Patent ID: 8873154

Claim:
A tele-side converter lens, to be removably mounted to an object side of a master lens so as to increase a focal length of an entire system, the tele-side converter lens comprising, in order from the object side to an image side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, the first lens unit and the second lens unit being formed with a largest air interval therebetween, wherein: the first lens unit includes one or two positive lenses; the second lens unit includes one negative lens and one or two positive lenses; and the following conditional expressions are satisfied: −12.50×10 −3 <(θ gF 2 pa−θgF 2 n )/(ν d 2 pa−νd 2 n )<−5.50×10 −3 ; −2.05×10 −3 <(θ gF 1 pa−θgF 2 n )/(ν d 1 pa−νd 2 n )<−1.65×10 −3 ; −1.05<( f 2 ×νd 1 t 0)/( f 1 ×νd 2 t 0)<−0.95; 22.0 <νd 1 t 0 −νd 2 n< 32.0; 10.0 <νd 2 n−νd 2 pa< 14.5; 1.55 <NdG 1; and 1.30<β<1.60, where νd 1 pa and θgF 1 pa respectively represent an average Abbe constant and an average partial dispersion ratio of materials of positive lenses constituting the first lens unit, νd 2 pa and θgF 2 pa respectively represent an average Abbe constant and an average partial dispersion ratio of materials of positive lenses constituting the second lens unit, νd 2 n and θgF 2 n respectively represent an Abbe constant and a partial dispersion ratio of materials of the negative lenses constituting the second lens unit, νd 1 t 0 represents a combined Abbe constant of materials of the lenses constituting the first lens unit, νd 2 t 0 represents a combined Abbe constant of materials of the lenses constituting the second lens unit, f 1 and f 2 represent focal lengths of the first lens unit and the second lens unit, respectively, NdG 1 represents a refractive index of a material of a positive lens disposed closest to the object side, and β represents a magnification of the tele-side converter lens, provided that a combined Abbe constant νdi of an i-th lens unit is expressed by the following equation: vdi = ( 1 / fi ) / ∑ k = 1 m ⁢ { 1 / ( fik × vik ) } where m represents a number of lenses constituting the i-th lens unit, and fik and νik respectively represent a focal length and an Abbe constant of a k-th lens from the object side in the i-th lens unit.