INTERNAL FOCUSING TYPE TELEPHOTO LENS

摘要

PROBLEM TO BE SOLVED: To reduce the size while maintaining superior optical performance by specifying the focal lengths of respective lens groups and the whole lens system, and the refractive index, radius of curvature, and Abbe number of a negative meniscus lens in an object-side lens group. ;SOLUTION: This lens system is equipped with a lens group G1 which has positive refracting power, a lens group G2 which has negative refracting power, and a lens group G3 which has positive refracting power in order from the object side, the lens groups G1 and G2 form nearly an afocal system, and the lens group G2 is moved for focusing. Here, conditions (1) 0.7|f|.f3/(f2.F)1.3, (2) 0.05|f2|/f10.55, (3) 1.65Na, (4)30νa58, and (5) -1.0(Rb-Ra)/(Rb+ Ra)-0.05 are satisfied, where f1 to f3 and F are the focal lengths of the lens groups G1 to G3 and the whole lens system, Na the refracting power of the negative meniscus lens G11, Ra and Rb the radii of curvature of the object- side and image-side surfaces, and νa the Abbe number.;COPYRIGHT: (C)1997,JPO