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Home Telescopes Optical Tube Assemblies Celestron Optical Tubes Celestron C14 SCT XLT CGE Fastar Optical Tube Assembly
The most revered model of Celestron's celebrated Schmidt Cassegrain design, and the choice of the world's finest amateur planetary imagers. The quality of some of the lunar/planetary images caught on modern CCD chips by enthusiastic amateurs, exceed the levels reached by professional observatory instruments from the previous fifty years. Many SCTs have come and gone over the years, the C14 still retains its position as the leading telescope of its kind. It now has legendary status as one of a very small and elite group of astronomical instruments that have defined and still define post-modern amateur astronomy. What is it about the C14 that since its original introduction several decades ago, has been the telescope that many observers and astrophotographers aspire to owning?
It has fourteen inches of aperture, vital for delivering extremely bright images, vital for the detection of very faint deep-sky objects, an important ingredient for the resolving of globular clusters and detail within deep-sky objects (DSO), and excellent in revealing fine detail in extended detail objects such as the moon and planets. It has a focal length of 3910mm. This means, for imagers, a large image scale for capturing condensed DSOs, lunar and planetary images. It also means that for medium and high magnifications whilst observing, long focal length eyepieces with comfortable eye-relief can be used. Observing with a C14 is as comfortable and relaxing as it gets, the modern trend in bino-viewing adds yet a further dimension to the C14 experience. For wider fields of view (both visually and photographically), the addition of a Celestron reducer/corrector permits the capture of the larger DSOs by the reduction of the focal ratio to 63% of the normal f/11 focal ratio. The C14-AF XLT model is Fastar compatible. This means that the secondary mirror can be removed and replaced by a corrected camera for extreme wide-field photography at f/2.1. The C14 is the only SCT in current world production that offers this unique facility. All of these advantages are realised within a compact tube. There are no extreme weight and weight distribution issues with a Schmidt Cassegrain when choosing a mount, even with the C14. Because of the compact design, most of the weight of the tube assembly is held centrally with a German equatorial mount, and centrally within the arms of a fork mount. There has been much said and written regarding the optics in the SCT. Essentially, the combination of a spherical primary, an aspherized secondary and a Schmidt plate (a thin glass plate, plano (flat) on one side, and with the Schmidt curves on the other), creates a wavefront that is free from Lower Order Spherical aberration (LSA), free from Higher Order Spherical aberration (HSA or zones), a diffraction limited field free of coma and astigmatism, and the field free of Chromatic aberration (CA). The design has much greater freedom from off-axis coma than the equivalent focal ratio Dall-Kirkham, much greater freedom from off-axis coma than the focal ratios usually found in Newtonians, does not suffer from tube currents in common in open tube Cassegrain focus instruments such as the Dall-Kirkham, the Klevsov, the sub-aperture meniscus Maksutov and the standard Cassegrain, a smaller secondary than the photographic Ritchey-Chrétien and none of the chromatic aberration associated with achromatic refractors. 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. Celestron’s original tried and tested method has worked and worked very well over the decades, one of the reasons the C14 and more recently the C9.25 have attained a cult status amongst serious observers and astrophotographers. Some competing catadioptric telescopes have found it difficult to match Celestron in this regard. 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. Celestron’s 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. 14" Schmidt-Cassegrain Optical Tube Assembly Aluminum Optical Tube Fastar Compatible Celestron's premium StarBright XLT coatings 3910mm focal length (f/11) 40mm 2" eyepiece included (98x) Visual back allows for use with 2" accessories 9x50 finderscope to help accurately find objects 2" mirror diagonal provides more comfortable viewing position when observing objects that are high in the sky Includes dovetail rail compatible with CGE mount SpecificationsOPTICAL DESIGN: Schmidt-Cassegrain DOVETAIL COMPATIBILITY: CGE Mount/ Orange APERTURE: 355.6 mm FOCAL LENGTH: 3910 mm FOCAL RATIO: 11 FINDERSCOPE: 9x50 OPTICAL TUBE: Aluminum FASTAR COMPATIBLE: Yes EYEPIECE 1: 40 mm MAGNIFICATION 1: 97.75 xSTAR DIAGONAL: 2" OPTICAL COATINGS: StarBright XLT SECONDARY MIRROR OBSTRUCTION: 114.3 mmSECONDARY MIRROR OBSTRUCTION BY AREA: 10 %SECONDARY MIRROR OBSTRUCTION BY DIAMETER: 32 %OPTICAL TUBE LENGTH: 787.4 mmOPTICAL TUBE WEIGHT: 45 lb (20.41 kg)
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