SV197 cheshire collimating eyepiece can be inserted into 1.25 inch focusers or diagonals. How To Collimate Telescope With Cheshire Eyepiece: The view through the Cheshire eyepiece during the collimation will differ between telescopes. For fast telescopes (f5 and below), it will be little off-center, and for the slow telescopes (f5 and above), the view will be more centered and easier to collimate. 1.The goal here is to center the primary mirror reflection in the secondary mirror and reflection from the Cheshire with the secondary mirror. 2.To achieve that, you have to use the adjustment screws on the secondary and primary mirrors while looking through the Cheshire eyepiece collimator tool. Steel Crosshairs. The cross-hair adopts strong and durable steel wire instead of easily broken copper wire or aluminum wire. EVA lined packaging. Ensure transportation safety and easy storage. This SVBONY red laser collimator has a 1.25" barrel and comes with a 2" adapter. It is suitable for both 1.25" and 2" Newtonian reflector telescopes. When you upgrade your 1.25" telescope to a 2" telescope, you do not need to buy an additional collimator to calibrate the 2" telescope. This is a newest 1.25" laser collimator includes removable 2" adapter;the triple cemented lens to improve the stability of dot;it's designed for accurate collimation of all Newtonian and SCT reflector telescopes.