A simple variant of option 3.1 is the use of an internal illuminator within the 2MASS camera to measure only the detector component of the flat-field ( i.e. the high spatial frequency, pixel-to-pixel gain). A correction map, produced as described above, would be used to characterize both the optical transfer function of the telescope/camera and the residual response variations. This procedure has similar advantages and disadvantages to the previous strategy except that it would not require calculating the existing dark-sky flats. This will not be tested until the 3 channel camera comes on-line.