WFPC2 Field of View Projected on the Sky. The narrow-band filters are designed to have the same dimensionless bandpass profile. Center wavelengths and profiles are uniformly accurate over the filter clear apertures, and laboratory calibrations include profiles, blocking, and temperature shift coefficients. The UV capability is also enhanced by control of UV absorbing molecular contamination, the capability to remove UV absorbing accumulations on cold CCD windows without disrupting the CCD quantum efficiencies and flat field calibrations, and an internal source of UV reference flat field images. Finally, there is a set of four polarizers set at four different angles, which can be used in conjunction with other filters for polarimetric measurements.
Internal optics provide spherical aberration correction.
There are no instrument safety issues associated with bright targets. Detection of faint targets is limited by the sky background for broad band filters at visual wavelengths. CCDs are thick, front-side illuminated devices made by Loral. They have a Lumogen phosphor coating to give UV sensitivity. In the presence of background, the effect is reduced.