Patent ID: 8605363
Filing Date: 2013-12-10
Classification: G02B

Abstract:
1. An internal focusing lens comprising sequentially from an object side: a first lens group having a positive refractive power; a second lens group having a negative refractive power; and a third lens group having a positive refractive power, wherein during focusing, the second lens group is moved along an optical axis and, the first lens group and the third lens group are fixed, a conditional expression (1) 0.31<f1/f<0.58 is satisfied, where f1 is a focal length of the first lens group and f is a focal length of the entire optical system, at infinity focus, and the first lens group includes sequentially from the object side: the first sub-lens group includes sequentially from the object side: a surface on an image side of the negative meniscus lens is aspheric, and a conditional expression (2) 0.0047<asp1nr|/f<0.0088 is satisfied, where asp1nr is a degree of aspheric deformation of the surface on the image side of the negative meniscus lens.