JPS5967505A - Automatic focusing device of video camera - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an autofocus device for a video camera using the so-called TTL method.

In general, TTL autofocus devices can detect the focal length using a portion of the image that can actually be observed on a TV screen, so it is possible to detect whether the video camera is facing the subject you want to focus on or not. In addition to being able to immediately know which subject is in focus, accurate focusing can be achieved for close-up subjects because there is no parallax between the imaging plane and the autofocus sensor. It has the following advantages. However, in the case of a lens having a large zoom ratio, such as a photographing lens of a video camera, the imaging magnification of the subject image on the imaging surface changes greatly between the telephoto side and the wide side. That is,
When comparing the telephoto side and the wide side, even if the object is at the same focal length, the image will be larger on the telephoto side, but it will be imaged very small on the wide side.

Therefore, on the wide side, even if it is limited to a certain portion of the imaging plane, various miscellaneous object information will be imaged. Since the autofocus sensor has a certain area relationship with respect to the imaging surface, on the wide-angle side, the autofocus sensor similarly forms an image with various miscellaneous and detailed object information mixed therein. As a result, even if the advantages of a TTL autofocus device are taken advantage of on the telephoto side, as you move towards the wide side, various subjects at various focal lengths will enter the autofocus sensor, so it will be difficult for any subject to be photographed. It cannot be determined unambiguously which subject to focus on, or which subject the video camera should point towards. Therefore, the usability of the autofocus device deteriorates, and the autofocus device becomes difficult to use. This has the disadvantage that the focusing operation becomes unstable.

In addition, conventionally, autofocus devices for video cameras have actually been external light type or ultrasonic type.
In many of these autofocus devices, the detection area of the autofocus sensor is constant, and it is unclear which subject is being detected. This drawback is T
A similar problem can occur in the case of a TL autofocus device, and these drawbacks cannot be eliminated unless the detection area of the autofocus sensor is changed depending on the focal length.
l An object of the present invention is to make the detection area of the autofocus sensor larger on the telephoto side and smaller on the wide side, thereby making it possible to take advantage of the advantages of a TTL autofocus device regardless of the focal length, and making it easier for photographers to To provide an autofocus device for a video camera that is extremely easy to use.

The autofocus device for a video camera according to the present invention has the following configuration. A subject image is formed on the imaging surface by a photographing lens that has a zoom lens driven by a motor or manually, and a focus lens driven by a motor, etc., and a part of this subject image is transferred to a zoom splitter etc. A TTL autofocus device that detects distance information to the subject by forming an image on an autofocus sensor, and then drives the focus lens based on the detected distance information to align the focus of the subject image. It is a premise. In such an autofocus device, a circuit for detecting the focal length of the zoom lens is provided, and the detection area of the autofocus sensor relative to the imaging area of the video camera is changed based on the output signal of this circuit. More specifically, by making the detection area of the autofocus sensor larger on the telephoto side and smaller on the wide side, the autofocus device's focusing operation is stabilized and the usability for the photographer is improved. The improved usability for the photographer is achieved by displaying the changed detection area of the autofocus sensor on an electronic viewfinder or the like. This can also be achieved by manually varying the detection area of the autofocus sensor. Such variable operation may be achieved by simply providing an automatic/manual changeover switch.

Embodiments of the present invention will be described below with reference to the drawings.

A photographic lens 1 of a video camera is composed of a zoom lens 2 and a focus lens 3, which are fitted to each other so as to be relatively rotatable about a common optical axis. zoom lens 2
is driven by a motor or manually, and its zoom link 2
A focal length detection circuit 4 is provided that detects the absolute rotational angle or position of a with respect to the focus lens 3 to detect distance information to a subject (not shown). The focal length detection circuit 4 is connected to a sensor area change circuit 6 via an automatic/manual changeover switch 5, and the sensor area change circuit 6 is connected to an autofocus sensor 7 and a sensor area display circuit 8.

The autofocus sensor 7 is arranged at a conjugate position with the imaging surface 10a of the imaging device 1o via a beam splitter 9 arranged on the optical axis, and the output end of the autofocus sensor 7 is connected to the processing circuit 11. There is. The processing circuit 11 is connected to a motor drive circuit 12, and the motor drive circuit 12 is connected to a motor 13.

A pinion 14 is attached to the rotating shaft of the motor 13,
The pinion 14 meshes with a focus ring drive gear 15 that is integrally attached to the focus ring of the focus lens 3.

The changeover switch 5 has an automatic shifting contact A and a manual side contact M, and the manual side contact M is grounded via a variable resistor 5a. Further, the output end of the sensor area display circuit 8 will be connected to an electronic viewfinder (not shown).

The action will be explained below.

When the zoom lens is driven to perform zooming, the focal length detection circuit 4 detects distance information to the subject. The detected distance information is input to the sensor area change circuit 6, and the sensor area change circuit 6 outputs sensor area information corresponding to each focal length to the autofocus sensor 7 based on the input distance information.

On the other hand, the subject image that has passed through the photographic lens 1 is captured by the imaging device 10.
An image is formed on the imaging surface 10a of , and a part of the image is also formed on the autofocus sensor 7 by the beam splitter 9. As mentioned above, since the sensor area information is inputted to the autofocus sensor 7 from the sensor area change circuit 6, the detection area of the autofocus sensor 7 is limited based on this sensor area information. Therefore, the autofocus sensor 7 outputs a part of the subject image formed by the beam splitter 9 to the processing circuit 11, and the processing circuit 11 outputs a part of the subject image formed by the beam splitter 9.
A focusing signal is emitted to the subject image within the detection area limited to . As a result, the motor 13 rotates and rotates the focus link via the pinion 14 and the focus ring drive gear 15, thereby performing an autofocus operation on the subject image within the limited detection area.

At this time, the sensor area change circuit 6 also outputs the sensor area information at each focal length to the sensor area display circuit 8, so the sensor area display circuit 8 displays the sensor area on an electronic viewfinder (not shown). The display method is to mix the sensor area signal into the image signal and display it at a white or black level. This allows the person taking the video camera to visually confirm the sensor area.

Various switching methods as shown in FIG. 2 or 3 can be adopted for switching the sensor area. FIG. 2 shows one autofocus sensor 16 extending horizontally at each focal length f1~
What is displayed on the imaging screen 17 is shown divided into sections 5 for each fS. In addition, FIG. 3 shows autofocus sensors 18.1 with different areas for each focal length f1 to f5.
9.20.21.22 are displayed vertically in the image capture screen 17 to indicate what to select. In addition to the method described above, various methods of switching the sensor area can be used, such as changing the focal length of the autofocus optical system with respect to the imaging side to change the image magnification.

Note that when the changeover switch 5 is switched to the manual side contact M side, the sensor area can be made variable regardless of the focal length by operating the variable resistor 5a.

As explained above, according to the autofocus device for a video camera of the present invention, even if the focal length changes and the size of the subject image changes, the sensor area of the autofocus sensor can be varied accordingly. Therefore, it is possible to fully utilize the advantages of a TTL autofocus device, and it is also extremely easy to use.

In particular, when using a video camera with a large zoom ratio at the wide end, the sensor area at the wide end can be restricted, making it possible to obtain stable autofocus operation.

In addition, if you display the sensor area on the video camera's viewfinder, you can easily select and confirm the point to focus on, making it easier to use when using the video camera on the wide side. get.

If an automatic/manual switch is provided and used on the manual side, the sensor area can be varied regardless of the focal length, allowing an autofocus device to select any area for autofocus. The effect is that it is possible to expand the range of use of the .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the autofocus device of the present invention, and FIGS. 2 and 3 are diagrams each showing a method for switching sensor areas. In one example, two autofocus sensors are used separately, and in FIG. 3, a plurality of autofocus sensors are arranged in parallel in the vertical direction. ■...Photographing lens, 2...Small lens, 4...
Focal length detection circuit, 5... Changeover switch, 6... Sensor area change circuit, 7... O1 to focus sensor, 8... Sensor area display circuit. Figure 1■ Figure 2 Procedural amendment (voluntary) November 20, 1980 Commissioner of the Japan Patent Office 1. Indication of the case 1988 Patent Application No. 177531 2. Title of the invention Video camera autofocus device 3. Relationship with the case of the person making the amendment Patent applicant address 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Name (0
52) Asahi Optical Industry Co., Ltd. 4, Agent 107 Phone: 583-6939 Address:
6-6-4-5 Akasaka, Minato-ku, Tokyo, subject of correction Akira Kinutsu 6, contents of correction (1) Correct "same focus" on page 2, line 19 of the specification to "same focus from the camera -J" (2) Add "Focus J" after "Detected" on page 7, line 14 of the specification of the photographing lens. (4) After “input” on page 7, line 16 of the specification, “
Add "Focus".ノ、之

Claims (3)

[Claims] (1) A TTL video camera that detects distance information to the object by focusing a part of the object image that has passed through the photographic lens on an autofocus sensor, and performs focusing using the distance information. An autofocus device for a video camera, characterized in that the autofocus device detects a change in focal length of a zoom lens to change a detection area of the autofocus sensor relative to an imaging area of the video camera. (2) The autofocus device for a video camera according to claim 1, which displays the changed detection area of the autofocus sensor on a finder. (3) The autofocus device for a video camera according to claim 1, wherein the detection area of the autofocus sensor can be changed manually.