A Bahtinov mask with a special pattern for reflecting telescopes. It allows easier focusing and collimation control at the same time.

This mask fits on GSO 8" f/8 Ritchey-Chretien telescopes of various brands, e.g. from Teleskop Service / TS-Optics / Astroshop.

The special feature of the mask is that it can be stored under the cover of the telescope, which is very convenient.

The pattern of the mask is calculated according to an improved formula and brings better illumination, see the discussion on Cloudy Nights forum and the original design on GitHub.

The mask was calculated for the 1050mm focal length, but works very well with the original focal length of 1624mm. This allows it to be used with or without a reducer.

Please note that:

• the mask is created in two parts, which are then glued. Traces of glue along the border between the parts are possible. But this does not affect the function of the mask.
• the mask is 3D-printed and the material of the mask is sensitive to heat. It starts deforming at temperatures above 50˚C. The mask should not be left in the sun, for example. Well, this should not be a problem for astrophotography 😉