Special Features:

Round flat disk; each edge chamfer 0.020/0.030 lg by 45 deg; one surface neutral density reflective coating; surface quality central zone 0.800 in. Min diameter 40-20; surface quality outer zone 1.500 min.Dia 60-40; 2.0 millidiopters max spherical power or astigmatism; transmission at 0.540 micron to be8 12 percent; transmission in visible region between 0.450 and 0.650 micron equals that of 0.540 micron within 50 percent; light deviation not to exceed 30 seconds of arc; rim and chamfers ground; optical glass cl 1 gr c type 523-586

Properties:

An item having two plane-parallel surfaces and used in the telescopic system of an optical instrument to modify the density or spectral intensity of light by absorption. Several filters having varied characteristics are usually mounted in such a manner that any selected filter may be moved in or out of the optical axis as light conditions warrant. Excludes window, optical instrument.