JPS6231814A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To prevent the hunting at the time of focusing and to execute the stable securing at the time of the focusing by judging the focusing condition and sending the stop instruction after the threshold processing is executed fro the BPF output level and the modulating signal level. CONSTITUTION:The output of a comparator 12, which is the output signal of a BPF 5, is read, the height of the signal level is judged, and when the level is judged to be high, the output of a comparator 13, which is the level of the modulating signal, is read. When the height of the read modulating signal level is judged and the level is low, the focusing condition is considered, by a stop control means 15, the stop instruction is issued to a focus lens driving device 1 and the focus flag is set to one. Thus, the hunting at the time of focusing is prevented, even when the BPF output level descends due to the camera shaking, etc., the stop condition is held is by a timer 16 function of a microcomputer 14 and the stability at the time of focusing can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focusing device for a video camera.

Conventional technology One of the autofocus devices applied to video cameras is one that modulates the optical path of a subject image passing through an imaging lens at a constant cycle.
There is a method (hereinafter abbreviated as JTTL focusing method) that determines the focal direction from the modulation signal and drives the imaging lens to an appropriate focusing position.

The principle of TTL focus adjustment will be explained below.

FIG. 3 shows the relationship between the output of the video signal that has passed through the band pass filter (hereinafter abbreviated as BPF) and the focus lens position. Modulating the optical path length of the imaging lens at a constant cycle corresponds to slightly displacing the focus lens position back and forth. When the optical path is modulated with the waveform Ao at point A, the output of the BPF becomes . At point B near the focal point, even if the optical path is modulated at the same level as R, the output will be B"
Therefore, the signal level becomes smaller. If the optical path is modulated at the 0 point beyond the in-focus point, an output of C" is obtained, but the phase is shifted by 180 degrees with respect to . From the above, the change in the BPF output signal before and after focusing is due to the phase difference. 18d' difference.Also, the closer to the focal point, the smaller the change in the output signal becomes, and it becomes zero at the focal point.By applying this principle, by comparing the phase of the optical path modulation signal and the BPF output signal,
The direction of the focusing position is determined, the degree of focus can be detected based on the amplitude level of the output signal change, and the driving speed of the focus lens can be controlled.

FIG. 4 shows the basic configuration of a TTL focus adjustment device based on the above principle.

(1) is a 4-image lens housing, (2 is a focus lens, (
3) is an optical path modulator, (4) is an imaging device, (group is BP
F, (6) is a modulation signal detector, and B by optical path modulation
A change in the output of PF (5) is detected. (7) is a double-wave rectifier, which converts the amplitude of the modulation signal detected in (6) into a DC voltage. (8) is an optical path modulation signal generator, (
9) is an optical path modulator driving device, which drives the optical path modulator (3) with a signal from the optical path modulation signal generator (8). [
A synchronous detector compares the phases of the output of the modulation signal detector (6) and the output of the optical path modulation signal generator (8).

0 is a focus lens drive circuit.

Next, the operation of the above conventional example will be explained. Optical path modulator (
The optical image optically amplitude modulated in step 3) is converted into an electrical signal by an imaging device (4). The signal after passing through the BPF (5) changes depending on the focus state as described above. The modulation signal detector (6) extracts the change in the output of the BPF (5), and the synchronous detector [phase] compares the phase of this signal with the output signal of the optical path modulation signal generator (8). The focusing direction is determined and the driving direction is output to the focus lens driving device (2). Further, the driving speed of the focus lens C) is controlled by the output voltage of the double-wave rectifier (7), and the speed decreases as the lens approaches focus.

As described above, the driving direction and speed of the focus lens are detected and controlled to automatically adjust the focus.

Problems to be Solved by the Invention However, in the above-mentioned conventional automatic focusing device, the driving direction of the lens frequently reverses when near in-focus, resulting in development (called hunting) in which the in-focus point goes back and forth. In addition, when there is camera shake, it is difficult to maintain a stable focusing state. The present invention is intended to solve these conventional problems, and aims to provide an excellent automatic focusing device that can prevent focusing near focusing and ensure stability during focusing. In order to achieve the above object, the present invention utilizes BPF.

a first comparator that thresholds the output level; a second comparator that thresholds the output of the modulation signal detector; It has a stop control means that determines the focus state from the output of the second comparator and outputs a stop signal to the lens driving device, and is equipped with a micro combinator that also has a timer function for said control. .

Therefore, according to the present invention, the state where the BPF output level is high and the modulation signal level is low, that is, the in-focus state, is set to the first. A second comparator detects this and outputs a stop signal to the lens drive device. Furthermore, once the lens is fully aligned, the timer function allows the lens to stop even if the video signal changes due to camera shake, etc. can be retained.

Embodiment FIG. 1 shows the configuration of an embodiment of the present invention. However, parts in the figure that are equivalent to those in FIG. 4 are given the same reference numerals. @ is the first comparator that thresholds the output of the BPF (5), D) is the modulated signal detector (second comparator that thresholds the output of 0, I is the micro combinator, and the stop control means ( It consists of a timer means (a) and a timer means (b).

Next, the operation of the above embodiment will be explained. As the focus approaches, the output level of the BPF (5) increases and the output of the modulation signal detector (6) decreases (see Figure 3).
. The former is detected by O's comparator ■, and the latter is detected by a second comparator Ω. The stop control means (g) consists of these two comparators 12.
Take the AND of the output of 13 and use the focus lens drive device 0.
send a stop signal to At the same time, the timer (Le) is reset. During the period when this timer (T) is valid, the stop control means is activated even if the output signal level of the BPF (5) decreases, that is, the output of the first comparator υ is disabled. The stop signal continues to be output to the focus lens drive device σ1 even if

The control operation of this microcomputer will be explained using the flowchart shown in FIG. This control starts with step So, and in step Sl, the output signal level of BPF (5), that is, the output of the first comparator @ is read, and the high/low of the signal level is determined. If it is determined that the modulation signal level is high, in step S2, the level of the modulation signal, that is, the output of the second comparator 0 is read, and it is determined whether the modulation signal level is high or low. In step S3, a stop command is given to the focus lens driving device (2), and in step S4, the focus flag is set to 1. If it is determined that the BPF output level is low in step S1, it is checked in step S5 whether the previous state was in focus, and if it is in focus, the timer means 1
Operate 0. Next, in step S9, the focus flag is reset to 0, and the process returns to step Sl. If the focus flag is not set in step S5 and if the modulation signal level becomes high in step S2, step S6
The stop of the lens is released in step S7, and the focus flag is reset in step S7. One process is completed in step SIO.

Similar processing is executed thereafter.

Invention = Effect of Plan i As is clear from the above embodiments, the present invention is such that the micro combinator determines the in-focus state based on the BPF output level and the result of threshold processing of the modulation signal level, and the lens driving device determines the in-focus state. This system sends commands to prevent hunting when focusing.Furthermore, even if the BPF output level drops due to camera shake, the microcomputer's timer function can maintain the stopped state. It has the effect of ensuring stability over time.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of an automatic focus adjustment device according to an embodiment of the present invention, FIG. 2 is a flowchart showing the operation of the above embodiment, and FIG. 3 is an explanatory diagram of the operating principle of the TTL automatic focus adjustment device. , FIG. 4 is a schematic block diagram of a conventional automatic focus adjustment device. 1... Imaging lens housing, 2-track focus lens, 3
... Optical path modulator, 4... Imaging device, 5...
...BPF. 6...Modulation signal detector, 7...Double wave rectifier, meter...Optical path modulation signal generator, 9...Optical path modulator drive device, 10...Synchronized detector, 11... ...Focus lens drive device, Bi. 13...Comparator, 14...Micro combinator, 5-track stop control means, 16...Timer means Name of agent Patent attorney Toshi Nakao Haka1ml
Mouth lI 2 Figure 3 Figure 4121

Claims (1)

[Claims] a first comparator that performs threshold processing on the output of a bandpass filter that extracts a high-frequency component of a video signal including an optical path modulation component; a second comparator that performs threshold processing on a modulation signal component of the optical path modulation; The in-focus state is determined based on the output of the second comparator,
An automatic focus adjustment device comprising a stop control means for outputting a stop signal to a focus lens driving device during focusing, and a timer means for holding the stop control means for a certain period of time.