Front and rear surfaces to be coated with a 3 layer, high efficiency anti-reflective coating as produced by optical coating laboratory inc., or equivalent in accordance with mil-c-675 except that the following toerances apply; 0 degrees angle of incidence-for 450 to 675 millimicrons, reflectance to be 0.6 pct absolute-for 425 to 700 millimicrons, reflectance to be 0.5 pct average; 30 degrees angle of incidence-for 450 to 625 millimicrons, reflectance to be 1.0 pct absolute-for 425 to 700 millimicrons, reflectance to be 0.5 pct average: size in in., 2.980 to 2.995 diam, thickness 0.125 porm 0.016
