TW330245B - Zoom projection lens with very long rear focal length - Google Patents

Abstract

A zoom projection lens with a very long rear focal length comprises: - A front lens group including a first lens which is a convex lens, a second and a third lenses of negative meniscus which are convex toward the object side, a fourth lens of positive meniscus with the surface of the smaller radius of curvature facing the object side; and - A rear lens group including a fifth lens which is a planoconvex lens with the plane surface facing the object side, a sixth lens which is a biconvex lens, a seventh lens of negative meniscus cemented to the sixth lens with the surface of the larger radius of curvature facing the image side, an eighth lens of negative meniscus with the surface of the larger radius of curvature facing the object side, a ninth lens which is a planoconvex lens with the plane surface facing the object side, and a tenth lens which is a biconvex lens. The front and rear lens groups must satisfy the following conditions: 1.2 <= [|f.sub.A| / f.sub.W] <= 1.5 V.sub.3 x N.sub.3 >= 90 V.sub.6 - V.sub.7 > 30 [|f.sub.A + f.sub.B| / f.sub.B] <= 0.2 where f.sub.A is the focal length of the front lens group, f.sub.B is the focal length of the rear lens group, f.sub.W is the focal length of the entire zoom lens system at its wide-angle end, N.sub.3 is the refractive index of the third lens, V.sub.3 is the Abbe number of the third lens, V.sub.6 is the Abbe number of the sixth lens, and V.sub.7 is the Abbe number of the seventh lens.1