Starlight Instruments Holographic Attachment with Concentric Circle Pattern for Holographic Collimator

Removable diffractive optical element for use in Glatter Holographic Collimators. A nine-concentric circle pattern that spans 10 degrees and will reach to the edge of f/ 5.7 optics. Recommended for scopes around this focal ratio or slower. The laser light is spread over a smaller area it is brighter than the square grid pattern, and this makes it particularly useful with Cassegrain scopes, where the pattern impact is sometimes scrutinized on the mirror surface. The projected pattern is seen only by light that is scattered from dust, dirt, or optical roughness, so a brighter pattern is better, especially if the mirrors are very clean.