The photometric response over the FOV may not be flat even after having divided by the nightly flat field. For many IR arrays this so-called photometric surface correction (or illumination correction) believed to originate in scattered light in the system, is needed. Some data has now been taken to map the illumination correction for the H-band.
Some few observers spent part of their observing time to obtain illumination correction data for the H-band, and they have also made a model based on these data. A bright standard star was dithered across the array, and the procedure was repeated 15 times with small step offsets in between. The model they developed and used to correct their NOTCam data will be published in a paper (Janz et al., submitted October 2012), together with an H-band illumination model for NICS/TNG. The most pronounced effect of the surface correction is a vertical gradient over the array with a 10% gradient from the bottom to the top of the array. This is in agreement with the slope we find when calibrating point source photometry. It is not entirely clear whether this photometric surface correction varies with time. Similar data will need to be obtained in the J and the Ks filter.
Thomas Augusteijn 2013-05-10