This is a made in Germany Schott Borofloat glass blank. It is 150mm in
diameter and 22mm thick. Or in english just under 6" diameter and about
.9" thick. Schott borofloat glass is a high tech glass with incredible
thermal stability. The glass is ground to an approx F5 curve and is
very smooth so some fine grinding was done on it. This blank bought in
Germany would cost over $300.00.
Filed under: Eyepieces & Accessories