Camera - objective with a long rear focal length and a large opening ratio of

摘要

PURPOSE:To produce a photographic lens, which has a higher aperture ratio than 1:14, a larger angle of view than 46 degrees and a higher back focus than 73% of the focal length of the whole optical system and which has its aberrations compensated to a satisfactory extent, by composing the optical system of such seven lenses as has optical dimensions satisfying preset conditions. CONSTITUTION:A lens system having a focal length f is composed of seven lenses, i.e., positive meniscus lenses 1 and 2, a negative meniscus lens 3 and negative and positive lenses 4 and 5 arranged in this order from an object, a positive meniscus lens 6 having a concave side at an object side and a positive lens 7 having both concave sides, and a diaphragm 10. The radius of curvature 4, refractive index n, Abbe's number and air distance d of the respective lenses are so selected as to satisfy the conditions expressed by formulas I to - or + . Then, it is possible to produce an excellent photographic lens which has a higher aperture ratio than 1:14, a larger angle of view than 46 degrees, a longer back focus than 0.73f, which has its spherical aberration and chromatic aberration compensated and which has a long back focus and a large aperture ratio.