"The item has a diameter of 1.600 inches, with a center thickness of 0.150 inches and centering accuracy within .0005 inches. The First Surface Radius (FSR) is 1.0 minute TIR, and the Effective Focal Length (EFL) reference point is at 4.213 inches. The Back Focal Length (BFL) reference point is at 4.125 inches. The material used is Schott Optical Glass, Type 691547, with a coating of SLAR 101."
AGAV
End Item Identification
"The item identification number is AN/AAQ-9, and it is classified as an Infrared detecting set."