| 摘要 |
PURPOSE:To attain a large aperture ratio and a large zoom ratio while keeping the aperture of a diaphragm to a small one by relocating the diaphragm arranged between the pre-group and post group of the 4th lens group to a position in the pre-group or immediately after the post group. CONSTITUTION:The zoom lens consists of the 1st lens group G1 to be moved on the optical axis for focusing and having a positive refractive power, the 2nd lens group G2 to be moved on the optical axis for power variation and having a negative refrac tive power, the 3rd lens group G3 to be moved on the optical axis to keep an image surface position at a fixed value, and the 4th lens group G4 to be acted as a relay group for image formation which are successively arranged from the object side. The 4th lens group G4 is constituted of the pre-group G41 on the object side and the post group G42 on the image side, and at the time of power variation, the object side main point HG41 of the pre-group G41 is positioned on the object side from the image side main point HG3 of the 3rd lens group G3 at a position where the 3rd lens group G3 approaches most close to the pre-group G41. In addition, the diaphragm S arranged between the pre-group G41 and the post group G42 of the 4th lens group G4 is relocated in the pre-group or immediately after the post group to contract the diameter of the diaphragm S. |
