| 摘要 |
PURPOSE: To obtain a good imaging performance when the above lens is used as a photograph enlarger by forming the lens which consists of two groups and satisfies specific conditions relating to the combined focal length of the respective lens groups, the distance between the principal points, etc. CONSTITUTION: This variable focal length lens has the first lens group G1 having a negative focal length as a whole and the second lens group G2 having a positive focal length as a whole. The focal length of the entire system of the lens is changed by changing the distance between the first lens group G1 and the second lens group G2. The lens is so constituted as to satisfy the following condition equations when fa is defined as the combined focal length of the front group Ga of the second lens group G2, fb as the combined focal length of the rear group Gb of the second lens group G2, f2 as the combined focal length of the second lens group G2, f1 as the combined focal length of the first lens group G1 and D as the distance between the principal point on the rear side of the front group Ga and the principal point on the front side of the rear group gb in the second lens group G2: 0.8<|fa/fa|<1.7, 0.5<|D/f2|<1.2, 1.4<f1/fb<2.5.
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