Baffle design for a Cassegrain telescope

Abstract

The baffle design and analysis of a panchromatic push-broom camera were investigated for a Cassegrain telescope in this paper. A specially designed flower-look baffle is surrounded by the hole of the primary mirror and secondary mirror. With this design, the flower-look baffle can block the direct-hit stray light and reduce the off-axis field of view (FOV) vignetting. The modulation transfer function (MTF) of this design is increased 10 % as compared to the performance of the traditional baffles. This camera is equipped with a large field of view (FOV) which can get a wide swath and can provide high-resolution image for observation and monitoring of environmental pollution and disaster. The optical system assembly (OSA) of the camera is a kind of Cassegrain telescope which contains two reflection mirrors and five corrected lenses. Compared with other off-axis telescopes, this traditional optical configuration can be manufactured and aligned much easily. In a large FOV Cassegrain design, the central hole of the primary mirror is larger than that in a traditional Cassegrain design. The rays out from FOV pass though the central hole easily and reach the focal plan assembly (FPA) directly. This kind of stray light carries strong energy flux which significantly reduces the image performance. A baffle subsystem is needed in order to avoid the direct stray light exposure. The performance evaluation of the baffle system and the MTF comparison results from two kinds of baffle shapes are included in this study. It indicates that the flower-look shape is more efficient in keeping the relative illumination and MTF than traditional tube shape. The maximum benefit of the flower-look baffle is found for increasing off-axis tangential MTF.