|HST Primer for Cycle 25|
The WFPC2 was retired during SM4, but data from the instrument will continue to be available for archival research. It had three “wide field” CCDs and one high resolution (or “planetary”) CCD. Each CCD covered 800 x 800 pixels and was sensitive from 1150 Å to 11,000 Å. All four CCDs were exposed simultaneously, with the target of interest being placed in one of the camera apertures.The three Wide Field Camera (WFC) CCDs were arranged in an “L”-shaped field of view whose long side projects to 2.5', with a projected pixel size of 0.10". The Planetary Camera (PC) CCD had a field of view of 35" x 35", and a projected pixel size of 0.0455". The WFC configuration provided the larger field of view, but undersampled the cores of stellar images; the PC configuration sampled the images better, but had the smaller field of view.A total of 48 different filters could be inserted into the optical path. Polarimetry could be performed by placing a polarizer quad filter into the beam and exposing through the different quads and/or different filter wheel rotations. There were a total of 18 narrow-band and medium-band filters, as well as two narrow-band quad filters that each yielded four different central wavelengths. There were also four linear ramp filters that effectively allowed imaging of a ~10" region in an arbitrary 1.3% bandpass at any wavelength between 3700 Å and 9760 Å, by means of a variety of filter wheel orientations and target placements within the FOV.Beginning in 2003, a serious electronic anomaly appeared in the WF4 CCD detector of WFPC2, resulting in sporadic corruption of images (which could be photometrically corrected). The frequency and severity of the problem increased slowly, and by late 2005, a significant fraction of images taken in WF4 were blank and unusable. Early in 2006, a workaround was found, which allowed good data to be taken even though the WF4 electronics continued to slowly fail. WF4 continued to produce good data for several more years. The other three CCDs appeared unaffected, and in fact, small targets were usually placed on the PC1 or WF3 CCDs, so the WF4 anomaly had much less impact than it otherwise could have.