This was sold by Celestron several years ago. It 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 by a factor of about .6 or so. It is in excellent condition, in the origional box. Asking $50 shipping included in CONUS. Paypal+3% is OK.