see, despite the now ubiquitous appearance of those snazzy new refractors with low dispersion glass that have become the object of burning desire for so many contemporary amateurs, it pays to remember that not a single discovery has been achieved visually with them. Who can inform me of one object, an atmospheric feature on a distant planet perhaps, a lunar target, double star or nebulous patch maybe, that was not noted by our telescopic ancestors? The answer, of course, is no one can!

That fact alone alerts us to a noble truth. Those myriad dusty tomes from the rich lore of historical astronomical literature reveal that our love of colour pure observing in refractors is merely a cultural phenomenon and, thus can be unlearnt. We have become addicted to colour pure observing, intolerant of even modest amounts of secondary spectrum, and more believing of the bench test than the sky test. Like the Victorian obsession with sugar during the heyday of Empire, too many of us have developed an Über-sweet tooth and consequently find it difficult to imagine life without it. But there was life before sugar, and in many ways, we have been healthier for it. Stripped of much of its natural goodness, sugar is refined in a similar fashion to heroin and is almost certainly responsible for the alarming increase in the incidence of tooth decay in the 20th century, as well as contributing to the development of diabetes and ischaemic heart disease, two of the biggest killers in the contemporary western world.

Old Clothes & Porridge

Now, don’t get me wrong. I am not suggesting that ED refractors are bad for your health. But some of their users create a misleading impression, which exaggerates their powers. You won’t see any more with an apochromat compared with a good, traditional achromat. With patience and practice, your eyes will easily bridge the gap. Nor will you necessarily become a better observer in possessing the former. Expensive, fancy glass will not turn you into an E.E Barnard or a Reverend Dawes. Those Righteous Dudes were made of altogether different stuff to the majority of us.

Neither was the apochromat developed in response to some sort of mass outcry from the amateur community. As I have shown elsewhere, refractors with better colour corrected glass prescriptions were first produced in the late 19th century for photographic purposes and not as a result of the petitions from an army of visual aesthetes. And it is in this application that their sweetness shines through for sure.

Me? I’ve never had much of a sweet tooth, despite experiencing the views through a wide range of doublet and triplet apochromats from 60mm to 150mm. And with these thoughts in mind, I decided to return to old clothes and porridge, as it were, a way of life that would ‘cut my sugar intake’ to see where it would lead me. And that sent me harkening back to the land of the Czars.

I have spoken before of my admiration for Russian achromatic optics. Over the years, I have owned and used no less than five 4-inch f/10 Tal 100R telescopes and have been duly impressed by their consistently high quality. Assembled in the Novosibirsk Instrument Making Plant, Siberia, I have yet to encounter a lemon among them! Furthermore, after traversing the length and breadth of the country, and having being used to death by previous owners in the fickle British climate, they invariably delivered very satisfying views of Sol, Luna and bright planets with astonishing efficiency. And, as for double stars, these 4-inchers proved magnificent!

But there was another Tal refractor I had my eye on for many years. Larger than its 4” sibling, it sported a 5” (125mm) doublet objective with a focal length of 1125mm (f/9) in a uniquely tapered tube. Called the Tal 125R, this telescope was as rare as hens’ teeth in the UK and considered by many to be a modern classic. Owning one proved to be a pipe dream for me, as when ever a sample came up for sale, it was sold on to someone else within minutes or hours. But early in 2012, a unique opportunity presented itself.

Man bearing gifts

A fellow amateur astronomer and keen planetary observer based in the UK, described his experiences with a Tal 125R in a leading online astronomy forum. To cut a long story short, the encounter proved trenchantly disappointing for him. Looking at Jupiter and the Moon, the images were only useable at low power. Shocked by his descriptions, I felt there was something terribly wrong with the instrument. Warts and all though, I crossed the Rubicon and decided to contact him directly, with an offer.

Last year, I acquired a fine old Meade 127ED with great, colour-pure optics. I liked that ‘scope very much and indeed described my experiences with it in a CN review. But as good as that scope was, it didn’t set my mind racing quite as much as that ill-conditioned 5” Russian glass. I suggested we barter the instruments in a straight swap and to my glee, he agreed. So, in early February, my most excellent ED refractor went south and his big crown-flint travelled north of Hadrian’s Wall, to the heart of central Scotland.

First impressions

The instrument arrived on a cold, damp, overcast day. It was well packed in a nice, light-weight pinewood case. Opening it up, the instrument looked unscathed, a paragon of simplicity itself, with only a 6 x 30 finder scope, 2-1.25” adaptor, dedicated tube rings and a dovetail plate.

The 125R arrives in a light-weight, but secure pinewood case that can be easily transported from place to place. The tube is essentially identical to the smaller 4-inch model until it tapers out near the top to accommodate the larger (5”) object glass.

The instructions were entirely in Russian, with the serial number 1427 on the finder scope matching that stamped in the instruction manual. The instrument appears to have been made in 2004.

Just a sticker: the famous Tal logo.

Having to depart for European Astrofest on the following day, I only had a brief chance to check out the optics in daylight. Examining some pine needles on a distant conifer tree at low, medium and high power, I noticed nothing untoward until I switched to high magnifications. The images were soft alright and difficult to focus. Still, I was chuffed to bits with the acquisition, confident that I could resolve the problem. After all, why would a well respected telescope manufacturer outfit a very nicely made optical tube with a substandard lens? It just didn’t stand to reason, as the following photos show:

Well designed: the innards of the optical tube.

A blackened flint element to block stray light arriving obliquely at the object glass.

Looking up the tube from the focuser end shows that stray light is non-existent. The three spacers show the lens is working at its full aperture.

The nicely threaded all metal dew shield protecting the multi-coated air spaced objective.

The tres cool Tal 6x30 finder with helical focuser.

When I returned, I waited for the next available opportunity to test the instrument under the stars. But the heart is deceitful and that’s when the first reality check showed its teeth. Examining some bright stars at powers of about 100x, it was easy to see that the elements were horribly misaligned, creating hopelessly comatic images. And, to cut a long story short, while I was able to make significant improvements myself, I suspected there was a problem with the spacing of the elements. So, I entrusted the help of a professional, Es Reid, based in Cambridge, who enthusiastically agreed to have a look at the cell for me. He confirmed my suspicions, s****ed the spacers clean and replaced one that was overly thick. In addition he placed some softer brass tips on the bare steel centring screws.

When the cell was returned to me, it star tested fine, requiring only one, minor self-adjustment to achieve perfect collimation and squaring on with the tube.

Es confirmed that the object glass was slightly over corrected but had a nice, smooth figure. Star testing in the field echoed his assessment. Using a light green Wratten #23 filter, I estimated the figure to be marginally better than the ¼ wave standard, maybe about 1/5th wave ptv at best. The extra-focal rings were unusually clean though, with little in the way of diffused light between them. That’s a sure sign of a very well polished optic. Overall a good result for a 5” f/9 achromat!

The Land of Milk & Honey

The sky is littered with sights that nourish a curious mind. I began my evaluation of this instrument towards the end of February but the Lion’s share of my impressions were conceived beginning mid-March 2012, when an enormous, high pressure bubble ensured that nearly every evening for the following fortnight was attended by the most innocent blue sky at sunset. Indeed, in the last week of March, Scotland basked in swelteringly high temperatures, the likes of which were not seen since 1957. Eyes wide open with hope, into that sky I aimed my Siberian Tiger. What follows is a distillation of my experiences.

Planetos: The Spring of 2012 was an exceptional time to watch the planets and though not a diehard planetary observer, I spent the early evenings, observing Jupiter and Venus, followed later in the night, by vigils of Mars and Saturn. I started in twilight and with Venus, when the air can be tranquil for a phase. Using my 7mm eyepiece yielding 161x, I centred that intensely bright hot house world in the finder and then had a look. It was amazing! The Cytherean phase was weakly gibbous, intensely white and sharp, surrounded by the most gorgeous halo of blue light. To my eye, that unreal halo didn’t seem to harm the image. Indeed, I was so moved by the experience, I dragged my wife and sons out for a look. It brought a smile to all their faces.

Jove, often located within a few degrees of the Evening Star, was even more impressive. The disk was sharp and replete with a wealth of atmospheric detail. The SEB was very active, and the telescope was able to easily resolve filamentary details within its borders. Several fainter bands, some very fine, were observed at higher and lower latitudes and his polar regions were distinctly shaded. The giant planet was surrounded by a rim of unfocused blue light but, yet again, I did not think it degraded the image in any critical way. It was plenty pretty enough! What’s more, comparing the view to a top class 4 inch refractor set up along side it, I judged that more detail could be resolved with the extra aperture, despite the slightly crisper images rendered by the smaller instrument.

A very good planetary scope!

With a 13” Mars transiting later in the evening, many opportunities afforded themselves to assess the quality of the images garnered by the 125R. On average nights, with noticeable turbulence in the atmosphere, I felt 225x was about as high as I could push the instrument. The planet was surrounded by a reddish glow which seemed to choke off some of the surface details. On such nights, I resorted to using an age old recipe for improving the view of the Red Planet. By inserting a light green Wratten filter, the glare was reduced and I was able to better see the polar regions, demerara deserts and bright morning mists on the planet’s limb. On the best nights though, which were often hazy and cold, the images of Mars could be very good indeed and didn’t seem to be improved by filtration. On these nights, I could press the highest powers (~280x) into service more productively.

Saturn was not as well placed during this apparition, owing to its very low altitude (not much beyond 20 degrees for much of the night), but on the best nights, sometimes well after midnight prior to opposition, I observed a beautiful butterscotch world using powers up to 225x, with the Cassini Division clearly on show, as well as many subtle atmospheric features on the planet’s globe. God knows how beguiling it might have looked had it been placed higher up in the sky.

Sol Invictus: On the afternoon of March 30, Aeolus began to exert his power once again, sweeping a gentle polar wind along the valley, capping the temperatures more effectively than the breeze-free days preceding. Yet the sky remained resolutely blue, with not a cloud to be seen from horizon to horizon. What a perfect time to engage in some daylight solar viewing! So, I ran upstairs and fumbled around in an old, dusty box hidden under my bed until I retrieved an inexpensive white-light solar filter made with Baader AstroSolar material. Carefully securing it over the dew shield, I aimed her at mighty Sol. Using a 18mm ocular, I ‘discovered’ a giant sunspot near the centre of our yellow dwarf star. The biggest one I had ever seen! Resolution was excellent. Like some giant, benign, melanoma, I struggled to remember which part was which. Was the brighter region the Umbra or Penumbra? Who cares?

Inserting a higher power eyepiece, delivering 125x, I could make out much fine structure; granulation in the photosphere and a ‘loftier’ view of smaller, fainter and more fragmented sunspot groups on the limb of the solar disk.

The 125R is a dapper solar scope!

Luna: On several evenings in late March, I trained the Russian 5” glass on the waxing crescent Moon, following her changing aspect right up to First Quarter. The evening of March 26 presented one of the most resplendent celestial apparitions I have witnessed in recent years. Selene, bathed in glorious earthshine, hung in the sky above the conifers that mark my western vantage and just a few degrees to the East, the goddess of love shone with an intensity seldom seen. And mighty Jove, rendered truly inconspicuous in comparison, was sinking fast into the dense turbulent air below them. I set the great glass up in the early evening with the express intention of showing my students some close-ups of that extraordinary conjunction. As they arrived and left, I trained the instrument on the Moon, inserting my trusty 18mm ocular. Almost filling the field of view, they each enjoyed an awe-inspiring spectacle, with the crater-scarred bright phase contrasted against a swathe of lunar dark. I think I converted a few souls that evening!

A few days later, on the evening of March 29th, Luna loomed much higher in my evening sky. Setting up after work, I showed my brother in law, who was visiting us at the time, the majestic Apennine Mountain Range at 225x, and the eerie shadows cast by its tallest peaks. We followed the shoreline of the Sea of Tranquility and tracked down the Apollo 17 landing site, nestled in a minor ‘glen’ at the foot of Mons Argaeus. He was most taken though by the vast wilderness of the Southern Lunar Highlands and the wealth of high resolution detail visible way up north, inside the craters, Hercules and Atlas.

The same night, I returned to my box of tricks and pulled out a dusty T-adaptor that allowed me to mate my beat-up old DSLR body to the optical tube. Focusing as best I could, I used a remote control cable to make a series of bracketed exposures of the lunar countenance. Having dabbled in astrophotography many years ago, I was genuinely surprised by how quickly the ways of that dark art came flooding back to me.

Single shot at f/9 prime focus using a Canon Digital Rebel. ISO 100, 1/150th sec exposure.

Deep sky: As wonderful as astrophotography is, it cannot pretend to capture the fire and the life of the stars that only visual observing can deliver. I spent an evening round New Moon, exploring the vast open country of the deep sky. With gay abandon, I stuck in my inexpensive 40mm Antares Erfle, yielding a very expansive, near-on 2.3 degree field at 28x. The Double Cluster in Perseus on this mild March evening was glorious. I plied the vacuous wastes of the Alpha Persei Association and moved southward into Auriga to visit the beautiful ‘wild flowers’ of M36, M37 & M38 at low and medium powers. I finally ended up 'lost' somewhere in Gemini but managed to find that magical spot on the northern foot of the Caelian Twins, staring for God knows how long at the inky black skies surrounding the sprawling archipelago of stars we sky gazers revere as M35.

At f/9 my 40mm Erfle delivers crisp, high contrast views across a 2.3 degree field.

Taking a break, I ventured out again in the wee small hours to seek out a special cluster of stars, known prosaically as M13. My astronomical friend, John Nanson, an evangelical double star observer from North-western Oregon and co-founder of that fantastic online resource for fun-loving double star junkies (http://bestdoubles.wordpress.com/) suggested I take a look at it through the 5 inch glass. Now only about half way up the sky, just a couple of hours shy of dawn, I sought out the fifth magnitude fuzz in the Keystone of Hercules. Inserting a 7mm eyepiece yielding 161 diameters, I was greeted by a beautifully sharp bauble of starlight. John was dead right about this great globular cluster! It presents a unique view in a refractor of this aperture class; far more satisfying than any 4 inch ‘scope can deliver and approaching that of the more compelling views seen with a larger light bucket, such as a 8- or 10-inch Dob.

This telescope, as I expected, excels at ferreting out double stars. Its decent aperture, good optical figure, and the superior thermal properties of crown & flint over modern low dispersion glasses, make it difficult to beat in the field. Indeed, this instrument enabled me to indulge in my singular passion; sweeping the sky at high magnification (225x), examining all bright stars for faint companions. Under favourable conditions, eye & telescope harmonised to resolve a host of tricky pairs, but for the record, I have used the instrument to cleanly resolve;

Alkalurops (2”)

Xi Ursa Majoris (1.7”)

Porrima: 1.5”

32 Orionis: (1.2”)

I tested the Tal 125R out on other systems noted more for the large magnitude differences between the pairs than their separation. Delta and Kappa Geminorum, near twins in my estimation, were cleanly resolved at 225x. When I consulted Haas’ text on double stars, I was delighted to read her account of Kappa;

“The data suggest a brilliant star with a small companion. It's harder to resolve than the data suggest. 125mm has repeatedly failed to do so."

Another system, Theta Aurigae, which often proves problematical for backyard observers, was split with impressive frequency with this glass (six out of seven successive nights).

Finally, on the last day of March, after a solid week of trying, I finally bagged my nemesis, the companion to Propus (Eta Geminorum) in exceptionally good seeing conditions. It was a colder day than the ones that preceded it and thus, I reasoned in retrospect, the land had less thermal energy to radiate. I began observing in twilight (20:45BST) Using my 4mm orthoscopic eyepiece (281x) I detected a faint spark just resolved from the ochre primary in the 8 o’ clock position. It was visible intermittently throughout 15 minutes of observation. Let me tell you; Propus ought to have been named the ‘demon star’ because it is an exceptionally difficult system to crack with modest apertures. My previous attempts using other 4- or 5” refractors (with or without ED glass) have, more often than not, ended in complete failure.

The trickiest double stars require good optics and accurate focusing for best results. The Spartan 2-inch rack and pinion on the 125R is a bit course, but with some practice, works well.

Some amateurs have claimed that the secondary spectrum thrown out by an achromat would 'drown out' such faint members. But that conjecture simply had no basis in reality. I believe it's just another logical construct, a solipsistic 'deduction', unsubstantiated by actual time spent at the telescope. Moreover, history silences those egregious ‘conspiracy theorists’. For example, the celebrated double star observer S.W. Burnham, discovered the companion to Propus in 1881 using an achromatic refractor that showed considerably more false colour than my humble instrument!

Playing to Pay

I hope this article will give you a flavour of what can be achieved with a good, medium focus 5” achromat. And though I may have portrayed it as such, there is, I believe, nothing intrinsically superior about this Tiger, forged as it was from the ice and fire of a Siberian telescope factory. I look back with fondness at the sterling views I enjoyed through a good Meade AR5 of Chinese origin several years ago. And more recently, I have put another Oriental incarnation of the 125R through its paces. Though one unit showed some astigmatism when pressed to high power, a replacement sample revealed none and indeed displayed slightly better spherical correction than the Tal, yet its glass was polished less well than its Russian counterpart. In focus though, I felt there was little to distinguish the views between the instruments, particularly on mild evenings.

What about other 5” f/9ish achromats?

That said, the modest over-correction of the Russian lens actually helps when temperatures are falling, as a lens that cools is naturally under-corrected, so they tend to cancel each other out. Indeed, I have noticed that the 125R marginally pulls ahead of its Chinese counterparts on the coldest nights, where the latter seems to struggle more at the highest powers. Since there are many nights here in Scotland where the temperatures continue to drop throughout an observing run, I consider this ‘defect’ to be a boon. Serendipitous? I don’t know (n=1). But Russia is known for its extremely harsh winters!

It is my belief that this particular class of achromatic refractor represents one of the best deals in the hobby. Even good ones are fairly inexpensive. They are powerful without being cumbersome. They cut deeper than the finest 4-inchers out there and cooperate even in so-so conditions. You could say they are wholesome all-round ‘scopes. Indeed, if I had to own just one telescope, a 5” f/9 achromat would be near the top of my list.

On paper, my humble 125R might be worth a few hundred dollars. But add a zero for the joyous views it delivered. Add another zero and you just might begin to understand why I have gone to the trouble of adopting her as one of my own. So, without further ado, I’d like to introduce you to Tonya, a Russian appellation which means “faithful companion.” Despite the traumas she undoubtedly suffered in a previous life, there is nothing bitter about this honeymoon spyglass from the banks of the River Ob.

My faithful and ebullient companion, Tonya.

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

His sister book on Classic Telescopes hits the shelves in the summer of 2012.

More wholesome stuff

Is Sugar Killing You?

http://www.dailymail.co.uk/femail/article-489613/Is-sugar-killing-you.html

“My Astro-Physics Traveler”

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4618465/page/38/view/collapsed/sb/5/o/all/fpart/1

An inconvenient truth about small achromatic refractors: Stranger than Fiction:

http://www.cloudynights.com/item.php?item_id=2529

Why old glass did so well; a case study;

http://www.cloudynights.com/item.php?item_id=2667

A great place for friendly double star enthusiasts (Prigs not permitted);

http://bestdoubles.wordpress.com/

Don’t take my word for it! Have a look at what other folk think about 5” f/9 achromats and form your own consensus.

http://irwincur.tripod.com/meade_lxd55.htm

http://www.cloudynights.com/item.php?item_id=941

http://www.excelsis.com/1.0/entry/apogee-127/1140-12-503.html

http://www.excelsis.com/1.0/entry/burgess-1278-12-546.html

http://www.excelsis.com/1.0/entryvotes.php?sectionid=12&entryid=360

http://www.excelsis.com/1.0/entry/photon-127mm-f9-refractor-12-135.html

http://www.cloudynights.com/item.php?item_id=1284

http://www.cloudynights.com/item.php?item_id=1298

http://www.cloudynights.com/item.php?item_id=751

http://www.cloudynights.com/item.php?item_id=978




0 Comments



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics