JPH0580386A - Video system camera - Google Patents

Abstract

PURPOSE:To improve the accuracy of an AF function by preventing uncertainty in AF operation, to make the range of an F value wider when the brightness of an object is high and to restrain ghost from becoming conspicuous in the case of counter light in a video camera and an electronic still camera. CONSTITUTION:An iris 3 and a light quantity adjuster 2 are inserted in a lens part. In the case of the AF operation, when the brightness of the object is very high, a microcomputer 6 allows the iris 3 to be in an opening direction and controls the light quantity adjuster 2 to restrict light, so that the depth of focus is prevented from getting large by stopping down the iris 3. Since the depth of focus gets small, focusing on the object is facilitated, and uncertainty in the AF operation is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera such as a video camera, an electronic still camera (hereinafter collectively referred to as "video camera"), and more specifically, an improvement in AF accuracy and a subject brightness (illuminance). The present invention relates to an AE device for a video camera, in which the F value is widened and the ghost is less noticeable.

[0002]

2. Description of the Related Art The video AF system, which is the mainstream of the current video cameras, uses the high frequency component contained in the video signal taken out from the CCD image pickup device.
This is an image processing method for performing focusing by utilizing the fact that the amplitude of the high frequency component (image contrast) of the video signal becomes maximum when the lens is in focus. Specifically, the focus lens is driven so that the evaluation value obtained by detecting the high frequency component of the luminance signal and integrating the AD converted value over the entire focus frame for each field is always the maximum. In addition, an iris that is a mechanical diaphragm is built into the lens optical system, and the iris is controlled by a photometric circuit. This iris control device detects the amount of light after passing through the lens, although there are differences depending on the photometry method (average photometry, center-weighted photometry, etc.), and the aperture is servo-controlled to compare with the target aperture value, and the optimum image is obtained. It is controlled automatically so that Naturally, when the subject brightness is high, the iris is controlled in the direction of narrowing down, and by narrowing down, the depth of field becomes deep.

[0003]

The AF device of the video camera having the above-mentioned structure has various drawbacks as described below. When the subject is a mixture of perspective and perspective, the phenomenon of "background shadow" is likely to occur. This is a phenomenon in which the focus is on the background instead of the subject at the center of the screen, and is caused by the occurrence of a plurality of evaluation value peaks. FIG. 3A shows a typical example of such a perspective mixed subject. There is a focus frame 16 at the center of the image frame 15, and the focus frame 16
The person who is the main subject and a tree in the distance are captured inside. As shown in FIG. 3B, the peak output of the evaluation value occurs at the positions of the person and the background tree. When a plurality of peaks occur in the evaluation value in this manner, the background tree is focused instead of the person, or hunting occurs in which the person and the tree are alternately focused. This phenomenon is likely to occur especially in bright outdoor photography. This is because the brightness of the subject becomes high and the iris is inevitably narrowed down to deepen the depth of field and bring the background into focus. When the above shooting conditions occur, the AF is apt to get lost.

When it is backlit, a ghost is likely to occur. Ghosting occurs when light from a high-intensity object point, such as the sun, is reflected on a lens surface, a low-pass filter, or the like twice or more, and then formed as unnecessary light on the image surface.
Under such shooting conditions, the aperture is often small, and the depth of focus of the unnecessary light flux itself becomes deep, which is more prominent.
In many cases, an ND filter is attached to one iris of the iris to adhere to the iris in order to prevent hunting when the aperture is small. However, this ND filter is made of polyester film or the like, and a ghost may occur due to reflection from the filter, master lens, low-pass filter, or the like. Since it is a polyester film, anti-reflection coating cannot be applied.

It is not possible to sufficiently cope with a wide range of changes in subject illuminance. That is, there is a method of changing the shutter speed or mounting an ND filter on the front surface of the lens, but there is a limit when the illuminance range is wide. With a video camera, the shutter speed can be changed from 3 to 6 steps, but depending on the purpose of drawing, when shooting a blurred background by opening the diaphragm, 3 to 6 steps may not be applicable.

There are some which use only a liquid crystal diaphragm instead of a mechanical iris (Japanese Patent Laid-Open No. 28744/1990).
5, JP-A-2-113676, JP-A-2-28744
8, JP-A-2-287447), however, is inadequate because it cannot actually completely shield light. An object of the present invention is to solve each of the above-mentioned drawbacks, improve the accuracy of the AF function without causing confusion, widen the F-number when the subject brightness is high, and prevent ghosts during backlighting. An object of the present invention is to provide a video camera that can reduce the visibility of the image.

[0007]

In order to achieve the above object, a video camera according to the present invention is a video camera having an AF function, in which a lens system is provided with a mechanical iris and a light quantity adjuster, and during the AF operation. When the illuminance of the subject is very large, the mechanical iris is controlled in the opening direction to limit the amount of transmitted light of the light amount adjuster to control the exposure appropriately. Further, the light quantity adjuster may be composed of a liquid crystal or an electrochromic device.

[0008]

The present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic view showing an embodiment of a lens unit of a video camera according to the present invention. The lens unit 1 is composed of a variator 1a and a focus lens 1b (master lens). The zoom unit is composed of a variator 1a. The focus section is composed of a focus lens 1b. A mechanical iris 3 is built in the lens unit 1. A low-pass filter 14 is arranged in front of the CCD image pickup device 4. Further, the light amount adjuster 2 is arranged between the low-pass filter 14 and the rear portion of the lens unit 1.

FIG. 2 is a circuit diagram showing an embodiment of the circuit portion of the video camera according to the present invention. Motors 11, 12 and 13 which are driven under the control of the microcomputer 6 are connected to the microcomputer 6. The motor 11 drives the variator 1a back and forth along the optical axis to set the magnification specified by the microcomputer 6. The motor 12 opens and closes the iris 3 to adjust the light amount. The motor 13 drives the focus lens 1b back and forth along the optical axis to adjust the focus position. The optical image formed on the CCD image pickup device 4 is converted into an electric signal and sent to the camera signal processing circuit 5. The camera signal processing circuit 5 performs a predetermined process such as adding a synchronization signal and sends the video signal to a recording circuit or the like (not shown). The camera signal processing circuit 5 outputs a brightness signal for iris control and a light amount adjuster, and a brightness signal for AF.

The AE device comprises a microcomputer 6, a motor 12, an iris 3 and a light quantity adjuster 2 which receive an iris controlling and light adjusting brightness signal from a camera signal processing circuit 5. The high-pass filter 7 extracts high-frequency components from the brightness signal for AF. The extracted high frequency component is amplified by the amplifier 8 and then detected by the detection circuit 9
Is detected by. The detected signal is converted into a digital signal by the A / D converter 10 and sent to the microcomputer 6. The microcomputer 6 controls to drive the focus unit in the direction in which the signal from the A / D converter 10 becomes larger, that is, in the direction in which the output level of the high frequency component increases. As a result, the focus lens 1b is brought to the position with the highest contrast, that is, the in-focus position. A liquid crystal or an electrochromic element is used as the light amount adjuster 2 used together with the iris 3 of the AE device. The liquid crystal utilizes its dynamic scattering effect to continuously change the intensity of transmitted light depending on the strength of voltage. Further, the electrochromic element changes the transmitted light intensity by utilizing the phenomenon that the iridium hydroxide film is colored (gray) by the injection of ions by a voltage and is decolorized (colorless) by the direct current of the opposite polarity. This electrochromic element has a memory property and retains the density when the power is cut off at an arbitrary coloring density.

In normal photography in which the illuminance of the subject is not particularly high, the AE device increases the amount of transmitted light of the light amount adjuster 2 and controls the exposure with the iris 3. In the case of outdoor photography, when the illuminance of the subject becomes extremely large during the AF operation, the microcomputer 6 automatically switches from the normal exposure control so that the mechanical iris 3 does not become small and the depth of field does not become deep. Then, the iris 3 is controlled in the opening direction so as to limit the transmitted light amount of the light amount adjuster 2. That is, even if the iris 3 moves in the opening direction, the density of the light quantity adjuster is increased so that the illuminance on the image plane is always constant. By controlling the exposure in this way, the depth of field is made shallow and only the subject is easily focused, so that the phenomenon of "background blurring" can be reduced. Even in the case of backlight photography, the iris 3 is controlled so that it is fully open, so the depth of focus of the unnecessary light flux itself becomes shallow, and the occurrence of ghost can be made inconspicuous to some extent. In the case of an extremely high-brightness object that cannot be dealt with only by opening and closing the normal iris 3, the iris 3 can be narrowed down and the density of the light quantity adjuster can be controlled to be large for shooting.
By changing the shutter speed, the diaphragm can be opened or reduced depending on the purpose of drawing. A combined F value of F1500 or more is possible. The liquid crystal or the electrochromic element is arranged near the diaphragm that is close to the parallel light flux or behind the master lens as described above. As the liquid crystal or electrochromic element thus arranged, a low-pass filter or a CCD face plate which is adhered and integrated with an optical adhesive may be used in order to reduce interface reflection. It is also possible to apply a transparent coating to the cover glass of the liquid crystal or electrochromic device. In this embodiment, an example has been described in which the normal exposure control is automatically switched when the illuminance of the subject becomes very large, but the photographer can also arbitrarily switch the exposure control.

[0012]

As described above, according to the present invention, the lens system is provided with the mechanical iris and the light quantity adjuster, and when the illuminance of the subject becomes very large during the AF operation, the quantity of light transmitted through the light quantity adjuster is limited. Then, a control means for controlling the mechanical iris in the opening direction is provided. Therefore, the following various effects can be obtained. ○ It is possible to suppress the “background lightening” phenomenon during AF, and the AF operation does not get lost. ○ It is possible to reduce the depth of focus of the unnecessary light flux itself, and reduce the visibility of ghosts. ○ Aperture-priority shooting is possible, and you can freely shoot for the purpose of drawing. ○ It can cope with a very wide range of changes in subject brightness. That is, the combined F value can be increased. ○ It is not necessary to attach a small ND filter or the like to the tip of the blade of the auto iris. ○ It is not necessary to attach the ND filter to the front surface of the lens even when shooting with the mechanical iris open. ○ The light quantity adjuster can basically be placed at any position in the optical system. Further, since there is no movable portion, the lens barrel structure becomes simple. ○ Utilizing the memory property of the electrochromic device is effective for protecting the imaging surface when the power of the camera is cut off. Also,
It also saves energy.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a lens unit of a video camera according to the present invention.

FIG. 2 is a circuit diagram showing an embodiment of a circuit unit of a video camera according to the present invention.

FIG. 3 (a) is a diagram showing an example of a subject in which perspective is mixed,
(B) is a characteristic diagram showing the occurrence of a peak of the evaluation value at that time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Lens part 2 ... Light quantity adjuster 3 ... Iris 4 ... CCD image sensor 5 ... Camera signal processing circuit 6 ... Microcomputer (microcomputer) 7 ... High pass filter (HPF) 8 ... Amplifier 9 ... Detection circuit 10 ... A / D conversion Device 11, 12, 13 ... Motor 14 ... Low-pass filter 15 ... Image frame 16 ... Focus frame

Claims (2)

[Claims] 1. In a video camera having an AF function, a lens system is provided with a mechanical iris and a light quantity adjuster, and the mechanical iris is controlled in the opening direction when the illuminance of the subject is very large during the AF operation. A video camera, comprising control means for limiting the amount of transmitted light of the light quantity adjuster and controlling the exposure appropriately. 2. The video camera according to claim 1, wherein the light amount adjuster is a liquid crystal or an electrochromic device.