This is a certified precision Bausch & Lomb optical grating. Much of the following information was taken from the nomenclature label fixed to the back of the grating substrate.

Grating size - 65 x 65 mm
Focal length - infinity
Grooves / mm - 8
Blaze angle - 26 degrees 45 minutes
Catalog number - 35-53-09-99
Serial number - ECH-4-3-11
Coating - Al (?)

This is a most unusual grating with only 8 lines per mm. The aluminum coating seems to have a few flaws, but the grating itself appears very good.

Photo set 1659