| 摘要 |
<p>A recognition rate for characters or the like, captured in a near view image, of software is improved without reduction in depth of field. A focus extending optical system (11) has optical lenses (11) and a focus extender. The optical lenses form an image of light, from an obj ect (14), on an image sensor. The focus extender adjusts a wavefront so as to change an image-forming position of the optical lenses (11) in accordance with a distance from an optical axis (L0) and thereby extends a focus range. The focus extending optical system satisfies a condition that a value of a second MTF is less than or equal to three times a value of a first MTF. The first MTF is an MTF at a spatial frequency of 1/2 of a Nyquist frequency of the image sensor (12). The second MTF is an MTF at a spatial frequency of 1/4 of the Nyquist frequency.</p> |
