Optical Design and Engineering

Optical design of off-axis Cassegrain telescope using freeform surface at the secondary mirror

[+] Author Affiliations
Suryakant Gautam, Amit Gupta, Ganga Sharan Singh

Academy of Scientific and Innovative Research, Training and Development Complex CSIR Campus, CSIR Road, Taramani, Chennai 600113, India

Central Scientific Instruments Organization, Council of Scientific and Industrial Research, Chandigarh 160030, New Delhi, India

Opt. Eng. 54(2), 025113 (Feb 19, 2015). doi:10.1117/1.OE.54.2.025113
History: Received July 12, 2014; Accepted January 27, 2015
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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 XY 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.

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© 2015 Society of Photo-Optical Instrumentation Engineers

Citation

Suryakant Gautam ; Amit Gupta and Ganga Sharan Singh
"Optical design of off-axis Cassegrain telescope using freeform surface at the secondary mirror", Opt. Eng. 54(2), 025113 (Feb 19, 2015). ; http://dx.doi.org/10.1117/1.OE.54.2.025113


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