ULTIMATE SENSITIVITY WITH ISOCAM

We discuss the instrumental factors which constrain the sensitivity limits of the mid-infrared camera (ISOCAM) of ESA's Infrared Space Observatory (ISO). The observing strategy judged to be best suited to faint-source detection is described. A data analysis technique adapted to the extraction of the faintest point-sources is discussed. We report the application of these techniques to an extremely deep mid-IR observation of high redshift gravitationally lensed objects, in two filters, looking through a lensing galaxy cluster.