Patent ID: 7986460

Claim:
An erect life-size lens array comprising: a first lens array in which plural first lenses each having a convex exit surface are arranged in a direction orthogonal to an optical axis; a second lens array in which plural second lenses each having a convex incidence surface and a convex exit surface are arranged to correspond to the plural first lenses in the direction orthogonal to the optical axis and on which a light beam emitted from the exit surface of each lens in the first lens array is incident; a third lens array in which plural third lenses each having a convex incidence surface are arranged to correspond to the plural first lenses in the direction orthogonal to the optical axis; a first aperture having plural circular holes formed therein corresponding to the plural first lenses and the plural second lenses and is disposed between the first lens array and the second lens array; and a second aperture having plural circular holes formed therein corresponding to the plural second lenses and the plural third lenses and is disposed between the second lens array and the third lens array, wherein if a distance between a second principal plane of the second lens and a first principal plane of the third lens is ξ 1 , a distance between a second principal plane of the third lens and a design image surface is ξ 2 , a radius of the circular hole of the aperture is r a , and a defocus amount is ξ 3 , the erect life-size lens array is for causing an MTF at a spatial frequency (line-pair/mm) ν to become MTF target or more and satisfies ( J 1 (2π· r a ·((1/ξ 1 )+(1/ξ 2 ))·ν·ξ 3 ))/(π· r a ·((1/ξ 1 )+(1/ξ 2 ))·ν·ξ 3 )≧ MTF target , where J 1 is a first type first-order Bessel function.