This is a 1 1/4 inch diagonal with a built in focal reducer. It threads onto the rear cell of a C8 or compatable scope. It was designed for visual use, and reduces the focal length of a S-C by a factor of about .63 so your f10 scope becomes an f6.3. It is in excellent condition, and produces beutiful wide field views. Packed in the origional box. Asking $50 shipping included in CONUS. Paypal+3% is OK.