| 摘要 |
PURPOSE:To make a zoom lens small-sized, by changing the interval of two lens groups having positive focal lengths to vary their powers. CONSTITUTION:A small-sized two-group zoom lens system consists of the first lens group, which performs focusing and corrects the movement of the image surface due to variable power and has a positive focal length, and the second lens group which varies its powers, and has a positive focal length, and the first and the second lens groups are arranged in order from the object side, and each of both groups consists of one positive lens and one negative lens at least. When the focal length of the first lens group, the focal length of the second lens group, the length between the rear-side principal point of the first lens group and the front-side principal point of the second lens group, and the interval between the rear-side principal point of the second lens group and the image surface are denoted as f1, f2, t1, and t2 respectively, a resultant focal length (f) of the whole of the system is given by an equation I . The interval t2 is approximately equal to a back focus fB and is given by an equation II. |
