Diffractive optical element and photographic optical system having the same

• US 6,507,437 B1
• Filed: 12/21/1999
• Issued: 01/14/2003
• Est. Priority Date: 12/24/1998
• Status: Expired due to Fees

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Nakai, Takehiko
• Primary Examiner(s): CHANG, AUDREY Y
• Application Number:
  US09/468,864
• Publication Number:
  US 20020196545A1
• Time in Patent Office: 1,120 Days
• Field of Search: 359/568, 359/566, 359/569, 359/575, 359/576
• US Class Current: 359/576
• CPC Class Codes: G02B 5/1866 Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence

Abstract

To obtain a diffractive optical element of high diffraction efficiency over a wide range of wavelengths with no conspicuous color flare and a photographic optical system having the diffractive optical element, at least two diffraction gratings of different materials in dispersion are stratified, the first order is chosen as the design order and two wavelengths which, when multiplied one times, amounts to the maximum optical path length difference in the grating structure are used as the design wavelengths, wherein each of the values of the plurality of design wavelengths is determined so as to make white or nearly white flare caused by the diffracted light in the zero and second orders.

Claims

1. 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 λ

0;

2. A photographic optical system according to claim 1, wherein the shortest design wavelength λ

01 among the design wavelengths of said diffractive optical element satisfies the following condition;

3. A photographic optical system according to claim 1, wherein the longest design wavelength λ

0L among the design wavelengths of said diffractive optical element satisfies the following condition;

4. A photographic optical system according to claim 1, wherein an interval Δ

λ

0.a between adjacent two of the design wavelengths of said diffractive optical element satisfies the following condition;

5. A photographic optical system according to claim 1, wherein at least one of the plurality of diffraction gratings differs in orientation of grating from the other diffraction gratings.

6. A photographic optical system according to claim 1, wherein the diffraction gratings are layered on a substrate and, when the diffraction gratings are consecutively numbered, from the diffraction grating nearest to the substrate, as the first diffraction grating, the second diffraction grating and up to the i-th diffraction grating, a material from which the first diffraction grating is made is the same as a material of the substrate.

7. A photographic optical system according to claim 1, wherein the plurality of diffraction gratings are arranged in intimate contact or in closely spaced relation.

8. A photographic optical system according to claim 1, wherein said optical elements satisfies the following condition for each of the design wavelengths:

9. A camera comprising:

a photographic optical system according to claim 1; and

a CCD as the image pick-up means.

10. A camera comprising:

a photographic optical system according to claim 1; and

color film as the image pick-up means.