Patent ID: 6600609
Filing Date: 2003-07-29
Classification: G02B

Abstract:
An inner-focus type lens comprising, in sequential order from the object side:a first lens group having a positive refractive power and formed of, in sequential order from the object side and without any intervening lens element, one or two positive lens element(s), a negative lens element, and a positive lens element; a second lens group having a negative refractive power and formed of, in sequential order from the object side, a negative lens element and a positive lens element; a third lens group having a positive refractive power and formed of, in sequential order from the object side, a positive lens element, a negative lens element, and a positive lens element; wherein there are no intervening lens elements between the first and second lens groups and focusing is performed by moving the second lens group as one unit along the optical axis, and the following Conditions (1)-(3) are satisfied 0.581/f<0.84â€ƒâ€ƒCondition (1) âˆ’0.58<f2/f0.4â€ƒâ€ƒCondition (2) 0.54<f3/f<1.2â€ƒâ€ƒCondition (3) wheref is the focal length of the entire lens when focused on an object at infinity, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.