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. 1.25in Diagonal fits telescopes with 1.25in focusers. Accepts standard 1.25” eyepieces, filters, Barlow lenses and other accessories with a 1.25in insert barrel. 90° Viewing Angle. For more comfortable overhead viewing through refractor and Cassegrain type telescopes. Upright Image. Correct upside down and left right reversed image. It will look like trying to read a sign in a mirror. Suitable for space viewing, for there is NO upside down or right side up in space. Brass Compression Ring. Brass lock Screw for eyepiece or adapter and brass Compression rings features more precision and prevent barrels or the surface of eyepieces from marring and scratching. The SV224 dovetail base is suitable for most kind of telescopes and has strong compatibility. The dovetail base includes two large screws which are fit into the recessed slotted mounting holes. Precision machined dovetail base, made of high strength aluminum with anodizing aluminium process, durable for long time use. The aluminum material makes the product lighter and easier to carry.