A removable diffractive optical element with a 10 x 10 line square grid pattern for use in Glatter Holographic Collimators. It spreads 21 degrees which allows centering of optics as fast as f/ 2.7.  This pattern is recommended for general use because it can be used with the fastest telescopes likely to be encountered.

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.

New Version Howie Glatter Collimators are manufactured with a larger course thread size to facilitate changing the attachments in the dark. Note that the old version SI-HOLA-SQUARE grid attachment with the fine thread is no longer available.

The photo below shows the two versions. The old thread is 5/16″ diameter and 56 TPI. The new thread is 3/8″ and 32 TPI.