All about the Ritchey-Chretien Carbone Kepler GSO 8" 200mm f/8

The "Ritchey-Chretien" configuration is particularly appreciated by professionals, it is the optical formula of choice for the largest telescopes in the world such as those of the VLT, the Hubble or Herschel space telescopes or even the Keck or Subaru telescopes. The Taiwanese manufacturer GSO offers optical tubes at extremely attractive prices that allow astrophotographers to equip themselves with specialized large-diameter photographic instruments (200 to 355mm).

Optical design

The formula proposed by GSO is a true Ritchey-Chretien formula, with hyperbolic primary and secondary mirrors, without integrated corrector. It has the main advantage of offering excellent correction of coma and spherical aberration and therefore of offering a flat field over a large image circle, even if this is done to the detriment of field curvature. The Ritchey-Chretien therefore appeals to deep sky photographers equipped with large sensor imagers, wishing to cover the widest field possible at a medium/large focal length. This formula is very well suited to imaging galaxies, for example, but it is always possible to add a focal reducer if the field covered is not sufficient, especially for larger objects.

Mechanical concept

The mechanical construction is neat, the 230mm diameter tube is made of carbon and has 2 Vixen type dovetails. The one positioned above will allow the installation of accessories such as counterweights or guide bezel. The collimation is carried out only by means of 2 sets of screws located on the secondary and on the barrel of the primary. It will be greatly facilitated by an optional collimation eyepiece as it must be taken care of to minimize astigmatism and obtain an optimal result. We systematically carry out verification and collimation on an optical bench for these instruments.

Additional advantage: compactness and reduced weight thanks to the carbon tube. The RC8 Kepler can easily be used in astrophotography on an equatorial mount of the HEQ5 type. This KE096 version is equipped with a Crayford microfocuser type focusing system with guide rail. These devices respectively make it possible to guarantee very precise focusing and better rigidity without play in rotation.

0.67x CCD reducer for astrophotography

The CCD47 improves the focal ratio from F/8 to F/5.36, reducing exposure time to less than 50%. With this you can capture nebulae and galaxies with moderate exposure times. Ideal for enhanced use for deep sky imaging (optional ref: CCD47)

Features

•     Optical formula: Ritchey-Chretien
•     Useful diameter: 203mm
•     Focal length: 1624mm
•     Aperture Ratio: F/D 8
•     Separating power: 0.57 arc seconds
•     Limit visual magnitude: 14.2
•     Clarity: 1145x
•     Obstruction: 42% (area 17.6%)
•     Focuser: Crayford 50.8/31.75mm GSO with 1:10 microfocuser
•     Tube diameter: 230mm
•     Tube length: 580mm
•     Weight: 7kg
•     Format of the 2 dovetails: Vixen type

Items delivered

•     1 Ritchey-Chretien Kepler 203/1624 optical tube
•     1 crayford M-LRS with microfocuser and guide rail
•     1 finder shoe compatible with Kepler or Sky-Watcher (finder not supplied)
•     1 set of extension rings to achieve focus
•     2 Vixen type dovetails fixed above and below the tube