IMAGE PICKUP APPARATUS

• US 20080037125A1
• Filed: 08/10/2007
• Published: 02/14/2008
• Est. Priority Date: 08/10/2006
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: TAKAMIYA, Makoto
• Granted Patent: US 8,199,231 B2
• Time in Patent Office: Days
• US Class Current: 359/568
• CPC Class Codes: G02B 5/1871 Transmissive phase gratings

Abstract

An image pickup apparatus which is capable of suppressing generation of shadows even when the aperture of the photographic lens is stopped down. A digital camera as an image pickup apparatus includes a photographic lens, a image pickup element that picks up an image of an object, and an optical low-pass filter disposed between the photographic lens and the image pickup element. The filter includes a liner phase diffraction grating having unit cells which are disposed in a regular pattern at a grating pitch P and are formed by equal-width recesses and equal-width protrusions adjacent to each other. When a shortest wavelength of a reference wavelength employed is λS, and a longest wavelength of the reference wavelength is λL, an optical path difference ΔH between lengths of optical paths of light of which a phase is varied by the phase grating is larger than λS/2 and smaller than λL/2.

Claims

1. An image pickup apparatus comprising:

a photographic lens configured to receive light incident thereon from an object;

an image pickup element configured to pick up an image of the object; and

an optical low-pass filter disposed between said photographic lens and said image pickup element, said optical low-pass filter including a phase grating having unit cells disposed in a regular pattern at a grating pitch P, said unit cells being formed by equal-width recesses and equal-width protrusions adjacent to each other,

wherein when a shortest wavelength of a reference wavelength employed is λ

S, and a longest wavelength of the reference wavelength is λ

L, an optical path difference Δ

H between lengths of optical paths of light of which a phase is varied by said phase grating is larger than λ

S/2, and at the same time smaller than λ

L/2.

2. An image pickup apparatus according to claim 1, wherein said optical low-pass filter and said image pickup element are arranged such that a spacing D between said phase grating and said image pickup element satisfies a relationship of P2/4λ

L<

D<

P2/4λ

s.

3. An image pickup apparatus according to claim 1, wherein said image pickup element is formed by a plurality of pixels arranged at a pixel pitch P′

, and

wherein an F-number of said photographic lens is larger than 3.2×

P′

.

4. An image pickup apparatus according to claim 2, wherein said image pickup element is formed by a plurality of pixels arranged at a pixel pitch P′

, and

wherein an F-number of said photographic lens is larger than 3.2×

P′

.

5. An image pickup apparatus according to claim 1, wherein said protrusions of said unit cells are elongated in shape.

6. An image pickup apparatus according to claim 1, wherein said phase grating is formed by a staggered grating as a two-dimensional shape, in which said protrusions are formed by placing first and second unit cells elongated in shape, one upon the other.