|HST Primer for Cycle 25|
The FOC was designed to provide high resolution images of small fields. It consisted of two independent optical relays that magnified the input beam by a factor of four (f/96) and two (f/48). A variety of filters, prisms (for slitless spectroscopy), and polarizers could be placed in the optical beam. The f/48 relay also had a longslit spectrograph. The FOC photocathodes limited the wavelength range from 1200 Å to 6000 Å.When corrected by COSTAR, the field of view (FOV) and pixel size of the f/96 camera were 7" x 7" (512 x 512 format) and 0.014" x 0.014", respectively; a field of 14" x 14" could be used with the 512 x 1024 pixel format and a rectangular pixel size of 0.028" x 0.014". Without COSTAR in the beam, the corresponding parameters for the f/96 camera were: 11" x 11" FOV in the 512 x 512 format with pixel size 0.0223" x 0.0223", and full-format field of 22" x 22" with 0.0446" x 0.0223" pixels. The corresponding values for the (little used) f/48 camera were twice those of the f/96 camera.The f/96 camera was the primary FOC imaging workhorse. High voltage instabilities limited the use of the f/48 relay to mainly long-slit spectroscopy after the installation of COSTAR.Most of the FOC data in the Archive are unique because the spatial resolution of the FOC is greater than that of any other HST instrument. Also, the UV sensitivity was significantly higher than WFPC2, but less than STIS, although a larger variety of filters was available. Finally, polarizers in the f/96 relay had very low instrumental polarization and excellent polarizing efficiencies.A major reprocessing of the entire FOC science archive (science and non-science data) has been completed by ST-ECF, CADC, and STScI. This effort substantially improves the data quality and homogeneity. For more information about the reprocessed data, see ISR FOC-99. The reprocessed data have been incorporated into the HST Archive and are available through MAST.