JPH0332172A - Focusing device for solid-state image pickup camera - Google Patents

Abstract

PURPOSE:To improve the focusing accuracy by opening an aperture of an image pickup lens prior to focusing and using an electronic shutter function of a solid- state image pickup element so as to control the effective exposure time during opening thereby obtaining a video signal with a prescribed strength without distortion. CONSTITUTION:A solid-state image pickup element 3 provided with an electronic shutter function controlling electrically the effective exposure time is used to open an aperture 2 of an image pickup lens 1 by using interlocking switches SW1, SW2 prior to focusing of the image pickup lens. Then the effective exposure time of the solid-state image pickup element 3 is controlled so that the output level of the solid-state image pickup element 3 is a prescribed value for the opening period. Since the aperture of the image pickup lens 1 is opened prior to focusing and the object depth of the image pickup lens 1 is focused with the shallowest state, the focusing accuracy is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] Regarding a focusing device suitable for use in a video camera or an electronic still camera using a solid-state image sensor, in particular, a focusing device using a T T L (Through The L)
The present invention relates to a focusing device that can accurately and quickly focus using a simple mechanism when applied to an ens) method.

[Summary of the invention]

The present invention provides TTL (Through Th
eLens) type focusing device, prior to focusing, the aperture of the photographing lens is opened, and while the aperture is opened, the effective exposure time is controlled by the electronic shutter function of the solid-state image sensor to achieve a predetermined intensity without distortion. This is a focusing device that improves focusing accuracy by obtaining video signals.

[Conventional technology]

There are various types of autofocus devices used in video cameras, each of which is said to have advantages and disadvantages, but recently TTL (Through Thele)
ns) method is increasingly used. The TTL method is a method for obtaining focus information using a signal obtained by receiving light through a photographic lens, and recently, passive methods have been increasingly used. The above-mentioned TTL passive type autofocus device can accurately adjust distances over long distances compared to active type autofocus devices that use reflections of infrared rays and ultrasonic waves. There is no parallax in the field of view, and it is also possible to use a telephoto or wide-angle converter lens.

Furthermore, compared to the active method, the mechanism is simpler, production costs can be kept low, and power consumption during distance measurement can be reduced, among other advantages.

Furthermore, the S/N ratio of the solid-state image sensor (
Improvements are progressing due to improvements in signal-to-noise ratio, etc.

The TTL passive method is roughly classified into a phase difference detection method and a contrast detection method depending on the distance measurement method. The phase difference detection method detects a phase shift in out-of-focus states called front focus and rear focus, but by adding an optical system for phase difference detection to a part of the photographic lens, it is possible to It is necessary to provide a distance measurement sensor, which imposes restrictions on the design of the photographic lens and lens mechanism, and there is a problem that the configuration becomes complicated.

The contrast detection method is a method that works the focusing servo in the direction where the high-frequency component signal of the video signal obtained by receiving the image with the image sensor for video shooting becomes stronger, and adjusts to the point where the high-frequency component signal is strongest. Although this simplifies the mechanism, there is a problem in that it takes a long time to measure the distance to reach the optimal focus. In other words, in order to find the direction in which the high-frequency component signal becomes stronger, first try moving the lens a little in any direction, and then operate the focusing servo in the determined direction.
This is because it takes time to return to the maximum value a little past the position where the maximum value can be obtained.

One way to solve the problem of the contrast detection method requiring long distance measurement is to use a piezo element or the like to adjust the focusing lens or image sensor to a frequency of, for example, 15Hz.
A mechanism is known in which the focus direction is constantly searched by mechanically vibrating in the optical axis direction at a certain level, but this also has the problem of complicating the mechanism. In contrast, the applicant
Previously, in Japanese Patent Application Laid-Open No. 62-247314, an autofocus control device was proposed that can search for a focusing direction without providing the vibration mechanism.

However, even if these focusing direction search methods are used, if the captured image is significantly blurred, contrast changes cannot be detected, and it may be necessary to move the focus ring, etc. for focusing over a wide range from infinity to close range. Since the focus is searched, there is a problem in that an unnatural image appears, especially when a video camera is used to take a picture.

Further, as a common tendency in TTL systems, when the depth of field of the photographing lens is shallow, the focusing accuracy tends to be high, and when the depth of field is deep, the focusing accuracy tends to decrease. This tendency has the effect of increasing the focusing speed by reducing the amount of lens movement for focusing when the taking lens has a short focal length when it is satisfactory to obtain approximate focusing, but A problem arises when you want good focus. For example, problems may occur where the background of two people standing side by side appears more clearly, or the branch of a tree in the foreground appears more clearly.

Recent video cameras are often equipped with auto iris (automatic aperture adjustment) devices, which narrow down the aperture of the lens and focus with a deep depth of focus, making this tendency even stronger. This is a significant disadvantage when viewing images on a large television receiver or when preserving a still image or hard copy of the screen.

In addition, depending on the shooting intention, you may want to perform focusing manually regardless of whether you are shooting a video or a still image, but in the case of the TTL method, it is necessary to maintain the output of the image sensor at a predetermined value, so it is necessary to manually perform focusing for particularly bright subjects. However, focusing was only possible when the aperture was stopped down, and focusing accuracy became a problem.

[Problems to be solved by the invention] The various problems mentioned in the prior art are solved, and the focus can be achieved with high precision using a simple mechanism, and even when applied to an autofocus device using a contrast detection method, the in-focus position can be quickly approached. , a focusing system that can prevent unnatural images caused by unnecessarily wide focusing, can be easily incorporated into video cameras equipped with an auto-iris device, and can improve focusing accuracy even with manual focusing. The challenge is to obtain a focusing device.

[Means to solve the problem]

In the focusing device of the present invention, a solid-state image sensor equipped with an electronic shutter function that can electrically control the effective exposure time without using a mechanical shutter is used as an image sensor, and the imaging for forming an image on the solid-state image sensor is performed. Prior to lens focusing, the aperture of the photographing lens is opened, and during the period when the aperture is opened, the effective exposure time of the solid-state image sensor is set so that the output level of the solid-state image sensor becomes a predetermined value. It is characterized by having a configuration for controlling. The aperture may be configured to return to its original value instantaneously after focusing is completed.

[Effect]

In the focusing device of the present invention, the aperture of the photographic lens is opened prior to focusing, and focusing is performed with the photographic lens having the shallowest depth of field, so that focusing accuracy can be improved.

In addition, even when the photographic lens is opened, the exposure time is effectively shortened using an electronic shutter function, as previously proposed by the applicant in Japanese Patent Application Laid-Open No. 63-105579, so there is no distortion. It is possible to obtain a video signal of a predetermined strength without causing interference such as blooming or smearing, and to analyze the focus position using high-frequency components.

Therefore, for example, for a high-frequency component signal of a video signal, the signal strength ratio between the in-focus position and a slightly shifted position can be increased. You may shoot while following the subject in this state, but in the standby state (the image sensor is operating but not recording), first focus on the target subject with the shooting lens wide open, and then When you start shooting using a normal auto iris device, you can accurately focus on the target subject in advance and then start shooting, so you can immediately capture the target subject without moving the focus over a wide range and obtain a natural image.

In addition, the electronic shutter function is used to control the output level of the image sensor when the aperture of the photographic lens is wide open.
Returning to the auto-iris state can be performed by switching instantaneously, and there is no problem in incorporating the present invention into a camera having an auto-iris function.

Also, manual focusing can be performed with high precision when the aperture of the photographic lens is wide open.

〔Example〕

An embodiment of the present invention will be described with reference to the main block diagram shown in FIG.

The light passing through the photographing lens 1 is converted into an electric signal by a solid-state image pickup device (for example, a charge-coupled device, CCD) 3 with an electronic shutter function, and extracted as a video signal by a first signal processing circuit 4. The output signal of the first signal processing circuit 4 is divided into three signals a, b, and c, and the signal a is sent to the second signal processing circuit 6 and outputted as a video signal in a predetermined format.

The signal is sent to the autofocus circuit 5, for example, passes through a bandpass filter to obtain a high frequency component, uses the high frequency component as an evaluation value, and drives a focusing servo in accordance with a focus control signal based on the evaluation value. Served to move the lens towards the focal point. Although these circuits are not shown, conventionally well-known techniques can be used in various combinations or selections.

What should be noted in this embodiment is the first signal processing circuit 4.
This is the fate of the output signal C.

The signal C becomes, for example, direct current or low frequency in the detection circuit 7,
The autofocus circuit 5 is made to operate in this state. In arrangement example A, the configuration is such that the auto iris state is returned to each time the focus is completed, but with button C, the aperture 2 is in the open state and you can shoot while focusing while tracking the subject. Although the hot spot becomes shallower, it has the effect of maintaining high focusing accuracy, making it possible to take effective pictures depending on the subject.

In the above, a case has been described in which the present embodiment is applied to a focusing device, but by providing a plurality of shutter speed setting voltages V and a plurality of aperture control voltages V2, a shutter-priority auto-iris device and an aperture-priority auto-iris device can be used. Needless to say, it is possible to provide

〔Effect of the invention〕

By implementing the present invention, the aperture of the photographic lens is opened prior to focusing, and during the period when the aperture is opened, the effective exposure time is set to M by the electronic shutter function of the solid-state image sensor.
By controlling and obtaining a video signal of a predetermined strength without distortion,
A focusing device with improved focusing accuracy can be obtained.

By using the focusing device of the present invention, you can simply focus on the target subject in advance when the video camera is on standby, and then take a picture using the normal auto iris. A video camera capable of capturing images can be realized using a lens system with a simple configuration that does not have a dedicated optical system or vibration mechanism for focus detection, and a focus mechanism with a simple configuration.

Further, by using the focusing device of the present invention, it is possible to obtain a video camera that can improve focusing accuracy even during manual focusing, and further to obtain an electronic still camera that can perform highly accurate focusing even when the aperture is wide open. You can also do it.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of main parts of an embodiment of the present invention. l-・・−・〜・−Photographing lens 2−−−−−−・・−Aperture 3−・・・−・−Solid-state image sensor with electronic shutter function (C
CD) 5-----Autofocus circuit 7-
---------1 detection circuit 8------1.-Comparator 9---1 electronic shutter circuit 10--
～−Single stop drive circuit

Claims (1)

[Scope of Claims] A solid-state imaging device having an electronic shutter function that can electrically control effective exposure time, and prior to focusing the imaging lens for forming an image on the solid-state imaging device, Focusing characterized in that the aperture is opened and the effective exposure time of the solid-state image sensor is controlled so that the level of the output of the solid-state image sensor becomes a predetermined value during the period when the aperture is opened. Device.