Patent ID: 6757104
Filing Date: 2004-06-29
Classification: G02B

Abstract:
A picture taking apparatus having a diffractive optical element, which forms an image on photosensitive surface by using said diffractive optical element in an optical system, said diffractive optical element having a grating structure obtained by stacking a plurality of diffraction gratings made of at least two types of materials with different dispersion properties to enhance diffraction efficiency for a particular design order throughout a predetermined wavelength region and the grating structure is designed in such a way that a maximum optical path length difference becomes an integer multiple of a predetermined wavelength, wherein said diffractive optical element having a design wavelength &lgr;0, as the predetermined wave length, satisfying conditions given below:U1,n(&lgr;0)âˆ’U1,r(&lgr;0)>0.75[U3,n(&lgr;0)âˆ’U3,râˆ’1(&lgr;0)]U1,n(&lgr;0)âˆ’U1,r(&lgr;0)>U3,n(&lgr;0)âˆ’U3,r(&lgr;0) U1,n(&lgr;0)âˆ’U1,r(&lgr;0)>0.5[U2,n(&lgr;0)âˆ’U2,râˆ’1(&lgr;0)]U1,n(&lgr;0)âˆ’U1,r(&lgr;0)âˆ’U2,n(&lgr;0)âˆ’U2,r(&lgr;0) (arbitrary integer satisfying OU1,n(&lgr;0), U2,n(&lgr;0), and U3,n(&lgr;0) being given by U1,n&it;(Î»&it;â€ƒ&it;0)=&Sum;p=m-nm+n&it;&Integral;Î»1Î»2&it;{L&it;(Î»)&it;T&it;(Î»)&it;F1&af;(Î»)&it;Dp&af;(Î»&it;â€ƒ&it;0,Î»)&it;Sp&af;(Î»)}&it;&dd;Î»U2,n&it;(Î»&it;â€ƒ&it;0)=&Sum;p=m-nm+n&it;&Integral;Î»1Î»2&it;{L&it;(Î»)&it;T&it;(Î»)&it;F2&af;(Î»)&it;Dp&af;(Î»&it;â€ƒ&it;0,Î»)&it;Sp&af;(Î»)}&it;&dd;Î»U3,n&it;(Î»&it;â€ƒ&it;0)=&Sum;p=m-nm+n&it;&Integral;Î»1Î»2&it;{L&it;(Î»)&it;T&it;(Î»)&it;F3&af;(Î»)&it;Dp&af;(Î»&it;â€ƒ&it;0,Î»)&it;Sp&af;(Î»)}&it;&dd;Î»and, U1,r(&lgr;0), U2,r(&lgr;0), and U3,r(&lgr;0) being given by U1,r&it;(Î»&it;â€ƒ&it;0)=&Sum;p=m-rm+r&it;&Integral;Î»1Î»2&it;{L&it;(Î»)&it;T&it;(Î»)&it;F1&af;(Î»)&it;Dp&af;(Î»&it;â€ƒ&it;0,Î»)&it;Sp&af;(Î»)}&it;&dd;Î»U2,r&it;(Î»&it;â€ƒ&it;0)=&Sum;p=m-rm+r&it;&Integral;Î»1Î»2&it;{L&it;(Î»)&it;T&it;(Î»)&it;F2&af;(Î»)&it;Dp&af;(Î»&it;â€ƒ&it;0,Î»)&it;Sp&af;(Î»)}&it;&dd;Î»U3,r&it;(Î»&it;â€ƒ&it;0)=&Sum;p=m-rm+r&it;&Integral;Î»1Î»2&it;{L&it;(Î»)&it;T&it;(Î»)&it;F3&af;(Î»)&it;Dp&af;(Î»&it;â€ƒ&it;0,Î»)&it;Sp&af;(Î»)}&it;&dd;Î»forâˆ«Dm(&lgr;0,&lgr;)L(&lgr;)T(&lgr;)F1(&lgr;)d&lgr;=âˆ«Dm(&lgr;0,&lgr;)L(&lgr;)T(&lgr;)F2(&lgr;)d&lgr;=âˆ«Dm(&lgr;0,&lgr;)L(&lgr;)T(&lgr;)F3(&lgr;)d&lgr;whereDp(&lgr;0, &lgr;): a diffraction efficiency of a wavelength &lgr; when a diffraction order of said diffractive optical element is represented by p and a design wavelength is represented by &lgr;0, Dm(&lgr;0, &lgr;): a diffraction efficiency of the wavelength &lgr; when the diffraction order of said diffractive optical element is represented by m and the design wavelength is represented by &lgr;0, m: a design order, n: an order (n>0) contributing to flare, &Sgr;: an addition symbol; although &Sgr; in each equation states that values from P=mâˆ’n to P=m+n are added, p=m is not included, an integration symbol, &lgr;1 and &lgr;2: a shortest wavelength and longest wavelength in a predetermined wavelength region, Sp(&lgr;): a contribution ratio at the wavelength &lgr; of p-order diffracted light in a specific area on a light-receiving surface (an imaging position of a design order), L(&lgr;): a spectral characteristic at the wavelength &lgr; of a light beam incident on said optical system, T(&lgr;): a transmittance of said optical system at the wavelength &lgr;, and F1 (&lgr;), F2(&lgr;), and F3(&lgr;): spectral sensitivity characteristics of photosensitive surface each serving to detect light in a given wavelength range; a wavelength at which the spectral sensitivity becomes highest increases in the order of F1(&lgr;), F2(&lgr;), and F3(&lgr;).