The application of optical systems may be conveniently grouped into guidance applications, in which the position of a
star, planet, or other body is sensed in order to maintain vehicle attitude and position; into surveillance applications, in
which a view is maintained toward space to detect and track missiles, other space vehicles, or celestial bodies. When
spacecraft moves around earth, volatile condensable material (VCM) recondensing on the surface of the window induces
the degradation of optical performance. In order to insure spacecraft fulfilling its work successfully, space optical
designers must think of sublimation, decomposition, and offgassing of materials in vacuum and the possible deposition
of products from such actions onto optical surfaces. Still now, lots of antipollution works have been done. But little
work is done to analyze VCM how to influence imaging. However, it not means that such work is not important.
First of all, it is supposed that the VCM which looks like circle grain spreads on the surface of optical system equably.
Then the point spread function (PSF) of optical system under kinds of contamination spread density is obtained. The
result indicates that the envelope line of PSF widens. This means that the resolution of optical system will reduce,
which induce low detection sensitivity. It is obtained that VCM leads not only low optical transmissivity but also worse
imaging quality. And it is emphasized PSF effecting on imaging quality in this paper.