| 主权项 |
1. An image reading lens which reads an original image, comprising:
a front group lens system on an object side; and a back group lens system on an image side, the front group lens system including three lenses having two positive lenses and a negative lens, and the back group lens system including a plastic negative lens, wherein the following conditional expressions are satisfied where ΣdnN/dt (N) is a sum of values 106 times a refractive index temperature coefficient for an e-line in the negative lens of the front group lens system at 20° C. to 40° C., Σdnp/dt (P) is a sum of values 106 times a refractive index temperature coefficient for an e-line in the positive lens of the front group lens system at 20° C. to 40° C., fa is a focal length of the front group lens system, f is a focal length of an entire image reading lens, d9 is a distance on an optical axis between the front group lens system and the back group lens system, and D is an entire length of a lens,
0<ΣdnN/dt(N)−ΣdnP/dt(P)<17 [1]0.20<fa/f×d9/D<0.90. [2] |
