Patent ID: 6507437
Filing Date: 2003-01-14
Classification: G02B

Abstract:
A photographic optical system comprising a diffractive optical element having a grating structure in which a plurality of diffraction gratings made from at least two kinds of materials different in dispersion from each other are laminated, and a maximum optical path length difference in the grating structure being m times the design wavelength for each of the design wavelengths, where m is a design order of diffraction, said diffractive optical element satisfies the following conditions for the design wavelengths &lgr;0:0<E1(&lgr;0)+E2(&lgr;0)+E3(&lgr;0)<0.04 0E1(&lgr;0), E2(&lgr;0), E3(&lgr;0)}âˆ’min{E1(&lgr;0), E2(&lgr;0), E3(&lgr;0)}<0.02 where max{E1(&lgr;0), E2(&lgr;0), E3(&lgr;0)} represents a maximum value among E1(&lgr;0), E2(&lgr;0) and E3(&lgr;0), and min{E1(&lgr;0), E2(&lgr;0), E3(&lgr;0)} represents a minimum value among E1(&lgr;0), E2(&lgr;0) and E3(&lgr;0),where E1&af;(Î»&it;0)=&Integral;Dm-1&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F1&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»+&Integral;Dm+1&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F1&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»&Integral;Dm&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F1&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»E2&af;(Î»&it;0)=&Integral;Dm-1&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F2&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»+&Integral;Dm+1&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F2&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»&Integral;Dm&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F2&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»E3&af;(Î»&it;0)=&Integral;Dm-1&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F3&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»+&Integral;Dm+1&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F3&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»&Integral;Dm&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F3&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»where&Integral;Dm&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F1&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»=â€ƒ&it;&Integral;Dm&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F2&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»=â€ƒ&it;&Integral;Dm&af;(Î»&it;â€ƒ&it;0,Î»)&it;L&af;(Î»)&it;F3&af;(Î»)&it;T&af;(Î»)&it;&dd;Î»whereDmâˆ’1(&lgr;0,&lgr;), Dm(&lgr;0,&lgr;) and Dm+1(&lgr;0,&lgr;) represent diffraction efficiencies for a wavelength &lgr; in the (mâˆ’1)st, m-th and (m+1)st orders, respectively, in said diffractive optical element, and L(&lgr;) represents a spectral characteristic for the wavelength &lgr; of a light source, F1(&lgr;), F2(&lgr;) and F3(&lgr;) represent spectral sensitivity characteristics of blue, green and red light receiving means in an image pickup means, and T(&lgr;) represents a transmittance for the wavelength &lgr; of said photographic optical system.