MTF Measurement of a SWIR Imaging Telescope Using Star Test Images

MTF is the final and decisive parameter determining the image quality of optical imaging systems. To measure the MTF of a large-mirror telescope in a laboratory, an expensive collimator is necessary to make a collimated beam from a point or knife-edge source. Star-test is an old and traditional method giving some clues about wavefront error. In this study, we used the star-test to measure the MTF of an imaging telescope. We found the Line Spread Function (LSF) of a star on a line detector, and then derived the MTF using Fourier Transform of LSF. LSF is generated from the intensity distribution on the detector, by using different mathematical curve fitting methods. It is found that our telescope has an MTF greater than % 15 over the all fields at 20 lp/mm, which is the Nyquist frequency of 25 mu detector. We showed that a relatively large telescope (similar to 15 cm in diameter) can be built and tested without using expensive instruments such as collimator and interferometer. Also our telescope can be used with a 20 mu detector safely, considering % 10 MTF as the limiting case.