WFPC2 Technical Instrument Report 02-06:

Predicting Photometry Errors due to Linear Ramp Filter Offsets

-Shireen Gonzaga, John Biretta, and Sylvia Baggett

This document complements "Instrument Science Report 02-04, An Analysis of WFPC2 Filter Positional Anomalies", which documents a filter rotation anomaly seen in several WFPC2 filters. Only filters that projected unique filter features on flat-fields were studied because it was those filter features that showed the rotation error as a filter wheel moved from one position to another. In that ISR, the measured error offset was found to be 0.42. The filter wheel rotation offset causes a wavelength shift in linear ramp filters; this document describes a method for calculating the photometry error due to this effect.

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