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Wavelength resolution

In its normal mode of operation, UES is used with a 1 arcsec wide entrance slit, producing a resolution element of 43 microns at the detector. This corresponds to a resolving power at all wavelengths. With currently available CCDs this resolution element is just sampled adequately with two detector pixels; the IPCS allows better sampling of the instrumental profile with four detector pixels. The optical quality of the spectrograph can deliver with a sufficiently narrow slit (0.5 arcsec). While the WHT seeing is often well matched to such narrow slits, only the IPCS with its 10 micron pixels can at present take advantage of the resulting resolving power.

Tue Aug 15 16:42:46 BST 1995