JPS6126015A - Auto-focus method - Google Patents

Abstract

PURPOSE:To perform the auto-focus operation for macro-photographing with a simple mechanism by displacing and driving a magnification varying lens and a focusing lens of a zoom lens independently of each other. CONSTITUTION:The image projected onto an image sensor 12 by a zoom lens 10 is supplied to a control circuit 18 through an image processing circuit 14 and a focus detecting circuit 16. In case of auto-focus, the circuit 18 stops a motor driving circuit 22 and drives a motor 24 by a motor driving circuit 20 to displace and drive a focusing lens L1 in the direction of the optical axis. In case of macro-photographing, the auto-focus operation mode of the circuit 18 is switched to the macro-photographing mode by a switch SW. Then, the circuit 18 stops automatically driving of the motor 24 due to the circuit 20 and drives a motor 26 by the motor driving circuit 22 and displaces and drives a magnification varying lens L2 to perform the auto-focus operation, and the in-focus state is attained when a focus signal is maximum.

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to an autofocus method for automatically performing focusing in a video camera, etc.
The present invention relates to an autofocus method that allows autofocus operation even during macro photography.

(Prior technology) Auto extracts a focus signal corresponding to the degree of focus accuracy from a video signal captured by a zoom lens, and automatically achieves a focused state by displacing the lens so that this focus signal is maximized. Various focusing methods are known.

In this type of autofocus method, Japanese Patent Application Laid-Open No. 5-11900 is a conventional technology that enables autofocus operation even during macro photography in which comparatively small objects are photographed at close range.
There is a technique disclosed in Japanese Patent No. 7-186872.

However, this conventional technique has the following problems.

In other words, in this conventional technology, focusing is performed by displacing all or part of the master lens in the zoom lens. Therefore, in the autofocus operation during macro photography, the movement range of the master lens is
The focal length varies greatly depending on the focal length, and in order to achieve rapid autofocus operation, the amount of zooming must be constantly detected and the movement range must be corrected, which complicates the autofocus mechanism.

Additionally, since autofocus for macro photography is only possible by focusing with the master lens, the zoom lens barrel also requires a front lens extension mechanism as a normal focus adjustment mechanism. As a result, a focus adjustment mechanism is required at two locations, which complicates the lens barrel.

(Objective) An object of the present invention is to provide a novel autofocus method that effectively solves the above problems, enables autofocus operation during macro photography, and can be realized with a simple mechanism.

(composition) The present invention will be explained below.

The features of the present invention are as follows.

That is, the variable power lens and the distance adjustment lens of the zoom lens can be independently driven for displacement.

It is possible to switch between normal autofocus operation and autofocus operation during macro photography.

A normal autofocus operation is performed by driving the distance adjustment lens, and an autofocus operation during macro photography is performed by driving the variable magnification lens.

With this autofocus method, the normal autofocus operation and the autofocus operation during macro photography are
The lens that is driven for displacement is different, and in particular, the variable magnification lens is displaced during macro photography, so there is no need to detect each zooming amount in order to perform autofocus in the macro area.

Hereinafter, description will be given based on specific examples. The figure shows an autofocus mechanism of a video camera to which the present invention is applied.

In the figure, numeral 10 indicates a zoom lens, numeral 12 an image sensor, numerals 24 and 26 a motor, and numeral SW a switch, respectively.

The zoom lens 10 includes a distance adjustment lens L1, a variable magnification lens L2 . Correction lens L3. It is composed of a master lens L4. Such a configuration is common as a zoom lens configuration.

The image projected onto the image sensor 12 by the zoom lens 10 is converted into an electrical signal by the image sensor 12, and applied to the image processing circuit 14, where it undergoes predetermined image processing and becomes an image. converted into a signal. This video signal is input to the focus detection circuit 16. The focus detection circuit 16 extracts a focus signal corresponding to the degree of focus accuracy from the input video signal, and converts this focus signal into
is applied to the control circuit 18.

In normal autofocus operation, the control circuit 18 stops the motor drive circuit 22, causes the motor drive circuit 20 to drive the mortar 24, and drives the distance adjustment lens L1 to be displaced in the optical axis direction. That is, the control circuit 18 displacement-drives the distance adjustment lens L1 so that the focus signal becomes maximum. When the focus signal becomes maximum, a focused state is achieved.

The autofocus control itself, from video processing of the output signal of the image sensor 12 to control by the control circuit 18, is based on conventional technology, for example, Japanese Patent Laid-Open No. 57-18687.
The method known from No. 2 may be used.

Now, at the time of macro photography, the autofocus operation mode of the control circuit 18 is switched to the macro photography mode by the switch SW.

Then, the control circuit 18 automatically controls the motor drive circuit 2.
0 is stopped, and instead, the motor drive circuit 22 drives the motor 26 to drive the variable magnification lens L2 to perform an autofocus operation. Of course, the variable magnification lens L should be used to maximize the focal signal.
The second displacement drive is controlled, and a focused state is achieved when the focus signal becomes maximum.

(Effects) As described above, according to the present invention, a novel autofocus method for a video camera or the like can be provided.

In this autofocus method, normal autofocus operation and autofocus operation during macro shooting are
The lens that is driven for displacement is different, and especially during macro photography, the variable magnification lens is driven for displacement, so it is possible to eliminate the trouble of detecting the zooming amount one by one, and it can be realized with a simpler mechanism. In addition, the zooming motor can be used as is for the motor that drives the variable magnification lens, so for autofocus operation in the macro area,
No special additional mechanism is required.

In the embodiment, the motor that drives the distance adjustment lens and the motor that displacement drives the variable magnification lens are separate, but the same motor can be used and the displacement drive mechanism can be switched to the motor. , both lenses may be driven for displacement.

[Brief explanation of the drawing]

The figure is a block diagram illustrating one embodiment of the invention. 10 Zoom lens, 12・Image sensor-124
,'26...motor, sw switch, L・1...
Distance adjustment lens, L2...variable magnification lens procedure correction document August 17, 1982

Claims (1)

[Claims] A focus signal corresponding to the degree of focus accuracy is extracted from a video signal captured by a zoom lens, and the lens is displaced so that the focus signal is maximized to automatically achieve a focused state. In the autofocus system, the variable magnification lens and distance adjustment lens of the zoom lens can be driven independently, making it possible to switch between normal autofocus operation and autofocus operation during macro photography, and An autofocus method characterized in that during autofocus operation, the distance adjustment lens is displaced, and during macro photography, the variable magnification lens is displacement driven.