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. Eyepiece is an invaluable aid to centering guide stars and astrophotography target objects. Relatively high-power 6mm focal length telescope eyepiece with myriad uses is a welcome addition to any astronomer's accessory case. Folding down and removable rubber eye guard for wearing glasses and comfortable viewing as well as blocking stray light to increase the brightness of image. 16mm long eye relief, provides comfortable long term viewing for people with or without glasses. Blackened aluminum fully threaded 1.25" eyepiece barrel and inside thread design to avoid internal reflection and provide a crisp image. Lens edges is blackened to reduce scattering of stray light and maximize contrast;designed to enhance the functionality and pleasure of using your telescope. Planetary eyepiece 6mm; offer high magnifications; for observing small sized objects like planets and extreme close ups of the craters on the moon; among other tiny objects in the night sky.