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. SV121 develops a new generation of adjustable module function technology, which can effectively solve the pain points of previous calibration eyepieces: solves different axis problems of calibration eyepieces. SV121 collimation eyepiece can be used for precisely collimating the Newtonian and Schmidt-Cassegrain reflector telescopes for crisp image quality. Aligning the mirrors seems easy enough, in theory, but in practice it can be difficult without the proper tools. Allows you to calibrate your telescope more conveniently. SV121 sturdy laser unit allows you to swiftly and precisely collimate your Newtonian telescope. Only when the optics have been accurately collimated can the telescope offer you its full performance. Note: If the product can be used normally, there is no need to calibrate by yourself.