Patent ID: 8027097

Claim:
A rear attachment lens detachably attached to the image side of a main lens system to change a focal length of an entire system so as to become longer than a focal length of the main lens system, the rear attachment lens comprising: one or more positive lenses GMp, wherein, an Abbe number and a partial dispersion ratio difference of a material of the positive lens GMp are respectively ν d — P and ΔθgF —P , a focal length of the positive lens GMp is f —P , a focal length of the rear attachment lens is f, and (ΔθgF —P ×f)/(f —P ×ν d — P ) is a ratio P, wherein, one among the one or more positive lenses GMp having a maximum ratio P is a positive lens P 1 , the Abbe number, a partial dispersion ratio, and a partial dispersion ratio difference of a material of the positive lens P 1 are respectively ν d — P1 , θgF —P1 and ΔθgF —P1 , a focal length of the positive lens P 1 is f —P1 , and (ΔθgF —P1 ×f)/(f —P1 ×ν d — P1 ) is a ratio P —P1 , such that the following conditions are satisfied: −1.665×10 −7 ×ν d — P1 3 +5.213×10 −5 ×ν d — P1 2 −5.656×10 −3 ×ν d — P1 +0.7006 <θgF —P1 <−1.61783×10 −3 ×ν d — P1 +0.64046 20<ν d —P1 <50 1×10 −4 <P —P1 <1×10 −3 .