Fixed focal-length lens system

摘要

A fixed focal-length lens system includes a negative first lens group, a positive second and third lens groups. The first and second lens groups move toward the object side during focusing from an object at infinity to an object at a close-up distance. The first lens group includes a negative lens element having a concave surface on the image side, at least two positive lens elements, and a negative lens element having a concave surface on the image side. The second lens group includes a negative lens element having a concave surface on the object side, and at least two positive lens elements. The third lens group includes at least one negative lens element, and at least one positive lens element. The following condition (1) is satisfied:
−0.3wherein fG1 and fG2 designate the focal lengths of the first and second lens groups.

主权项

1. A fixed focal-length lens system comprising a negative first lens group, a positive second lens group and a positive third lens group, in that order from the object side, wherein said first lens group and said second lens group move toward the object side during focusing from an object at infinity to an object at a close-up distance,
wherein said first lens group includes a negative lens element having a concave surface on the image side, at least two positive lens elements, and a negative lens element having a concave surface on the image side, in that order from a side closest to the object to a side closest to the image, wherein said second lens group includes a negative lens element having a concave surface on the object side, and at least two positive lens elements, in that order from the object side, wherein said third lens group includes at least one negative lens element, and at least one positive lens element, and wherein the following condition (1) is satisfied:
−0.3