We evaluate the thermal contrast detected by a quantum detector in a focal
plane of an infrared instrument. The detected thermal contrast is shown to
consist of two terms. The term corresponding to the temperature dependence
of emissivity, previously neglected, is evaluated and shown to be a signifi
cant contributing factor. For the case of a metal mirror as a source of str
ay Light, ghost images, and narcissus, the error is estimated to be about 2
0%. The term in the detected contrast associated with the radiative emissio
n is shown to be proportional to temperature to the power of 2, rather than
3, published previously. (C) 1999 Published by Elsevier Science B.V. All r
ights reserved.