THE QUESTAR 12 TELESCOPE

The QUESTAR 12: in 1976 a larger and notable introduction was that of the Questar 12. By the mid 1970's research in laser transmission and reception was increasing the need for larger aperture yet robustly constructed optical systems. Among the markets for these new instruments was Light Detection And Ranging (LIDAR), and missile tracking - for film recording of rocket launches for example. Questar had up to this time offered systems with apertures as large as 7 inches (180mm), but competing products were coming available in 8 to 10 inch and larger apertures. So Questar began work on a larger optical system, settling on 12 inch (300mm) for production with hopes of marketing this new system for applications involving Geomatics, geography, geology, geomorphology, seismology, remote sensing and atmospheric physics. The instrument seemed to be a natural choice too for astronomical uses by advanced amateurs and schools.

The Questar 12 is a Maksutov-Cassegrain arrangement with aluminized mirrors and magnesium fluoride anti-reflection coatings. The production of the optics proved to be complex and time-consuming, hence resulting in a higher cost per unit than what had been initially hoped for. The system incorporates a very difficult to figure precise asphere on the concave side of the BK-7 (Borosilicate Crown) glass Corrector Lens, with some fifty (50) waves correction on the outer two inches of this component. The optics feature an uncommonly smooth figure (RMS) for systems of this period owing to the time consuming polishing process. It turned out that one experienced technician might devote as many as six months of labor in figuring and testing the system, matching the optics as a set. Worse still, it was possible to actually to work on the optics and pass the point of nominal figuring so that one might need to start all over again with new components!

Right: Questar 12 telescope on Questar Byers German Mount (155,980 bytes).
Click on image to see enlarged view (230,733 bytes).

For astronomical applications the famous Edward R. Byers company manufactured a precision German Equatorial mount to manage the heft of the Questar 12; this was marketed as the Questar Byers Mount and features prominently in the Questar 12 advertisements (as at right from 1979). The optical tube assembly was hard bolted onto the Byers mount saddle plate, to facilitate balancing with changing payloads the Questar 12 is provided with two sliding counterweight bars one attached on either side. The Questar 12 astro telescope was initially equipped with a refractive finderscope, but Questar changed this to a Questar 700 lens set up for wider field of view use (as low as 22x) with their 1.25 inch diameter mirror diagonal. The optics can provide striking images within the one half degree field of view limitations of this inherently high magnification design. One of the favorable published accounts of observing is "The Questar 12 Experience" by Walter Macdonald, in the Journal of the Royal Astronomical Society of Canada Newsletter, Vol. 80, p.L15. As good as the telescope can perform for visual astronomical applications when at its best, there are many more accounts of the telescopes requiring long hours to acclimate to ambient temperature changes.

For astronomical applications the Edward R. Byers company manufactured a German Equatorial mount to manage the heft of the Questar 12, this was marketed as the Questar Byers Mount and featured in the advertisements (as at right from 1979). The system incorporates worm gear driven Right Ascension and Declination axes, so an older mount could be adapted for use with a more modern 'go to' computer controlled system. The Right Ascension housing of the mount consists of not only the drive gear set and bearings but also an precision machined wedge made to support the mount atop a pier installed at the intended latitude of the system; minor pole alignment adjustments are made at the mount to pier and or pier to foundation attachment points.

The first Questar 12 was Serial No. 4001, while the last one sold was 4012. Most of these telescopes were sold for industrial and government applications. But given recent improvements in design and performance of ten to twelve inch aperture Maksutov systems made by other companies (most notably including Astro-Physics), any future production of the Questar 12 for astronomical applications would not seem to make the most sense.

And to clear up any rumors, in the mid 1980's Lonnie Benton, then Manager of Questar Corporation, and Martin Cohen of Company Seven discussed plans for production of an even larger instrument - the Questar 18. However, after considering the production difficulties and other practical issues, the very high cost and uncertain demand, the project was never pursued.