Image pickup lens and design method thereof

A design method of an image pickup lens for determining thickness and radius of curvature in the center of a lens body having a second face on an image pickup surface side of said lens body being formed into a Fresnel face and a diffraction element being unified with at least either a first face on the object side or the second face on the image pickup surface side of said lens body, comprising the steps of:

• under the condition that each aberration is maintained to be excellent except for distortion aberration, performing ray tracing simulation beforehand on a lens body group with a different combination of d/f value (where, d denotes thickness in the center of a lens body and f denotes focal length of a lens body) and |r2/r1| value (where, r1 denotes radius of curvature in the center of the first face of said lens body and r2 denotes radius of curvature in the center of the second face of said lens body);
• calculating the distortion aberration of said lens bodies so as to obtain dependency of the distortion aberration on the d/f value and the |r2/r1| value;
• selecting, according to the correlation, the combination of the d/f value and the |r2/r1| value to be a desired distortion aberration;
• and determining the thickness and the radius of curvature of said lens body on the basis of the d/f value and the |r2/r1| value.

An image pickup lens comprising a lens body having at least one face being formed into an aspherical face and at least either a first face on an object side or a second face on an image pickup surface side of said lens body being formed into a Fresnel face, wherein said lens body satisfies a condition represented by a following expression:

• 1.17<d/f<1.4 (4)
• where,
• d:
• thickness in the center of said lens body;
• and
• f:
• focal length of said lens body.

A design method of an image pickup lens for determining thickness and radius of curvature in the center of a lens body having at least a first face on an object side or a second face on an image pickup surface side of said lens body being formed into a Fresnel face, comprising the steps of:

• under the condition that each aberration is maintained to be excellent except for distortion aberration, performing ray tracing simulation beforehand on a lens body group with a different combination of d/f value (where, d denotes thickness in the center of a lens body and f denotes focal length of a lens body) and |r2/r1| value (where, r1 denotes radius of curvature in the center of the first face of said lens body and r2 denotes radius of curvature in the center of the second face of said lens body);
• calculating the distortion aberration of said lens bodies so as to obtain dependency of the distortion aberration on the d/f value and the |r2/r1| value;
• selecting, according to the correlation of the d/f value and the |r2/r1| value to be a desired distortion aberration;
• and determining the thickness and the radius of curvature of said lens body on the basis of the d/f value and |r2/r1| value.