library/televue/notes.html">Notes & Interesting Articles Company Seven | TeleVue Ranger Telescope Company Seven.

 

C-7 Home Page Products and Services Product Lines Order Consignment Library

Distribution History TeleVue Index News Notes & Interesting Articles Pricing Products

Accessories Eyepieces/Oculars Mounts Starbeam Sight Telescopes

"Ranger" 70.4mm f6.8 ED Doublet Apochromat Refractor (2.8" aperture)

Discontinued, posted for information purposes only

TeleVue Ranger telescope (58,778 bytes)
Above: TeleVue "Ranger" telescope with 1.25 inch Dia. 45 Degree Angled Image Erecting Prism, and 20mm Plossl ocular (58,778 bytes).

Since 1986 TeleVue has set new standards of versatility with their very compact refracting telescopes. In March 1993 TeleVue introduced the 70mm "Pronto" ED doublet refractor telescope which has become successful for birding (considered a "Reference Standard" in it's class), and well accepted by the astronomy community too. The Pronto is one of the most compact well made telescopes in the world today, the 2" focuser providing an extraordinary range of photo-visual fields of view, and versatility for many uses. But all of the features of the Pronto come at a cost, and with a weight that makes it less attainable for some. So by deleting some accessories, and incorporating a unique sliding draw tube with helical fine focus mechanism in place of the Pronto's rack and pinion focuser, TeleVue introduced a more rugged, lighter weight (40% less), economical version of the Pronto - this is the "Ranger".

The "Ranger" has become a popular first (or second) telescope choice among our clientele for several reasons:

  • The "Ranger" is very compact and simple to use, so much so that it gets used more often than larger telescopes when quick set up or incidental considerations are high priorities.

  • The "Ranger" is among the least costly good quality refracting telescopes made today. It employs very robust construction of machined aluminum components, and a good quality Achromatic doublet objective lens.

    A person who is interested in photography, or exploring the new hobby of astronomy, or one who already owns a larger telescope will be able to employ many interchangeable accessories. Most of the accessories that we would suggest for the "Ranger" are compatible with larger telescopes; some of these are top choices used in observatory class instruments! There is little obsoleting of accessories, and one can use any of a wide selection of eyepiece (oculars), and filters.

  • The Ranger's atypical focusing mechanism is streamlined and rugged. There is no fear of striking a focus knob accidentally and bending a pinion, there are no focus knobs hanging off the sides making it difficult to put the telescope in/out of a backpack, guidescope rings, etc.

  • The "Pronto" is extraordinarily versatile being suitable for introductory astronomy, birding, panoramic observing, photography, and more.

  • For astronomy not only can it be used as a good primary telescope, but if the "aperture fever" bug bites and you then find yourself wishing to see more with a larger telescope, then you are likely to keep the "Ranger" for use as a quick set up, second telescope to share with a crowd, or employ it onto a larger telescope as a first rate finderscope, or photo-guide telescope.

PERFORMANCE

The objective lens of the "Ranger" is an air spaced doublet design where two lenses are matched to work as one. The front element is a positive fluorocrown substitute of Extra-Low Dispersion ("ED") glass; the rear element is of high index flint. Each lens spherical surface is smoothly polished, and in another testament to Al Nagler's forward thinking - this design can be made well, consistently. This design allows good color correction and stars appear to snap into focus as intense diamonds against a black velour background - the typical high quality refractor experience! But at high magnifications some false violet may be noticed on very bright small objects (stars including Vega, the planet Venus for example) - but these objects are pretty harsh tests of any telescope. Images of birds and planets are presented showing good detail, and daytime objects viewed at commonly used magnifications will appear quite three dimensional, free of apparent false color, sharp and contrasty.

The current production objective's four air to glass surfaces have anti-reflection coatings providing an overall light transmission greater than 94% in the visual wavelengths. So the system has about 93 times the light gathering power of the unaided human eye. On most nights, the settling down time for the lens is on the order of minutes, and even in sub-freezing conditions it rarely requires more than 15 minutes to acclimate.

While many owners are satisfied using the telescope at up to 200X or so, we believe the "Ranger" is capable of operating at up to about 150X with optional lenses (any higher magnifications are not likely to show more detail), although some minor secondary color may become apparent to the trained eye at about 65X or higher. This telescope reaches that threshold necessary to clearly identify the major planets with several bands and their shades of color (beige, tan, browns) shown on Jupiter, the rings around and surface banding on Saturn, the polar cap on a fiery red Mars. With an eyepiece that shows 1/2 degree field or so, take a walk on our apparently three dimensional Moon! or follow its terminator throughout the moons phases (optional neutral density filter suggested to tone down its brightness). It will resolve objects on the moon as small as 6.4 km in diameter, it will see the four largest moons of Jupiter and their shadows cast on the surface when they transit past the planet!

With TeleVue's 1.25" focuser, and a matched wide angle ocular the "Pronto" has a good wide field of view capability showing an area of up to 3.21 degrees (an area wider and taller than 7 full moons) at 12X. With most small refractor long focal ratio telescopes, it's like trying to see the "Mona Lisa" through a straw...while "Pronto" shows more of the entire picture!

From a dark sky site, the "Ranger" can show most of the "Messier Catalog" of deep sky wonders. Or it can be employed for panoramic viewing of a seashore or countryside. Imagine a telescope that at a dark sky site has the combination of resolving power and field of view to sweep the Milky Way, find the Andromeda galaxy (M-31), and see the form of large Nebulae such as the Veil and North American Nebulae! The TeleVue "Ranger" can reveal all three stars of Orion's belt and the nearby Great Nebula (M-42) where is revealed the jewel like stars of the Trapezium - a birthplace of stars, with a sweeping wisps of greenish gas clouds surrounding it.

The "Pronto" compares favorably against many telescopes in field of view:

  • 1.9 at 22X for a common 80mm achromatic refractor,
  • 1.4 at 31X for a common 6"f8 reflecting telescope,
  • 2.1 degrees at 21X for an 5" Schmidt-Cassegrain (even when using an optional telecompressor lens)
  • 1.3 degrees at 32X for an 3-1/2" Maksutov-Cassegrain.

The cost the "Ranger" (equipped with either an optional Alt-Az or Equatorial mount) is positioned at about the same or lower cost than the above telescopes.

And as a practical matter for some applications in astronomy the nominal match of the "Pronto" telescope exit pupil to an average human eye will be obtained at magnifications of between 14X and 10X. While the best performance will be obtained at all magnifications if a wise choice of well corrected oculars is made; this goal is not attainable with several of the simpler eyepiece designs. Also consider that an optional good quality "Barlow" amplifying (negative) lens, or long eye relief TeleVue "Radian" ocular (introduced in 1999) will usually be put into use to attain the highest use able magnifications.

For film photography, the telescope (with our optional camera adapters) becomes a 480 f6.8 ED ultra telephoto lens for a 35mm camera. And for CCD imaging operations the telescope at prime focus can show about one degree across the diagonal of a common 2/3" detector (such as that employed on some of our SBIG CCD systems. Optional techniques and hardware permit imaging of the planets, or of wildlife at much higher magnifications.

For those interested in more critical astrophotography Al Nagler has designed an optional Field Flattener to eliminate the effects of curvature of field common to such relatively "fast" telescopes. The Field Flattener threads onto the male thread of the TeleVue telescope camera adapters, makes the Ranger telescope perform as a 520mm f7.4 Flat Field telescope, with only very slight vignetting at the extreme corners of the film negative. This accessory requires only an optional "T-Adapter" ring for Nikon, Minolta, etc.

The TeleVue "Ranger" can operate on a lighter weight camera tripod, ideally with a well designed alt-azimuth head such as the TeleVue "Telepod" or with the wood "Panoramic" mount; such a design maintains the telescope well balanced throughout its travel to zenith, and this head has adjustable elevation ad azimuth clutches. Of course, the lightweight telescope can be used on a number of lightweight photographic tripods.

MECHANICAL CONSTRUCTION

The "Ranger" has a fully machined lens cell (housing the objective lens), focuser housing, and mounting hardware; each is finished in a lustrous satin black anodizing. The barrel is powder coated in the customer's choice of either a mottled "Evergreen", or powder coated (appearing like a textured plastic covering) in a neutral ivory finish (as illustrated above), or in solid brass (with brass trim) by special order. The optical tube assembly is finished internally with an anti-reflective method unique to the TeleVue telescopes. The interior of the optical tube in lined with an economical yet highly efficient baffling material - coarse sand paper, which is finished anti-reflection black.

The objective lens cell is permanently aligned to the barrel as is the focuser assembly. Unless subjected to gross abuse this telescope will provide many lifetimes of service with no need for any other than cleaning of the front surface of the objective lens using common camera lens cleaning techniques. The construction is the most rugged we have seen in a multipurpose telescope; it will withstand all the handling that is typical of backpacking, or airline travel.

The objective lens is recessed within the cell by about one inch, this helps to protect the lens from contamination and dew while the anti-reflection threaded walls reduce the impact of off axis light sources. We do however suggest an optional thread on lens shade; TeleVue offers one of flexible rubber. The telescope is provided with a plastic snap on/off 77mm lens cover, with the TeleVue trademark tastefully painted across.

The telescope rear cell is also made of precisely milled aluminum. It incorporates one groove machined the 11:00 o'clock position to accommodate options including finder sights such as the compact Qwik Point, the deluxe "Starbeam", or a "Piggycam" piggyback photography mount.

The rear cell houses the focuser which accommodates 1.25 inch diameter accessories. This is a a two stage design where coarse focus is achieved by releasing a lock screw at 12 o'clock on the rear cell, and then sliding the draw tube in or out to attain an approximate focus. The fine focus is accomplished by turning the helical focuser; a rubber grip ring makes this easy to find and operate in the dark. Two nylon lock screws with a knurled head are at the proximal end of the female 1.25 inch barrel (nearest to the operator) to retain accessories such as the diagonal, or photo adapters. The customer can order the "Ranger" with a choice of either:

  • TeleVue 1.25" Diagonal: 90 degree 1.25 inch diameter precision mirror diagonal (1/8th wave quoted) which has has an enhanced aluminum reflective coating. This is a good choice for those who either seek the most economical or light weight configuration of the telescope, or who do not require a wider field of view than the 3.2 degrees at 12X provided by the lowest magnification 1.25" oculars.

  • TeleVue 1.25" Prism Diagonal: 45 degree 1.25 inch diameter precision image erecting prism diagonal with high transmission coating. This is a good choice for those who must have an image erect and correct left to right view, and who do not intend to use the telescope at higher magnifications (100X or more).

NOTE: the view when using the telescope with a 1.25 inch mirror diagonal will appear to be right side up, and is reversed left to right. This is not usually a problem for astronomy or nature observing because the image quality and unvignetted field of view provided by the high quality mirror is exceptional. And so while we do offer optional 45 degree inclined image erecting prisms, these prisms can only accommodate 1.25" oculars. Furthermore, the erecting prisms will not provide image quality to equal that of a mirror diagonal, this is particularly perceptible at higher magnifications. However, for low to medium magnification applications where one needs correct images (such as to read numbers, etc.) then the prism should be suitable.

As the focus mechanism is uncommon, so is the design of the mounting hardware. This consists of machined aluminum mounting block incorporating a female dovetail channel, and six inch long (1" tall x 7/8" wide) male dovetail plate. The block is bolted on to the rear cell of the telescope. Then the telescope slides onto the dovetail plate. The plate has three 1/4" - 20 tpi threaded holes along its forward length so that one may attach the telescope onto common tripods. One can slide the telescope to the front, or to the rear of the plate to balance the telescope with a variety of loads attached. The dovetail plate has travel limit Allen head set screws, one at each end of the plate so that the telescope will not accidentally slide off. It is a simple matter to remove the dovetail plate and mounting block to slip the Ranger into conventional mounting rings for use as a guide telescope, or finder.

The telescope can be furnished with an optional dense polyester foam lined nylon carrying case with a zippered lid. This case has a pouch to accommodate several oculars, a camera adapter, etc.

TELEVUE 70mm f6.8 TELESCOPE SPECIFICATIONS

SPECIFICATIONS
Color correction: Less than 0.03% focus variation from 706nm to 405nm
Clear aperture: 70.4mm (2.8")
Focal length: 480mm (18.9")
Visual Resolution: 1.64 arc seconds
Coatings: Fully Multi-coated. Overall transmission greater than 94% in peak visual wavelengths
Magnification range: 9x to 140x
Tube assembly: Powder coat finish, aluminum tube; fully baffled, permanently aligned cell construction
Focuser: 1.25" drawtube 2.5" travel (coarse),
helical 5/8" travel (fine)
Focuser Travel: 2-3/8 inches
Near Focus (20mm Pl. w/E.R. Prism): 19 feet 10 inches (6.1 m)
Tube assembly length: 15.25" overall
Tube assembly diameter: 3-3/8" overall
Weight: 3.5 lbs.
Carrying case: Optional 19" padded bag
Photographic Resolution 212 Line pairs/mm
35mm prime-focus field: 4.2 x 2.9 degrees @ 6.8
35mm field with 2x Barlow: 2.1 x 1.4 degrees @ f14
Focal length with Field Flattener: 520mm (20.5")
Standard Eyepiece: TeleVue 20mm Plossl, 1.25 inch Dia.
* Specifications are subject to change without notice.

SUGGESTIONS

  • Panoramic Mount and Tripod: Cradles the telescope at its center of gravity for ideal balance at any viewing position. Vertical travel from -17 degrees (below horizon) up to +85 degrees, with full 360 degree rotation. Head is precisely machined of black anodized aluminum, with brass bearings and clutches on both axes. American ash wood tripod, two section extension design, with accessory tray/leg brace.

    Pronto telescope with 1.25
    Pronto telescope shown with 1.25" Mirror diagonal on Ash wood Panoramic Mount.

    The Panoramic Mount is also available with a Walnut finish wood tripod, and with brass tripod head and trim to match the brass "Ranger", or "Pronto", or "85" telescopes.

  • Telepod Head: Provides vertical travel from -17 degrees (below horizon) up to +85 degrees, with full 360 degree rotation. It is precisely machined of black anodized aluminum, with brass bearings and clutches on both axes. Can be attached to most camera tripods.

  • Telepod Tripod: Telepod Head with adjustable height, lightweight aluminum field tripod. Weighs just 7 lbs., minimum height 28 inches, full extension 63-1/2 inches. The tripod foot pads retract to reveal spikes for use on soft ground.

  • "Starbeam" Finder: Beautifully machined and black anodized aluminum, on a quick release machined hardware. Battery powered illuminator is adjustable in brightness; it projects a 10 arc minute diameter red dot onto a transparent 40mm clear aperture window so that the dot appears to be over wherever the scope is pointed. Six arc minute accuracy make "star hopping" easy.

  • Field Flattener: threads onto the male thread of the TeleVue telescope camera adapters. This makes the "Pronto" telescope perform as a 520mm f7.4 Flat Field telescope, with only very slight vignetting at the extreme corners of the film negative. Requires only an optional "T-Adapter" ring for Nikon, Minolta, etc.

  • Eyepieces: The telescope is furnished with a TeleVue 20mm Plossl providing 2.04 degrees Actual Field of View at 24X magnification. This eyepiece pales in comparison to the optional sophisticated wide angle eyepieces we recommend (offering up to 3 degrees at similar magnification) but the 20mm Plossl is an economical choice, that gets the buyer up and running with sharp clear views.

    Company Seven provides excellent technical support and advice and in addition to the factory literature we include printed information with each telescope that will help you to make wise decisions. But basically speaking, the typical observer will want to be equipped with at least three magnifications. These may be accomplished by the proper selection of optional eyepieces, possibly with a magnification increasing lens that may double (or more) the magnification of the telescopes.

    • most people want to see changing features on the planets Jupiter, Mars, Saturn, and Venus. For these objects, it will be best to equip the telescope to operate as close to 200X or so as practical - on the Ranger this will be about 150X. This remains well within the useful range of the Telepod mount head.

    • For Deep Sky (and nature/terrestrial) observing, or for use as a finder telescope we suggest you equip the telescope with relatively low magnification wide field of view (40mm or 32mm Plossl, or a 22mm wide angle ocular).

    • Many people enjoy having an eyepiece that provides about 1/2 degree or so field of view since this can provide good close up views of the full Moon, the Sun (with optional solar filter), many deep sky objects, and terrestrial objects (on steadier days).

    Eyepiece designs such as the Plossl, Orthoscopic, traditional Erfle and wide angle eyepieces show sharp images only in the center of the field when employed with telescopes such as this. These are acceptable as long as you realize this limitation, and find this unobtrusive. If you object to less than perfect images at the edge of the field, then Company Seven recommends the TeleVue "Nagler", "Radian", or "Panoptic" eyepieces. These oculars have the best flat field images and will bring out the most in your "Ranger" and many other telescopes.

  • Barlow Lens: Company Seven suggests you consider any of a number of Barlow we offer to double or as much as triple the telescope magnification. Contact us for suggestions on how to to best meet your goals.

SOME TELEVUE EYEPIECE SPECIFICATIONS WITH THE RANGER:

Eyepiece Magnification Actual field of view Exit pupil
40mm Plossl 12x 3.2 degrees 5.9mm
22mm Panoptic 22x 3.2 degrees 3.2mm
20mm Plossl 24x 2 degrees 2.9mm
15mm Plossl 32x 1.5 degrees 2.2mm
10mm Radian 48x 1.3 degrees 1.5mm
6mm Radian 80x 0.7 degrees 0.8mm
5mm Radian 96x 0.6 degrees 0.7mm

Contents Copyright 1997-2000 Company Seven All Rights Reserved
back