JPS6160080A - Auto focusing device - Google Patents

Abstract

PURPOSE:To prevent the disturbance and instability of a picture due to the hand vibration and to attain the auto focusing with an excellent responsivity with respect to a subject for approaching to and retreating from a camera by stopping the auto focusing control when a de-focusing signal is produced in terms of continuously sampled focus signals after focusing signals continue by the prescribed number. CONSTITUTION:The output of an auto focusing sensor 20 is inputted as a sampling S to a de-focusing arithmetic circuit 23 by the operation of a sensor drive circuit 22, and the focusing or not and the quantity deviated from the correct focus position are detected. A focus signal for including the deviation quantity comes to a motor drive circuit 25 from a control circuit 24, drives a focus motor 14 normally or reversely to set it in the focused state, and executes the auto focusing control. A focusing number counter 26 counts the number of times of focusing signals G from the de-focusing arithmetic circuit 23. After the number reaches four times or more, the input of a de-focusing signal D is received. Then a timer circuit 27 is operated to stop the action of the control circuit 24.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to an autofocus device suitable for use in cases such as video cameras that require continuous autofocus control.

"Prior Art and its Problems" As video cameras become more widespread, more and more video cameras are equipped with built-in autofocus devices.

According to a video camera with an autofocus device,
Since there is no need for troublesome focusing, even beginners can enjoy video shooting.

This camcorder's autofocus device.

Usually, an autofocus sensor for focus detection is placed at a position optically equivalent to the imaging device, and the output of this autofocus sensor is used to autofocus control the focusing lens of the photographic lens. However, in conventional devices, this autofocus control is performed continuously, so if camera shake occurs during handheld shooting, the autofocus will follow the camera shake, so even though it is in focus, The photographic lens (
There was a problem in that the single lens) moved slightly, making the screen difficult to see.

In order to solve this problem, devices have been proposed in which the autofocus control system stops the autofocus control for a certain period of time once the object is in focus. However, since this device performs the above control without considering the conditions of the subject, it may not be possible to focus on a subject that is moving away at a high speed or a subject that is approaching. In other words, in the case of a subject whose distance to the camera changes rapidly, if autofocus control is stopped for a certain period of time even after being in focus, the subject may move outside the depth of field of the photographic lens during that stopping time. This causes a problem in that it is impossible to focus, or only focus control can be performed with poor response to the movement of the subject.

``Object of the Invention'' The present invention solves the problems of conventional autofocus devices, and enables rational focus control with good responsiveness even for subjects whose distance to the camera changes. The purpose is to obtain an autofocus device that can.

"Summary of the Invention" The autofocus device of the present invention does not stop autofocus control for a fixed period of time each time the in-focus state is achieved.
This was done based on the idea of solving the above problem by stopping autofocus control for a certain period of time only when the in-focus state continues for a certain period of time and then transitions to an out-of-focus state.

For this reason, the present invention drives the autofocus sensor at predetermined intervals to generate a sampling signal, and upon receiving this sampling signal, when the subject is in focus, a focus signal is generated, and when the subject is out of focus, a focus signal is generated. A defocus signal is generated respectively, and the number of times this in-focus signal is generated is counted. When this occurs a predetermined number of times in a row, it is determined that the in-focus state has continued, and when a defocus signal is generated after this, The feature is that for the first time, autofocus control is stopped for a certain period of time.

That is, in the present invention, when the focus state is continuously detected using a sampling signal, in the case of camera shake, a defocus signal is often issued after several focus signals are issued, and only in this case is a constant state of focus detected. It is sufficient to stop the autofocus control for a certain period of time.On the other hand, in the case of a subject that approaches or moves away from the camera, one focus signal will not continue for more than a predetermined number of times, so in this case, the autofocus control will not be stopped. This is how it was done.

"Embodiments of the Invention" The present invention will be explained below with reference to the illustrated embodiments. FIG. When the focusing lens drive gear 13 is rotated, the focusing lens 12 moves in the optical axis direction and changes the focal position. The focusing lens drive gear 13 meshes with a pinion 15 of a focus motor 14.

A beam splitter 16 and a master lens 17 are disposed on the optical axis of the photographic lens 11, and a subject image transmitted through the beam splitter 16 and the master lens 17 is photoelectrically converted into the body 18 of the video camera. An imaging device 19 is provided. On the other hand, a relay lens 21 is disposed below the beam splitter 16 to guide the subject light beam split by the beam splitter 16 to the autofocus sensor 20. The autofocus sensor 20 is located at a position optically equivalent to the imaging surface of the imaging device 19.

The autofocus sensor 20 detects the focus state of the subject, and is controlled by the sensor drive circuit 22 at a constant period (
For example, the sampling signal S is generated at a period of 80 Ils. This sampling signal S is input to the defocus calculation circuit 23, and the defocus calculation circuit 23 calculates the defocus amount (image plane displacement amount) according to the input sampling signal S, and controls based on this calculation value. Focus motor 4 via circuit 24 and motor drive circuit 25
drive in forward and reverse directions.

The defocus arithmetic circuit 23 also applies a single focused signal G or a defocus signal to the focusing number counter 26 depending on whether the input sampling signal S is a focus signal or a defocus signal. The 0-focus counter 26 operates the timer circuit 27 when the defocus signal is input after the 1-focus signal G continues for a predetermined number of times (assuming 4 times) or more, and keeps the operation of the control circuit 24 constant. The 0-focus count counter 26, which is stopped for a period of time (for example, 0.4 seconds), is activated when a defocus signal is input before the input count of the focus signal G reaches a predetermined number, and when the timer circuit 27 is activated. , will be reset.

The present device having the above configuration therefore operates as follows. The output of the autofocus sensor 20 is sent to the sensor drive circuit 2.
2, the sampling signal S is input to the defocus calculation circuit 23, and the defocus calculation circuit 23 detects whether or not the focus is in focus and the amount of deviation from the correct focus position. The focus signal including this shift amount is transmitted from the control circuit 24 to the motor drive circuit 25,
5 drives the focus motor 14 in forward and reverse directions to move the focusing lens 12 in the optical axis direction via the pinion 15 and the focusing lens drive gear 13 to bring it into focus.

When the defocus calculation circuit 23 receives the input of the sampling signal S, the defocus calculation circuit 23 converts the sampling signal S into the focusing signal G.
The focusing number counter 2G counts the number of times the focusing signal G is applied, and when the number of times reaches 4 or more, the defocusing signal is sent to the focusing number counter 26. When this input is received, the timer circuit 27 is operated and the control circuit 24 is stopped. This means that, for example, in hand-held shooting, autofocus control does not immediately stop once the subject is in focus. According to experiments, in the case of hand-held shooting, it is normal for the focus signal G to appear four times in a row after focusing, and then a defocus signal often occurs. Image distortion due to camera shake can be prevented. In addition, for the purpose of preventing image disturbance due to camera shake, it is desirable that the defocus signal that drives the timer circuit 27 be a defocus signal whose defocus amount is below a certain value. This is because if the value exceeds , it is not considered that camera shake is the cause, and it is not appropriate to stop autofocus control in this case.

On the other hand, in the case of a subject moving closer to and away from the camera, the faster the four-hour period, the less likely the focus signal G will be consecutive. In this case, a defocus signal always occurs. Therefore, the timer circuit 27 does not stop the operation of the control circuit 24, so that the autofocus function can be continuously performed even for subjects that approach and move away from the camera.

In other words, the number of consecutive times the focusing signal G, which is a condition for stopping autofocus, is determined according to the generation cycle of the sampling signal S, etc., so that the above effect can be obtained.

Note that the above circuit can be configured by a microcomputer.

``Effects of the Invention'' As described above, the autofocus device of the present invention is able to operate on the condition that the focus signal is consecutively sampled a predetermined number of times in the continuously sampled focus signal, and that the defocus signal is generated thereafter. Since the autofocus control is stopped, it is possible to prevent image disturbance and instability due to camera shake, and to perform autofocus with good responsiveness to subjects moving close to and away from the camera.

[Brief explanation of the drawing]

The figure is a system connection diagram showing an embodiment of the autofocus device of the present invention. DESCRIPTION OF SYMBOLS 11... Photographing lens, 12... Focusing lens, 13... Focusing lens drive gear, 14...
... Focus motor, 15... Pinion, 16...
・Beam splitter, 19...imaging device, 20...
Autofocus sensor, 22... sensor drive circuit,
23... Defocus calculation circuit, 24... Control circuit, 25... Motor drive circuit, 26... Focusing number counter, s, 27 °°° tie" circuit 5
°°°S7 preg signal/Goo.゛, Focus signal, D... Defocus signal.

Claims (2)

[Claims] (1) A video camera that inputs the subject light beam that has passed through the photographic lens to an autofocus sensor that detects the focus state, calculates the amount of defocus from the output of this autofocus sensor, and moves the photographic lens to the focus position. In an autofocus device, a focus sensor drive circuit drives the autofocus sensor at predetermined intervals to generate a sampling signal; and a focus signal when a subject is in focus upon receiving the sampling signal, and an out-of-focus signal; a defocus calculation circuit that generates a defocus signal when the defocus calculation circuit is in the state; a counter means that counts the number of times the focus signal is received from the defocus calculation circuit; and a counter means that counts the number of times the focus signal is received by the counter; An autofocus device comprising: timer means for stopping autofocus control for a certain period of time when a defocus signal is generated after successive defocus signals. (2) The autofocus device according to claim 1, wherein the defocus signal that drives the timer is a defocus signal whose defocus amount is equal to or less than a certain value.