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Tele Vue 102
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Adventures with the Televue 102
By Neil English, Scotland, UK.
I've been an observer on and off for nearly 30 years and have had the immense good fortune to look through many types of astronomical telescope. I say on and off because the British climate, as many are aware, can be very disappointing. Sometimes weeks go by between observing sessions because of endless cloud and rain. But I guess, that's what makes us northern Europeans so passionate about sky gazing! Having settled in a rural valley in central Scotland, good skies are few and far between, necessitating the need for a system capable of delivering the best quality views in an ultra-portable system. As an experienced observer, located in dark magnitude 5 skies, I have grown to prefer the lovely, 'contrasty' views of no-hassle refractors to the temperamental light gathering prowess of larger Dobs.
The venerable 4â€ refractor is considered by many to be the ideal instrument and I can understand why. It's large enough to collect enough light to keep a serious observer busy for years and when well made, can serve up views of the Moon, planets and double stars rivalling those seen through much larger reflectors. My first serious foray into the world of high-end 4-inchers came when I acquired a 'classical' Televue Genesis refractor (non-SDF). It was a beautiful 'scope, built like a tank and capable of producing wondrous, sharp images with a very flat field. Low power views more than five degrees wide were awe-inspiring. It was also a solid performer on luna and bright planets, taking magnification well and only showing a little bit of false colour on high-contrast objects when pushed above 150x or so. It was as close to the 'perfect' telescope as I was could get, but a few things niggled me about it. For one thing, because it was such as fast refractor, finding the sweet spot of fine focus was often a challenge, especially when used at high powers. When you have an F/5 refractor, there's no room for ambiguity; you're either in focus or you're not. In addition, it had a very short focal length- 504mm - and so was difficult to get ultra high power views. Thus, added to a four-element objective, I had to resort to adding a two-element Barlow lens and a five-element plossl eyepiece to get those savoured 200x + views that are achievable on the steadiest nights. That's a lot of glass to put between you and the heavenly realm; so much so that I wondered whether it would really take the edge off many high resolution images of the moon and planets. After briefly looking at a variety of double stars, Mars and Saturn through the economical Orion 100ED (a F/9 FPL-53 ED doublet), I was immediately convinced that my beloved Genesis was indeed failing to deliver the best high power views it could.
Having become accustomed to the joyful simplicity of the rugged Televue 'scope I found myself wondering whether it was time to trade in my 1991 Genesis for one of their current line of APO refractors. The NP101 was my obvious first choice, but it would burn a great big hole in my wallet. Then, as luck would have it, I chanced upon an opportunity to trade in my Genesis as part-exchange for a very lightly used Televue 102. I had already heard some good things about the TV102, and judging by the fact that so few come up on the second-hand market, it ought to be a solid performer. After dithering for some time, I finally crossed the rubicon; I would be sacrificing a degree or two of field for an instrument that would be a better performer at high power- and I look at close binary stars a lot. It broke my heart to part with my old Genesis but I quickly got over it once the TV 102 arrived.
The original Televue F/5 Genesis on a Gibraltar mount.
What I received was the Televue 102 package; optical tube assembly (OTA) with clamshell, 2" Everbrite diagonal, with a 1.25" adaptor and a 20mm Televue plossl. All the items arrived securely in a robust and slightly over-sized Televue case. The OTA was as good as new. The beautiful powder-coated ivory coloured tube gleams in the sunlight topped by a super quality matt-black retractable dew shield. The 2" focuser looks immaculate. The rack and pinion focuser is buttery smooth to operate and the hefty 2" Everbrite diagonal with its 99% reflectivity the perfect complement to the OTA. When I unscrewed the dew shield to examine the glass I gasped with a mixture of relief and delight. The lens almost disappeared in dim light. In short, the TV 102 looked every bit as good as the Genesis I had reluctantly given away.
Ready for action: the TV 102 atop the Gibraltar mount
The TV 102 also felt slightly lighter, having a marginally thinner aluminium tube than the F/5 Genesis- not a bad thing in itself since it would help the former cool off faster. Still, it was nice to know Televue's standards haven't slipped one bit in nearly two decades!
As a dedicated visual observer, I spent the vast majority of my time using the 102 on a a non-driven alt-az mount. My first choice was the sturdy Gibraltar mount which I had used to great effect with the Genesis. The bad things I've read about the Gibraltar simply aren't true. When properly adjusted, it provides a rock solid platform that can handle very high magnifications with poise. If anything, the 102-Gibraltar combo was even more stable than with the Genesis, the longer tube of the 102 contributing to easier leverage of the scope in altitude.
My assessment of the optical performance of the Televue 102 was carried out over a period of six months. I used four eyepieces with the 'scope. For wide field/finder views a 32mm MK80 was employed, giving a near 3 degree field at 28x. Next in line, a 14mm Pentax XW serving up 63x in a 1.1 degree field, a Meade series 5000 8.8mm UWA giving 100x and a FOV of 0.8 degrees and finally, for high power applications, a 3-6mm Nagler zoom providing continuously variable powers from 147x to 293x. All these eyepieces serve up crisp, distortion free images that extend almost entirely across their respective fields.
T Eyepieces used to test the TV 102
First up, the boring (exciting?) stuff. Star testing conducted over many nights using a green filter at 220x (the 4mm setting on the Nagler zoom) showed lovely, almost identical, concentric rings on either side of focus. I'd estimate the figure of this doublet lens to be a little better than 1/8th wave ptv. Bright stars such as Capella and Vega snapped to sharp focus at the same power yielding tiny well-defined airy discs accompanied by a single concentric ring; all signs that the optics on the 102 are first rate. For those 'CA avoidance junkies' out there, I can say that the scope lives up to status of APO.
The lovely rack and pinion focuser on the TV 102
By this I mean false colour is really a non-issue on this instrument at powers up to and beyond its sweet spot- which is in the region of 176X with the 5mm setting on the Nagler Zoom. When pushed to 50x per inch of aperture and beyond, the apochromatic performance of the TV 102 (and I suspect many other ED doublets) is both temperature sensitive and subject to change with atmospheric conditions. Careful tests carried out by day and night led me to the same conclusion; the TV 102 produces colour free images (virtually) when thermally equilibrated and under calm atmospheric conditions. More on that later.
Low power views through the MK 80 32mm eyepiece (which is considerably lighter and less expansive than a 31mm Nagler) were fabulous; the contrast in the images in the TV 102 was simply in a different league to what I had experienced in the Genesis. The greater number of elements together with marginally less effective coatings on the latter both contributed to this I reckon. I must add though that this conclusion was not drawn from a side by side comparison, as the Genesis left my hands shortly before the TV 102 arrived. That said, having spent many hundreds of happy hours behind the Genesis I could tell with one glance through the TV 102 that the latter had significantly higher contrast. Last February, I had one of best views of the great nebula in Andromeda (M31) I have ever experienced with a 'scope of this aperture. The image the TV 102 served up was simply stunning in the 28x, three-degree field of the 32mm MK80, The central nucleus was huge and mottled. I could trace the faint, outer extensions of the spiral galaxy with greater clarity than I could with the Genesis. The differences were subtle but I felt they were real enough to believe. M35 in Gemini was glorious; tucked away in a cavity of space as large as the full Moon, the 100x view through the Meade 8.8mm UWA beautifully framed the cluster from edge to edge. Many tens of brighter stars of varying hues were seen interspersed with innumerable lesser suns. The view made me appreciate me why the late Walter Scott Heuston rated it his favourite open cluster in the entire heavens. Such a contrasty 'scope as the TV102 is great for observing faint objects at high magnification. Popular close double stars such as Epsilon Lyrae, Izar and Xi Ursa Majoris are easy with this scope. So too is the triple system; Iota Cassiopeiae. The TV 102 takes magnification remarkably well; 293x is well within its comfort zone on a favourable night. On the other hand, I have split Mizar at 22x with a 40mm plossl and could just detect the double nature of both e1 and e2 Lyrae at 63x with the 14mm Pentax XW.
The Moon and bright planets are a joy to view with the TV 102. With a focal ratio of F/8.6, it's easy to get the position of best focus. It was just a breeze compared to the F/5 Genesis. Many speak highly of the 6:1 TV focusmate and other focusing 'appendages' produced by other manufacturers but I've honestly never really felt the need to upgrade the rack and pinion focuser. It's one of the smoothest in the industry. I had a chance to observe Mars on and off during its Christmas '07 opposition, where its high altitude from Scotland helped serve up some lovely, sharp views of the Red planet. Polar caps were always obvious at a glance. I could see the Syrtis Major more readily with this instrument than any other 4" refractor I have the pleasure of looking through. Saturn's rings were presented at a very shallow angle during its last opposition, but I could still make out the Cassini division at the ansae at 147x and almost always, some gorgeous atmospheric details on the planet's globe. I can't wait before the rings begin to open wide again. Jupiter could not be tested due to its hopelessly low altitude from my northerly vantage (latitude 56 degrees).
Having owned and loved an old Genesis and compared it (mentally anyway) with the TV 102 I was very keen to see how it would perform against Televue's other, contemporary 4-inch refractor - the venerable NP 101. A direct descendent of the Genesis, the NP101 boasts of even better performance in the total- I mean total- elimination of false colour. During my Easter vacation, I finally had a chance to do a shoot out (of sorts) with a well-to-do friend who purchased (I might have had something to do with his decision) an NP101 as a Mega 'birding 'scope'. We mounted the NP101 on an alt-az Vixen Porta and conducted our tests over a few unusually cold, March evenings. Our targets; Mars and Saturn. We used the 3-6mm Nagler zoom with both instruments and, to get magnifications that were comparable, we set the zoom to the 3mm setting on the NP101 yielding 193x. I set the zoom midway between the 4 and 5mm clicks on the TV 102 to give roughly the same power on the NP101.
There's no getting away from it; the NP101 is one impressive 'scope to look at (and through) and its low-power wide-angle views are something to be cherished. It's short and cute - more cute even than the TV 102. But here's what we found. The NP101 was harder to focus and took longer to reach thermal equilibrium with the outside air than the TV 102. No surprises there I guess. At first my friend (a self-declared non-astronomer) could detect very little difference between the images of the Red planet served up by either 'scope. He had to 'learn' to see the differences I found significant; namely that, on an average night, where a modest amount of atmospheric turbulence had to be contended with, the NP 101 delivered totally colour-free (that we could make out) images of Mars. The TV 102, we both agreed, showed up a very slight but definite trace of false colour on the limb of the planet that came and went with the seeing. Planetary detail was, for the most part, the same for both instruments, with the nod perhaps going to the TV 102. I say 'nod' in the sense that while both 'scopes served up sharp, high- contrast views, the image in the NP101 was just a tad mushier, as if a very thin veil were placed in front of it. But when we assessed the quality of the image of Saturn as it floated across the field of view we noticed the NP101 held a distinct advantage; while the TV 102 held out to about 85% to the edge of the field before the image became slightly distorted, the image in the NP101 held up right to the edge. To my surprise the image brightness in both 'scopes was much closer than I anticipated. If anything, the TV 102 was a little more contrasty.
Summary: The Televue 102 is an impressive former. As a purely visual observer, it delivers views that are always rich in contrast and detail. It can attain fields of view over 3 degrees wide with 2" eyepieces- more than enough for most deep sky observers. It takes magnification well and is an excellent instrument for the dedicated lunar, planetary or double star enthusiast. Its colour correction is sensibly perfect in every conceivable situation but very minor CA is there at very high powers if you really go look for it. What about the NP101? Well, my friend does lots of daytime photography with it and it's great for that. It is also a fantastic night sky performer that has clearly transcended many of the weaknesses inherent to the original Genesis. But it's Â£1000 more expensive than the TV 102. If you're purely a visual observer who can resist the ultra-wide views the NP101 can deliver, the TV 102 provides a very attractive alternative and is heartily recommended.
The author has no commercial links with Televue Optics.
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