Observers can apply for time with the following common-user instruments on the 4.2-m William Herschel Telescope:

• ISIS - single-slit spectroscopy, R < 10000, 4' slit, spectro-polarimetry
• LIRIS - IR spectroscopy, R < 4000, and imaging, 4' field
• ACAM - optical imaging, low-resolution spectroscopy, 8' field
• Prime-focus imager - optical imaging, 16' field
• AF2/WYFFOS - multi-object fibre-fed spectroscopy, R < 9000, 40' field
• NAOMI/OASIS - integral-field spectroscopy with or without natural-guide-star adaptive optics (NGS AO), R < 4000, 17" field
• NAOMI/INGRID - IR imaging with or without NGS AO, 40" field (coronagraphy is also possible, with OSCA, 25" field)

Visiting instruments are mounted at the Cassegrain or Nasmyth f/11 foci. Recent visiting instruments include CANARY, EXPO, FASTCAM, GHaFaS, INTEGRAL, PLANETPOL, PNS, SAURON, SPIFS, TRIFFID and ULTRACAM. The enclosure at the spare Nasmyth focus includes an optical bench, and can be used for experimental work, e.g. for instruments requiring mechanical stability.

Targets with significant proper motion (e.g. comets) can be observed with differential tracking, but autoguiding is not currently available with differential tracking (project in-hand, 2011).

The median seeing at the WHT is 0.7 arcsec. The dark-of-moon sky brightness at high ecliptic latitude is similar to that at other good dark sites, V ~ 21.9 mag arcsec².