Payload-level testing. Top: flat-field image from the Calibration Unit at 720 nm taken during the Payload-level testing after bias subtraction and gain correction. The reduced flux at the corners of the focal plane is as expected from the Calibration Unit design. The contrast on this image was set very high, as is evident from the greyscale bar below the image. It also indicates the correct orientation of the unit on the Payload Module baseplate. Bottom: the image of a bright source directed into the gap between CCDs near the centre of the focal plane. The 12 diffraction spikes (six each from the collimator and telescope) confirm the correct orientation and registration of the image. Also evident in this image are the faint vertical stripes on some CCDs which result from the amplifier glow in the readout register, at a level of less than 1 ADU (1 ADU = 3.5 e⁻) and a ghost image from the dichroic to the right of the bright source. The greyscale for each quadrant is individually calculated in this image.