Glas FK61 (similar to Ohara FPL51), has blackenededges, a measured transmission von over 99% from 400 nm to 700 nm, optimized for F/4 Newtonian-Telescopes. The barlow has a negative focal length of - 62.9 mm and a working backfocuse of 105 mm from center last lens to focuse ( eyepiece field stop). You will need now a 1.25" eyepiece holer 104 mm long
Item condition: new and original packed
