Patent ID: 8432617
Filing Date: 2013-04-30
Classification: G02B

Abstract:
1. An image forming optical system comprising in order from an object side to an image side: a first lens group having a positive refractive power; a second lens group having a negative refractive power; and an image-side lens group having a positive refractive power, wherein a distance between the first lens group and the second lens group changes at the time of zooming, and a refractive optical element A having a positive refractive power is positioned in the first lens group, the first lens group comprises a cemented optical element D which is positioned on a most object-side, the cemented optical element D is arranged such that the refractive optical element A is positioned between an optical element B which is positioned on the object side and an optical element C which is positioned on the image side, and the image forming optical system satisfies the following conditional expression (1-1), conditional expression (1-2), and conditional expression (2) where, nd νd θgF fG1 denotes a focal length of the first lens group, and fG2 denotes a focal length of the second lens group.