JPH04264402A - Light quantity adjustor and image pickup device using the same - Google Patents

Abstract

PURPOSE:To obtain the light quantity adjustor which properly limits the quantity of passing light and has excellent low-pass effect even when a photography system is put in a small aperture state and the image pickup device which uses the light quantity adjustment device by limiting the quantity of passing light by ND filters and properly setting the arrangement of the ND filters and its optical characteristics when the low-pass effect is obtained by using an optical low-pass filter. CONSTITUTION:The ND filters 3 and 4 which vary in optical density continuously or stepwise in accordance with the distance from the optical axis are mounted on parts of stop blades 1 and 2 in the light quantity adjustor which limits the quantity of passing light by varying the stop aperture diameter by using >=2 stop blades 1 and 2, and the quantity of passing light is limited by using the ND filters. For the image pickup device, the light quantity adjustor is arranged in part of the photography system which has the phase grating type low-pass filter.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is capable of appropriately controlling the amount of passing light while maintaining good optical performance.
The present invention relates to a light amount adjustment device suitable for a video camera using an imaging means such as a CD, and an imaging device using the same.

0002

[Prior Art] Conventionally, a light amount adjusting device for controlling the amount of passing light in an imaging device such as a video camera is shown in FIG. 8(A).
As shown in (B), two aperture blades 11 and 12 are used, and an ND filter 1 is attached to a part of one aperture blade 12.
4 is installed.

[0003] When the subject is bright, the aperture diameter is not narrowed down to a very small value, the aperture aperture is kept constant, and instead an ND filter is positioned on the optical axis 5 to limit the amount of light passing through. This prevents the difficulty of mechanical control when reducing the aperture diameter of the imaging device and the deterioration of imaging performance due to the diffraction effect of the aperture aperture when the aperture diameter becomes small.

0004

[Problems to be Solved by the Invention] Generally, video cameras and the like use a CCD as an imaging means. For this reason, if the subject contains high spatial frequency components near or higher than the sampling frequency of the imaging means, the resulting image will generate false signals with patterns that are not present in the original image, contrast inversion, etc. .

[0005] For this reason, conventionally, an optical low-pass filter is disposed in a part of the optical system to limit spatial frequency components above a certain level that the subject has.

However, when a phase diffraction grating type low-pass filter is used as an optical low-pass filter, as the aperture diameter of the aperture is made smaller, for example, when the aperture diameter becomes less than two periods of the phase diffraction grating, phase diffraction occurs. A problem arises in that the amount of light diffracted by the grating decreases, and the low-pass effect deteriorates.

[0007] Furthermore, the blurring of images due to the low-pass effect is reduced, and the focus detection accuracy is also reduced in so-called TV automatic focus detection type cameras, which detect focus by processing signals obtained from an image sensor. Problems arise.

[0008] The present invention limits the amount of passing light using an aperture and an ND filter, and when obtaining a low-pass effect using an optical low-pass filter, the amount of passing light is appropriately set by appropriately setting the arrangement of the ND filter and its optical characteristics. It is possible to obtain a good low-pass effect even when the shooting system is set to a small aperture, and to obtain an image with a good bokeh.For example, it is possible to adjust the light amount to enable high-precision TV automatic focus detection. The purpose is to provide a device and an imaging device using the same.

[0009]

[Means for Solving the Problems] The light amount adjusting device of the present invention changes the aperture aperture diameter using two or more aperture blades,
In a light amount adjustment device that limits the amount of light that passes through, an ND filter whose optical density changes continuously or stepwise depending on the distance from the optical axis is attached to a part of the aperture blades, and the N.D.
It is characterized by the use of a D filter to limit the amount of light passing through it.

Furthermore, the imaging apparatus of the present invention is characterized in that such a light amount adjustment device is disposed in a part of an imaging system having a phase grating type low-pass filter.

[0011]

[Embodiment] Figs. 1 to 4 are schematic diagrams of main parts of Embodiment 1 of the light amount adjusting device of the present invention, and Fig. 5 is an example in which the light amount adjusting device of the present invention is arranged as a part of the photographing system. FIG.

FIGS. 1(A) to 4(A) each show the aperture blade 1.
, 2 in the horizontal direction H to control the diaphragm aperture to become smaller sequentially. FIG. 1A shows the aperture at its maximum aperture, and FIG. 4A shows the aperture at the minimum aperture.

In the figure, 3 and 4 are ND filters, respectively.
For example, they are made of glass or plastic, and are attached to a portion of the aperture blades 1 and 2, respectively. The optical density (transmittance) of the ND filters 3 and 4 changes continuously or stepwise depending on the distance in the horizontal direction H from the optical axis 5 (the optical axis of the imaging system, the same applies hereinafter), and the optical density (transmittance) changes continuously or stepwise in the vertical direction. The optical density is the same for V. For example, it is set so that the optical density increases continuously (the transmittance decreases continuously) as it moves away from the optical axis 5 in the horizontal direction H.

FIGS. 1(B) to 4(B) each correspond to FIG. 1(A).
- The optical density in the horizontal direction H within the diaphragm aperture diameter corresponding to FIG. 4(A) is shown. In the figure, the horizontal axis shows the position of the aperture in the horizontal direction, and the vertical axis shows the optical density. For example, when the aperture in FIG. 1(A) is opened, the optical density (transmittance) in the horizontal direction H is 0 (transmittance is 100%) in the central wide area D1 and on the optical axis 5, as shown in FIG. 1(B). On the other hand, the optical density gradually increases as it moves away from the region D1 (
The transmittance gradually decreases).

Furthermore, as the aperture blades 1 and 2 are moved in the horizontal direction H, the aperture aperture becomes smaller as shown in FIG.
When parts of the D filters 3 and 4 come into contact with each other, the optical density at the center of the optical axis becomes 0, as shown in Figure 3(B).
(transmittance is 100%), but the optical density gradually increases as the distance increases (transmittance decreases).

When the aperture blades 1 and 2 are further moved in the horizontal direction to make the aperture the minimum aperture as shown in FIG. As shown in FIG. 4(B), the optical densities of the ND filters 3 and 4 in the horizontal direction are averaged and become uniform over the entire area. As a result, the transmittance is constant over the entire aperture area.

The ND filters 3 and 4 in this embodiment are each attached to a part of the aperture blades of the aperture 23 of the photographing system, and when the subject is bright and the aperture aperture must be stopped down to a certain value or less, the aperture aperture is set to a certain value. Instead, an ND filter is used to limit the amount of passing light.

[0018] This prevents deterioration in optical performance due to diffracted light that occurs when the aperture aperture is made small, and also improves the optical performance by allowing the light beam to enter a wide area of the optical low-pass filter when an optical low-pass filter is used. This allows a low-pass effect to be obtained.

In this embodiment, the same effect can be obtained even if the optical density distribution of the ND filter is not changed continuously but is changed stepwise.

Next, each element when the light amount adjusting device of the present invention shown in FIG. 5 is arranged as a part of the photographing system will be explained.

In FIG. 5, reference numeral 20 denotes a photographing lens, which has a front group 21 and a rear group 22. The front group 21 includes a focus lens group, a variable power lens group (variator, compensator), an afocal lens group, and the like. The rear group 22 has an imaging lens group (relay lens group). 23 is an aperture, which is arranged between the front group 21 and the rear group 22. For example, as shown in FIG.
have. ND filters 3 and 4 are attached to two aperture blades 1 and 2.

27 is an optical low-pass filter;
It consists of a phase diffraction grating. 24 is an imaging means;
It has a CCD 24a, and an object image is formed by the photographing lens 20 on the surface of the CCD 24a. A signal processing circuit 25 processes the image signal from the imaging means 24 and transmits the image signal to, for example, a television receiver. Further, the signal from the signal processing circuit 25 is input to the aperture drive control motor 26 to limit the aperture opening of the aperture 23 so that the video signal level remains constant.

In this embodiment, when the aperture aperture of the aperture 23 is stopped by the aperture drive control motor 26 based on the signal from the signal processing circuit 25, if the subject is too bright and the aperture aperture must be kept below a certain value, Instead of making the diaphragm aperture smaller, the ND filters 3 and 4 are positioned on the optical axis to limit the amount of light passing through.

[0024] This limits the amount of light passing through the lens and prevents deterioration of optical performance due to diffracted light generated from the diaphragm aperture. Furthermore, the light flux is made incident on a wide area of the optical low-pass filter 27, so that a good low-pass effect can be obtained.

FIGS. 6 and 7 are schematic diagrams of main parts of a second embodiment of the light amount adjusting device of the present invention. In this embodiment, the aperture is composed of three aperture blades 6, 7, and 8. Each of the aperture blades 6, 7, and 8 is moved in a direction perpendicular to the optical axis by a driving means (not shown) to change the aperture diameter.

FIG. 6 shows the aperture at the aperture, and FIG. 7 shows the aperture at the minimum aperture. Each aperture blade is equipped with an ND filter 9, 10, 11 whose optical density changes continuously or stepwise as the distance from the optical axis increases. In addition, when the minimum aperture is shown in FIG. 7, each ND filter 9,
Aperture blades 6, 7, 8 so that 10, 11 overlap each other
is being moved. In this embodiment, there are three aperture blades 6 and 7.
, 8 and ND filters 9, 10 attached to each aperture blade,
11, the same effect as in Example 1 is obtained.

In the present invention, two or more diaphragm blades may be used and an ND filter may be attached to each diaphragm blade, which is preferable because the diaphragm aperture diameter can be made approximately circular.

[0028]

According to the present invention, when the amount of passing light is limited by an aperture and an ND filter and a low-pass effect is obtained using an optical low-pass filter, the arrangement of the ND filter and its optical characteristics are appropriately set as described above. By doing so, it is possible to appropriately limit the amount of passing light and obtain a good low-pass effect even when the shooting system has a small aperture.
In addition, an image with good blur can be obtained, and for example, a light amount adjustment device and an imaging device using the same can be achieved, which are capable of highly accurate TV automatic focus detection.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of Embodiment 1 of the light amount adjustment device of the present invention when the aperture is open.

FIG. 2 is a schematic diagram of Embodiment 1 of the light amount adjustment device of the present invention when the aperture is slightly stopped.

FIG. 3 is a schematic diagram of Embodiment 1 of the light amount adjusting device of the present invention when the aperture is closed down to a large number.

FIG. 4 is a schematic diagram when the aperture of Example 1 of the light amount adjustment device of the present invention is set to the minimum aperture.

FIG. 5 is a schematic diagram when the light amount adjustment device of the present invention is applied to a part of an imaging system.

FIG. 6 is a schematic diagram of Embodiment 2 of the light amount adjustment device of the present invention when the aperture is open.

FIG. 7 is a schematic diagram when the aperture of Example 2 of the light amount adjustment device of the present invention is set to the minimum aperture.

FIG. 8 is a schematic diagram of a diaphragm of a conventional light amount adjustment device.

[Explanation of symbols] 1, 2 Aperture blades 3,4 ND filter 5 Optical axis 6, 7, 8 Aperture blades 9, 10, 11 ND filter 20 Photography system 21 Front group 22 Rear group 24 Imaging means 24a CCD 25 Signal processing circuit 26 Aperture drive control motor 27 Optical low pass filter

Claims (2)

[Claims] Claim 1: In a light amount adjustment device that uses two or more aperture blades to change the aperture diameter and limit the amount of light passing through, a portion of the aperture blades each has an optical density depending on the distance from the optical axis. 1. A light amount adjusting device, characterized in that an ND filter that changes continuously or stepwise is installed, and the amount of light passing through the ND filter is limited using the ND filter. 2. An imaging device characterized in that the light amount adjusting device according to claim 1 is disposed in a part of an imaging system having a phase grating type low-pass filter.