To evaluate the MTF performance of optical systems, the TOR option ofthe CODEV software from Optical Research Associates Inc. (ORA) is used for assessing MTF changes due to such tolerance aspects as decenters and tilts. In this evaluation, CODEV assumes internal coupling (X tilt with Y tilt )ofthe tolerances and a Rayleigh function for this tolerances probability distribution , which assumption is well suited to serial models. However, where one or more models are manufactured on a one-offbasis, e.g. models of space instruments, this probability distribution is not realistic, in view ofthe independent nature and Gaussian distribution ofthe decenters generated on space instruments. To study this case and present the first results, AEROSPATIALE uses a new feature ofthe TOR option, which allows the user to modify the probability density functions.

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