INTERNAL-FOCUS LENS SYSTEM, INTERCHANGEABLE LENS DEVICE, AND CAMERA SYSTEM

摘要

An internal-focus lens system provided with an object-side-most lens group, a first image-side-most lens element, and a second image-side-most lens element next to the first image-side-most lens element on the object side thereof. The object-side-most lens group has positive power and remains fixed with respect to the image plane during focusing. One or both of the first image-side-most lens element and the second image-side-most lens element has negative power. This internal-focus lens system satisfies the relations (FNO 2×f×L)/(Y2) < 30 and BF/Y < 1.75 (with FNO representing the f-number of the entire system, f representing the focal length of the entire system, L representing the total lens length, Y representing f×tan(ω), ω representing the half-angle of the entire system, and BF representing the distance to the image plane from the image-side-most point of the image-side surface of the first image-side-most lens element).