This green laser collimator is designed for collimating Cassegrain type telescopes. It projects a pattern of concentric green circles. We recommend this laser for use in collimating our Hyperion telescope. Fits 2" or 1.25" focusers or visual backs. The collimator includes a diffractor that threads into the front of the laser, creating the concentric circle pattern. With the diffractor removed, the laser produces a standard single green dot.
This image shows the pattern projected onto a wall from the front of a Cassegrain telescope