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Optical Engineering

Optical design of off-axis Cassegrain telescope using freeform surface at the secondary mirror
Author(s): Suryakant Gautam; Amit Gupta; Ganga Sharan Singh
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Paper Abstract

Freeform surfaces enable imaginative optics by providing abundant degrees of freedom for an optical designer as compared to spherical surfaces. An off-axis two-mirror–based telescope design is presented, in which the primary mirror is a concave prolate spheroid and the secondary mirror is freeform surface-based. The off-axis configuration is employed here for removing the central obscuration problem which otherwise limits the central maxima in the point spread function. In this proposed design, an extended X−Y polynomial is used as a surface descriptor for the off-axis segment of the secondary mirror. The coefficients of this extended polynomial are directly related to the Seidel aberrations, and are thus optimized here for a better control of asymmetric optical aberrations at various field points. For this design, the aperture stop is located 500 mm before the primary mirror and the entrance pupil diameter is kept as 80 mm. The effective focal length is 439 mm and covers a full field of view of 2 deg. The image quality obtained here is near diffraction limited which can be inferred from metrics such as the spot diagram and modulation transfer function.

Paper Details

Date Published: 19 February 2015
PDF: 7 pages
Opt. Eng. 54(2) 025113 doi: 10.1117/1.OE.54.2.025113
Published in: Optical Engineering Volume 54, Issue 2
Show Author Affiliations
Suryakant Gautam, Academy of Scientific and Innovative Research (India)
Central Scientific Instruments Organisation (India)
Amit Gupta, Academy of Scientific and Innovative Research (India)
Central Scientific Instruments Organisation (India)
Ganga Sharan Singh, Academy of Scientific and Innovative Research (India)
Central Scientific Instruments Organisation (India)


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