Tele Vue Optics
Sky & Telescope Review

S&T Test Report

Ranger Multipurpose Telescope
Tele Vue Optics
100 Route 59
Suffern, NY 10901

Price: $795, including 20-mm Tele Vue Plossl eyepiece and 1 1/4-inch mirror star diagonal or 45 degree image-erecting prism. Other accessories available.




Ranger can be mounted on a photographic tripod
or used with Tele Vue's standard altazimuth
mounting seen here. The optional shoulder
bag (inset) had a zippered pocket for accessories.

The Multipurpose Ranger

WE HEARD in January that Tele Vue was planning to offer a multi-purpose, lightweight refractor, and immediately arranged to get an early production model for testing. Featherweight spotters are a new arena for Tele Vue, so Sky & Telescope looked forward to putting the new scope through its paces.

Ranger arrived packed in an optional l9-inch-long padded nylon shoulder bag with a carry strap and internal zipper pocket for accessories. A glance at the compact instrument revealed obvious departures from the familiar Tele Vue style. Missing were the hefty 2-inch focuser housing and chunky mounting rings that define the look and feel of the company's other instruments. For the Ranger, designer Al Nagler has replaced them with a sleek but robust tailpiece and a compact adjustable mounting bracket for a tripod.

OPTICS

Ranger's business end packs a 70- millimeter (2.8-inch) objective, a twin to the one used in the company's high-end Pronto. The lens is described as a two-element semi-apochromat. The front element

 

OBJECTIVE:                  Air-spaced, two-element semi-apochromat. 
                            Front element: crown ED; 
                            Rear element: high-index flint.
LENS COATINGS:              Rear surface of ED element is multicoated, 
                            all others magnesium fluoride. 
DIMENSIONS:
   TOTAL LENGTH:            387 mm (15 1/4 inches)
   OBJECTIVE CELL DIAMETER: 85 mm (3 3/8 inches)
   CLEAR APERTURE:          70 mm
   FOCAL LENGTH:            480 mm
   FOCAL RATIO:             f/6.8
MATERIALS:                  All machined aluminum, exclusive of optics 
                            and fasteners. 
FINISH:                     Enameled tube, black anodized fittings. 
                            Eyepiece holder: standard 1 1/4-inch diameter. 
COARSE FOCUS:               63-mm (21/2-inch) drawtube.
FINE FOCUS:                 Helical, 17-mm (5/8-inch) range at 3 mm per 
                            3/4 turn. 
MOUNTING:                   Sliding clamp on 6-inch long, 1-by-1 dovetail 
                            track, 1/4x20 threaded mounting holes.
is crown ED (extra-low-dispersion) glass and the rear element is high-index flint glass. All lens surfaces are coated. Three feature magnesium fluoride, and the rear surface of the ED element is multicoated to discourage internal reflections.

According to Tele Vue, airspace between the lenses is maintained by a ring individually sized to optimize each objective's corrections. The 480-mm focal length gives Ranger an f/ratio of 6.8, about average for spotting scopes but fast for an astronomical doublet.

MECHANICS

The scope is all machined aluminum exclusive of incidentals and fasteners, with the exterior surfaces of fittings anodized black. The eyepiece holder is US. standard 1 1/4 inches with a nonmarring knurled locking screw. Focusing is accomplished with an internal-helix mechanism similar lo the kind used in telephoto lenses, so the eyepiece itself does not rotate.

Ranger's focuser is mounted on a drawtube, once a common feature of refractors but now lamentably rare. The drawtube has 63 mm (almost 2 1/2 inches) of travel for rapid coarse focusing and locks with a knurled thumbscrew. It provides the ability to quickly reach close focus, which is especially useful in terrestrial viewing (see the accompanying commentary by Leif Robinson). The drawtube also allows quick adjustment for accessories with different focal requirements such as a Barlow lens, image erector, nonparfocal eyepiece, or even a binocular viewer.

Ranger can be supported by a standard photographic tripod or any of Tele Vue's current mounts. The mounting clamp rides on a 6-inch dovetail track and locks with yet another knurled thumbscrew. A series of 1/4X20 holes tapped underneath the track allows a balance point up to 5 inches in front of the clamp position to offset heavy accessories.

A Tele Vue 20-mm Plossl eyepiece and 90 degree mirror star diagonal are standard equipment. The company also sent 32-mm and 21-mm Plossl oculars, a 7- mm Nagler wide-field, and a newly designed 2x Barlow lens. The alternative diagonal for the standard package, a 45 degree erecting prism, was also sent.

The novel fitted bag

accessory available for Ranger allows "under-cover" viewing on or off the tripod by unzipping both ends to expose the eyepiece and objective.

OBSERVING TESTS

As is appropriate for an "anytime" portable instrument, Ranger was tested in the suburbs on a night with a waxing Moon about 80 percent illuminated. The limiting magnitude was about 4.5 to 5.0, with intermittent haze. Seeing averaged 5 to 6 on a scale of 10, with more turbulent patches at intervals.

The mount used was an old photographic tripod with a friction head and no slow motions. Ranger's dovetail bracket proved to be sturdy and shake- free. While the adjustable track would probably prove very useful for balancing piggyback on another telescope, changing the settings had little effect on tripod balance at typical viewing angles in the sky.

Later on, Ranger was tried out on Tele Vue's standard altazimuth mount and tripod (shown on the facing page). Ease of use was considerably enhanced. Smooth motions on both axes made star-hopping a breeze. The sturdy ash tripod damped out vibrations quickly and rapidly adjusted to comfortable height.

The bright Moon nearing culmination was an obvious test object. Because the glare was tolerable, no filtration was used. A glance in the 32mm Plossl (15X, 3.3 degrees field) showed the Moon in a field containing several nearby stars A crisply defined terminator neatly halved the walled plain Gassendi north of Mare Humorum. Interior shadows were black and featureless, a good indication that the optical system was scattering little light.

Scanning northeastward across Mare Imbrium revealed bright crater-ray patterns that showed distinct contrast with the generally neutral-tinted lunar surface. Details of scalloped cliff edges were visible at the feet of Promontorium Laplace and Promontorium Heraclides that jut into the mare from the ends of the Montes Jura range.

Ranger's fine focuser is

an internal helix unit like that on a telephoto lens. The eyepiece itself does not rotate.

Cranking the little scope up to 30x, then to 60x caused no optical strain. Using the 2x Tele Vue Barlow lens with the 7-mm eyepiece achieved almost 140x and brought even more detail into view through the slow waves of seeing. Well, we expect to be able to use a magnification of 50 times the aperture in inches with a good refractor, right'?

Out came my 5-mm orthoscopic eyepiece, a very clean Japanese unit giving 192x with the Barlow. Hmmmm . . . very good. Now a 4-mm German ortho, obtained from an old glass-pusher who rails against newfangled eyepiece tom-foolery. At 240x there was no break- down of the image. I could see faint traces of the various ridges that traverse the Mare Imbrium near Sinus Iridum. The bright lunar limb exhibited no spurious color at this magnification.

Altair, conveniently nearby, displayed a tiny, white, shimmering image at focus, which expanded to a yellowish Fresnel ring pattern when the focus was turned in a little. The tints of the target changed lo violet and green outside focus. The diffraction images were round and concentric at both focal positions with closely similar ring widths. In other words Ranger appears to be nicely corrected.

Speaking of rings, Saturn's were edge on at the time of testing, and the planet appeared like a small, pale cousin of Jupiter. The mediocre seeing was a problem, but even at the highest magnification available Ranger showed the moon Titan as a pinpoint and a clear- edged planetary disk of pale beige- yellow with hazy equatorial banding.

The Double-Double star Epsilon Lyrae was riding high in a very transparent spot. With a separation of 2.6 arcseconds, the northern component, Epsilon-1, showed plenty of black space and a striking brightness difference between its magnitude-5.1 A4 and 6.1 Ft components. A hint of yellowish color showed in the fainter star-this with a scope I picked up with one hand and carried across the yard!

The globular cluster M15 in Pegasus showed partial resolution of its outer stars at 60x and a distinct granularity to its core at 120x. The rich area around Gamma Cygni sported clouds of pin point stars. Even in the strong moonlight, the tiny, elaborated trapezium of M29 stood out clearly against a dark charcoal background. The companions of the Andromeda Galaxy, M32 and NGC 205, showed clearly after a few moments at the eyepiece.

CONCLUSIONS

Ranger is just the right size and weight to use as a travel telescope for astronomy, wildlife, or sports. It could even serve well as an outstanding, if pricey, wide-field mega-finder on a large instrument.

The helical focuser abetted extensive accessory changing during my tests. Its turning ratio is generous, with no slop or detectable side play even at the tiny focal tolerances of high magnification. The drawtube functioned well: coarse refocusing after changing eyepiece types or adding a Barlow lens was simply a matter of looking and sliding.

That is not to say the maker has thought of everything. For instance, the lack of any glare-stopping baffles in the main tube was surprising, although the drawtube does has several machined baffling shoulders. It must be admitted, however, that stray light was not a problem in testing, even on the nearly full Moon.

In the unit we tested, a seam in the black-flock lining of the main tube had sagged, causing a shred of fabric to nearly nick the light path at the top of the lens. This cosmetic flaw did not degrade performance, but it was bothersome to think the situation might degrade. Since the product brochure warns not to remove the lens cell for any reason, return to the factory would be necessary to rectify this minor problem.

Tele Vue states that the instrument is made in the U.S., with all mechanical parts locally machined. The source of the optics is proprietary, the maker stating only that the optical work is contracted to a U.S. firm. Still, I'd like to know where this nice bit of glass is being fabricated.

Having used several small refractors over the years, I have lost my beginner's amazement at pinpoint star images, high- contrast planetary detail, and breathtaking dark backgrounds. These can be seen in any competently made refracting telescope. Ranger s optics are extremely good, hut I was even more impressed with the success of the overall design. From a practical observer's viewpoint, it is nice to know there is finally a true multipurpose small telescope available.

M. BARLOW PEPIN

So How Does Ranger Perform in Daylight?



A GREEN-BACKED heron probed an estuary's muddy bank, and I saw details absent from my recollection of countless other telescopic views- pronounced light edgings to feathers on its sun- scorched back, faint gray streaking on its deeply shadowed belly, a tiny white crescent behind the eye. That's amazing detail on a 45-centimeter bird seen at a distance of 200 meters (the critter subtended 8'). I could even spot "field marks" on fiddler crabs scurrying in terror as this predator charged.

Granted, I was viewing though calm air-across water and the Spartina grass that fringes my back lawn. Yet this was midday, a time when 30x is the most magnification that is usually useful; I was at 56x. From this experience alone, I can say Ranger is one fine telescope for naturalists.

I tested four Tele Vue eyepieces: 32-, 21-, and 17-mm Plossls and a 7-mm Nagler. All provided natural, bright color and super crispness, which also says more than a little about Ranger's primary optic. All the eyepieces suffered from pincushion distortion, which could easily be detected about a third of the way to the edge of the field. Nevertheless, the image at the edge remained crisp. That's the important point; everything you see is in sharp focus. Despite my best efforts, while looking at a metal pole with one side strongly sunlit and the other in shadow, I'm not sure I saw any fringe of spurious color.

I quickly adopted the 32-mm as my favorite eyepiece, for it provides 15x and a fabulous 3.3 degrees field of view. It also has enough eye relief for me to see the whole scene while wearing eyeglasses. The other eyepieces didn't, allowing only about an 80 percent view with the 21-mm (1.5 degrees actually seen), 70 percent with the 17-mm (1.2 degrees), and 20 percent with the 7-mm (0.2 degrees). But I'm not condemning these eyepieces; they're not designed for use with eyeglasses.

What's even better is the depth of field that the Ranger provides. With the 32-mm Plossl at a range of 100 meters, many meters near and far from the critical-focus distance were adequately sharp. This is of enormous value when you are looking at scattered flocks of birds, like sandpipers along a beach, because it gives you a great shot at picking out a rarity. And what a blast it is to use this eyepiece, with and without the 2x Barlow, to look at a feeder 7 meters away! That's the closest this system can normally go.

Right-angle and 45 degree erectors are not my favorite devices; they stick out and don't allow a sight- line along the telescope's barrel. The right-angle also swaps left and right, so it takes some getting used to. Yet, after a couple of hours, I felt comfortable - sort of. (When Questar was king-of-the-hill, it was the darling of professional tour leaders despite such "deficiencies.")

So who's the (daytime) Ranger for? It should be looked at by anyone considering the purchase of a 70- or 80- mm-class spotting scope, such as those from Bausch & Lomb, Kowa, and Swarovski. (Prices are in the same ballpark; you'll lighten your purse by about a grand.) They are all less than 1 1/2 feet long and weigh about 3 pounds. If I were buying Ranger strictly for terrestrial observing, I'd go for the 32-mm eyepiece and add the 21-mm with Barlow if my pockets were deep.

LEIF J. ROBINSON

ROBINSON advised Bausch & Lomb during the development of its Elite line of binoculars and spotting scopes. Because of bird watching and his job as Editor in Chief of Sky & Telescope, he sleeps on the wing like an albatross.

Prices subject to change.