Hoya Corporation

Akitoshi Usui

Yutaka Takakubo

An imaging optical system includes a positive or negative first lens group including a negative lens element closest to the object, a diaphragm, and a positive second lens group. The negative lens element closest to the object has an object-side aspherical surface including a paraxial convex surface, a paraxial curvature that is the greatest within the effective aperture, and a portion within the effective aperture having a curvature less than &#xbd; of the paraxial curvature. These conditions are satisfied:1/&#x3c;1.351/&#x3e;0.4&#x2212;2.5&#x3c;1/&#x3c;&#x2212;1.3&#x3e;56'f' designates the overall focal length; f1, R1 and D1 respectively designate the focal length, paraxial radius of curvature of an object-side surface, and thickness, of the negative lens element closest to the object; and V designates the Abbe number regarding the d-line of a lens element, within the second lens group, closest to the diaphragm.

Imaging optical system

An imaging optical system includes a positive or negative first lens group including a negative lens element closest to the object, a diaphragm, and a positive second lens group. The negative lens element closest to the object has an object-side aspherical surface including a paraxial convex surface, a paraxial curvature that is the greatest within the effective aperture, and a portion within the effective aperture having a curvature less than &#xbd; of the paraxial curvature. These conditions are satisfied:1/&#x3c;1.351/&#x3e;0.4&#x2212;2.5&#x3c;1/&#x3c;&#x2212;1.3&#x3e;56

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Tokyo, Japan

Akitoshi Usui