Patent ID: 8379315

Claim:
A teleconverter lens system that is attachable to or detachable from an object side of a main lens system and that facilitates performing telephotographing, the lens system comprising: a first lens having a negative refractive power; a second lens having a positive refractive power; a third lens having a negative refractive power; and a fourth lens having a positive refractive power, wherein the first, second, third, and fourth lenses are sequentially arranged from an object side to an image side of the teleconverter lens system, the first and second lenses are cemented together, the second lens has a meniscus shape in which a convex surface is formed on the object side of the second lens, and the teleconverter lens system satisfies the following Expression: 2≦4Shape≦4, where 4Shape is (r2+r1)/(r2−r1), r2 is the radius of curvature of the image side surface of the fourth lens, and r1 is the radius of curvature of the object side surface of the fourth lens.