The main constraints on ISOCAM sensitivity come from the flat-field error and the stabilisation of the detectors. For the faintest detections small local transients introduced by cosmic particle hits may also be significant. The observer is encouraged to note the following points:
Concerning the question of what is the best choice of flat-field, one should consider raster observations. This is because flat-fields made from the background region of a raster (or microscan) can reach an accuracy better than 1% of the background level for sufficiently long observations (1 hour or more). This is possible because there is no strong structure of the zodiacal light at the scale of ISOCAM images; during a raster or microscan, the detectors can reach a fairly stable gain level, making it possible to construct very good flat-fields from the rasters themselves. However, flat-fields are not perfectly reproducible from one observation to the next because of small jitters in the wheel's positions. Thus a flat-field derived from a raster or micro-scan can generally not be used on a subsequent staring observation. Therefore observers should not choose CAM01 staring observations for sources less bright than about 10% of the background level or more extended than 1/4 of the array.