| 摘要 |
PROBLEM TO BE SOLVED: To obtain a zoom lens a long in back focus, high in performance and suitable for an electrophotographic equipment by satisfying the focal distance of the whole lens system at a wide angle end and the back focus with a specified condition respectively. SOLUTION: When BFw denotes the back focus at the wide angle end and Y0 denotes the maximum image height, the conditional inequality of 2.0<BFw<8.0 is satisfied. Besides, when fw denotes the focal distance of the whole lens system at the wide angle end, D23w denotes an axial air distance between a 2nd lens group G2 and a 3rd lens group G3 at the wide angle end and D23t denotes an axial air distance between the lens group G2 and the lens group G3 at a telephone end, the conditional inequality of 0.03<(D23t-D23 w)/fw<0.6 is satisfied. Thus, the high performance zoom lens having the long back focus and capable of attaining a satisfactory image forming performance in either of an infinite system and a finite system is obtained. Besides, by changing the distance between the lens group G2 and the lens group G3 to a linear or nonlinear shape, the improved image forming performance is obtained in an intermediate focal distance state. |
