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 SV152 20mm premium 1.25" wide angle eyepiece includes an illuminated Single crosshair reticle that greatly simplifies centering celestial objects in the eyepiece for more accurate go-to alignment and tracking; An invaluable aid to centering guide stars and astrophotography target objects. It is the field of view that matters. Wide 70-degree apparent field of the sky allowing you to find objects and alignment stars more easily than shorter focal length eyepieces ;Comfortable 16mm eye relief; lets you easily find and locate target objects. There are also other uses for the SV152 crosshair eyepiece; The lighting part of the product is removable;with it you can use it as an illumination eyepiece.;remove it and you can use it as ordinary eyepiece. SV152 red Single Crosshair design: 1.The reticle is laser engraved.Not silkscreen and differentiated silk. 2.Not easy to diverge on high magnification telescope, easy to track and locate.