In 2008 an amateur telescope maker and astronomer ppublished an
ingenious new way to easily focus your DSLR, webcam or CCD camera for
taking astrophotos. The method is simple, very intuitive and the device
has universally been named after the inventor. The Bahtinov Mask.
Farpoint manufactures this *LIFESAVING* astrophotography
tool out of virtually indestructable ABS plastic and comes in two major
types and in a range of sizes. The mask pictured below left is a general
purpose mask designed to fit refractors and newtonian telescope. The
mask pictured below right is designed to fit Schmidt Cassegrain
telescopes. Both types of mask are available in a range of sizes to
cover your needs.