$\star$ Very good calibration

Instrument WFPC2 was designed to make photometry of precision in particular to make measurements of distance from stars céphéides (freedman2001). It thus gained from a meticulous calibration before its launching in space, the transmissions of the instrument (including/understanding the filters and CCDs) were given and followed by very precise manner, we will see in the continuation that their use makes it possible to make extremely precise measurements of flux.

The instrument does not undergo the variations of the transmission of the atmosphere: the calibration does not depend in theory on time. In practice, it derives slowly (and in a monotonous way) because of irradiation from the detectors and the filters.

This instrument gained from a very significant programme of calibration in orbit. In particular, zero points and the terms of color were given with a very high degree of accuracy (holtzman1995b & dolphin2000a). These calibrations are in concord with the transmissions of the filters determined since the ground.

The WFPC2 is to date the instrument of photometry best included/understood and gauged.