Imaging lens and image readout apparatus using the same

An imaging lens comprising, successively from an object side, a positive first lens having a convex surface directed onto the object side, a negative second lens having a concave surface directed onto an image side, a third lens made of a positive meniscus lens having a convex surface directed onto the object side, a fourth lens made of a positive meniscus lens having a convex surface directed onto the image side, a negative fifth lens having a concave surface directed onto the object side, and a positive sixth lens having a convex surface directed onto the image side, said first and second lenses being cemented to each other, said fifth and sixth lenses being cemented to each other, said first and sixth lenses satisfying the following conditional expression (7):

• Nd+0.015vd>2.58 (7)
• where
• Nd is the refractive index of a lens material at d-line;
• and
• vd is the Abbe number of the lens material.

An imaging lens comprising, successively from an object side, a positive first lens having a convex surface directed onto the object side, a negative second lens having a concave surface directed onto an image side, a third lens made of a positive meniscus lens having a convex surface directed onto the object side, a fourth lens made of a positive meniscus lens having a convex surface directed onto the image side, a negative fifth lens having a concave surface directed onto the object side, and a positive sixth lens having a convex surface directed onto the image side, said first and second lenses being cemented to each other, said fifth and sixth lenses being cemented to each other, said imaging lens satisfying the following conditional expressions (1) to (5):

• 0.01<d6/f<0.17 (1)
• 0.9<f3/f<1.8 (2)
• −0.4<f/f12<0.4 (3)
• 0.51<f34/f<0.72 (4)
• 1.15<v1/v2<1.65 (5)
• where
• f is the focal length of the whole system;
• f3 is the focal length of the third lens;
• f12 is the composite focal length of the first and second lenses;
• f34 is the composite focal length of the third and fourth lenses;
• d6 is the distance between the sixth and seventh surfaces;
• v1 is the Abbe number of a material of the first lens;
• and
• v2 is the Abbe number of a material of the second lens,
• wherein said imaging lens satisfies at least one of the following conditional expression (6) concerning said second and fifth lenses and the following conditional expression (7) concerning said first and sixth lenses:
• θg,F+0.0019vd<0.650 (6)
• where
• θg,F is a partial dispersion ratio of a lens material expressed by:
• θg,F=(Ng−NF)/(NF−NC)
• vd is an Abbe number of the lens material expressed by:
• vd=(Nd−1)/(i NF−NC)
• where
• Ng is the refractive index of the lens material at a wavelength of 435.8 nm,
• NF is the refractive index of the lens material at a wavelength of 486.1 nm,
• NC is the refractive index of the lens material at a wavelength of 656.3 nm, and
• Nd is the refractive index of the lens material at a wavelength of 587.6 nm;
• Nd+0.015vd>2.58 (7)
• where
• Nd is the refractive index of a lens material at a d-line, and
• vd is the Abbe number of the lens material.

An imaging lens comprising, successively from an object side, a positive first lens having a convex surface directed onto the object side, a negative second lens having a concave surface directed onto an image side, a third lens made of a positive meniscus lens having a convex surface directed onto the object side, a fourth lens made of a positive meniscus lens having a convex surface directed onto the image side, a negative fifth lens having a concave surface directed onto the object side, and a positive sixth lens having a convex surface directed onto the image side, said first and second lenses being cemented to each other, said fifth and sixth lenses being cemented to each other, said imaging lens satisfying the following conditional expressions (1) to (5):

• 0.01<d6/f<0.17 (1)
• 0.9<f3/f<1.8 (2)
• −0.4<f/f12<0.4 (3)
• 0.51<f34/f<0.72 (4)
• 1.15<v1/v2<1.65 (5)
• where
• f is the focal length of the whole system;
• f3 is the focal length of the third lens;
• f12 is the composite focal length of the first and second lenses;
• f34 is the composite focal length of the third and fourth lenses;
• d6 is the distance between the sixth and seventh surfaces;
• v1 is the Abbe number of a material of the first lens;
• and
• v2 is the Abbe number of a material of the second lens,
• wherein said imaging lens satisfies the following conditional expression (8):
• 0.05≦|β|≦0.7 (8)
• where
• β is the magnification of the whole system.