FOS Instrument Science Report 085

"FOS Aperture Throughput Variations with OTA Focus  8/92
by D. Lindler and R. Bohlin

Abstract excerpted from the report:
  The attached figures show the variation in the throughput for several FOS
  entrance apertures as a function of the focus error with respect to the HST
  "optimal focus" position. The results were derived from point spread functions
  computed using the Telescope Image Modeling (TIM) version 27 software package
  and should be used to make small corrections to the FOS aperture transmissions
  for changes in focus. These small corrections are relative to unity at the 
  focus positions where the transmission was last measured. The last FOS
  aperture transmission data were obtained in June 1991 at focus error=+-1 on
  the blue side and in December of 1991 at focus error between -8 and -19
  microns on the red side. The reason for uncertainty in late 1991 is the 
  question of whether the OTA focus changed gradually or made a sudden jump
  toward negative focus error sometime during the hiatus of more than 4 months
  in precise measurements.


For more information, please contact the above author(s).