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Specification

Source of data

• Manufacturer's technical data.

Manufacturer description #1

Called by Modern Photography "the best" the Questar 700 is unique in bringing to the telephoto market a lens that guarantees theoretical optical perfection and flatness of field from edge to edge, with no linear distortion. Precise focusing from infinity down to 10 feet is accomplished with a single turn of the focusing ring, and at the 10-foot distance the image magnification is 1:4, an unheard-of ratio in telephoto lenses. Only Questar can deliver such performance. The Questar 700 can be connected to virtually every 35 mm SLR camera. Questar Corporation, New Hope, PA 18938.

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The Many Focal Lengths Of The Questar 700

An extremely useful feature of the 700 is the manner in which the focal length of the lens can be varied for different applications. When the camera with its own adapter is attached to the swivel coupling, the focal length is 700 mm. A 1 1/2X Barlow, used between camera and 700 lens, will increase the focal length to 1050 mm.; a 2X Barlow will double the basic focal length to 1400 mm.; and for the greatest enlargement of the image size, two Barlows in the system will increase the focal length to 2800 mm.

Photography With The Questar 700

If you are new to the field of telephotography there are three things you may encounter - for the first time you may become aware of heat waves over a long air path; second, you are apt to see the microscopic motion in your equipment magnified by long focal lengths at high powers; and, finally, you will realize how important exact focus becomes with the fine detail you are trying to capture on film.

Focusing The Questar 700

Focusing the 700 will take some practice. Just bear in mind that the object you will see in your viewfinder will not be as bright as the one you are accustomed to with a regular camera lens. Moreover, the clarity of the viewfinder groundglass varies from one camera to the next; some brands are quite grainy. You must change your groundglass to one that is intended for use with a telephoto lens. Your camera manufacturer will list the appropriate screen for this purpose.

Focusing is accomplished with the wide rubberized focusing ring. This provides internal focusing of the system from 10 feet to infinity with one smooth 360° turn.

Manufacturer description #2

A Questar ad (1981):

There is Nothing Like A Questar 700 Mark II

Have you tried the Questar system of getting photographs at distances you can't reach otherwise? Have you ever seen Questar's resolution, not possible with other telephoto lenses, focused with a single turn of the focusing ring from infinity to 10 feet? Are you familiar with optical perfection that is guaranteed, and flatness of field from film edge to film edge? This is performance that no other lens can match.

Now there are two models of the Questar 700 - the Mark I and the Mark II. You'll be amazed at what we have come up with now.

From the Modern Photography magazine (January 1977)

Thank God somewhere in the U.S. there are designers and manufacturers who still settle for nothing but the best. This has been the guiding principle of Questar Corp. of New Hope, Pa., famed makers of the exquisite Questar telescopes. Last July we gave you the preliminary report of a preproduction Questar 700mm lens designed exclusively for photography - a long, but hand holdable mirror lens in which quality would be the primary thrust of design, manufacture, assembly and testing. What Questar planned was a lens of very long focal length whose optical quality would far outdistance all others. It would not be the smallest mirror lens or the lightest, merely the best by a long shot. They've made it. Given good atmospheric conditions, accurate focus with a well aligned camera and a very steady support, the lens can equal in resolution what you might expect from a good, normal focal-length lens on a 35mm SLR!

The lens itself appears massive (which it should, being some 200mm longer than most similar hand holdable mirror lenses and built to very sturdy specifications). It measures some 8 in. in length, is 4 3/8 in. in total diameter and weighs 4 lbs. Virtually any 35mm SLR can be fitted to the attaching tube at the rear with a screw-on, T-adapter.

The Questar lens barrel is provided with a massive 2 in.-square tripod platform with standard 1/4 in.-tripod thread. A knurled screw at the right rear of the lens allows the camera and mounting tube to rotate for horizontal or vertical shots or just to true up the alignment. A 2 in.-wide rubberized-focusing ring provides adequately smooth movement of the secondary mirror and corrector plate from infinity to 10 ft. in a 360° turn - 10 ft. focusing! Yes, delivering a magnification of 1:4 unheard of in a mirror lens before, but a Questar specialty since Questar telescopes are also incredibly close focusing. Filters can be threaded into the rear attaching tube. Questar claims no sunshade is needed up front.

Focusing the Questar 700 takes some practice and precision. The view on most standard SLR finders tends to be somewhat grainy, and of course, not as brilliant as you would get with an f/2 or faster, normal optic. Because of the smaller aperture, most split-image rangefinders and microprisms will prove inadequate. Instead, the fine-focusing collar should be used. (The actual T, or light transmission stop, of the Questar is about T/11.)

From the Industrial Photography magazine (February 1979)

Questar's 700mm mirror system is part of a family of Maksutov cassegrain catadioptric lenses which compresses long focal lengths into short barrels. As an example of the contrast between "normal" size requirements and an equivalent focal length mirror lens, consider that a 50 or 60-inch telescope barrel can be compressed into a cylinder of only eight inches in length. The accompanying reduction in weight is equally impressive.

The catadioptric cassegrain lens, such as the 700, is simply a system that incorporates both reflecting and refracting components and has rotational symmetry about an axis. The Maksutov system employs a fairly thick meniscus lens of low negative power in order to yield overcorrect spherical aberration of a concave spherical mirror. This type of optical arrangement is generally free from chromatic aberrations and is therefore ideal for photographic use.

Included in the Questar system is a convex mirror located in the convergent beam to allow the image to return down the axis of the system. This technique, which provides an important method of obtaining an accessible focal plane, represents a cassegrainian system.

Questar's 700mm lens contains only four elements, which should not be construed as a lack of the necessary ingredients for professional optics. Mirror lenses just don't require as many elements to get the job done as standard optical formulas. This unit has a single aperture, f/8, which requires the user to regulate light transmission by means of N.D. filters. This is not generally a major problem, but since the glass filters must be inserted into the rear section of the optical system, the lens must first be removed from the camera, making it a bit inconvenient at times.

In the vital statistics department, the clear aperture area measures 88.9mm; focus range extends from ten feet to infinity, and the angle of acceptance is three degrees at 25 feet. Regarding bulk, the lens weighs in at four pounds, is eight inches long and 4-3/8 inches in diameter. Not bad for a 700mm focal length! At a distance of ten feet, image magnification is 1:4, which to our knowledge is well beyond the capability of conventional telephoto lenses.

The standard screw-thread T-mount adapters offered by Questar make it quite easy to mate the lens with most 35mm slr cameras, including Alpa, Canon, Leica, Nikon, Olympus, Minolta and a host of others. Also available are a large number of accessories, including camera cradles, cases, adapters, counterweights, eyepieces and optical glass filters. The lens itself has a list price of $1375.

Typical characteristics of mirror (reflex) lenses

• Catadioptric system consisting of curved mirrors and optical glass;
• Much shorter, lighter and less expensive designs than conventional super telephoto lenses;
• Outstanding correction of chromatic aberrations;
• Since the aperture is fixed, neutral density filters are used to obtain a smaller aperture;
• Doughnut-shaped out-of-focus highlights.

Lenses with similar focal length