Erecting equal-magnification lens array plate, image sensor unit, and image reading device

An erecting equal-magnification lens array plate including a stack of a plurality of individual lens array plates built such that pairs of corresponding lenses form a coaxial lens system, where each individual lens array plate is formed with a plurality of lenses on one or both surfaces of the individual lens array plate, the erecting equal-magnification lens array plate receiving light from a substantially straight light source facing one side of the erecting equal-magnification lens array plate, and the erecting equal-magnification lens array plate forming an erect equal-magnification image of the substantially straight light source on an image plane facing the other side of the erecting equal-magnification lens array plate, wherein

• a light shielder operative to shield light not contributing to imaging is formed in a neighborhood of a position in the intermediate plane in the erecting equal-magnification lens array plate where an inverted image of the substantially straight light source is formed,
• a main lens arrangement direction differs from a main scanning direction of the erecting equal-magnification lens array plate,
• the light shielder restricts a light transmitting region of each lens such that lens regions outside a slit opening, which is substantially parallel with the main scanning direction, are totally prevented from transmitting light, and
• given that the individual lens array plate has a plate thickness t, the lens's working distance is denoted by WD, the individual lens array plate has a refractive index n, the lens pitch is denoted by P, and a lens arrangement angle is denoted by θ, a width w of the slit opening in the sub-scanning direction is in the range given by
• w<2×{1+t/(WD×n)}×P×sin θ.

An erecting equal-magnification lens array plate including a stack of a plurality of individual lens array plates built such that pairs of corresponding lenses form a coaxial lens system, where each individual lens array plate is formed with a plurality of lenses on one or both surfaces of the individual lens array plate, the erecting equal-magnification lens array plate receiving light from a substantially straight light source facing one side of the erecting equal-magnification lens array plate, and the erecting equal-magnification lens array plate forming an erect equal-magnification image of the substantially straight light source on an image plane facing the other side of the erecting equal-magnification lens array plate, wherein

• a light shielder operative to shield light not contributing to imaging is formed in a neighborhood of a position in the intermediate plane in the erecting equal-magnification lens array plate where an inverted image of the substantially straight light source is formed,
• a main lens arrangement direction differs from a main scanning direction of the erecting equal-magnification lens array plate,
• the light shielder restricts a light transmitting region of each lens such that lens regions outside a slit opening, which is substantially parallel with the main scanning direction, are totally prevented from transmitting light, and
• given that the individual lens array plate has a plate thickness t, the lens's working distance is denoted by WD, and the individual lens array plate has a refractive index n, a width of the slit opening in the sub-scanning direction is denoted by w, and the lens pitch is denoted by P, a lens arrangement angle θ is set to be larger than θ1 that fulfills a condition w=2×{1+t/(WD×n)}×P×sin θ1 and smaller than an angle θ2 obtained by subtracting θ1 from a first lens abutting angle determined by the arrangement pattern of the lenses.