Why Buy from CCTS?
Every telescope we receive is physically and optically inspected by our experts for proper collimation and flawless operation.
Visit Our Online Store
CCTS Star Party Events
catadioptric telescope has a closed tube system, using a
combination of mirrors and lenses to form an image.
There are two common catadioptric telescopes available
on the market, the Schmidt-Cassegrain and the Maksutov
The Schmidt-Cassegrain has a long history. In 1672 M. Cassegrain invented a reflecting telescope which utilized a concave primary mirror that gathers light from the sky and reflects it up to a convex, adjustable secondary mirror. The light then reflects down through a hole in the primary mirror to the Cassegrain focus.
This design helps to remove the coma, a common problem with Newtonian reflectors as discussed previously. It also places the focus at a more symmetrical position, allowing for easier installation of such additional equipment as cameras. The Schmidt part of the system has to do with a specially-shaped corrector plate that covers the front end of the tube assembly. This corrector plate is coated, like a camera or binocular system, to allow light to transmit as undisturbed as possible to its destination.
Putting the Schmidt and Cassegrain features together, you get a telescope that is compact for its aperture size, yet yields deep-sky and planetary views of high quality. The Schmidt-Cassegrain telescope is one of the most popular designs today due to these attributes, plus the wide availability of accessories. The most common sizes available are the spotting scope, which fits on a photographic tripod, and the 5", 8",10",11", 12", 14", and 16" astronomical telescope.
The Maksutov-Cassegrain has been considered a rare bird, but Meade Instruments has just introduced a 7" fl5 that is creating a lot of interest in astronomy magazines. Instead of an aspherical corrector plate like the one used in the Schmidt, a crescent-shaped lens is used. This corrector plate is shaped like a shallow bowl, curving inwards, and has a reflective spot on the corrector itself, which acts as a secondary mirror.
Since this corrector lens is slightly diverging, it can be placed nearer the primary mirror, and a shorter tube can be used in comparison to the Schmidt Cassegrain design. Meade's Maksutov telescope is a 7" fl5 model, but the tube is only slightly longer than the 8" f10 Schmidt Cassegrain.
Since it is fl5, its contrast is better, and few viewers will notice the darker background sky than with a faster telescope. In other words, the Maksutov is like a refractor-Cassegrain combination, offering the best of both types of telescopes.
There is a very wide price range with these telescopes, ranging from $1,000 to well over $2,500, depending on mounts and electronics.
There are two basic kinds of mounts available for the Schmidt-Cassegrain or Maksutov-Cassegrain telescopes: the fork mount and the German equatorial.
German Equatorial Mount
This is the same mount as the standard equatorial, but designed for heavy duty use. In order to hold the weight of a Schmidt-Cassegrain or Maksutov-Cassegrain, or a large refractor or Newtonian reflector, the mount would have to be much stronger than one that is meant to hold a 60mm, 80mm, or 90mm refractor or a four and a half inch reflector.
Such mounts are generally machined to much higher tolerances, and the tripods that accompany these mounts are of the same quality as a good tripod that comes with a fork-mounted system.
Fork Equatorial Mount
The fork mount holds the optical tube assembly of the telescope suspended between two arms so that it may swing freely up and down and through the arms for easy movement in declination. The arms resemble the tines of a tuning fork, hence the name.
The forks are mounted in turn on the drive base, a horseshoe-shaped box where the electronics of the telescope are found. The forks rotate in right ascension from a pivot point in the center of the drive base. The drive base is either attached to an equatorial wedge by way of removable bolts or is attached to a central bolt directly to the tripod base for altazimuth operation.
Come see us at NEAF 2012!
10 South Ocean Ave
Follow us on Facebook!