INSTRUMENT SCIENCE REPORT
	SPACE	TELESCOPE SCIENGE INSTITUTE

TITLE:	FOS ENTRANCE APERTURE SIZES (CALIBRATION PLAN 10B)
	AUTHOR:	D. J. Linder, R.C. Bohlin & G. F. Hartig DATE:  July, 1985

Abstract

*	The sizes of 22 FOS entrance apertures are measured directly
 	with a microscope, and the light transmittance is measured
 	with the aperture map technique. The light transinittance is
 	determined by the area of an aperture, so the aperture map
 	results can be compared with areas measured with the
 	microscope. Results show that the areas measured from the
 	aperture maps are consistent with the areas measured by
 	microscope for the larger apertures. As the aperture size
 	decreases the area measured by the aperture map deviates
 	further from the microscope area, reaching 31% for the 0.1
 	arcsec aperture. This indicates the deviations may be due to
 	diffraction of light through the smaller apertures. Future
 	analysis of aperture sizes versus wavelengths will verify the
 	diffraction effects.