The GSO 12" f/8 Ritchey-Chrétien Astrograph is a dream telescope for astrophotography. The telescope is fitted with a stable Carbon Fiber Truss tube and a precise 3" dual speed Monorail focuser.
The GSO 12" f/8 Ritchey-Chrétien Truss Tube Astrograph is a true RC telescope and will give you spectacular photo results also with large format camera sensors.
The telescope is perfect for small observatories and will be carried from mounts in the EQ8 class.
12” f/8 true Ritchey-Chrétien hyperbolic mirror optical design
carbon fiber truss tube design with CNC-machined stainless steel and aluminum components
low thermal expansion quartz primary and secondary mirrors
99% reflectivity non-tarnishing multi-layer dielectric mirror coatings
three built-in cooling fans in rear cell
focuser attachment collar isolated from the primary mirror and baffle tube
3" MONORAIL Focuser with better stability
dust covers and finder shoe
Big corrected flat field without need for additional correctors
The focuser can be adjusted (tilted) independently from the primary mirror.
GSO has optimized this 12" RC especially for astrophotography
The OTA comes with carbon trusses having a thermal expansion of nearly 0. The OTA weight is 24 kg and it has a Losmandy style dovetail rail on both sides.
Our 12" f/8 RC Astrograph illuminates a max. field diameter of approx. 70 mm
Without corrector, 35 mm are possible. In the latter configurtion, you have a pure mirror system without any lenses. You don´t need an IR cut filter and can use the full spectrum with a suitable CCD camera.
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 the 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 Carbon Fiber Truss Tube Design :
Three CNC-machined aluminum support rings form the basic structure of the optical tube. Light-weight and rigid carbon fiber tubes connect the support rings in a Serrurier truss design, using CNC-machined stainless steel ball and socket hardware.
The Serrurier truss solves the problem of optical tube flexure by supporting the primary and secondary mirrors with two sets of opposing trusses mounted before and after the center support ring. The trusses are designed to have an equal amount of flexure, which allows the optics to stay on a common optical axis. When flexing, the "top" truss resists tension and the "bottom" truss resists compression. This has the effect of keeping the optical elements parallel to each other. The net result is that the optical elements stay in collimation regardless of the orientation of the telescope, including passing through the meridian during imaging.
The truss tubes are made of a light weight/high strength woven carbon fiber-reinforced composite material with extremely low thermal expansion characteristics. This reduces the possibility of temperature-related focus changes that can occur with steel or aluminum optical tube scopes during extreme temperature swings.
The 12RCT is 33-1/8" (841mm) long without focuser. The supplied focuser adds 5.25" (133mm) with the drawtube retracted. The center and rear truss tube support rings are 17.25" (438mm) in diameter, while the front support ring is 15" (381mm) in diameter. The 12RCT weighs 49.8 lbs (22.6 kg) without focuser. The supplied focuser adds 2.2 lbs (1 kg).
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.
- 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
Optical Highlights :
The hyperbolic primary and hyperbolic secondary are made from low expansion fused quartz, and finished with a scratch-resistant highly reflective 99% dielectric coating for great contrast. The primary mirror is fixed in place in an 18-point metal mirror cell, and the secondary resides in a metal housing that can be collimated. The secondary mirror has a center mark for easy and accurate collimation.
Cooling Fan :
The RC telescope has three small cooling fans in the rear cell that help create an ambient temperature within your telescope for more stable viewing and less fluctuation in focus. The fans are powered by an external battery pack. This battery holder accepts 8 AA batteries (sold separately).
A Fixed Primary Eliminates Image Shift :
Schmidt-Cassegrain, EHD, ACF... & Mak-Cassegrain telescopes achieve focus by moving the primary mirror back and forth inside the optical tube assembly, and this movement can cause image shift. While manufacturers have done a pretty good job of minimizing image shift on their telescopes, a moveable mirror makes it almost impossible to eliminate it completely. The Ritchey-Chrétien has a primary that is fixed in place, removing the possibility of image shift and also the job of collimating the primary.
Why RC Telescopes are better than Schmidt-Cassegrain telescopes with correctors :
This is also the advantage of RC telescopes against Celestron EHC or Meade ACF telescopes. These telescopes needs a lens corrector wich is integrated in the optical system. The RC is a true reflection system without lens corrector and with a really bright image.
The optical advantages of RC Ritchey-Chrétien Astrographs for astrophotography :
The GSO Astrograph is a real Ritchey-Chrétien reflector telescope. Contrary to Maksutovs or Schmidt-Cassegrains which have spherical mirrors and need image correctors, and contrary to Newtonians that need coma correctors, the RC system is a well corrected photographical instrument that uses only mirrors (no false colour!) and does not require any corrector with many cameras.
Mount Recommendations :
You need a strong mount to carry the weight of 24 kg + focuser + camera equipment. We suggest:
- Skywatcher EQ8 / Orion HDX 110
- Celestron CGEM-DX or CGE Pro
- iOptron CEM60
- Losmandy G11