Patent ID: 6339509
Filing Date: 2002-01-15
Classification: G02B

Abstract:
A variable focal length optical system comprising at least three lens groups in order from an object side:a first lens group having a positive refractive power; a second lens group having a positive refractive power; and a third lens group having a negative refractive power; wherein each lens group moves to the object side such that an air gap between said first lens group and said second lens group increases, and an air gap between said second lens group and said third lens group decreases when a state of lens group position is changed from a wide-angle end state to a telephoto end state; wherein an aperture diaphragm is arranged between said first lens group and said third lens group, said second lens group comprises a positive lens having double aspherical surfaces arranged adjacent to said aperture diaphragm, and the following conditional formulae are satisfied; Da/f<0.08â€ƒâ€ƒ(1) 0.3where Da denotes an air gap along an optical axis between said aperture diaphragm and said positive lens, f denotes a focal length of said variable focal length optical system, Ra denotes a radius of curvature of a surface of said positive lens facing to a space where said aperture diaphragm exists, and Rb denotes a radius of curvature of a surface of said positive lens facing opposite to said space where said aperture diaphragm exists, where Rb<0.