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11 October 2010 Fabrication and test of a concave oblate ellipsoid with large relative aperture
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Fabrication and test of the concave oblate ellipsoid becomes more difficult as the mirror relative aperture gets larger. The concave oblate ellipsoid discussed in this paper, has a very large relative aperture. Two processing methods are introduced. One is drilling sub-mirror from the mother mirror, the other is processing sub-mirror merely. A novel method to calculate aspheric grinding amount of the latter method is proposed. As the clear aperture and aperture decenter of the concave oblate ellipsoid in this paper are not large, the former processing method is finally adopted. Two online processing testing methods are proposed. One is reflective auto-collimating test; the other is refractive auto-collimating test. As for the former, a negative power lens is applied to compensate the positive spherical aberration of the concave oblate ellipsoid. The compensator has a negative - negative - positive configuration. As for the latter, the back surface of the spherical is designed to be an auxiliary spherical one. Its compensator is negative- positive- positive compensator. Besides, a high-precision plane is used to realize auto-collimating test. And the form test is selected for its online processing testing. By optical design of the compensator and gradual aberration optimization of its alignment, the test accuracy of the oblate ellipsoid shape can be achieved 1/10λ (632.8nm).
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Ke-xin Li, Li-yin Yuan, and Pei-ming Hao "Fabrication and test of a concave oblate ellipsoid with large relative aperture", Proc. SPIE 7656, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment, 76562T (11 October 2010); doi: 10.1117/12.868036;

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