Farpoint Bahtinov Focus Mask - 2.5 Inch to 4.5 Inch Telescopes
Farpoint Bahtinov Focus Mask is an ingenious new way to easily focus a telescope. Insert pegs/screws and adjust the grommets to fit telescopes with dew shield or tube from 2.5″ to 4.5″ in diameter.
Bahtinov Focus Masks
In 2008 Pavel Bahtinov, an amateur telescope maker and astronomer published an ingenious new way to easily focus your DSLR or other imaging cameras for taking astrophotos. The method is simple, very intuitive and the device has universally been named after the inventor. The Bahtinov Mask.
Simply attach a camera to the telescope, center a fairly bright star and achieve rough focus. Then place the mask over the front aperture of your telescope by “hanging” it on the plastic screws from the front dew shield. Take a short exposure or use the live view function. The image of the star will show diffraction spikes. The “center” set will most likely be shifted to one side or the other. This is showing the defocus. (See images below)
Adjust the focus of the telescope and re-expose the star, once again showing the diffraction spike pattern. Iterate the process until the central diffraction spike is centered against the star and the other spikes. When a symmetrical pattern is achieved, the best possible focus is then reached. Simply remove the mask, center the target object and take amazing, sharp images!
Farpoint manufactures this "lifesaving" astrophotography tool out of virtually indestructible ABS plastic, which comes in two major types and in a range of sizes. In addition to Bahtinov masks for telescopes, Farpoint also makes Bahtinov masks for DSLR camera lenses.