Choosing DIT

Recommended Values for DIT

Appropriate values of DIT the integration time (DIT secs) for each individual integration, are lmited by various considerations. [N.B. Ndit individual Integrations each of DIT secs are coadded to form a single Exposure of time Ndit*DIT].

The recommended minimum DIT is one sec (the minimum possible exposure time) or the value at which the noise becomes sky (rather than detector) limited. Values are given in the Table below.

The recommended maximum DIT is such as to keep the detector wells less than half full. This should minimise problems with: saturation, persistence, non linearity, dynamic range, and not saturating the 2MASS stars (one or two magnitudes above the 2MASS limit) which used as astrometric references. As the background will be variable, particularly at the longer wavelengths, the values here should be considered indicative, and will likely need revision once the camera is tested on VISTA in Chile.

For the default sky backgrounds used in the ETC (which correspond to those in the ISAAC ETC, rather than to those on the ESO Paranal sky brightness page ) the recommended DIT values are