JPS60102606A - Auto focus controlling circuit - Google Patents

Abstract

PURPOSE:To obtain an auto focus controlling circuit for executing an auto focus control at a low speed so that a variation of a view angle does not attract attention at the time of zoom-down, by detecting a zoom state, and controlling a control gain of a focus control motor. CONSTITUTION:A volume VR for setting a resistance value corresponding to a turning position of a zoom ring ZR through a decelerating mechanism rolling and contacting to the ZR functions as a turning position detecting means of the ZR, and divides a power supply voltage V in accordance with the resistance value. A PWM oscillating circuit 14 for inputting the divided voltage changes a pulse duty in accordance with a divided voltage output level, and sets the pulse duty of the time of zoom-down smaller than that of the time of zoom-up. An output limiting gate 15 by which a PWM output becomes a gate control input functions as a gain control means, and limits a passing of a focus control output C by the PWM output. As a result, a gate output D inputted to a focus motor FM sets the duty small continuously in accordance with a degree of zoom- down, therefore, a control output gain of the time of zoom-down becomes small, and a focus control response is delayed.

Description

Detailed Description of the Invention 0) Industrial Application Field The present invention is directed to an autofocus control circuit for a video camera.
Regarding.

(b) The autofocus control mechanism of a conventional video camera uses a focus motor to rotate a shift focus ring to a focused position. On the other hand, video cameras are also equipped with a zoom mechanism. This zoom mechanism changes the angle of view for the subject V, but at the same time it also changes the depth of focus for the subject. That is, when zooming up, the depth of focus becomes shallow, and when zooming down, it becomes deep. Therefore, there is no need to speed up the focus control response in the zoom-down state. However, in the conventional autofocus control circuit as disclosed in Japanese Patent Application Laid-open No. 176608/1982, the rotation of the focus motor is controlled regardless of the zoom state, and only the variation in the angle of view is noticeable in the zoom-down state.

(c) Purpose of the Invention Therefore, the present invention proposes a novel autofocus control circuit that performs focus control at a low speed so that fluctuations in the angle of view are not noticeable when zooming down.

B) Structure of the Invention The present invention detects the zoom state and controls the control gain of the focus control motor.

(e) Implementation example DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below according to an illustrative embodiment.

In this embodiment, the present invention is applied to an autofocus control circuit of a video camera that controls the rotation of the focus ring by regarding the imaging state in which the high frequency component in the video signal is maximum as the in-focus state. It is.

FIG. 1 shows a circuit block diagram of this embodiment, in which the number of objects imaged on the solid-state image sensor (1) is input to a preamplifier (2) as a photoelectrically converted image output, and after amplification, the image processing circuit (Input to 3J. The video processing circuit (3) derives the color video signal, while inputting the luminance signal to the bypass filter +4J VC. This bypass output is bipolar, so it is sent to the absolute value conversion circuit (5). The absolute value output is input to the sampling gate circuit +61VC, and only the absolute value output corresponding to the sampling area at the center of the screen is sampled.

The sampling area in this embodiment is from 1/4 to 3/4 in the vertical direction and from 1/4 to 3/4 in the horizontal direction, which corresponds to a reasonable 1/4 of the entire 69 screens. The selected sampling output is integrated at the field period in an integrating circuit (7). The integral output level follows the overall level fluctuation of the output, and is increased as it approaches the in-focus position.

When the integration is completed, the AD conversion circuit (8) performs AD conversion of the integrated output level at the field period. The digitized AD conversion output is first transferred to the first memory (9) and after one field is further transferred to the second memory 1G. Therefore, the first memory (9) and the second memo 1G store the AD conversion outputs of the adjacent fields. Both memory outputs are input to a comparison circuit συ, which compares successive integral output levels, and derives a digital comparison output according to the difference. This comparison output shows that when the first memory output is small, the zoom ring (ZR) is rotating in the direction of the in-focus point, and when it is small, it is rotating in the opposite direction to the in-focus point. Show that. The focus motor control circuit α2, which inputs this comparison output, inverts the control output polarity every time the comparison output becomes negative, whereas the focus motor (13) is driven in one direction in the initial state.
) is reversed. Note that the focus motor control circuit σ changes the control output level derived according to the comparison value, and the rotation of the focus motor 1131Q near the in-focus position becomes slower.

The feature of this embodiment is that in the conventional configuration described above, the control output gain is controlled according to the zoom state vc6.

In other words, the volume (VR) that sets the resistance value according to the rotational position of the zoom ring (ZR) via a reduction gear mechanism that contacts the zoom ring (ZR) is used as a rotational position detection means of the zoom ring (ZR). It functions to divide the power supply voltage (to) according to the resistance value. The PWM oscillation circuit (141) that inputs the divided voltage changes the pulse duty according to the divided voltage output level, and sets the pulse duty smaller when zooming down than when zooming up.The PWM output is used as the gate control input. The output limiting gate functions as a gain control means and limits the passage of the focus control output (q) by the PWM output.Therefore, as shown in FIG. When the output is 0, the duty is continuously set to be small depending on the degree of zooming down, so the control output gain during zooming down is small and the focus control response is slow.

In this embodiment, the gain is changed by PWM modulating the focus control output, but it goes without saying that the amplification factor of the focus control output may be changed depending on the zoom state.

Furthermore, although the autofocus control circuit of this embodiment employs a method that evaluates a video signal, the present invention may be applied to other control methods that optically measure the distance to the subject and perform autofocus control. It goes without saying that it can be done.

(f) Effects of the Invention According to the present invention, since the focus control response when zooming down is slow, changes in the angle of view are hardly felt, and the effect is excellent.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram of the main parts thereof. Explanation of main drawing numbers (1)...Focus ring, (ZR)...Zoom ring, (FM)...Focus motor, (VR)...
... Volume (rotational position detection means), US-... Output limiting gate (gain control circuit).

Claims (1)

[Claims] (1) In a video camera that detects the in-focus position of a focus ring and rotates the focus ring to the in-focus position using a focus motor, a rotation position detection means for detecting the rotation position of the zoom ring, etc. An autofocus control circuit comprising: a gain control circuit that controls a control output gain for the seven orcus motors according to the detection output, and lowers the control output gain during zooming down compared to when zooming up.