Televue "Ranger"
Most of my purchases from fellow NOVAC club members are impulse-based, driven by the desire to try some new and well-regarded piece of equipment for a bargain price. While I am not a refractor fan at all and certainly not a high end apochromat nut (I have been underwhelmed and unappreciative of the views through Takahashi and AP scopes, as well as Swarovorski binoculars -- "clear but tiny" would be my epithet of choice), I couldn't resist the chance to try out a third-hand 70mm f/6.8 Televue Ranger for a veritable song. The catch behind this fire sale price? Some previous owner had dinged the scope hard enough to dent the optical tube near the lens ring, and at least one astronomy store owner opined that this had knocked the optics out of collimation. The prior NOVAC owner has enough visual astigmatism that he couldn't verify this, and sold it to me on a trial basis. (He also had talked to David Nagler at Televue, and already had an RMA so that the scope could be returned and overhauled to "like new" condition for $130.)
Since I had always heard that these budget stable mates of the benchmark Televue "Pronto" were among the reigning champions of small travel refractors until the recent rise of the small mid-priced apo's, I figured this was a "no lose" situation. I had been planning to recycle the cheap Short Tube 80 (400mm f.l.) from "Frankenscope" into a stand-alone wide field (3.5 degree) scope, but knew that the optics of this scope would probably yield pretty ugly views. The Ranger, on the other hand, is considered an optical gem that can be used at 200X if the seeing permits, and thus should certainly render crisp images at low power even if the collimation were somewhat less than perfect. The Ranger managed to shed nearly half the weight (and a considerable fraction of the price) of the Pronto by moving to a drawtube/helical focuser and 1.25" barrel, while keeping the same optics that made the Pronto such a success.
With my 22mm Panoptic the Ranger yields a 3.2 degree field of view at 22X. I knew that I could mount the scope on my Bogen 3010 camera tripod and use the 3265 "pistol grip" handle. First light occurred during the day -- in a break in the ~12" of rain that fell during a five day period-- and sufficed to show that:
a) the 3-6mm Nagler zoom was a good match for this scope (producing 60-180X magnifications)
b) there really is a "snap" to perfect focus on premium refractors, and
c) that the Bogen tripod is too light (vibrates readily with short eye relief eyepieces) and the 3265 tripod head less suited for high power work than a dedicated astronomical tripod with slow-motion controls. Fortunately I have a surplus Orion "EQ-2" clone (which came with my 102mm Mak-Cass acquired from another NOVAC member) that I can use for around home view, relegating the Bogen setup to air travel use only.
Since the scope did not come with a diagonal, I borrowed the 1.25" Orion one from my 102mm white light Mak-Cass for "first light", but decided to buy a premium one to match with the scope. (With a tiny aperture, sacrificing light to the diagonal mirror and introducing wavefront errors to an exquisite image seems counterproductive.) Rather than spending $80+ on a Williams Optics one, I tried placing a want ad on Astromart first, and ended up landing a mint conditions "Astro Tech" WO clone complete with 1/10 wave mirror, 99% dielectric coatings, compression ring, and massive metal construction for $50 shipped. I still had the spare mounting base from my Rigel Quikfinder, and therefore borrowed the zero mag Rigel from the now-dormant "Natasha" to serve as the finder on the Ranger. I was in business!
Scope on the EQ-2 tripod Close up side view w/Panoptic 22 and Quikfinder attached Rear view
I was hoping to bring the scope on a business trip to San Antonio, Texas, where I planned to make a side excursion to "Bortle 1" skies, but the weather forecast was dicey enough that I opted not to bring the scope. First astronomical light therefore occurred on a somewhat hazy quarter moonlit night from my front yard. I saw some orange hues of chromatic aberration around the limb of the moon, but nothing too objectionable. The moon took "crazy" levels of magnification without discernable image breakdown-- 360X, which was the most I could generate without stacking Barlows. The image was somewhat dim at that absurd power level, but still clean and crisp. Very impressive performance for a 70mm scope! Even at 60X (generated by the fairly narrow FOV Nagler zoom at the 6mm setting) the disk of the moon fit fully in the FOV with a comfortable margin around it -- my eyepiece spreadsheet shows a 38 minute FOV at that setting, and an even more mind-boggling 19 minute (nearly two thirds of the moon) at 180X. Jupiter, on the other hand, was a bit disappointing -- the image was too dim to be able to discern much detail at over 60X. This may have been the hazy atmosphere, rather than the collimation of the scope, so the jury is still out on that score. Star testing was problematic, since the clouds rolled in.
Update: later testing on "hot and hazy" nights that were stable but not clear enough to show diffraction rings shows that the scope seems to render nice round and reasonably sharp stars at up to 360X-- the highest I tried. As you might expect, the image was pretty dim at this power level-- this is, after all, a 70mm scope! I found that the moon holds up reasonably well-- not perfectly, but "OK"-- at 360X. The lunar image is fairly dim at even 180X-- useable, but not great in terms of illumination. In one sense the Ranger is a nice lunar scope, since it renders decent images without needing to have a lunar/polarizing filter installed!
I was impressed by the panoramic wide field of view of the scope with the Panoptic 22, and think this scope could come into its own under dark skies and with my UHC or OIII filters attached. It closely rivals the nominal performance specs of my 20 x 80mm Oberwerk binoculars (3.5 degree FOV and 20X), so I look forward to testing it head-to-head against these big binos-- and the Short Tube 80 f/5 refractor on Frankenscope-- to see how the 70mm aperture of the Ranger compares to the 80mm of its larger but lower quality brethren. (UPDATE: the Ranger has the edge in contrast and detail, the ST80 in light grasp. The overall viewing experience is comparable for both...) I also look forward to testing it against the 80mm Tuthill superfinder mounted on my 24" Dob Brutus.
What lies ahead for this impulse purchase scope? Currently it is set up in my garage as a 'grab and go' scope, although since it only takes me ~5 minutes to have the 24" Dob in operation, I am uncertain how much eyepiece time it will actually get. Depending on the results of field testing, perhaps it could become my --somewhat heavy-- finder on the 24", which would give me the ability to combine superlative high-quality wide field images of deep sky objects like the North American and Veil nebulae with the light grasp and magnification of the big Dob. Time will tell...
