Pirich's Full Review: Televue Evergreen GXC-3370 Telescope
The Televue scopes have, perhaps more than any other make, brought high quality refractors to the world. The Televue 85mm scope comes in evergreen, ivory, and polished brass. The telescope comes in ivory and evergreen (and I have used both), just with different paint on the outside, but are listed as separate items. Televue TI33370 and TG33370 are the same telescope except for the color the outside of the tube is painted. These are not cheap telescopes, as I am sure anyone looking at this review has seen. The real question is: is it worth it? Especially since the introduction of the comparable Celestron 80ED refractor, #52280, the price to value question for this telescope has been thrown open. More general information on getting a telescope is in my article on Picking a Telescope. To address that question, I have written this review in sections:
Background
Description
Performance
Summary
Background
The apochromatic refractor is a descendant of the early telescopes used by Galileo and Cassini to do the first astronomical observations. The refractor operates by bending light to concentrate light to produce an amplified and magnified image. Unlike reflecting telescopes, which bounce light in a process independent of the color of light, refractors use refraction, which bends light according to its wavelength. As a result, a lens from a single material will bend colors of light differing amounts depending on their color. Red light will therefore come to a different focal point from blue light, and all the colors in between will focus at different points. This makes the image look like it has colored halos when it is in focus. This effect is called chromatic aberration.
The most basic strategy to reduce this effect is to stop down the lens with a large baffle. This technique only uses the very center of the lens, which bends light the least. This is often found in cheap telescopes of the type one finds in a department store. The problem with this approach is it sacrifices the light amplification the larger area had as well as the higher resolution of the wider lens. In short, it gives you a dimmer and fuzzier image in return for getting rid of brilliant blue halos around everything.
The more advanced approach to this is problem is to make what is called an achromatic or "Non colored" lens. This type of refractor has a front lens made of two lenses made of two different kinds of glass with different indexes of refraction. These are tailored to reduce the amount of light scattering by picking two types of glass to do the opposite kind of chromatic aberration to the image. The most common is to use crown glass and flint glass. This technique greatly reduces the aberration effect. These are the most common economical serious astronomical refractors. The main appeal of these telescopes is they do outperform compound telescopes such as Schmidt Cassegrains for any given diameter. However, for large diameters it should be pointed out the Schmidt Cassegrain and Newtonian designs can be very economical. Please see Picking a Telescope for more background on this.
The Achromatic designs have serious problems if one tries to give them short focal ratios. The goal of producing a telescope which can produce good images of large expanses of the night sky as well as being able to zoom in on planets. This "Dream" telescope has largely been unfeasible due to focal ratio effects where a telescope designed for wide sky views will break down at high magnifications, and telescopes designed for planet viewing have narrow fields of view so they can't see wide expanses. In recent years, short tube achromatic telescopes have been introduced by Orion and others with short focal lengths. These refractors show vivid purple halos around bright objects, but the images are fairly sharp. These aren't high magnification telescopes, but they are very inexpensive, so they have made a niche for themselves.
The apochromatic telescope is designed to be a no compromise do-it-all telescope. The ideal here is to produce telescopes somewhere between f/6 and f/8 capable of wide sky views as well as vivid planetary images. Due to the severity of this problem, exotic optics are called for. Telescopes from televue, Astro Phyics, Takahashi, Vixen (Orion), and Thomas M. Back (TMB) use exotic types of glass such as calcium fluorite which are very difficult to work (in one estimate I read, three calcium lenses much be produced to get a single usable lens) to get the extreme refraction properties needed to bend light without causing chromatic aberration.
These telescopes are the most expensive designs per inch of aperture of any type. They have very short focal lengths compared to their diameter, and yet they have glass so perfectly matched for color it is possible too push them to very high magnifications without having he image break down. As a result, they are designed to be the one telescope capable of doing it all, if one had a telescope (the other apparent solution to this problem has been the Schmidt Cassegrain telescope, which is far less expensive since it is a reflecting design). Apochromatic telescopes have become renowned for the quality of their optical tubes since the price of the optics is so high, it makes obvious sense to spend the small amount needed to make the rest of the assembly first-rate as well.
The apochromatic (APO) telescope isn't a single given type, and these have been evolving quickly over the last 20 years. Televue and the other APO manufacturers have been continuously developing their deigns, so there is no single configuration for such a telescope. The "Apochromatic" name means "without color" and is generally reserved for telescopes with fluorite glass elements in them. A set of telescopes similar in performance with extra low dispersion glass (or ED for short) has come into existence in recent years with levels of color correction between the APO and achromatic telescopes. Since there is no official regulation of this terminology, about the easiest way to tell what is what has been to look at the price tag.
In the last year, however, Chinese made APO telescopes such as the Orion 80ED and the Celestron 80ED have shifted the balance as they offer well corrected color combined with a cost 1/4 of the telescopes previously in the market. This does change everything, and I am revising my estimation of the Tele Vue 85 to keep up with the times.
Description
Even at first glance, the Tele Vue telescopes are obviously a bit different from the garden variety telescope. Their construction is extremely rugged. All of the primary components are metal, with most components made from aluminum (except for the rack and pinion, bearings, etc.).
The main tube is painted with a rough finish green paint. It also comes in ivory, which gives it a sort of antique white look. Either finish looks distinctive compared to the common gloss paint on most telescopes. The other components, such as the lens shade/dew cap and focuser assembly are black anodized. with a glossy finish. The dew cap is a neat component- it is made so it slides back along the tube to make the telescope smaller for transportation. The interior of the dew cap has a black felt lining to make it slide easily and to make it absorb light and prevent internal reflections. The dew cap doesn't lock when extended, and will wiggle around (i.e. it doesn't stay perfectly parallel with the tube). This isn't the sort of telescope I'd suggest modifying, so this is something to live with, and to be fair, one has to really be paying attention to notice.
Looking into the focuser with the diagonal removed makes the interior features visible. The interior of the optical tube has an interesting treatment to reduce glare. Instead of having ring after ring of internal knife-edge baffles, Televue has come up with an extremely rough flat black paint. The paint is so rough it almost looks like crepe paper inside.
The glass in the TV-85 is all multi-coated to reduce reflections. The front end is simple and elegant in appearance, without silly round-the-ring writing (after all, anyone who didn't already know what this was wouldn't be helped by such a label, anyway).
The focuser has nice large knobs with rubber treading on them. The rack and pinion is extremely smooth and has no detectable backlash. The motion is buttery smooth and cleanly reverses. The draw tube in the focuser is beautifully chrome plated. A simple thumb screw on top of the focuser adjusts tension and/or locks the focuser for photography. Even compared to a Takahashi, the Televue telescopes look distinctive. The only telescopes I have seen with a better appearance for display have been the Questar Maksutovs, which cost twice as much.
The TV-85 has a special oversize tube clamp which lets the user attach the telescope to either a conventional equatorial mount, or to a twin-arm fork mount. It would be nice if other manufacturers made such useful and flexible attachment components standard equipment. This also is where siting devices such as red dot pointers mount. The telescope can have its balance adjusted for what it is carrying on the back end (eyepieces, cameras, binocular viewers, etc.) by sliding the scope in this sleeve.
In summary, the TV-85 is a beautiful telescope to behold. It is easy to operate, has rugged construction, and looks like it is built to be an heirloom you will pass on after a lifetime of continuous use.
Performance
Looking through a TV-85 is a neat experience. The telescope is so small, it is easy to hold on to to move it to an observation target. The use of a low power eyepiece makes it pretty easy to find objects since the magnification can drop down to what many finder scopes operate at. At f/7, the scope has a wide field of view even for an 85mm telescope, though not quite as wide as the cheap Chinese f/5 achromatic scopes. Interestingly, it is almost exactly the same as the new Chinese-made 80mm f/7.5 APO telescopes (I doubt this is a coincidence).
The feature these are most famous for is the "Snap" focus, where an image is either obviously out of focus, or suddenly in focus. These do, in fact, do that. When looking at Mars , I found the planet jumped into focus. the only problem is though the image is nice, it isn't higher resolution or brighter than what a Celestron C5 SCT can produce (a telescope with greater aperture, 2 lbs lighter, physically shorter, but 1/4 the price). Where the performance picks up is on objects such as star clusters, which fill a large portion of the sky and where the individual stars are focused to smaller pinpoints in a refractor than in a telescope with a secondary obstruction (most reflecting scopes).
On the Pleiades, the TV-85 easily fits the whole group into a field of view. The individual stars are brilliant pinpoints and are truly beautiful with an effect like diamonds on velvet. This appears to be this telescope's forte, and is far more impressive than the planetary views. After a bit, I realized there was a little bit of violet around the stars, but it was still very pretty.
On nebulas, this telescope has the small scope advantage against light pollution. the guys writing for Sky and Telescope claim aperture is aperture, and the bigger scope is always better since the contrast is absolute. If one is using a camera, this is true. However, for the human eye, which is a very non-linear receptor, smaller telescopes do show detail more easily in things like the Orion nebula since the background is also dimmer. To prove this works, all you need to do is put a zoom eyepiece in a 5" or larger telescope. Start at low power and zoom in and you will find there is a point when the perceived dark sky suddenly gets much darker and the detail in the object you are interested in becomes obvious.
As a result, the Televue 85mm looks to be a pretty good deep sky telescope for an urban observer. As for being a utility telescope, there is one major test- the moon. This is the point where the TV-85 has shocked and surprised me. Looking at the moon at 25X, where the entire moon is visible, the TV-85 showed a lot of color. Around the edge of the moon, in to about 1/8 of its diameter the color was a yellow green. At the outside of the moon, there was a bright purple band. The unusual thing was how even the coloration was- not so much as fading out, but like a constant width belt. To be frank, I feel this is difficult to accept in such an expensive instrument. Now I own an 80mm refractor costing a quarter of what this one does which does NOT have this false color, I find this simply unacceptable. After finding this, I looked at other bright objects and found it exists to some degree on them, too. Mars is an interesting case because its delicate peach color prevents some of this effect. Jupiter, on the other hand, is pretty close to white and false color is visible as a blue-violet halo. in a word, this outcome is disappointing.
Summary
Certainly the telescope itself is beautiful. The fit and finish are very pleasing, and it looks really nice. If mounted on one of the beautiful Televue Gibraltar mounts, it would make a very handsome addition to any living room. However, when compared to how much it costs, I find myself having reservations.
The telescope has smooth mechanisms and tight construction. The materials are first rate. If you compare it to the Celestron 80ED 80mm scope, you will find it has bolder sculpting and the fit and finish are better. The 80ED lacks some neat details like the felt lined retracting dew shield and the more compact tube clamp. The real question is, is the Tele Vue $1500 better? The Tele Vue looks a little better, is famous (so folks will know what you paid), has false color the Celestron doesn't, but has slightly better contrast (your mileage may vary).
And keep in mind, the same amount of money for this optical tube alone will now buy an 11" Schmidt Cassegrain on a computer controlled equatorial mount which will show no false color and has far greater performance. The main downside of the larger telescope is it isn't so mobile and can't show as large a patch of sky at once.
In the past, the justification for these telescopes is nothing can outperform them for their size. In this case, that clearly is no longer true. I like the telescope, but finding that much false color compared to far cheaper competitors has already caused me to get the Celestron 80ED instead. At this point, reviewing this telescope has gone from difficult to painful as it is clearly obsolete, today. Al Nagler, the founder of Tele Vue moved the world with his fine designs, and has introduced some new designs in larger sizes in recent years. I can only hope an outstanding replacement for this telescope is just around the corner.
I have found I always choose performance over appearance. Small telescopes can open the night sky because taking them out to observe with them is quick and easy. The size and cost versus performance question always hinges on the balance of what a scope can do for both the money and energy which must be devoted to it. I find I am not really as concerned as much by the outward appearance of the telescope in comparison. With the introduction of the Celestron 80ED, the Tele Vue 85 seems to me like driving a Dodge Viper and discovering a Chevy Malibu will out accelerate and out-turn it. That is, appearance doesn't trump performance for me.
If you are looking for absolute performance regardless of cost, Takahashi and Astro Physics make incredible hardware, though it looks like it takes its styling cues from industrial machinery. If you are looking for bang for the buck, There is now a long list of telescopes under this one's cost which will outperform it by any criterion you choose. If you are looking for reasonable performance, light weight, and something drop dead gorgeous in the living room, and to be able to claim you own a Tele Vue, then this is your scope.
The Televue TV85 telescope is a superb travel scope, measuring only 21.5" (546mm) in length and weighing 8 lbs. (3.6 kg).23.6" (600mm) focal length co...More at OPT Telescopes
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