A hybrid lens with a high numerical aperture is described. The hybrid lens comprises
a refractive surface that refracts incident light and a diffractive surface that
diffracts light exiting the lens, the diffracting surface designed by a sag satisfying
the following Equation:
##EQU1##
wherein fD is a distance from a center peak to a focal point of
the hybrid lens, r is a height from a center axis to each peak of the hybrid lens,
n is the refractive index of the hybrid lens, is the wavelength of incident
light and m is an integer. The hybrid lens is small and lightweight and capable
of removing chromatic aberration.
