Questar Gift
Malcolm Saunders
Questar Gift: In late April, BPAA unexpectedly received the generous gift of a 7 inch Questar telescope, donated by Magie Biehl, a former Bainbridge Islander who has moved to San Diego. It comes with a sturdy tripod and one eyepiece. This telescope is available for loan to BPAA members.
Questar telescopes are sometimes referred to as the Rolex of amateur telescopes— fi nely made; meant to outlast a lifetime. Questar began producing telescopes in 1954, mostly of 3.5 inch diameter. This 7 inch model went into production in 1967. http://www.company7.com/questar/ surveillance/que7bar.html
Questar telescopes in general are of the Maksutov optical design, invented by Dmitri Maksutov in the 1930s and 1940s (http://tec.idcomm.com/ tec_us/company/DmitriMaksutov.html). This is a catadioptric design, like the Schmidt-Cassegrain design that has become common in the past decade. Catadioptric telescopes are combined refl ector/refractor telescopes. They rely on a mirror as the primary optical element, but they add a lens at the opening, or front, of the telescope to correct for aberrations introduced by the mirror.
The lens at the top end, or front, of the telescope also closes the telescope tube which helps to keep the optical elements clean and reduces problems caused by air currents within the telescope tube. In the case of the Maksutov design, both the mirror and the lens are spherical sections. This makes them relatively easy to grind and polish, compared to the paraboloid used in Newtonians or the paraboloid and hyperboloid used in Schmidt- Cassegrains. The importance of these simple optical shapes has diminished in recent years as computer aided design and manufacturing have become commonplace. Both Schmidt-Cassegrains and Maksutov telescopes have long focal lengths in a short tube, making them unusually portable.
For example the Questar 7 telescope we just acquired has f/14 focal ratio, for a focal length of 2413 mm. This focal length is similar to the large telescope on the roof of the BPAA observatory. For more information about the Maksutov, Cassegrain and other telescope designs have a look at this Wikipedia article.
Our newly acquired Questar comes with a built-in fi nder scope as well as a built in barlow lens. That means that, simply by fl ipping small levers, the telescope can show the same object at three different magnifi cation powers. The tripod is sturdy, and lightweight, but not well suited for astronomy as it is currently confi gured. This is because it will not point high in the sky. We can change that by adding a “wedge” to the top of the tripod. The telescope also has provision for placing a camera at the prime focus, although we are missing one part to accommodate the camera.