Patent ID: 6366405
Filing Date: 2002-04-02
Classification: G02B

Abstract:
A diffractive-refractive achromatic lens that has a positive resultant power, said lens comprising:a refractive lens system with a positive lens having relatively small dispersion, a negative lens having relatively large dispersion and an additional refractive lens, said additional refractive lens consisting of an additional positive lens, said refractive lens system exhibiting longitudinal chromatic aberration that is substantially proportional to wavelength such that the back focus of said refractive lens system decreases as the wavelength becomes shorter; and a positive diffractive grating that corrects the longitudinal chromatic aberration of said refractive lens system, wherein the following condition is satisfied: 0.005D<0.2 â€ƒwhere f is focal length of the entire lens system, and fD is focal length of said positive diffractive grating, wherein said refractive lens system comprises a refractive achromatic lens that is corrected in chromatic aberration at two different wavelengths, and said additional refractive lens generates longitudinal chromatic aberration such that the back focus of said refractive lens system decreases as the wavelength becomes shorter.