The Auxiliary Port Imager (API, also abbreviated as Aux) is an optical camera mounted at the auxiliary port of the Cassegrain A&G box of the 4.2m William Herschel Telescope.

The default detector is a 2148x4200 pixel E2V CCD44-82, with a pixel scale of 0.067"/pixel and an unvignetted (circular) field diameter of 2.2'. The previous TEK2 detector has been retired and is no longer available. The default mode for the detector is 2x2 binning in SLOW readout, which saves on readout time by a factor of two while preserving a small pixel scale of 0.134"/pixel. We also suggest adopting a ~2Kx2K pixel window for observing since half of the chip area is not illuminated, but this is not set by default. This window will need to be set manually as [1:2148,900:3000].

Six filters (UBVRIZ) are permanently mounted in the aux-port filter wheel; changes to these filters are permitted only for scheduled runs allocated specifically for aux-port imaging.

The Aux-Port Imager is always available when the Prime Focus Camera is not in use, and therefore it is especially suited to imaging override programmes.

You can either apply for observing time with Aux through one of the ING time-allocating committees or through the ING Service Programme.