The 12 inch GSO Ritchey-Chrétien astrograph is a large aperture true RC, a dream telescope for astrophotography.
The Ritchey-Chrétien telescope with 254 mm aperture is designed for full illumination of the "35 mm format" (24 x 36 mm). For cameras with a small sensor, particularly most CCD cameras, no field flattener is needed. For cameras with a larger sensor we recommend the use of a field flattening lens. A better alternative for astrophotography than a modified SC telescopes.
Aperture 12" / 304 mm
Focal Length 2432 mm
Focal Ratio f/8
Metal tube with 2 Losmandy level dovetail bars
99% dielectric high-reflectivy coating on main- and secondary mirror
Big corrected flat field without need for additional correctors
3 " MONORAIL Focuser with better stability
Computer optimized internal baffle system
The 10" f/8 RC Astrograph can illuminate a field diameter of max. ca. 60 mm
(including optional RC corrector). Without corrector, the usable field has ca. 30 mm diameter. Here, you have a pure mirror system that can be used without UV/IR cut filter. Most of the CCD cameras are sensitive in this spectral range.
The image is absolutely free from chromatic abberations and the resulution is higher than most apochromatic refractors in this price range.
 
How to find the focus
The RC has a generous back focus allowing to attach many accessories like off-axis-guiders, filterwheels and much more. The distance from the 2" connection of the focuser to the focus point is 127 mm.
To reach the perfect focus position, we suggest an extension rings. The position of the rings is between focuser and tube backside. So you always have a good position of the draw tube.
 
The 3" M-LRN Monorail Focuser
The 3" Monorail focuser is a further development of the Crayford design. The load is not carried by four (often underdimensioned) ball bearings but on a stainless steel track on the base, thus preventing tilting and bending even under high loads. It is countered by a big knurled screw that centers the inner tube exactly to the rail. The load is distributed evely across the rail´s surface.
Technical details of the focuser:
Travel: ca. 80 mm
Clear aperture: 68 mm
Guidance: by massive and fixed steel rail
1:10 transmission for precise focusing
360° rotation
Adaption to 2" and (when screwed off) female M68 thread, directly fitting to TS 2.5" off-axis guider
 
TS Ritchey-Chrétien (RC) telescopes
TS Ritchey-Chrétien (RC) telescopes are known for their excellent optical performance, especially for photographical applications. But RC telecopes are also well known for their expensive price. with the help of GSO we offer a full line of true RC telescopes for the amateur to an affordable price.
 
Features of the 10inch RC Telescopes
True RC Optics with a hyperbolic primary and a hyperbolic secondary mirror
Primary and secondary mirror are made of low thermal expansion quartz
The secondary mirror has a center mark for better and more simple collimation
99% reflectivity non-tarnishing dielectric mirror coatings
Big well corrected flat field without need of a seperate corrector
Enough backfocus for correctors and reducer
Less dew problems against Schmidt Cassegrain or similar
Fast cooling down time because it is an open system
Each RC is tested and checked before dispatch
 
Hyperboloid primary mirror
Made of low thermal expansion quartz. Ground and polished under precision computer control and tested for accuracy multiple times during fabrication on Zygo interferometers. Unlike catadioptric designs (SCTs, Maksutovs, etc.) that move the primary mirror fore and aft in the optical tube to focus (which can lead to image shift and focal length changes as the mirror moves), the AT10RCT primary mirror is fixed to eliminate both image shift and focal length changes, as well as the frequent primary mirror collimation requirements of a Newtonian reflector. Primary mirror collimation is pre-set at the factory, but can be adjusted if needed using three traditional push/pull locking adjustment screw sets.
 
Hyperboloid secondary mirror
Made of low thermal expansion quartz, rather than Pyrex. Ground and polished under precision computer control and Zygo interferometer tested. Mounted in a CNC-machined four-vane spider and fully collimatable using simple standard Cassegrain reflector collimating techniques. The secondary mirror is precisely center-spotted to make collimation easier. Unlike complicated RC designs that use motors to move the secondary mirror fore and aft to focus, which can lead to focal length changes, the RC 10 secondary mirror is fixed and focusing is done externally by means of an optional external focuser, discussed below. 
R-C’s fixed primary and secondary mirrors “eliminate image shift, which has been the bane of Cassegrain scopes with moving-mirror focusing systems . . . It also keeps the effective focal length of the system constant, and the infinity focal point remains at a fixed point outside of the telescope, neither of which is the case with moving-mirror systems that change the separation between a Cassegrain’s primary and secondary mirrors."
 
Low Thermal Expansion Quartz primary and secondary mirrors with 99% reflectivity
Designed for astro imaging, RC mirrors are made of low thermal expansion quartz, rather than the ordinary optical glass used by competitors. Ground and polished under precision computer control to diffraction-limited or better surface accuracy. Both primary and secondary mirrors have a full 99% reflectivity for the brightest possible images. This is substantially higher than the 88% reflectivity of competitors’ conventional aluminum coatings or the 94-96% reflectivity of enhanced aluminum coatings.