|Seat||Torrance , California|
In 1950 the American Tom Johnson founded Valor Electronics in Torrance, California. Encouraged by the construction of a telescope for his son, he founded Celestron Pacific in 1964 as a part of Valor and began in 1966 as the first manufacturer worldwide to build Schmidt-Cassegrain telescopes (SCT). As early as 1969, the SCT product range comprised 6 to 22 inch openings. 1997 Celestron was sold to competitor Tasco, 2001 with Tasco to Bushnell Optics , another telescope manufacturer.
In 2003, a hostile takeover by direct competitor Meade , with whom Celestron shared the market for SCT, failed . Johnson bought his company back after a US federal court ordered the sale to Meade et al. a. had forbidden because of monopoly position.
Originally, Celestron manufactured professionally manufactured devices with larger openings, the Celestron C-12, C-16 and C-22 in particular. In addition, there was a C-4, C-6, C-8 and C-10 as early as the 1960s. All of these devices were painted blue and white. Without exception, the number of units of these devices remained very low.
In the first half of the 1970s, Celestron changed its range of devices. The gray-orange devices that were now produced were cheaper and were produced in large numbers. The so-called Celestron C-8, an 8 inch Schmidt-Cassegrain telescope with a free aperture of 200 mm and an aperture ratio of f / 10 ( focal length 2000 mm), was and is very successful and widespread among amateur astronomers The optical performance, ease of use and portability set standards, and the large numbers made it affordable. Above all, a patented process (US Pat. No. 3,837,124) was groundbreaking, with which the difficult grinding of the Schmidt corrector plate by means of negative pressure on a mold plate could be carried out precisely by machine and thus considerably less laboriously than before. SCT are characterized by a very short overall length in relation to the focal length (C-8: approx. 40 cm). The relatively thin and therefore rapidly cooling corrector plate lies directly at the tube entrance and is susceptible to fogging up with dew in certain weather conditions, so that dew caps or ventilation are necessary.
In the same design as the C8, the C-5 (opening 5 "= 125 mm) and the C-14 (14" = 360 mm) came on the market at the same time, followed by the C-11 (11 "= 280 mm), later also a C-9 1/4 with 9.25 "and a C-6 with 6". A Celestron C-5 was the on-board telescope for research on various NASA shuttle flights. The first series of C telescopes were shining orange ("Celestron-Orange") with light gray attachments. In the 1980s, the color palette was expanded to black or dark gray. The latest model series "Edge-HD" (with white tube) has an improved look that clearly shows has a lower coma and fully compensates for the design-related field curvature.
These telescopes in the classic design are supported by a very easy-to-use and extremely compact equatorial mount in the form of a fork mount (without the need for counterweights) with tracking by stepper motors of various types. The optical tube can also be used on so-called German mounts with counterweights or altazimuthal systems without mechanical adaptation to the rotation of the earth, the latter now partly computer-controlled allowing the telescope to be tracked to compensate for the rotation of the earth. Comprehensive accessories make the Celestron-Schmidt-Cassegrain series a versatile product for a wide variety of applications (visual and photographic).
In contrast to classic Cassegrain telescopes, the SCTs are not day-blind due to their special inner screens, so that they can be used not only for astronomical purposes, but also during the day, for example for nature observation. Another special feature is the internal focusing via the main mirror, which together with the high re-magnification of the secondary mirror (approx. 5x) results in an exceptionally large focus area. In contrast to conventional larger telescopes, the systems can also be used as a “distance microscope” for observing very close objects (a few meters), for example for image-filling observation of very small animals (e.g. insects or spiders) from an undisturbed distance. The C telescopes are therefore also widely used in nature photography (some with a reduced focal length, e.g. C5 televariant with a focal length reduced from 1250 mm to 750 mm). The slight tilting of the optics when moving the mirror forwards and backwards, which is typical for internal focusing (“shifting”), is irrelevant for the image quality, since the SCT main mirror is spherical and is not parabolized. The Schmidt corrector plate compensates for the spherical shape error.
Today the company mainly produces telescopes with fully automatic positioning, also using GPS- controlled motors; in terms of optics, however, the proven systems described above are still used.