| 摘要 |
PURPOSE:To obtain a focal length shorter than that at a wide-angle end by moving the 1st and the 2nd lens groups in the optical-axis direction, and moving the 4th lens group in the optical-axis direction at a different speed. CONSTITUTION:The 1st, the 3rd, and the 4th lens groups having positive refracting power and the 2nd lens group having negative refracting power are arranged successively from the object side. When the lens is zoomed to the normal telephoto side, a group L1 is moved to the object side Z1, a group L2 is moved to an image side Z2, and a group L3 is put in reciprocal motion Z3 to the image side while a group L4 is fixed. When the focal length is shortened, the groups L1 and L2 provide negative refracting power as one body and move from the wide-angle end of a variable focal length range to the object side as shown by A1, the group L3 is fixed, and the group L4 moves to the image side as shown by A2. Therefore, high performance is maintained continuously in a zoom range and needs to be obtained only at the end terminal of a focal length expansion range, so the power of each group needs not be increased and aberration compensation is facilitated, thereby maintaining the high performance. |
