The Lumicon Enhanced Aluminum Diagonal reflects 96 to 97 percent of the light from the telescope's primary optics directly into your eyepiece. Its single 1/8 wave precision-polished surface is superior to the three surfaces of prism diagonals. Threaded for use with Lumicon renowned light pollution blocking filters, making eyepiece changing a breeze while using your Lumicon filter. Excellent condition. $125 shipped. Paypal OK.