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Hubble Space Telescope
GHRS Instrument Science Report 033

GHRS Instrument Science Report 033

Preliminary Analysis of Best Focus for GHRS 08/90

Ronald L. Gilliland

Abstract excerpted from the report:

There may well be reason to desire different focus settings of HST to
maximize the scientific returns of the various instruments. It is the
purpose of this note to address the question of which focus setting
would be serve GHRS science goals.

The GHRS functions only in the UV, shortward of 3200A, its primary
aperture is a 0.25 arcsec square. (We have argued in earlier notes
that observations through the small aperture will in general be
preferred to those through the large aperture coupled with
deconvolution analysis.) The optimal focus for GHRS is to first
approximation simply that which will put the most UV light down a 0.25
arcsec square aperture. We will also address secondary issues:
Throughput of the larger 2.0 arcsec aperture, degradation of resolving
power through the LSA for different focus settings, target acquisition
sensitivity, etc.