24 May 2018 Freeform optics complexity estimation: comparison of methods
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In the present paper we compare different approaches for estimation of freeform and aspherical surfaces complexity. We consider two unobscured all-reflective telescope designs: a narrow-field Korsch-type system with a slow freeform secaondary and a wide-field Schwarzschild-type system with an extreme freeform secondary. The performance improvement obtained due to the freeforms use is demonstrated. The Korsch telescope provides a diffraction-limited image quality for a small field 0.8x0.1° at F/3. The Schwarzschild design covers a large field of 20x8° and allows to increase the aperture from F/6.7 to F/3. Also, we analyze the freeforms shapes using different techniques. It is shown that the usual measures like root-mean square deviation of the sag are ineffective. One of the recommended way to estimate the surface complexity is computation of the residual slope and its conversion into fringes frequency. A simpler alternative is computation of the sag deviation integral.
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Eduard Muslimov, Emmanuel Hugot, Simona Lombardo, Melanie Roulet, Marc Ferrari, "Freeform optics complexity estimation: comparison of methods", Proc. SPIE 10679, Optics, Photonics, and Digital Technologies for Imaging Applications V, 106791M (24 May 2018); doi: 10.1117/12.2306671; https://doi.org/10.1117/12.2306671

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