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17 December 2014 Use of very low departure aspheric surfaces in high quality camera lenses
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Proceedings Volume 9293, International Optical Design Conference 2014; 92931J (2014)
Event: International Optical Design Conference, 2014, Kohala Coast, Hawaii, United States
High performance, compact cinematography lenses working over a large sensor area are demanding designs which are achieved using one or two high departure aspheric elements. With sag departures from best fit sphere of up to a few millimeters, the use of such aspheres is accompanied by a number of consequences. These include high cost metrology, very tight opto-mechanical tolerances and the potential for image artifacts produced during the sub-aperture grinding and polishing process. A modified asphere manufacturing process was utilized to reduce artifacts by eliminating the subaperture grinding and pre-polishing. This method is limited to aspheric surfaces which can be directly polished from a spherical base surface with aspheric departures of <15μm. These very low departure aspheres have the benefit of inexpensive metrology and tolerance relaxation compared with high departure aspheres. Interferograms, slope maps, and out-of-focus images demonstrate the feasibility and advantages of direct asphere generation from a polished sphere. A series of large format lenses covering focal lengths from telephoto to wide angle, were redesigned to determine the feasibility of the use of very low departure aspheres. Increasing the number of aspheric surfaces but reducing the aspheric departure to less than 15μm was demonstrated. We conclude that 3-5 very low departure aspheres are sufficient to provide similar performance to the high departure asphere designs for most focal lengths. One limitation encountered was in the wide angle lenses. The exception was the wide angle lenses where it is difficult to reduce departures below 30μm while maintaining the same optical performance.
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Kristen E. Dalzell, Reginald P. Jonas, and Michael D. Thorpe "Use of very low departure aspheric surfaces in high quality camera lenses", Proc. SPIE 9293, International Optical Design Conference 2014, 92931J (17 December 2014);

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