2" Blug for Howie Glatter Collimators.
In order to achieve the best possible resolution and contrast, the optical elements of a telescope must be put into near-perfect alignment. Collimation is the adjustment of the position and orientation of the optical elements to achieve best performance. Laser collimation is a relatively new way to accurately and precisely collimate a telescope.
When practiced with accurate tools and correct techniques the various methods of collimation will converge to the same result, but laser collimation has several unique advantages. The laser collimator provides its own light source, so collimation can be readily accomplished or checked after dark without additional equipment. Unlike passive collimation tools, your eye position is not constrained by a peep-hole and cross hairs, and you don’t need to scrutinize elements at different distances simultaneously.