Patent ID: 9690072
Date: 2017-06-27
CPC Classifications: G02B

Claim:
1. An image forming lens comprising a sequential arrangement of, from an object side to an image side, a first lens group having positive power, an aperture stop, a second lens group having positive power, and a third lens group having positive power, the image forming lens being configured to perform focusing from an infinite distance object to a short distance object by integrally moving the first lens group and the second lens group to the object side so as to increase a distance between the second lens group and the third lens group, wherein the first lens group comprises a sequential arrangement of four lenses with no intervening lens from the object side to the image side in order of a negative lens, a positive lens, a positive lens, and a negative lens having a concave surface on the image side, the second lens group comprises a sequential arrangement of three lenses with no intervening lens from the object side to the image side in order of a negative lens having a concave surface on the object side, a positive lens, and a positive lens, the third lens group comprises a sequential arrangement of two lenses with no intervening lens from the object side to the image side in order of a negative lens and a positive lens, and following conditional expressions are satisfied: f is a focal length of an entire system, f12 is a composite focal length of the first lens group and the second lens group, f3 is a focal length of the third lens group, R142 is a curvature radius of an image-side surface of the negative lens closest to the image side in the first lens group, and R211 is a curvature radius of an object-side surface of the negative lens closest to the object side in the second lens group.