JPH05161058A - Diaphragm structure for camera - Google Patents

Abstract

PURPOSE:To obtain the diaphragm structure without losing a low pass effect by forming a longitudinal direction of an aperture at the time of a small diaphragm along a pitch direction of a waving part of a diffraction plate and increasing the length in the longitudinal direction more than the pitch. CONSTITUTION:In the camera employing a diffraction plate 20 on one side of which a waving part is formed as an optical LPF of an object image, diaphragm plates 11, 21 are moved to overlap small diaphragm parts 13b, 14b of diaphragm apertures 13, 14 thereby forming a small diaphragm 15. Since the distance between tips of the small diaphragm parts 13b, 14b is selected to be properly a several number of multiple of a pitch of the waving part of the diffraction plate 20, the luminous flux passing through the small diaphragm 15 transmits through plural waving parts when the flux transmits through the diffraction plate 20, the low pass effect by the diffraction plate 20 acts on the luminous flux. Thus, a high space frequency component is eliminated from an object image and the object image made incident in the CCD 5 through a Rayleigh lens 4 is properly fogged to prevent occurrence of moire.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera equipped with a low-pass filter using a diffractive plate, and particularly to an electronic still camera using a charge-coupled device (CCD) as a solid-state image pickup device, even if the aperture is small. The present invention relates to a diaphragm structure that does not impair the effect of a filter.

[0002]

2. Description of the Related Art For example, when a subject image is captured by an electronic still camera using a CCD, the moire phenomenon occurs in the case of a fine pattern due to the relationship between the pattern or shape of the subject and the pixel pitch of the CCD. Occurs.

In order to prevent this moire phenomenon, an optical low-pass filter is interposed in the photographic optical system in order to forcibly blur a subject having a spatial frequency higher than a predetermined value. There is. For example, as shown in FIG. 6, a focusing lens 1, a variable power lens group 2, a diaphragm 3, and a relay lens 4 are sequentially arranged from the front of the camera, and a crystal plate is provided between the relay lens 4 and the CCD 5. An optical low pass filter 6 constructed is interposed. That is, the low-pass filter 6 removes a component having a high spatial frequency from the subject image transmitted through the photographing optical system,
The subject image is formed on the image pickup surface 5a of the CCD 5. Therefore, the image pickup surface 5a of the CCD 5 appropriately blurs a portion of the subject image corresponding to a component having a high spatial frequency, so that the moire phenomenon is prevented.

However, since a crystal plate is used for the low-pass filter 6, the cost of the camera increases because it is expensive. Further, in order to function sufficiently as the low-pass filter 6, an appropriate thickness is required, which makes it more expensive, and the size of the camera becomes larger, which hinders the reduction in size and weight of the camera.

Therefore, a camera using a diffractive plate has been developed as an optical low-pass filter instead of a crystal plate. This low-pass filter is formed by alternately arranging peaks and troughs on one surface of a plastic plate or the like so as to have a substantially sinusoidal cross section or a continuous trapezoidal shape. Since it is a lightweight material and does not require a large wall thickness, it can contribute to the reduction in size and weight of the camera.

[0006]

However, the diffraction plate has a shape in which peaks and valleys are formed continuously,
In order to appropriately correspond to the pixel pitch of the CCD in order to prevent moire, the pitch of the ridges or valleys cannot be made small, and for example, they are formed at intervals of about 1 mm, so the aperture is a small aperture. However, there is a problem that the function as a low-pass filter is lost.

That is, when the aperture is large, the peaks and the valleys of the diffractive plate correspond to the entire aperture, so that the diffractive plate can achieve the low-pass effect. On the other hand, in the case of a small aperture having a small aperture, the aperture aperture only corresponds to one peak or valley of the diffraction plate, and the low-pass effect cannot be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a diaphragm structure using a diffractive plate as an optical low-pass filter, which does not impair the low-pass effect even when shooting with a small diaphragm.

[0009]

As means for solving the above technical problems, a diaphragm structure for a camera according to the present invention is
In a camera that uses a diffractive plate in which peaks and valleys are alternately formed in a continuous wave pattern in one direction as an optical low-pass filter for a subject image, the aperture of the camera is formed to have the smallest aperture. In the small aperture state, the longitudinal direction of the aperture is aligned with the pitch direction of the wavy portion, and the longitudinal length of the opening is made larger than the pitch.

When the diaphragm is a small diaphragm, the length in the longitudinal direction is larger than the pitch of the corrugated portions, so that a plurality of peaks and valleys correspond to the aperture of the diaphragm. Therefore, the subject image light flux that has passed through the diaphragm and transmitted through the diffraction plate is subjected to the low-pass action of the diffraction plate.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The diaphragm structure according to the present invention will be specifically described below based on the illustrated embodiments. FIG. 2 is a plan view showing the structure of the photographing optical system of the video camera. From the front part of the camera, as in the case of the conventional photographing optical system of a camera, a zoom lens group including a focusing lens 1, a variator 2a and a compensator 2b. 2. A diaphragm 10 is arranged in this order. Then, a diffraction plate 20 as an optical low-pass filter is arranged behind the diaphragm 10, a relay lens 4 is arranged behind the diffraction plate 20, and a subject image transmitted through these photographing optical systems is arranged behind the relay lens 4. An image is formed on the image pickup surface 5a of the CCD 5 arranged at.

As shown in FIGS. 1 and 5, the diffractive plate 20 has a mountain portion 21a extending on the rear surface in the vertical direction.
The corrugated portion 21 in which the and the valley portions 21b are alternately arranged is formed. The sectional shape of the wavy portion 21 is a sine wave shape, a continuous trapezoidal shape, or the like. In addition, the pitch P of the wavy portion 21
Is formed to have a length corresponding to the spatial frequency to be removed from the subject image in relation to the pixels of the CCD 5.

On the other hand, the diaphragm 10 is a front diaphragm plate 11 and a rear diaphragm plate.
12 and 12 overlap with each other in the direction of the optical axis S, and each is movable in a direction intersecting the optical axis S by a drive mechanism (not shown). These diaphragm plates 11 and 12 respectively have diaphragm holes 13 and
14 are formed. FIG. 4 is a front view of the front diaphragm plate 11. The diaphragm hole 13 has an oval portion 13a whose left side is a large diameter side and the oval portion.
It is formed in a shape including a small narrowed portion 13b formed in a shape having a narrow width and protruding in a steeple shape from the tip of the small diameter side of 13a. Further, the diaphragm hole 14 of the rear diaphragm plate 12 is formed in line symmetry with the diaphragm hole 13 with respect to the vertical line including the optical axis S, and the oval portion 14 is formed.
A and a small throttle portion 14b are formed. Then, as shown in FIG. 3, these diaphragm holes 13 and 14 are overlapped with each other about the optical axis S to form a diaphragm opening 15 on the optical axis S.
The overlapping area of the diaphragm aperture 15 is changed by moving the diaphragm plates 11 and 12 in opposite directions. When the overlapping area is large, the opening is large (FIG. 3B), and when the overlapping area is small, that is, the small diaphragm portion.
When 13b and 14b overlap, it becomes a small aperture (Fig. 3).
(A)).

Then, in the case of a small aperture, the small aperture portion 13
The linear distance D (shown in FIG. 3 (a)) connecting the tips of b and 14b is appropriately several times the pitch P of the corrugated portion 21, and the area where these small aperture portions 13b and 14b overlap is incident on the CCD 5. The size is set so that a sufficient amount of light can be secured.

The operation of the embodiment of the present invention constructed as described above will be described below. The drive mechanism is actuated via the exposure control means based on the photometric data obtained by the photometric means (not shown), and the diaphragm plates 11 and 12 move in the direction intersecting the optical axis S. Due to this movement, the size of the aperture opening 15 formed by the area where the aperture holes 13 and 14 overlap is changed, so that the light flux passing through the aperture opening 15 is limited and a light amount suitable for photographing is obtained.

In order to obtain a large luminous flux when the subject brightness is low, as shown in FIG. 3 (b), the aperture openings 15 are superposed at appropriate portions of the oval portions 13a and 14a of the aperture holes 13 and 14, respectively. Big one. Then, when passing through the aperture 15 and passing through the diffraction plate 20, the high spatial frequency component of the subject image is removed by the diffraction plate 20 and passes through the relay lens 4,
It is incident on the CCD 5. Therefore, the occurrence of the moire phenomenon is prevented.

On the other hand, when the brightness of the subject is high, a sufficient amount of light can be obtained even if the luminous flux is made thin. Therefore, as shown in FIG. 3A, the diaphragm plates 11 and 12 are moved to form the diaphragm holes 13 and 14. Only the small aperture parts 13b and 14b are overlapped with each other to form a small aperture 15. Since the distance D between the tips of the small diaphragms 13b and 14b is set to an appropriate multiple of the pitch P of the wavy portions 21 of the diffraction plate 20, the light flux passing through the small diaphragm 15 passes through the diffraction plate 20. At this time, the light passes through the plurality of corrugated portions 21, and the low-pass effect of the diffractive plate 20 acts on the light flux, so that high spatial frequency components are removed from the subject image. Therefore, the subject image that has passed through the relay lens 4 and is incident on the CCD 5 is appropriately blurred and the occurrence of the moire phenomenon is prevented.

[0017]

As described above, according to the diaphragm structure of the present invention, the longitudinal direction of the diaphragm opening at the time of the small diaphragm is formed along the direction of the pitch of the wavy portion of the diffraction plate, and the diaphragm is formed. Since the length of the opening in the longitudinal direction is made larger than the pitch of the wavy portions, the light flux of the subject image that has passed through the aperture opening is transmitted through the plurality of wavy portions of the diffractive plate even when the aperture is small. Therefore, the low-pass effect of the diffractive plate acts on the subject image, so that high spatial frequency components are removed from the subject image. Therefore, the portion of the subject image incident on the image sensor corresponding to the high spatial frequency component is appropriately blurred and the occurrence of the moire phenomenon is prevented.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic partial configuration of a photographic optical system having this diaphragm structure.

FIG. 2 is a schematic plan view of a photographing optical system in which a diffraction plate is used as an optical low pass filter.

FIG. 3 is a plan view of a diaphragm showing this diaphragm structure, in which (a) shows a small aperture and (b) shows a relatively large aperture.

FIG. 4 is a plan view of a diaphragm plate having this diaphragm structure.

FIG. 5 is a rear perspective view of the diffractive plate with a part cut away.

FIG. 6 is a plan view of a photographing optical system using a quartz plate for an optical low pass filter.

[Explanation of symbols]

 1 Focusing lens 2 Variable magnification lens group 4 Relay lens 5 CCD 5a Imaging surface 10 Aperture 11 Front diaphragm plate 12 Rear diaphragm plate 13, 14 Aperture holes 13a, 14a Egg-shaped part 13b, 14b Small aperture part 15 Aperture aperture 20 Diffraction plate 21 Wavy part 21a Crest part 21b Valley part P Pitch S Optical axis D Longitudinal length of diaphragm aperture at small aperture

Claims (1)

[Claims] 1. A camera using a diffractive plate in which peaks and troughs are alternately formed in a continuous wave pattern in one direction as an optical low-pass filter of a subject image, and the aperture of the camera is minimum. In a small diaphragm state formed in the aperture of the camera, the longitudinal direction of the diaphragm is along the pitch direction of the wavy portion, and the longitudinal length of the aperture is made larger than the pitch. A diaphragm structure.