Patent ID: 7605986

Claim:
A zoom lens for optical alignment with an image sensor, the zoom lens comprising, from an object side to an image side thereof: a first lens module having a negative refractive power for being fixed relative to the image sensor, a second lens module having a positive refractive power for being disposed between the first lens module and the image senor and movable toward and away from the first lens module; and a third lens module having a positive refractive power for being disposed between the second lens module and the image sensor and movable toward and away from the second lens module, wherein when the zoom lens is reciprocally zoomable between a wide-angle position where the first lens module is fixed relative to the image sensor, the second and third lens modules are nearest to the first lens module and furthest from the image sensor, and a telephoto position where the first lens module is fixed relative to the image sensor, the second and third lens modules are furthest from the first lens module and furthest from the image sensor, and the zoom lens satisfies following expressions: 2.3 <|F 1 |/F W <2.9; 1 <|F 2 |/F W <1.5; 0.2 <|F BW |/TTL< 0.5; 2 <TTL/y< 4.1; and 2.5 <TTL/D 2W <4.5; wherein F 1 represents a focal length of the first lens module, F W represents a focal length of the zoom lens in the wide-angle position, F 2 represents a focal length of the second lens module, F BW represents a back focal length of the zoom lens in the wide-angle position, y represents an image plane height of the zoom lens, TTL represents a full length of the zoom lens, D 2W represents a distance between the first lens module and the second lens module in the wide-angle position.