There are other ways to design a catadioptric system at f/10 using the full aperture Schmidt type correcting plate, by generating a different aspheric curve on the secondary. However, for production purposes, the difficulty lies in producing a diffraction limited instrument using a different aspheric curve on the secondary, on a consistent basis. Regardless of theoretical advances that other designs may promise, the key lies in the consistent diffraction limited performance that is actually realised when a catadioptric telescope is factory produced. Celestrons original tried and tested method has worked and worked very well over the decades, one of the main reasons astronomers continue to trust Celestron's optical designs. Many competing catadioptric telescopes have found it difficult to match the optical consistency of Celestron.
The Celestron Schmidt Cassegrain design is also beneficial for planetary imagers over other catadioptric designs such as the Maksutov Cassegrain (both the standard Gregory type and the separate secondary configuration), due to the cooling times of the thick meniscus lens on Maksutovs. Maksutovs often show correction errors for long periods of time whilst cooling. On the larger instruments (greater than about 180mm) this can be quite protracted. The problem is often due to the differential cooling periods of both the primary mirror and the meniscus. For planetary imagers, this can sometimes mean an unproductive night waiting for spherical aberration to reach a minimum. The Celestron Schmidt Cassegrains cool at a much faster rate, which means a much longer period of observation with the telescope at optimum correction.
Celestrons Schmidt Cassegrains offer the amateur astronomer or the optical enthusiast the complete owning a telescope experience. The apertures range from five inches to fourteen inches and focal lengths between 1250mm and 4000mm. They are the scope of choice for planetary imagers, and deep-sky imagers because of the range of image scales. They represent the ideal observing instrument with medium to large apertures, medium to longer focal lengths for the comfortable use of higher magnifications, a large diffraction limited field free of aberrations, and rear eyepiece positioning for relaxed long periods of observing. The closed tube design keeps the important optical surfaces clean and prevents image-destroying tube currents seen in some Newtonians. The primary mirror focusing system permits close focusing with minimum spherical aberration, whilst enabling the observer to vary image scale, and all of this potential and performance in a closed compact easy to handle optical tube assembly.
11" Schmidt-Cassegrain Optical Tube Assembly
Aluminum Optical Tube
Celestron's premium StarBright XLT coatings
2800mm focal length (f/10)
40mm eyepiece included (70x)
Visual back allows for use with 1.25" accessories
9x50 finderscope to help accurately find objects
Star diagonal provides more comfortable viewing position when observing objects that are high in the sky
Includes dovetail rail compatible with CGX / Losmandy
OPTICAL DESIGN: Schmidt-Cassegrain
DOVETAIL COMPATIBILITY: CGE Mount
APERTURE: 279.4 mm
FOCAL LENGTH: 2800 mm
FOCAL RATIO: 10.02
OPTICAL TUBE: Aluminum
EYEPIECE 1: 40 mm
MAGNIFICATION 1: 70 x
STAR DIAGONAL: 1.25"
OPTICAL COATINGS: StarBright / XLT
SECONDARY MIRROR OBSTRUCTION: 95.25 mm
SECONDARY MIRROR OBSTRUCTION BY AREA: 12 %
SECONDARY MIRROR OBSTRUCTION BY DIAMETER: 34 %
OPTICAL TUBE LENGTH: 609.6 mm
OPTICAL TUBE WEIGHT: 27.5 lb (12.47 kg)
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