JPH0736058B2 - Automatic focus adjustment device - Google Patents

Description

The present invention relates to an automatic focus adjusting device for a camera, and more particularly to a so-called active automatic focus adjusting device that projects infrared light toward a subject and receives the reflected light.

Conventionally, this type of device is capable of measuring a long distance, so that a process of integrating a received light signal to increase the S / N ratio of the signal is used. When the distance measuring circuit having such a configuration is used in a camera such as a video camera or an 8 mm camera that continuously shoots, the integrated value of the received light signal is increased while the driving motor of the focusing lens is driven toward the focal point. Integrate until the specified value is reached,
When a predetermined value is reached, integration is stopped, in-focus or out-of-focus is determined, and the motor control cycle is repeated. By the way, the integration time varies depending on the reflectance of the subject with respect to infrared light and the subject distance. Further, if the integration time is different, the cycle for controlling the motor is also different, so that the stop position of the lens varies. At this time, it is desirable to provide a dead zone in order to prevent the lens from picking up and hunting when the focusing is stopped, and to set this dead zone width in accordance with a large variation in stopping the lens, that is, in accordance with the longest integration time.

However, with this setting, although the subject with high reflectance, that is, when the integration time is short, the result of distance measurement can be quickly obtained in a short cycle, but the variation in the stop position is reduced,
Since the focusing signal is also output in a short time, the lens concentrates near the entrance of the set dead zone and stops. This is an undesirable phenomenon because the center of the dead zone is originally the true focus position.

Hereinafter, a basic configuration of an example will be described in detail with reference to the drawings, and then problems will be described.

FIG. 1 is a block diagram of an active automatic focus adjustment device. Infrared light flashing at about 10 KHz is projected from an infrared light emitting diode (iRED) 3 through a light projecting lens 2 toward a subject 1 and its reflection is reflected. The light is photoelectrically converted by the light receiving element 7 via the light receiving lens 6. This light receiving element 7 has two adjacent images 7a.
It consists of 7b. The focusing lens 5 and the light receiving element 7 are interlocked via a mechanical interlocking member such as a cam (not shown). When focusing, the infrared spots on the light receiving element are two as shown in FIG. The light is received on the boundary line of the pixel. Pixel 7
Output signals from a and 7b are connected to high-pass filters (HPF) 10a and 10b for DC optical cuts, detection circuits 11a and 11b that perform detection in synchronization with blinking of the infrared light emitting diode 3, and integrators 12a and 12b. Has been done. An adder 13 adds an integrated voltage (hereinafter referred to as V _A ) obtained from the pixel 7a and an integrated voltage (hereinafter referred to as V _B ) obtained from the pixel 7b. _A subtractor 14 generates a V _A -V _B signal.

Reference numeral 15 is an absolute value conversion circuit that generates | V _A -V _B |. 16 is a comparator for comparing V _A + V _B with a predetermined threshold V _H , 17 is | V _A -V _B
| Is a comparator that compares a predetermined threshold value V _D , 18 is V _A -V
A comparator that compares _B and zero level, that is, A and B
Is a comparator for determining the magnitude relationship of. A microprocessor 19 controls the infrared light emitting diode 3 and the motor 8 via the infrared light emitting diode drive circuit 4 and the motor drive circuit 9 based on inputs from the three comparators.

In FIGS. 3, 5, and 7, (a) is the signal waveform of V _A + V _B , (b) is the signal waveform of | V _A -V _B |, and (c) is the energization of the motor 8. The state, (d), represents the amount of movement of the focusing lens 5.

First, the operation of the conventional example will be described with reference to FIGS. Initially, it is assumed that the lens is in a front focus state with respect to the subject. When V _A + V _B reaches V _H by the first integration, since | V _A −V _B |> V _D , the motor starts rotating in the far direction. As a result, the lens starts moving as indicated by the moving amount (d). Reset the integrator and perform the second integration, but this integration is still │V _A -V _B │> V _D ,
Continue this operation. At the time of the fourth integration, as shown by the solid line in FIG. 3 (b), | V _A −V _B | ≦ V _D , and it is determined that focusing is achieved, and the motor is stopped. By the way, when | V _A -V _B | of the 4th time slightly exceeds V _D , | V _A -V _B | ≦ by the 5th integration as shown by the dotted line in FIG. It becomes V _D , the in-focus judgment is made, and the motor stops. The difference between the stop positions of the lenses in these two cases is represented by E ₁ in FIG.
At normal timing, the stop positions are distributed in this E ₁ . Figure 5 shows the integration time when V _A + V _B reaches V _H (To)
Is the maximum value (T _MAX ) determined in advance. The stop variation width of the lens at this time is represented by E ₂ in (d). By the way, it is desirable to set the constants of the entire system so that even if the lens varies within the stop position width E ₂ , it falls within the allowable depth. However, it is actually difficult to set this width within the permissible depth over the entire aperture when the aperture is small, for example, assuming these constants assuming standard shooting conditions. Will be done. When this E ₂ is called the dead band of the automatic focusing device (Dead Band), the accuracy in this case is given by ± 1 / 2E ₂ . On the contrary, in FIG. 5, even when the lens is initially in the rear focus state with respect to the object, the stop variation width of the lens is similarly E ₂ and the accuracy is distributed in the range of ± 1 / 2E ₂ . On the other hand, when the integration time is smaller than To _MAX , the stop variation width E ₁ of the lens is E ₁ as shown in FIG. 3 (d).
<E ₂ , and the lens stop positions in this case are distributed as shown in FIG. Here, the distribution on the near side with respect to the true in-focus position is the case where the lens was initially on the near side, and the other distribution is on the far side on the far side. That is the case.

That is, in the conventional example, since a relatively wide and constant dead band width is given regardless of the size of the integration time, originally, a subject that should be capable of more accurate distance measurement, that is, a high integration time that is short For a subject having a reflectance, there is a disadvantage that the lens stops when it is out of the true focus position although it is within the dead zone width.

The present invention has an object of providing an automatic focus adjusting device capable of performing highly accurate distance measurement particularly on a subject having a high reflectance such that the integration time is shortened. To project the light, receive the reflected light, perform integration processing of the received light output by the integrating means while driving the focusing lens, and detect whether the integrated value by this integration processing is within a predetermined range. In an automatic focus adjustment device having a determination means for determining whether the subject is in focus or not, it is determined that the integrated value is within the predetermined range by the determination means, and it is determined that the subject is in focus. After that, the focusing lens is stopped after a delay time depending on the integration time by the integration means.

That is, as shown in FIG. 7 showing the embodiment, when the integration time is short, a predetermined time (T _D ) is delayed after the focus determination and then
The motor is stopped.

Due to this delay, the two distributions in Fig. 4 overlap as shown in Fig. 8 and the accuracy becomes ± 1 / 2E ₁ , which is ± 1 of the conventional value.
Significant improvement over / 2E ₂ .

Now, if the moving speed of the lens 5 is υ, the integration time for V _A + V _B to reach V _H is Tx, and the lens stop variation width at this time is Ex, Therefore, Becomes

Also, the degree of improvement Becomes

For example, when T _MAX = 30 msec and E ₂ = 0.05 mm in the conventional example, the lens stop variation width was 0.05 mm even for a subject having a short integration time, but in the present embodiment, when Tx = 5 msec. , T _D = 12.5 msec, the lens stop variation width is greatly improved to 0.0083 mm.

FIG. 9 shows a flow chart of the microprocessor according to this embodiment. The delay time T _D of the delay (delay) timer in the figure is assumed to be counted in the microprocessor 19 by an equation having a dependency relationship with the integration time. That is, it is executed programmatically. In addition, the focus timer is to turn off the infrared light emitting diode (iRED) for a predetermined time during focusing to save power and stabilize the lens stopped state. Generally, it is set to about 6 to 10 times the maximum integration time. To be done.

For the sake of convenience, the above description has explained that the overrun due to the inertia of the lens after the power supply to the motor is turned off is zero, but in an actual system, this overrun is slightly. Therefore, the delay time T _D should be slightly smaller than the value obtained by the equation. As an arithmetic expression, Becomes

Although the above description shows an example of the active type automatic focus adjusting device, the same delay is also effective in the case of the passive type.

Advantageous Effects of Invention The present invention, in an automatic focus adjustment device that performs integration processing of a distance measurement signal during driving of a focusing lens to perform in-focus determination, sets a delay time that changes depending on the integration time after a focus signal is output. Since the focusing motor is provided to stop the focusing motor, there is an effect that the ranging accuracy is significantly improved especially when the subject having a short integration time is measured.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an apparatus to which the present invention is applied. FIG. 2 is a plan view showing a light receiving element. 3 and 5 are signal waveform diagrams of a conventional example. FIG. 4 and FIG. 6 are diagrams showing the distribution of stop positions of the conventional lens. FIG. 7 is a waveform diagram of the embodiment of the present invention. FIG. 8 is a diagram showing the distribution of lens stop positions. FIG. 9 is a flow chart of the microprocessor. 7 is a light receiving element, 7a and 7b are pixels, 12a and 12b are integrating circuits,
Reference numeral 19 is a microprocessor, and 8 is a motor.

Claims (1)

[Claims] 1. A method of projecting light onto a subject, receiving reflected light, and performing integration processing of the received light output by an integrating means during driving of a focusing lens, and whether an integrated value of the integration processing is within a predetermined range. In an automatic focus adjusting device having a judging means for judging whether the object is in focus or not by detecting whether or not it is in focus, the judging means detects that the integrated value is within the predetermined range. The focusing device is characterized in that the focusing lens is stopped after a delay time depending on the integration time by the integration means after it is determined that