FOC Instrument Science Report # 87 12 Sept 1995 "The New f/96 Geometric Correction Models" by P. Greenfield Abstract excerpted from the report: Described are the new geometric distortion models determined for the post-COSTAR f/96 relay based on multiple, overlapping observations of crowded star fields. New distortion models were determined for the following f/96 formats: 512zx1024, 512x512, 256x1024, 256x256, and 128x128 using the method outlined in the previous Instrument Science Report FOC-086. Unlike the previous observations, the offsets between exposures appear to be as expected. The quality of the fits are good despite an apparent change of ~0.16% in plate scale over the course of all the observations. The consistency of fit star positions with the previous model is good. The consistency of the distortion fit with the previous 512x512 distortion fit using the new method is very good whereas the consistency with the previous 512zx1024 fit is less so. The evidence is strong that the photometric variations at the scan line beginning are not a direct result of distortion.