Baffles and vanes are usually used to block low-order stray light paths and are often the primary means of controlling stray light in an optical system. Baffles are cylindrical or conical shaped tubes used to enclose a system or block zeroth-order stray light paths, and vanes are structures that go on baffles to block scattering from them. Baffles are generally used to block light from sources well outside the nominal FOV of the system and should be designed to not vignette. They can be difficult to fabricate and add cost and weight to the system; however, they are essential in some systems to ensure proper functioning. An example of such a system is the baseline Maksutov-Cassegrain telescope, which has three baffles:
A large cylindrical baffle around the primary mirror to prevent direct illumination of the primary. Such a baffle is often called the main baffle. A baffle in the center of the primary mirror and another around the secondary mirror. These baffles block the zeroth-order external stray path through the hole in the primary mirror.
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