Patent ID: 6097547
Filing Date: 2000-08-01
Classification: G02B

Abstract:
A front converter lens system comprising a diffractive surface and mounted on an object side of a master lens system to vary a focal length thereof,said front conversion lens system comprising at least two lens groups, each comprising a diffractive surface,wherein each diffractive surface has a power of the same sign as that of a total power of its respective lens group wherein the diffractive surfaces satisfy the following condition:0.2<.vertline..phi..sub.DOE(1) /.phi..sub.DOE(2) .vertline.<1.6(1)where .phi..sub.DOE(1) is a power that the diffractive surface in the first lens group has at a position through which an axial marginal ray having a maximum diameter passes and .phi..sub.DOE(2) is a power that the diffractive surface in the second lens group has at a position through which an axial marginal ray having a maximum diameter passes.