Patent ID: 7450837
Filing Date: 2008-11-11
Classification: G02B

Abstract:
1. A zoom optical system for forming an optical image of a subject onto a light receiving plane of an image sensor for converting the optical image into an electrical signal, and performing zooming by varying distances between lens groups in an optical axis direction, the zoom optical system comprising in the order from an object side: a first lens group having a negative optical power; and a second lens group having a positive optical power, the distance between the first lens group and the second lens group being reduced in zooming from a wide-angle limit to a telephoto limit, the first lens group and the second lens group each being composed of three or less lens elements, the second lens group including a positive lens element having a refractive index of 1.7 or more, the positive lens element having at least one aspherical surface, and the second lens group satisfying the following conditional formulae (1) and (2): where f 2 represents a composite focal length of the second lens group, f W represents a composite focal length of an entirety of the optical system at the wide-angle limit, t 2 represents a moving distance of the second lens group in zooming from the wide-angle limit to the telephoto limit, and TL represents a maximal value of an optical axis distance from an apex of a lens surface of the lens element closest to the object to the light receiving plane of the image sensor.