The 40cm RitcheyChrétien telescope is located at Piszkéstető Mountain Station with a primary mirror of 40cm and has an effective focal ratio of f/6. The telescope was manufactured by Gemini Telescope Design. Currently the telescope is under developement and not working.
Contents 
Primary mirror diameter  400 mm 
Primary mirror focus  1405 ± 30 mm 
Secondary mirror diameter  160 mm 
Secondary mirror focus  977 ± 22 mm 
Separation  907 ± 5 mm 
Focal length of the system  2460 mm (2840 mm without the focus reductor) 
Field of view  25.1 x 18.9 arcmin 
Pixel scale  0.453 arcsec/pixel 
FLI ML8300
Camera Chip Model  Kodak KAF 8300 chip 
CCD type  Front illuminated 
Maximum Cooling  60°C Below Ambient 
Full well capacity  25500 e 
chip size  17,96 x 13,52 mm 
chip size  3326 x 2504 pixel 
pixel size  5.4 μm 
Here are the formulas, how to calculate the basic optical parameters of a cassegrain telescope. First we have to declare the sign conventions we will use:
All Cassegrain telescopes consist of a concave primary mirror with a small secondary mirror inside the focus of the primary; the secondary redirects starlight toward the primary. The image, in most cases, lies behind the primary. The convex secondary multiplies the focal length by a factor M. This factor M is termed secondary magnification, and is defined:
The focal length of the system is:
We can calculate the basic parameters seen in the picture with the formulas below:
Where f_{1} is the focal length of the primary, f_{2} is the focal length of the secondary (it is a negative value because of the conventions), and d is the separation. b is the back focus of the system, and bfl is the back focal length.
The focal surface has a radius of curvature:
Where R_{F} is the radius of curvature of the focal surface, r_{1} is the radius of curvature of the primary and r_{2} is the radius of curvature of the secondary.
The sagitta of the mirror is: (sagitta is the height of the mirror at a given radius.)
where z is the sagitta, h is the radius where we calculate the height of the mirror, r is the radius of curvature of the mirror, SC is the conic constant (explained later).
The conic constant, or Schwarzschild constant defines the shape of a conic section.
where e is the eccentricity of the conic section.
We will use the dimensionless quantities defined by Schwarzschild:
The thirdorder Seidel Coefficients for a twomirror Cassegrain are:
Spherical aberration:
Coma:
Astigmatism:
To simplify the formulas above, we will use additional quantities:
Since the spherical aberration is zero; A_{cass} = 0, we can calculate the different conic constants of the primary and secondary mirrors.
For the classical Cassegrain, the primary is parabolic SC_{1} = − 1, so the secondary is:
For the RitcheyChrétien, both spherical aberration and coma are eliminated, so

