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23 December 2016 Vertex radius measurement of an off-axis parabola with a three-ball spherometer
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Abstract
A spherometer is often used to precisely measure the radius of curvature of a spherical surface. It can also measure the vertex radius of a more complex surface such as an off-axis parabola (OAP). This paper provides a reliable algorithm to find the vertex radius of an OAP by solving a few equations based on the test geometry. This algorithm can also be easily expanded to any conic surface with high-order aspheric coefficients. The algorithm was verified by measuring an 8-inch diameter OAP and comparing the results with its known prescription. Results show good agreement. An example of measuring the vertex radius of a 4-m diameter OAP is also presented. In addition to this, a calculation was done to show that the coma and astigmatism are independent of the clocking of the spherometer on the optic.
© 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) 0091-3286/2016/$25.00 © 2016 SPIE
Margaret Z. Dominguez, Jianxin Li, Ping Zhou, and James H. Burge "Vertex radius measurement of an off-axis parabola with a three-ball spherometer," Optical Engineering 55(12), 124107 (23 December 2016). https://doi.org/10.1117/1.OE.55.12.124107
Received: 22 October 2016; Accepted: 29 November 2016; Published: 23 December 2016
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