We evaluate performance of the 4K × 4K mosaic CCD camera system developed at the Indian Institute of Astrophysics using four Thomson CCDs in a buttable configuration. The camera system consists of a mosaic CCD dewar developed to mount the four CCDs and an electronics controller designed to control the mosaic configuration. A window based data acquisition software is used to configure the controller and acquire images from the camera. The calibration measurements indicate that all 4 CCDs have similar characteristics with a gain of about 3.9 e/ADU, rms noise of ~ 19 e, full-well capacity of ~ 57 000 ADU, non-linearity of ~ 0.4% and peak quantum efficiency of ~ 40% in the red region. The problem of cross-talk is faced in this multi-readout system and a solution is offered. The performance of the mosaic CCD camera has been found satisfactory at the telescope
