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Hubble Space Telescope
FOC Instrument Science Report # 86

FOC Instrument Science Report # 86              15 February 1995

"Deriving the Geometric Correction from Crowded Fields" 
by P. Greenfield

Abstract excerpted from the report:

Described in this report is a new method of deriving the FOC
geometric distortion model. The new method involves both a
new representation for the distortion function (spline
functions) as well as using overlapping observations of a
crowded star field to determine the distortion function. The
method appears to work well based on data obtained from SMOV,
with the exception that it was necessary to use the reseau to
determine the overall scale and orientation because the offsets
of the images were not known because of an FGS problem. New
distortion models were determined for the following f/96
formats: 512zx1024, 512x512, 256x1024 and 256x256.