There is a shutter between the camera sensor and the lens. This shutter is used to perform a non-uniformity correction (NUC). During NUC, the shutter presents a uniform temperature source to each detector element in the array. While imaging the flat-field source, the camera updates the offset correction coefficients, resulting in a more uniform image after the process is complete.

The NUC process takes about 0.5 second for FLIR Ax5 cameras. While the shutter is in the field of view of the sensor, the image just prior to the shutter moving is frozen and displayed until the NUC process finishes and the shutter moves out of the field of view of the sensor. A faint "click" may be heard when the shutter moves in front of the sensor.

When power is supplied to an Ax5 camera, two mandatory shutter events occur: one within 2 seconds of start-up; the other within 6 seconds after the first shutter event. Ax5 cameras are normally configured at the factory to automatically perform NUC at a specified interval following the initial two shutter events. The NUC interval is based on time and the camera temperature. Except for the initial two shutter events, the NUC interval parameters can be modified by the user by changing the GenICam commands NUCIntervalFrames and NUCTempDelta. The default values have been determined to maximize the video output quality and to minimize the number of shutter events the camera performs; FLIR does not recommend that users modify the NUC time or temperature interval. An NUC can be performed on command by the user, regardless of whether the NUC is in the automatic mode or not, by accessing the GenICam register NUCAction.