Focus depth extension image forming optical system, focus depth extension element, and imaging apparatus
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United States of America Patent
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Jan 16, 2018
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Feb 26, 2016
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Mar 3, 2015
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Abstract
A focus depth extension image forming optical system includes a focus depth extension element that extends a depth of focus of an image forming optical system. The focus depth extension element added to the image forming optical system has an aspheric surface shape rotationally symmetric about an optical axis of the image forming optical system, a sag amount Z of the aspheric surface shape changes at least to be negative, positive, and negative or positive, negative, and positive in accordance with an increase in a distance from the optical axis, in a range of 0<|t|<0.4 where |t| is a normalized radius of the aspheric surface shape, a maximum value of |dZ/dt| is 0.4 or more, and in one or more point of a range of 0.4≦|t|<0.8, dZ/dt=0.
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