Patent ID: 8681435

Claim:
A macro lens system which does not change in optical length as selected lens groups in the system are moved to bring an object on the object side of the lens system into focus on the image side of the lens system comprising, in order from an object side to an image side of the lens system: a first lens group having a positive refractive power that is fixed while the image is brought into focus; a second lens group having a negative refractive power that moves while the image is brought into focus; a third lens group having a positive refractive power that is fixed while the image is brought into focus; a fourth lens group having a positive refractive power that moves while the image is brought into focus; and a fifth lens group comprising only a single lens having a negative refractive power that is fixed while the image is brought into focus, wherein, during focusing to correct a change of an image plane caused by a variation in an object distance, the first lens group, the third lens group, and the fifth lens group are fixed, and the second lens group and the fourth lens group are moved, and wherein the macro lens system satisfies the expression: - 1.0 ≤ c f + c r c f - c r ≤ 1.0 where c f denotes a curvature of a lens surface of the third lens group nearest to the object side, and c r denotes a curvature of a lens surface of the third lens group nearest to the image side.