Patent ID: 9612425
Date: 2017-04-04
CPC Classifications: G02B

Claim:
1. A rear attachment lens that is attachable to a main lens, which is an imaging optical system, and changes a focal length of an entire lens system, in which the rear attachment lens has been attached to the main lens, to a longer focal length than a focal length of the main lens by being attached to an image side of the main lens, the rear attachment lens consisting of: a first lens group; and a second lens group in this order from an object side, wherein the first lens group consists of a negative lens and a positive lens in this order from the object side, wherein the second lens group comprises at least one negative lens and at least one positive lens, wherein the lens closest to an image side in the second lens group of all of the lenses in the second lens group is a positive lens, wherein an Abbe number for the d-line and a partial dispersion ratio between the g-line and the F-line of the negative lens in the first lens group are νd wherein a refractive index for the d-line of the negative lens in the first lens group is Nd