NEdT (noise equivalent differential temperature) is the key figure of merit which is used to qualify midwave (MWIR) and longwave (LWIR) infrared cameras. It is a signal-to-noise figure which represents the temperature difference which would produce a signal equal to the camera’s temporal noise. It therefore represents approximately the minimum temperature difference which the camera can resolve. It is calculated by dividing the temporal noise by the response per degree (responsivity) and is usually expressed in units of milliKelvins. The value is a function of the camera’s f/number, its integration time, and the temperature at which the measurement is made.