INTERNAL FOCUSING TELEPHOTO LENS FOR AUTOMATIC FOCUSING CAMERA

摘要

PURPOSE:To make the focusing movement quantity of a 2nd group small by employing positive, negative, and positive three-group constitution, performing focusing by the movement of the 2nd negative group, and making the 1st and 3rd groups meet specific requirements. CONSTITUTION:The 1st group G1 has a front group G11 with positive refracting power which consists of a 1st positive lens L1, a 2nd positive lens L2, and a 3rd negative lens L3 and a rear group G12 which has weaker positive refracting power than the front group G11; and the 3rd group G3 has a positive lens L7 and satisfies inequalities I. In the inequalities I, PHI is the effective diameter of the object-side lens surface of the lens L1 which is the closest to the object side in the 1st group G1, F the focal length of the whole system, f1 the focal length of the 1st group G1, R1 the radius of curvature of the object-side lens surface of the positive lens L7 in the 3rd group G3, and R2 the radius of curvature of the image-side lens surface of the positive lens L7 in the 3rd group G3. Consequently, the internal focusing telephoto lens which is short in focusing movement quantity and compact is obtained.