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18 October 1996 Comparison between subsystem and system optical MTF for GOES imager
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Starting with SN05 Imager the optical MTF of the visible optics assembly has been measured at subsystem and at system level testing. For the visible detector MTF at 18,000 cycles/radian relative differences of 16 percent have been observed between system and subsystem data. The test setups are quite different, however, the MTF values should be dominated by the detector's field of view MTF and thus the differences should be small. Descriptions of the two configurations are given along with a discussion of some of the important differences. The investigation into the differences led to the testing of the imager and test collimator with a parabolic mirror as collimator and an MTF analyzer. The MTF values using the parabola with the instrument were about 12 percent better than with the test collimator. Observations of the image of a pinhole at the Cassegrain focus led to the analysis of spider vane diffraction which accounts for 2.7 percent MTF reduction. In addition analysis has also been performed on the collimator interferogram that indicates a reduction in MTF due to a number of steep zones within the collimator wavefront. The analysis predicts a 9.7 percent reduction in MTF, at 18,000 cycles/radian due to the test collimator of which 1.4 percent is a result of the collimator secondary spider vanes. The verification of the analysis awaits a new collimator with slope errors reduced to less than 0.12 waves/inch.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Frederick L. Williams, John C. Ehlert, and David R. Wickholm "Comparison between subsystem and system optical MTF for GOES imager", Proc. SPIE 2812, GOES-8 and Beyond, (18 October 1996);


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