Jump to content

  •  

- - - - -

TMB92SS with FeatherTouch Focuser


Discuss this article in our forums

The TMB92SS, now this is a telescope I can get excited about! Perhaps I should say right up front that I love this telescope. It is not without it’s drawbacks though, so please read on. I purchased the telescope from the wonderful folks at Astronomics with the Feathertouch focuser. The TMB arrives in an Astro-Tech style fitted aluminum case containing high density foam. The telescope itself is incredibly compact but a bit heavy for its size - this has been described in detail elsewhere (see the recent Sky & Telescope review article). When I first lifted it from the case, I was actually very surprised by the sheer mass of it. Due to this weight, I was at first a bit reluctant to use it on my AT Voyager mount. But, having purchased a quality dovetail bar which allows for good balance adjustment, I find that even with a heavy eyepiece such as the Nagler 31mm, the Voyager will handle it nicely.

On the night in question I had the Voyager on my concrete patio, probably the worst-case test for a mount in terms of vibration isolation. It settled in 2-3 seconds from a firm bump on the optical tube and although some vibration is apparent during focusing, with care and by using the fine focus knob on the Feathertouch one can get a perfect focus with little effort or vibration.

I use the TMB92SS as its own finder at 27x with a 19mm Panoptic. One might be better served by using a somewhat longer focal length eyepiece but in keeping with the grab n’go concept, I chose to use only the following three eyepieces; 19mm Panoptic, 11mm Nagler, 7mm Nagler, and the 2x Televue Barlow. Basically I can throw these in my pocket or put them in a tripod tray and I am not burdened by a lot of equipment. A red-dot finder can be a real useful tool however, and I have the AT version I intend to mount eventually. My only issue is that the finder must be removed before storing or transporting the telescope in its case. One more thing to do that gets in the way of grab n’go.

I will not comment in this review about the optics of the telescope, I am not an optician, nor am I trained to evaluate telescope optics, and further I feel that these discussions tend to be meaningless for the most part as I am not interested in AP or the various subtleties of optical physics. For visual use, an instrument either works for you or it doesn’t. This one works! The one thing I will say is that as others have attested, it is simply color-free even at high power and on bright objects. Perfect, crisp, contrasty images. Lovely. Snap-to-focus made even more pleasurable by the remarkable Feathertouch focuser.

Which reminds me, I cannot say enough about the Feathertouch focuser. Silky smooth and of course it will hold some weight. No problem with a 31mm Nagler. I suspect it will hold whatever eyepiece/Barlow/Powermate combination you’d ever care to attach without any problem at all.

Sidebar: TMB92SS with the 31mm Nagler. This combination is, in my humble opinion, simply one of the most remarkable combinations in portable telescopes available today. The widefield views (5 degrees at 16x) simply have to be experienced to be believed. This scope and eyepiece give one a celestial window through which to experience the Universe that is, quite frankly, breathtaking in extent. The winter clusters in Auriga are unbelievable. The region of Orion’s belt is just incredibly rich and one can spend hours there. I cannot wait until Sagittarius and the North America Nebula complex in Cygnus are high in the summer sky to use this combination in their exploration from a dark-sky site! In my opinion, the TMB92SS and the 31mm Nagler compliment each other perfectly. Both are somewhat spendy, but hey how often do you get the chance to really experience the Universe up close? It’s worth every penny. My only issue with the whole setup is that the 31mm Nagler tends to reveal my astigmatism quite obviously. This most likely is due to the large exit pupil. As a result, you may find it necessary or desirable to use a corrective lens. I find I can comfortably view with my glasses or use my left eye which is not astigmatic.

Last night the transparency was incredible and of course the seeing wasn’t….but I did get out for a couple of hours with the TMB92SS setup as I described earlier. I decided to have a quick look at M35 in Gemini while it was still above the neighboring rooftops and hills. Wow, what a jump up in detail and resolution from my 66mm refractor! This always remarkable cluster was…well….remarkable! M35 has that curious way of revealing more and more the longer you observe it, and tonight was no exception. A large number of stars were resolved. An interesting feature not apparent in photographs of M35 is the dark heart of the cluster. O’Meara sees two dark areas, but I felt there was a single dark center. This effect is pronounced in the TMB92SS for whatever reason. At its southwest edge lies a pointer or “arrowhead” of stars showing the way to M35’s tiny companion cluster, NGC2158. At mag. 9.0 or so, NGC2158 is difficult in light polluted suburban skies. Fortunately, my western sky is less impacted by the light pollution dome. Using averted vision, NGC2158 was readily visible in a 92mm instrument in both the 11mm Nagler at 46x and in the 7mm Nagler at 72x! I think it was actually better in the 11mm however. I have never been able to observe this elusive cluster from my yard in anything less than a 6-inch refractor and I dare say the view of it last night in the TMB92SS approached that in the CR150 refractor. This from a suburban backyard with all its light pollution, yard lights, etc., a testament to the quality of this instrument and the incredible contrast possible from small aperture apochromats. I really need to complete my sketch of these two objects as hopefully that way I can capture the essence of the experience. Wow, I was dumbfounded and spent a lot of time with these two objects. What a wonderful experience!

While time permitted, I decided to scan over into Auriga. I’ve found I can sight along the tube and from experience I can usually wing it with good accuracy to the location of the three incredible winter clusters, M36, M37, and M38. I usually observe these clusters with wide fields and low powers but tonight I took a little time with each and examined them at higher power. Many folks recommend a sweet spot in the eyepiece focal length for a scope that is twice the f-number in focal length. I believe that to be true for the TMB-92SS as the best views were obtained with the scope through the 11mm Nagler eyepiece. Makes me wonder what the view would be like with that new 10mm Ethos in the TMB?? Uh-oh, I fear I may have to try this! This scope is so remarkable it is worth using the expensive glass. M36, a fairly sparse cluster was well resolved. Its neighbor M38, a little larger and a bit fainter also well resolved and crystal clear (it was a remarkably transparent night). I now regret not having conducted a diligent search for its companion, NGC1907. I’ll bet it is visible. That will be my project next time I get out but it had better be soon as Auriga is disappearing in the west quickly. O’Meara feels NGC1907 is particularly susceptible to light pollution and hence is not visible even in larger instruments from urban areas. From my suburban backyard, maybe.

The main reason I forget to look for NGC1907 is that I usually cannot wait to get to M37 the showpiece of winter clusters. It is incredibly rich and compact. M37 rates higher for me than even M35 with its companion cluster. I threw a little power at it, 46x and 72x, and in the TMB, M37 will take some magnification well. But I prefer to view celestial wonders for the most part in their “setting” in the sky so I default to those wide field lower to mid-power views. Here again the TMB excels with the 11mm focal length Nagler, approximately twice its f-number of 5.4. But the 19mm Panoptic provides that panoramic view that I am completely addicted to! (However, please do see my sidebar note on the 31mm Nagler….).

I think this gives you some general idea for the performance of this scope on brighter deep sky objects and a faint fuzzy (NGC2158) as well. I was tempted, but did not go galaxy hunting in Leo and Ursa Major. Next time, I promise! Moving through Leo along the ecliptic last night was Saturn. I put in the 19mm Panoptic and, whoa! There it was! Gotta go for higher power…in goes the 7mm Nagler at 72x. Saturn was, well, breathtaking. Okay, I keep using that same adjective over and over. But truly the view was awesome. Razor thin rings, ring shadows, and subtle shading were all evident along with some moons popping in and out of visibility with the seeing. With the 2x Barlow at 144x, WOW! Again, in those moments of steady seeing, the rings appeared just razor thin. Obvious moons, and the same subtle shading detail on the globe. I am not a planetary observer but I will return to Saturn in the coming weeks with this scope. And a note about the AT Voyager mount at 144x; quite stable, actually, but I now use a GEM for most of my observing with the TMB92SS.

At this point I could not resist having a look at M13, the great globular cluster in Hercules. Bathed in urban light pollution low in the Eastern sky, I didn’t expect too much. But much to my surprise the cluster was actually quite pleasant. Teetering on the verge of resolution, its myriad stars seemed to me as perfect as I have ever seen them. A little magnification helps in reducing the background skyglow and here again the TMB92SS showed excellent performance. A bit hard to judge given the circumstances and it only served to whet my appetite for a truly dark-sky view of M13.

The TMB92SS combined with quality eyepieces and a simple alt/az mount will make a very nice grab n’go setup for anyone whether your interest is planetary or deep sky. But I must admit its short 500mm focal length does not lend itself to planetary viewing all that well. By the way, first light with this instrument was during a nearly full moon. In that 19mm eyepiece the moon was an incredibly detailed cream and jet-black surface that appeared to be 3-dimensional. No false color anywhere. And, while I did not use high powers, I can’t imagine that performance would degrade at all. One of my other telescopes is a TV-101. And, while the TMB is not its equal in aperture, it may very well be its equal in performance. Perhaps I should do a side-by-side comparison one-of-these-days.

I understand a TMB92SS light model is available with a lighter-weight Crayford style focuser. Why anyone would not want to go the extra and get the Feathertouch is beyond me, even if you only plan as I do, to use it visually. The Feathertouch is that good. Next for me will be a binoviewer and a second 19mm Panoptic (or a pair of 24mm Panoptics). The scope has a removable section allowing it to reach focus in a binoviewer at low power without the usual required Barlow lens. That’s how I will enjoy the summer Milky Way!

I am now using the TMB92SS on a Vixen Great Polaris Mount, and it has become my grab n’ go setup. I can haul the telescope and mount with counterweights attached outside in one trip, put a couple of eyepieces in the tray and I am ready to observe just that quickly (with a bit of cooldown time…) It’s truly a wonderful telescope!

Summary:

Pros: Perfect, contrasty images.

Portable for grab n’go.

Feathertouch Focuser.

Cons: It is heavy for it’s size.


Thanks for reading this far, Clear, Dark Skies!

Tom Nirider





  • Scott Beith likes this


0 Comments



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics