Biconcave lens, N-BK7, Ø 12.7 mm, f = -20 mm, mounted, ARB2-VIS

Biconcave singlet in N-BK7, Ø 12.7 mm, focal length -20 mm, in a mount. ARB2-VIS broadband AR coating. Negative focal length: diverges the beam, for beam expanders and to shorten system length.