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Abstract

A rod lens array 10a includes a plurality of gradient-index rod lenses 1b arrayed to have optical axes parallel to each other, and forms an erecting equal-magnification image. The gradient-index rod lenses 1b each have a refractive-index distribution in a radial direction thereof. The refractive-index distribution n(r) is approximated by n(r)=n₀⋅{1-(A/2)⋅r²}, where a refractive index at a center of the gradient-index rod lens 1b is represented by n₀, a refractive-index distribution constant of the gradient-index rod lens 1b is represented by \A, and a distance from the center of the gradient-index rod lens 1b is represented by r. The gradient-index rod lens 1b has an aperture angle θ of 3 to 6°, the aperture angle θ represented by θ=sin⁻¹(n₀\A⋅r₀), where a radius of the gradient-index rod lens is represented by r₀. The rod lens array 10a has an imaging distance of 45 to 75 mm and a depth of field of 1.5 to 3.0 mm with value of modulation transfer function (MTF) of 30% or more at a spatial frequency of 6 Ip/mm.

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First Claim