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23 January 2003 Modulation transfer function measurement of IR optics at extreme temperatures
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We report on the development of methods and equipment which facilitates the measurement of the Modulation Transfer Function (MTF) of IR optics exposed to both high and low temperatures. The MTF is a very powerful measure of the quality of any optical system, and is a common way to test the performance. However, because of the large apparatus needed to perform the testing it is generally not possible to measure the MTF at temperatures other than room temperature. A thermally insulating enclosure was designed in which the optics under test is placed on a temperature-controlled fixture. The enclosure permits the radiation to reach the optics under test and allows the MTF measurement probe to reach the image plane. Meanwhile the MTF measurement bench is kept at room temperature. In this way it is possible to vary the temperature of the optics under test between -30 °C and +85 °C and simultaneously measure the MTF. Using the same equipment it is also possible to measure bore sight error, ensquared energy, and focus position as a function of temperature. A commercially available MTF measurement bench was specially adapted for this purpose. Measurements can be made both on- and off axis and both MWIR and LWIR measurements are possible.
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Mikael Lindgren, Peter Ljungberg, Kjell Nilsson, and Ralf G. Kihlen "Modulation transfer function measurement of IR optics at extreme temperatures", Proc. SPIE 4820, Infrared Technology and Applications XXVIII, (23 January 2003);


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