The efficiency curves for FOS-I and FOS-II are
plotted as a function of wavelength in Figures 
and
respectively.
The peak efficiency of FOS-1
in first order is 76 per cent, and for FOS-2 is about 70 per cent.
[ TIFF ]
Figure: The efficiency of FOS-1
[ TIFF ]
Figure: The efficiency of FOS-2
The efficiency of the total system (atmosphere, telescope and FOS with the extended blue response CCD) derived from observations of flux standards under photometric conditions is 12.5% for FOS-1, and 17% for FOS-2, at 7000Å, measured at the zenith.
The AB magnitude for 1 photon/s/Å/ at the zenith is given in Tables
and in Appendix .