JP2981481B2 - Video camera with automatic focusing means - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera having automatic focusing means. 2. Description of the Related Art Conventionally, a focusing device provided in a video camera measures a distance between the camera and a subject using a principle of triangulation such as a so-called double image matching method, and then measures the distance. A method is adopted in which the front lens portion of the lens is moved by a motor to a position previously configured on a distance axis so as to focus on the lens. In this method or a similar method, an autofocus function can be obtained for a subject whose normal distance is, for example, 1 m to ∞ (infinite distance). It is powerless at the time of close-up photography when not far away, that is, at the time of so-called macro photography. There are three main reasons why this method cannot perform an autofocus operation during macro photography. (1) With the triangulation method or a similar method, accurate distance measurement over a large distance range of several meters to ∞ cannot be performed. That is, in the triangulation method, the deflection angle of the mirror is converted and used according to the distance. However, the deflection angle width of the mirror for measuring several cm to ∞ is required to be several tens of degrees, which is unrealistic. Value. (2) For a subject several centimeters away, the parallax between the unit for triangulation and the lens becomes large, and the probability that the measured distance is not always the distance to the subject to be photographed significantly increases. (3) The auto-focus device focuses by controlling the rotation of the distance ring of the front lens portion of the lens. Normally, focusing in the macro range is performed using the zoom ring. Cannot be focused. From the principle, it can be seen that these reasons can be solved by using ultra-high-precision mirror deflection angle correction control, parallax correction means, and means for sending and controlling an autofocus signal to the zoom ring. At present, its feasibility is nearly impossible. Further, the method of controlling the position of the front lens portion is not suitable for downsizing a video camera because the movement amount (extending amount) of the front lens portion is large. Further, if an attempt is made to realize a front lens control type autofocus by using a high-frequency component of an imaged video signal as a detection signal indicating the degree of focus correctness, as described in Japanese Patent Application Laid-Open No. 55-76309, a change in focal length (magnification) is required. Changes the depth of focus. For this reason, the detection signal also changes in accordance with the focal length. To realize a stable focusing operation which is not affected by the change, the control itself becomes complicated as described in JP-A-55-76309. Further, since the change in the focal length accompanying the movement of the front lens is relatively large, the angle of view fluctuates during the focusing operation, and the captured image becomes unsightly. On the other hand, a method of controlling the position of the rear lens portion in accordance with the zoom magnification after focusing once to prevent defocus even if the zoom magnification changes is disclosed in, for example, Japanese Patent Publication No. 52-15226. Although disclosed in the official gazette, even in this known example, there is no disclosure about performing automatic focusing at a very short distance immediately before the lens. Further, in the method of controlling the rear lens, as described in this known example, since the lens position of the focusing group differs depending on the zoom magnification even at the same object distance, the lens position of the focusing group depends on the object distance and the zoom magnification. Is required, and the focusing operation is extremely complicated. SUMMARY OF THE INVENTION An object of the present invention is to provide a video camera having a focusing device which is highly accurate and suitable for miniaturization. According to the present invention, there is provided a zoom lens having a master lens disposed at a rear portion of a lens system, wherein a zoom magnification is variable within a predetermined range. An image sensor that converts an optical image obtained from the zoom lens into an electric signal, which is arranged in the vicinity of the rear of the master lens, and a power camera circuit including a signal processing circuit that processes the electric signal to obtain a video signal; A focus amount detection circuit that detects a degree of focus correctness for each vertical scanning cycle based on the video signal output from the camera circuit, a driving unit that moves the master lens back and forth, and the zoom In accordance with the degree of focus correctness detected by the focus amount detection circuit over the entire predetermined range of magnification, the mass Automatic focus means for controlling the position of the target lens, and for reducing the moving range of the master lens position for covering the same distance range of the subject as the zoom magnification is smaller. [0013] With this, the master lens can be moved in the very close range at a very low zoom magnification at a very close distance where zooming is unnecessary, so that accurate focusing can be performed even at the very close distance. Since the video signal itself of the video camera is used as a signal corresponding to the degree of focus correctness for controlling the position of the master lens,
An imaged video signal obtained by imaging an object at a very short distance in a state where the zoom magnification is low is a signal corresponding to the degree of focusing at the very short distance. Further, the feedback control system including the power lens circuit, the focus amount detection circuit, and the focusing means automatically controls the position of the master lens in accordance with this signal.
Without performing complicated processing as disclosed in Japanese Patent Application Laid-Open No. 226/226, a correct focusing state can be obtained even at a very short distance immediately before the lens, and even if an assembly error occurs between the zoom lens and the power lens circuit. A correct focus state is obtained. In addition, since focusing is performed by moving the master lens, the amount of movement is small, and a more compact video camera can be realized. Since the detection signal is not affected by a change in zoom magnification even if the
No complicated processing as described in Japanese Patent No. 76309 is required, and a stable and natural focusing operation can be performed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to a system configuration block diagram shown in FIG. 1 and a characteristic diagram shown in FIG. In FIG. 1, reference numeral 1 denotes a zoom lens,
It has a configuration in which focusing operation can be performed by moving part or all of the master lens. Reference numeral 2 denotes a camera circuit including an image pickup device and a signal processing circuit of a video camera. Reference numeral 3 denotes a focus amount detection circuit. Reference numeral 4 denotes a difference detection circuit. Reference numeral 5 denotes a motor drive circuit. A motor to be driven, 7 is a zoom position detector such as a potentiometer that rotates in conjunction with a zoom lever to detect the zoom position of the zoom lens 1, that is, a focal length, 8 is a movement range calculation circuit, and 9 is the focus adjustment. A lens position detector 10 for detecting at which distance the structure matches, and 10 is for setting whether this configuration performs an autofocus operation in a normal distance range or sets an operation in a macro range. Push button switch. Reference numeral 11 denotes a switch for switching between automatic and manual operations, and reference numeral 12 denotes an operation switch for performing manual focusing when the switch 11 is switched to the manual side. First, a description will be given of a case where the structure shown in FIG. 1 performs an autofocusing operation at a normal distance, for example, within a range of 1 m to ∞ (infinite distance) by the push button switch 10. A subject image incident on the zoom lens 1 is converted into an image pickup video signal by a camera circuit 2 and is input to a focus amount detection circuit 3. The focus amount detection circuit 3 calculates the difference between the degree of focus of the screen during shooting, that is, the amount of the high frequency component of the video signal corresponding to the sharpness of the outline of the screen, every one screen period, for example, every 1/60 second. Input to the detection circuit 4. Therefore, when the above function is operated while moving the focusing structure of the zoom lens 1 by the motor 6 in the motor drive circuit 5, the output of the difference detection circuit 4
If the direction of rotation of the motor is in focus, a positive voltage output is obtained. Conversely, if the direction of focus is out of focus, a negative voltage output is obtained. The autofocus operation is performed by keeping the direction as it is, and in the case of a negative voltage, reversing the rotation direction of the motor 8. Here, focusing of the zoom lens 1 is performed by moving a part or the whole of the master lens system. In this case, the position of the master lens and the object distance at which the subject is in focus are shown in FIGS. 2A, 2B, and 3C. In the case of an object at a distance of ∞, the master lens is in focus even when the zoom magnification changes. Is constant. However, for subjects at other distances,
The position of the in-focus master lens changes with a change in magnification (in the case of a subject at a close distance of 1 m, (c) in the figure)
Curve for a subject at a distance of 2 m (curve (b) in the figure). That is, the focal length is minimum (the zoom magnification is minimum)
In the case of (1), for example, when the value of A1 is used, the moving range of the master lens position for covering the same distance range of the subject as when the focal length is the maximum (A2) may be a small value of 0 to B1 in FIG. . The difference in the moving range of the master lens position due to the difference in the focal length is almost proportional to the square of the zoom magnification of the zoom lens 1. For example, when a 6 × zoom lens is used, a master at a magnification of 1 × is compared with a moving range of a master lens when a subject at a distance of 1 m to ∞ is photographed at a magnification of 6 ×. The movement range of the lens is about 1/36 of that. For this reason, when photographing at a low magnification without photographing the macro area, if the range of the master lens is limited in order to minimize the movement of the master lens in the blur direction, the autofocus operation can be performed quickly. . In the auto-focusing operation in the normal distance range, the focal length is detected by the zoom position detector 7 linked to the zoom ring of the zoom lens 1, and the focal length is detected by the moving range calculation circuit 8 incorporating the characteristics of FIG. By inputting, the motor 6 is controlled via the motor drive circuit 5 while referring to the output of the lens position detector 9 for detecting the master lens position, so that the moving range of the focusing structure of the zoom lens 1 is minimized. It is better to stay within the value range. Next, a case where the configuration shown in FIG. 1 operates as an auto-focusing device in a macro range, that is, several cm to 1 m by the push button switch 10 will be described. When performing focusing by moving the master lens, so-called macro operation is possible when the focal length is any value,
For simplicity, the case where the focal length is the minimum value A1, that is, the zoom magnification is the minimum, will be described. Focal length is A
In the case of 1, when imaging a subject in the normal distance range, the master lens can be focused within the moving range of the range 0 to B1 as described above. However, the movement range is not limited to this, and even when the focal length is A1, the master lens movement range is 0 to B2 when the zoom magnification is the maximum value.
By moving the master lens in the range from (infinity end to the closest end), the range of the subject distance that can be focused is
Almost (normal distance range
) To ∞. That is, when the zoom magnification is 6 times, the photographing of the object from 1 m to ∞ is possible, and when the zoom magnification is 1 time, the photographing of the object from 2.8 cm to ∞ is possible. In other words, when the autofocus operation in the macro area is designated by the push button switch 10, the autofocus operation in the macro area in the configuration of FIG. Is possible. Of course, unless the pushbutton switch is deleted from the configuration of FIG. 1 and the moving range of the master lens is not limited, photographing in the macro range is always possible, and a configuration without such a pushbutton switch is acceptable. According to the present invention, the position of the master lens is automatically controlled by the feedback control system based on the video signal itself of the video camera. Therefore, when the zoom magnification is small, the same subject can be covered. In this case, it is possible to reduce the moving range of the master lens position, and to eliminate the influence of the assembly error between the zoom lens and the camera circuit. can get. In addition, a more compact video camera can be realized, and the detection signal is not affected by a change in zoom magnification even if a high-frequency component of the captured video signal is used as a detection signal corresponding to the degree of focus correctness in the rear lens control method. Since the angle of view does not fluctuate during focusing, a stable and natural focusing operation can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a video camera autofocus apparatus according to the present invention. FIG. 2 is a characteristic diagram illustrating the operation of the master lens of FIG. [Description of Signs] 1 ... Zoom lens, 2 ... Camera circuit, 3 ... Focus amount detection circuit, 4 ... Difference detection circuit, 5 ... Motor drive circuit, 6 ... Motor, 7 ... Zoom position detection circuit, 8 ... Moving range calculation circuit,
9: lens position detector, 10: push button switch.

Claims (1)

(57) [Claims] It has an objective lens, a variable power lens and a master lens,
In a video camera having an automatic focusing unit of a zoom lens having a structure capable of focusing by driving a part or all of the master lens by driving a driving unit, a drive for controlling the driving unit of the master lens A means control circuit refers to an output of the movement range calculation circuit, which calculates a movement range of the master lens, according to a detection result of a zoom position detection unit that detects a zoom position of the zoom lens. A drive circuit for controlling the drive means of the master lens by limiting the movement range of the master lens to the movement range calculated by the movement range calculation circuit. Having a video camera. 2. The moving range calculation circuit has a built-in table indicating the relationship between the position of the zoom lens and the position of the master lens that is in focus on an arbitrary subject. 2. The moving range of the master lens according to the distance is calculated.
A video camera according to claim 1. 3. The moving range calculation circuit has a built-in equation indicating the relationship between the position of the zoom lens and the position of the master lens that is in focus on an arbitrary subject. 2. The moving range of the master lens according to the distance is calculated.
A video camera according to claim 1.