Patent ID: 6147815
Filing Date: 2000-11-14
Classification: G02B

Abstract:
An imaging optical system having a focal length f and a maximum imagewise numerical aperture and comprising, objectwise to imagewise along an optical axis:a) a front lens group having at least one refractive optical element;b) a diffractive optical element provided with a diffractive surface having positive diffractive power and a focal length f.sub.DOE ;c) a rear lens group having at least one refractive optical element; andd) wherein RSA is an amount of spherical aberration at the maximum imagewise numerical aperture, as measured with respect to e-line wavelength light, in the limit as said positive diffractive power approaches zero, wherein LA is a maximum amount of axial chromatic aberration of said imaging optical system over a wavelength range of 400-850 nm as measured with respect to e-line reference wavelength light, and wherein the following conditions are satisfied:0.01<RSA/f<0.01 (1)-0.002<LA/f<0.002. (2)