Ghosts in the Machine: the Astro-Tech AT111EDT...
Jun 13 2015 11:23 AM by jrbarnett
My NexStar 5 Journey
Jun 13 2015 10:29 AM by orion61
Review of the William Optics 102 GT
May 25 2015 11:22 AM by Perseus_m45
Review- Printing Astro photos on Metal with Bay...
Apr 16 2015 02:36 PM by ScenicCityPhoto
Categories See All →
- CN Reports
- User Reviews
- How to . . .
- Observing Skills
- Astronomical History
- Optical Theory
- Vision and Related Experiments
- How to Gain the Support of your Family for your Astronomical Pursuits
- Evaluation Tips
- Special Events
- The Elements
- New Articles in [!monthname!]
- Telescope Articles
- Submit a Review / Article
- Monthly Guides
- Behind the Scenes
- About Us
- Copyright ©
- Terms & Conditions
- Tiny Eyes on the Skies
- From the Editor's Desk
- What's Up . . .
- The Light Cup Journals
- Who is this Super Light Cup?
- Cloudy Nights T-Shirts
- Imaging Contest
- Small Wonders
- Previous Imaging Contest Winners
- This Month's Skies
- Mike's Corner
- The Cloudy Nights Friends and Family Discount
- Uncle Rod's Astro Blog
- Fishing for Photons
- Binocular Universe
- Article Submissions
The TAL-1: A classic entry-level Newtonian
The TAL-1 and why I chose it
When I moved to London a few years ago, I thought my interest in astronomy would be swamped forever (and not
only by the light pollution). After a while it became clear that not only were the stars over my part of London
occasionally visible, the sky sometimes had reasonable transparency and seeing. Not high altitude dry desert skies
you understand, just better than I expected. Encouraged by the lack of any serious objection from my wife, I resolved
to buy a scope and resurrect at least a bit of my student interest in observing the heavens.
Question 1 was: What scope should I buy? At this point I must confess 2 things. It has always been my ambition to own a large-ish super-scope, but now was not the time. Secondly, I love Russian optical equipment. My affair started with the massive ex-Naval bino-telescopes that were hauled out on to the lawn, artillery like, by my University astro society whenever a comet was about. Their sumo-style proportions and the romantic rumour that they were mildly radioactive "because they came from a nuclear sub" (but I think more accurately, it was to do with their lens coatings), just fed my imagination. Actually, now that I've stopped to think about it, were they actually Russian?! Anyway, they were superb, I believed they were Russian and as a result, over the years I've bought Russian monoculars, binoculars and a spotting scope for use in sports. Four instruments in fact, for a total of only GBP125 - not bad. I have directly compared my Russian optics with other instruments. Each of my instruments is more robust and optically, compares very favourably with non-Russian kit of at least twice the price.
So when I saw TAL telescopes advertised in the UK mag Astronomy Now, I was interested, especially when the TAL-1 was described by one retailer as "Britain's best selling 4 1/2" telescope". It is a Newtonian reflector with a 110 mm (4.3 inch) primary mirror and a focal length of 805 mm (f/7.3). This was sufficient aperture for my needs in a relatively short tube. It cost a mere GBP199 (including tax and delivery). Ideally, I would have gone for the 150 mm (6 inch) TAL-2 or motorised 2M Newtonian reflector, but it was rather more bulky (1200 mm focal length, f/8) and over twice the price. The bigger scope would be harder to transport and carry through doorways. This is not a trivial point, as anything that adds hassle makes one less likely to go out and observe. I searched the web and found generally good reviews on TAL telescopes. Some of these are accessible from the Novosibirsk Instrument-Making Plant's website: www.telescopes.ru/plant.phtml This is a fascinating source of information and includes a copy of the service manual. I also found some less favourable comments on the net (see the first review of the motorised TAL-1M on www.excelsis.com).
On balance, 3 factors made me decide to purchase the (unmotorised) TAL-1: (1) my favourable experience of Russian optics combined with TAL's generally good reputation, (2) my other commitments and lack of clear dark skies meant I was not going to use it very often, so it shouldn't be inconvenient, bulky or expensive, and (3) a smaller aperture meant relatively low magnifications and no need for a motor drive or the complication of organising a power supply.
If you're interested in geography and/or history, Novosibirsk is a Russian city due north of western China and India and at about the same latitude as Newcastle in England. Its population is over 1.4 million and it is the third biggest city in Russia. The Novosibirsk Instrument-Making Plant was founded in 1905, originally to manufacture military optics. It started making astronomical telescopes in 1980 and began production of the TAL-1 in 1984. This model was intended for more advanced amateurs. The mass production of these popular telescopes constituted an important milestone for Russian amateur astronomy, and they have been widely available in shops throughout Russia ever since. The disintegration of the USSR brought extremely difficult economic conditions for the factory. As military production was greatly curtailed, the factory was compelled to compete on the world market. In 1993 TAL telescopes began to be sold abroad, at first in England, then in other countries.
Unpacking, setting up and first light
This was fun and very simple. The scope arrived in a cardboard box the size of a suitcase in which the instrument was packed inside polystyrene blocks. Admittedly, I was disappointed not to see any Siberian birch ply boxes, which I had understand are present with other TAL telescopes. A good selection of optics and accessories is included: 25 mm Plossl and 15 mm Kellner eyepieces, a 3X Barlow lens, a 6X30 finderscope, a selection of coloured eyepiece filters, a plastic screen (with clips for paper) that attaches to the counterweight arm and an off-axis aperture mask, both for solar viewing by projection, a cross hair reticle which fitted the 25 mm eyepiece, a lens brush and cloth, various lens caps and a mount for attaching a camera to the counterweight arm (call it guided "piggy-belly" astrophotography if you like).
The finderscope has an extendable plastic dew cap, but oddly, no caps for either end. Raiding the fridge, I improvised with the lid of an old maple-syrup jar. Finding a cap for the eyepiece was not so easy and I ended up using an old film canister with a split in its side. The purple tinge on the lenses of the finderscope and Plossl suggested multi-coating. The Kellner and Barlow had a slight blueish tinge, but I was not sure whether this was due to lens coating or the colour of the glass.
It took me about 15 minutes to assemble the scope on its pedestal mount in daylight. I set the polar axis to my latitude and applied grease to the few parts that I thought needed it. Other parts were generally well-greased already. The rack and pinion focuser and each of the axes were smooth. Taking the scope outside, I looked through the 25 mm eyepiece at a distant chimney. The smoothness and steadiness of the mount appealed immediately. Optically, the 32X view was very good.
Targetting the excellent finderscope was very easy as it had clear cross-hairs and was mounted with hand-tightened screws fore and aft. I popped in the 15 mm eyepiece, but was disappointed with the slightly blurred 54X view and the lack of 'snap' when focussing. Taking the eyepiece out, I eyeballed the secondary. Sure enough, the collimation seemed a little out because the secondary was not in the middle of the focusing tube. I quickly tried the 3X Barlow lens with both eyepieces and disappointingly, also found the 96X and 161X images a little blurred. The image of a group of (microwave/radio?) aerials atop a tower-block building approximately 1 km away was also disappointing.
As my student observing was through large refractors I was unfamiliar with the collimation procedure. So I spent
some enjoyable time learning about it. The illustrations and instructions in Dickinson and Dyer's Backyard Astronomer's
Guide were very useful and I also referred to the section on "derangements" in the instruction manual.
The manual is readable and easier to understand than some consumer electronics manuals I've come across. However,
it is obviously not a "certified translation" from Russian. Like Bill Brady who reviewed the 6"
TAL-2 (on this website), I also wondered what "slushing" was and e-mailed the optical plant in Novosibirsk
to find out. I received a prompt reply explaining that it means "greasing". That's superb customer service!
However, in terms of literature supplied with the scope, the manufacturer has not really made full use of an excellent marketing opportunity. Why not include a brochure in the box on the rest of TAL's products? After all, the best customers are loyal customers.
Dickinson & Dyer's tip of making a collimating eyepiece out of a film canister was excellent. To this I
would add that pointing a torch into the telescope tube while looking down the focusser helps to provide a spatial
feel for the position of the secondary, but you need to experiment a bit. The diagram of the primary mount in the
manual did not make it easy to see which screws were set screws and which moved the mirror, but I figured it out
with a little trial and error.
Over the next few weeks, I went through the procedure 3 times, star-testing in between (see below). It was a process of refinement, until I was sure that I'd achieved the best alignment possible. In particular, it was a while before I was happy that the secondary was directly under and axial with the focuser.
Using the collimated telescope and star testing
Looking in daylight at the rooftop chimney and distant aerials again, I was struck by the remarkable effect of collimation. The image was much clearer and 'snapped' into focus. I could easily see the threads of a bolt at ~ 70 m and make out printed arrows and the words THIS WAY UP on one of the aerials at ~1 km. Estimating that this required a resolution of 0.5 mm at 70 m and 5 mm at 1 km, respectively, a quick back-of-the-envelope calculation suggested the resolution to be around 1 to 1.5 arcseconds. TAL quotes a resolution of 1.3 arcseconds and after astronomical observations, I have no reason to doubt this.
I am not an expert on the star test. Conventional wisdom appears to suggest that it should be done at resonably high magnifications (25-40 times the aperture in inches) and preferably without a Barlow. The TAL-1's highest magnification without a Barlow is much lower at 54X (about 13X the aperture in inches). Suiter's book suggests the use of a 33% obstruction mask, especially when trying to assess levels of spherical aberration. For my own education, I tried doing star tests in 3 conditions:
Condition 1 is in a sense, a reference condition. I made a cardboard mask to increase the obstruction to 33%
of the aperture. By the way, I did not use the off-axis mask for star-testing because it resulted in triangular
fringes (obvious, really). Polaris was used and the scope was properly pre-cooled to reduce tube currents. Usefully,
the mirror cell has a removeable plug to assist with this. My observations were as follows:
Condition 1: Without the mask or Barlow, at focus I couldn't easily see an Airy disc. Presumably this is because the magnification was too low. The image snapped through focus nicely, showing the star as a pinpoint of light. Slightly defocussing, I saw nice circular fringes inside and outside focus, but the fringes were more blurred on one side of focus.
Condition 2: I could see the Airy disk - a dot of starlight and twinkly thin fringes around it. The first ring was evident, but I couldn't quite tell if there was a second ring. In the defocussed image starting from the centre, there was the tiny central Poisson spot, very thin fragile rings surrounded by a thicker and brighter ring around the obstruction shadow, with further faint rings outside this thicker ring. The rings were reasonably crisp. On the other side of focus the image was more blurry. I could see circular rings and a central obstruction shadow, but it was all more fuzzy and distribution of light was more uniform than on the other side of focus. In all cases, rings were circular and concentric.
Condition 3: The image seemed very similar to condition 2, but the obstruction shadow was more noticeable. I thought that the shadow was around the same size at about two to three times the distance one side of focus than the other.
As I understand it, the results suggest no astigmatism, surface roughness or zones. As far as I know, this is not supposed to be a parabolic mirror, so one would suspect some spherical aberration. Guided by Suiter's book there seemed to be some undercorrection. By the test in condition 3, this seemed to be just on the edge of being acceptable. As far as I could tell, stars at the edge of the field focussed at the same time as those in the centre suggesting that the field is sufficiently flat. There was no discernible coma (I saw coma in the uncollimated scope). Overall, I would say the TAL-1 has acceptable optics. The Barlow does not seem to introduce any major defects.
According to Astronomy Now, the apparent sizes of Jupiter and Saturn were about 35" and 17". At 161X,
I could clearly see Jupiter's belts, glimpses of detail in them and of course, its moons. However, there were odd
ghost-like reflections in the field of view, one of which appeared ring like, and slightly smaller than the planet.
I found it easy to ignore these and they did not seem to degrade the image of the planet. Turning to Saturn also
at 161X, I could just see the shadow of the globe on the rings. Under good conditions, I noticed the dimmer outer
ring and the slightly brighter inner ring. Occasionally, I felt I could glimpse the Cassini division and some darker
areas on the globe.
Lunar views were clean and crip. Tonal shading and plenty of detail were comfortably visible. Again, I preferred the highest 161X magnification for this and there were no "ghostly reflections". One particular mountain looked superb, with a long shadow trailing off into the terminator. By this time, I was really pleased with the TAL-1.
Generally, I found the 25 mm Plossl to produce more contrasty image, with no ghostly reflections. However, in combination with the Barlow, I found it difficult to place and keep my eye at the right distance from the eypiece. In contrast, the 15 mm Kellner is much easier to use, but suffered from occasional ghostly reflections described above.
Finding the open cluster M37 in Auriga was harder than it would have been at a dark site. In contrast, finding the famous double cluster between Perseus and Cassiopia was easy, as it could be seen in the finderscope. Individual stars were resolved and the images were pretty, this time at the lower magnifications. I could see the trapezium in M42 in Orion, and the familiar nebulousity was evident. However, I'll have to wait til next year for better views, as Orion sets early behind the houses at my site! Roll on the summer, and my favourite globular clusters in Hercules, the ring nebula in Lyra and the Andromeda galaxy.
One of the nice touches to the TAL-1 is the ease with which it can be used for solar projection. I tried this using the off-axis mask and found it easy. Some detail could be seen in sunspots, but I haven't really tested it enough to find out if the dimmer faculae can be imaged.
Comparing the 3X Barlow and 15 mm eyepiece with premium quality optics
I compared the Russian optics with Tele Vue's 15 mm Plossl and 3X Barlow (these are part of my long term plan
to own a super-scope). The most obvious difference was the lack of ghostly reflections (see above) when observing
Jupiter and Saturn. Contrast was better in the TV combination - for example, the sky seemed blacker and detail
in Jupiter's belts was glimpsed slightly more often. The TV Barlow provided a significantly wider field of view.
Interestingly, during star testing and when observing double stars, I didn't really notice much difference between
the TV optics and the TAL's. Airy discs and fringes were apparent in both. Also, during daylight terrestrial viewing,
differences in image quality were less noticeable - the TV optics provided only a marginally clearer view.
The result of this comparison is that, of course, the hugely more expensive TV optics provided a significant improvement in optical quality. TAL's 15 mm Kellner is nevertheless a respectable performer and the TAL Barlow does its job reasonably well, especially when one considers the cost factor. Actually, the most remarkable feature to emerge from the comparison is that the Russian optics represent fantastic value.
Double stars with a Meade Astrometric 12 mm eyepiece
This is a SMA (Super Modified Achromatic) eyepiece. It is a modified Kellner and "fully coated", so hopefully would not suffer from the stray reflections of the TAL Kellner. With the 3X Barlow, magnification was 201X, just short of the useful limit for an aperture of 110 mm.
I took a high-power look at Castor (alpha Gem). It was beautiful! At 161X, the dot of the primary looked brighter and was well separated from the dot of the secondary. Each dot was surrounded by twinkling, fragile diffraction rings. At 201X, I measured separation and position angle of this double and also the similar spaced, but orange double Gamma Leo. My results were in good agreement with The Cambridge Star Atlas (3rd edition, 2001, W Tirion) which lists Castor as 68 degrees and 4.0" and Astronomy Now which cites the separation of Gamma Leo as 4.4". Clearly, the TAL-1 has the ability to detect this difference, though the random error in the measurement method is rather high. On wider doubles, like Mizar and Alpha CVn, I reckon the random error in measurement of separation using this eyepiece is about +/- 5%. I could also split Epsilon Bootes (2.8") at 201X. This was the first time I've seen this double and the colour contrast between the orangy primary and much dimmer pastel blue secondary was very pretty.
The scope comes with a cross-hair reticle, but this only works with the 25 mm eyepiece. Although the 25 mm in conjunction with the 3X Barlow (97X) could just split Castor, it would be much more useful to have a scaled reticle which fitted the 15 mm eyepiece. Given the military background of the Novosibersk plant, I'm sure they could do this, but it's a question of cost.
The scope is definitely usable for brighter objects at the 201X level of magnification.
Conclusion, Pros and Cons
I heartily recommend the TAL-1 to anyone on a budget looking for a small telescope. Looking at the competition, I can't see how one could do better for GBP199. It has numerous advantages:
- Quality exceeds expectations
- Steady and smart-looking mounting
- Adequate optical quality (especially when compared to the more expensive rubbish I've seen on display in camera stores)
- An excellent finder
- Ease of use
In short, it provides owner satisfaction (and everything that Russian optics are known for). On the minus side:
- Some spherical aberration
- Finder has no lens caps
- Lack of marketing literature and "glossy brochures"
- Reticle would be much more useful if it worked with the 15 mm eyepiece and had a scale
- Those "ghostly" reflections when looking at the bright planets through the 15 mm Kellner.
Could the latter be conveniently avoided by lens coatings? Presumably, TAL's main objection to fixing these
last items would be the cost. I am sure that most buyers could tolerate a small (say 5%) increase in the purchase
price and I wonder if this would be sufficient to enable TAL to fix these items.
The author has no connection with any telescope manufacturer. For the sake of fairness, he did send a copy of this review to the manufacturer in Novosibersk for their comments prior to submitting it to cloudynights.com. The author holds a degree and PhD in physics, but is now a lawyer specialising in technology and intellectual property law.