DEFORMED GAUSSSTYPE FAST WIDEEANGLE LENS WHOSE BACK FOCUS IS LARGER THAN FOCAL LENGTH

摘要

PURPOSE:To obtain the wide-angle lens of long BF for 35-mm single-lens reflex camera by numerically limiting the composite focal length of the front group of the Gauss-type lens system of 6-group 7-element constitution, the spacing between the front group and rear group and the focal length of the 4th group. CONSTITUTION:The deformed Gauss-type by the 1st positive lens L1, a positive meniscus lens L2 of Abbe number around 40, a negative meniscus lens L3 of Abbe number 50 or over, a negative meniscus cemented lens L4, a positive meniscus lens L5 and a positive lens L6 from the object side is constituted. Conditions of formulas I, II are given to the front group lens system aperture space in order to make BF longer and this makes possible to use the Gauss-type of good aberration performances as the wide-angle lens for single-lens reflex cameras. Further, flare of offaxial light, spherical aberration and coma aberration are corrected by the conditions of formulas II, III, thus the lens system of F/2, angle of view 64 deg. is obtained.