Howie Glatter Self-Barlow Attachment for Laser Collimator

Primary mirror collimation is one of the most important goals of the collimation process. Fast focal ratios of modern telescopes introduce errors that exceed the tolerances of standard collimation. Nils Olof Carlin invented the Barlowed laser procedure to allow a much more accurate laser-based method of collimating Newtonian primary mirrors. This is done by inserting a laser collimator into a Barlow lens in the focuser and adding a paper screen to the front of the Barlow. This projects a silhouetted shadow of the primary mirror center mark onto the screen on the Barlow. Centering the shadow on the screen allows the primary mirror to be adjusted with a high degree of accuracy since it is fairly insensitive to any imperfections in focuser misalignment and the fit of the Barlow in the focuser.

Collimation with a regular Barlow lens works, but it forms a long assembly at the focuser that is subject to inherent inaccuracies in the way the focuser aligns the somewhat heavy Barlow lens. Howie Glatter has streamlined the procedure a little with several ingenious devices.

The self-Barlow attachment is a disc with a white screen on the front and a small built-in Barlow lens in the center of the disc. It is then screwed into the Howie Glatter laser collimator aperture and provides a highly compact method for Barlow-collimating.

As with regular Barlowed laser collimation, the shadow is projected onto the screen at the front of the disc at the focuser end so adjusting the mirror at the back of the scope can be difficult in some cases, especially with reflectors having a long focal length.