JPH0265475A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To attain accurate automatic focus adjustment by providing a control means controlling the drive period of plural focus modulation means in a prescribed relation and driving components used for the automatic focus adjustment and components not used synchronizingly. CONSTITUTION:A microcomputer 17 at camera side gives a reference signal fr to a drive section 19 to vibrate the image pickup element 13 at the frequency fr and a control signal mfr synchronously with the reference signal is fed to a microcomputer 11 at lens side via a data bus 18 to control the drive section 10 synchronously with the reference signal to vibrate a relay lens 6 synchronously with the reference signal fr, that is, the vibration of the image pickup element 13. The phase of the vibration of the relay lens 6 not in use for the automatic focus adjustment is managed to apply automatic focus adjustment without any hindrance by the modulation method even in the camera system where the vibrators are used duplicatedly for the lens and the camera.

Description

[Detailed description of the invention] [Industrial application field] It is.

[Conventional technology]

In recent years, with the development and spread of video equipment such as video camera systems, automatic focus adjustment devices have come to be standard equipment in video camera systems.

Various methods have been proposed for this automatic focusing device for a long time, but in recent years, one method has been to vibrate a part of the lens or the image sensor at a constant frequency parallel to the optical axis. Many proposals have been made regarding a method (hereinafter referred to as a modulation method) of automatically adjusting the focus using the amount of change in the image signal. According to this modulation method, the phase of the signal representing the change in the image signal is reversed before and after the in-focus point, so it has the advantage of being able to always distinguish between the front bin and the rear bin, and is being widely implemented. .

On the other hand, recently, interchangeable lenses have also been proposed in the field of video cameras in order to diversify their photographic functions. According to such a video camera system with interchangeable lenses, combinations of lenses and camera units compatible with each specific automatic focusing method can be considered. As one combination, if we consider the case where an automatic focusing device using the modulation method described above is applied, the camera unit has a function of vibrating the image sensor in the optical axis direction, and a part of the lens is vibrated. Lens units with different functions may be combined.

It is generally known that the modulation method requires a certain relationship between the period of reading the amount of change in the image signal and the period of vibration. In addition, when using a bimorph or voice coil as a vibrator, when the vibration is stopped, its position is not fixed due to the hysteresis effect, and the position of the imaging plane (focus plane if the lens vibrates) changes, so automatic focusing Even when not used for adjustment, it is necessary to always vibrate the vibrator in the direction of the optical axis around a predetermined position so that the imaging plane or the focus plane appears to be at the center of the vibration.

[Problem to be solved by the invention]

However, in the above-mentioned video camera system with interchangeable lenses, if a video camera system including a vibrating part in both a part of the lens and an image sensor is configured by any combination of the lens unit and the camera unit, the basic Generally, only one transducer is used for autofocusing, and the other is separated from the autofocusing system. Since this separated vibrator is not particularly controlled, a problem arises in that the apparent focal plane cannot be fixed.

Furthermore, even if the oscillator separated from the automatic focusing system is always vibrated parallel to the optical axis and the apparent focus plane is fixed,
Because the phase of this vibration is not properly synchronized with the vibration phase of the vibrator that is performing automatic focus adjustment, there is a problem in that accurate information for determining focus/out-of-focus cannot be obtained from the video signal. Ta.

[Means for solving problems]

The present invention has been made for the purpose of eliminating the above-mentioned problems, and is characterized in that, in a camera system including a plurality of focus modulation means for periodically changing the focus state, This is an automatic focus adjustment device equipped with a control means for controlling the drive period of the modulation means to a predetermined relationship.As a result, with the adoption of interchangeable lenses, a system in which the focus modulation means is present on both the lens side and the camera side has become available. Even in such cases, it is possible to accurately perform automatic focus adjustment by controlling each automatic focus adjustment device without deteriorating focus detection accuracy due to interference between the two.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the automatic focusing device of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a case where the automatic focus adjustment device of the present invention is applied to a video camera system in which a lens unit is detachably attached to a camera unit.

In the figure, 1 is a lens unit that includes a lens group, an aperture, an element for driving them, a control circuit, etc., and 12 is a lens unit to which the lens unit 1 can be attached or detached, and which also performs judgment for automatic focus control and image pickup as described below. A camera unit 20 is a mount section that serves as a boundary between the camera unit and the elements that control the driving of the elements.

Regarding the lens unit 1, 2 is a focusing lens that performs automatic focus adjustment, 3 and 4 are zooming lenses that vary magnification, 5 is an aperture, and 6 is a lens that forms an image on an imaging surface and uses an oscillator (described later) to adjust the optical axis. Relay lenses vibrated in the direction, 7 and 8.9 are focusing lenses, respectively.
A drive unit including a motor for driving a zooming lens and an aperture, 10 a drive unit including a vibrator (such as a piezo element) as a focus modulation means for vibrating the relay lens 6 in the optical axis direction, and 11 a camera unit 12 This microcomputer functions as a control circuit that communicates data with the microcomputer and drives and controls the mechanisms and circuits on the lens side, including each lens and diaphragm, based on the communication data.

Looking at the camera unit 12 side, 13 is an image sensor (for example, a CCD) that converts the subject image formed on the imaging surface by the lens group in the lens unit 1 into an electrical signal and outputs it, and 14 is the image sensor 13. a preamplifier for amplifying the video signal output from the 15 to a predetermined level;
16 is a video signal processing circuit that processes the video signal output from the preamplifier by adding a synchronization signal, blanking processing, gamma correction, etc., converts it into a standard television signal, and outputs it to the output terminal Vout; 16 is the output from the preamplifier 15; This is a focus detection video signal processing circuit (hereinafter referred to as an AF signal processing circuit) for detecting and outputting a signal related to the degree of focus from a video signal obtained by the camera, and its internal configuration will be described later.

17 determines in-focus or out-of-focus based on information from the AF signal processing circuit 16, and drives the focusing lens 2 so that the subject image formed on the imaging surface of the image sensor 13 is in focus. Control information for lens unit 1
This is a camera side microcomputer that sends data to the side microcomputer 11. 18 is a lens side microcomputer 11 and a camera side microcomputer 1.
A transmission bus 19 is used to perform data communication with the camera microcomputer 17, and a drive unit 19 includes a vibrator for vibrating the image sensor 13 in the optical axis direction at a frequency of a reference frequency f supplied from the camera-side microcomputer 17. Department.

FIG. 2 shows the AF signal processing circuit 16 in the camera unit 12.
This shows the internal configuration of the . A band pulse filter 161 extracts a predetermined high frequency component related to the degree of focus from the video signal output from the preamplifier 14 and supplied to the AF signal processing circuit 16 .

On the other hand, the image sensor 13 is driven by the drive unit 19 to the reference frequency f.
, the high frequency component undergoes amplitude modulation by the reference frequency component, and contains a component of the reference signal frequency f. Bandpass filter 161
The signal passed through the camera side microcomputer 17
A gate circuit 162 whose opening/closing is controlled by a gate pulse supplied from a gate circuit 162 extracts only signals in a range corresponding to a range measurement area set on an imaging surface (not shown), and a reference frequency detection circuit 163 in the next stage extracts a reference signal f. The frequency components of
The signal is compared with the reference signal frequency f, which is supplied to the reference signal, and synchronous detection is performed, and its phase and amplitude level are detected.

Based on the phase and amplitude level information output from the synchronous detection circuit 164, the microcomputer 17 determines whether the focus is in focus or out of focus, and determines whether the front bin or rear focus is on the image output from the image sensor 13. Focus information (AF information) is transmitted to the lens-side microcomputer 11 so as to drive the focusing lens 2 so that the amount of high frequency components in the signal is maximized.

This allows the focusing lens 2 to be automatically moved to the in-focus point.

In the embodiment shown in FIG. 1 described above, the vibrator for performing modulation is composed of the relay lens 6 on the lens side and the image sensor 1 on the camera side.
It is placed in two locations in 3. In this embodiment, the drive unit 19
A case will be described in which the vibration of the image sensor 13 caused by the vibrator is used for automatic focus adjustment, and the vibration of the relay lens 6 caused by the vibrator of the drive unit 10 on the lens side is not directly involved in the automatic focus adjustment.

FIG. 5 is a timing chart for explaining the basic operation of the modulation method used in the automatic focus adjustment device in this embodiment.

Reference numeral 201 in FIG. 3A indicates an apparent imaging surface, that is, the center of vibration of the imaging element at a certain position, the horizontal axis represents the passage of time, and the vertical axis represents the position of the imaging surface. 202 represents a change in the position of the imaging surface that changes over time based on the vibration of the imaging element 13. 203, 204, 20
Reference numerals 5 and 5 indicate changes in high frequency components in the video signal at the rear bin, focus, and front bin, respectively, and 206 indicates the video signal (high frequency component 1) within a distance measurement area (not shown) at the center of the screen. The gate pulse controls the opening and closing of the gate circuit 162 to capture the video signal, and when it is at a high level, the video signal is captured. 207 is a vertical synchronization signal (V-sync
).

By the way, FIG. 6 shows how the high frequency components of the video signal increase with respect to the position of the focusing lens 2. As is well known, the amount of high-frequency components of the video signal increases as it gets closer to the in-focus point, and decreases as the deviation from the in-focus point increases (as shown in FIG. 5(b)). As shown in , if the imaging surface is located behind the in-focus position in the rear focus state, as the imaging surface moves toward the rear focus side, the high frequency component decreases, and the imaging surface becomes When moving toward the front focus side, the focus position is closer, so the amount of high frequency components increases.

Further, when the lens group is in a position where the subject is focused at the above-mentioned center position 201, the imaging surface of the image sensor 13 is at the above-mentioned center position 201, as shown at 204 in FIG. 5(C).
When the imaging plane is located at , the amount of high frequency components is maximum, and when the imaging plane moves in either direction, toward the front focus side or the rear focus side, the high frequency components decrease.

Further, FIG. 5(d) shows a front focus state where the imaging surface is located in front of the in-focus position, and as shown at 205, the relationship is opposite to the characteristic 203 when the rear focus is achieved. When the imaging surface moves toward the rear focus side, the high frequency component increases, and when the imaging surface moves toward the front focus side, the high frequency component decreases.

As described above, in the modulation method, if the sampling timing of the ranging area gate pulse shown at 206 in FIG. 5(e) is not accurately synchronized with the change 202 in the imaging plane,
The capture position in the video signal shifts, making it impossible to determine whether the image is in focus or out of focus. In addition, in order to facilitate in-focus/out-of-focus determination, if a peak hold circuit is provided after the sampling or gate circuit 162, the front focus, center, and rear bin positions of the imaging surface, that is, the apex and node portions of the characteristic 202 The sampling number and time must be equal.

In other words, in a device that performs automatic focus adjustment by extracting a signal corresponding to the degree of focus from the video signal, the degree of focus is detected at the vertical synchronization cycle, and compared with the previous value to determine the degree of focus. The focus is adjusted based on the change. Therefore, in order to efficiently detect changes in the degree of focus, considering the movement of the image sensor 13, it is necessary to focus at the respective timings when the image sensor 13 moves to the front focus side and when it moves to the rear focus side. It can be seen that detecting and comparing degrees is the most effective method for accurate focus detection. For this reason, the timing and sampling time of extracting the video signal to obtain information regarding the degree of focus using the gate pulse for the ranging area, as well as the number of sampling times, are the same, and in particular, the image sensor shown in FIG. 3(a) In the position change characteristic 202 of , it is essential to perform sampling at the vertices and nodes.

Here, the relay lens 106 on the lens side that is not used for automatic focus adjustment must also be vibrated in order to prevent positional deviation due to the hysteresis characteristic described above, but the period and phase of the vibration can be adjusted arbitrarily. If it is captured, the time image signal, that is, the high frequency component, will change independently from the camera side, and the relationship between the characteristics shown in Figure 5 will collapse.
Accurate automatic focus adjustment cannot be performed.

Therefore, a reference signal f is supplied from the camera-side microcomputer 17 to the drive unit 19 to vibrate the image sensor 13 at the frequency f, and a control signal m f r synchronized with the reference signal is sent via the data bus 18. The reference signal f is supplied to the lens-side microcomputer 1, and the driving unit 10 is controlled in synchronization with the reference signal f, so that the vibration of the relay lens 106 is performed in synchronization with the reference signal f, that is, the vibration of the image sensor 13. It has become.

Figure 3 shows the relay lens 6 on the lens side and the image sensor 1 on the camera side.
3 shows an example of the timing of vibration. In the figure, the same symbols are used for timing waveforms having the same meaning as in FIG. 5.

FIG. 3(a) shows a characteristic 202 showing the positional change of the imaging surface of the image sensor 13 shown in FIG. 5(a), and FIG. 3(c) shows the characteristic 202 shown in FIG.
This is the same as the gate pulse 206 in e). In FIG. 3(b), 301 indicates the center of change in position of the relay lens 6, and 302 indicates change in position of the relay lens 6 over time.

In the modulation method, the image information obtained within each vertical synchronization period is compared at the vertical synchronization period, so as shown in Figure 5 (
As shown in b), if the vibration period of the relay lens 6 is set to 1/2 (m = outside) of the image sensor 13, when sampling the video signal by the gate pulse 206 in FIG. 6 is always at the same position, that is, on the center of change position 301, and changes in the video signal due to changes in the relay lens 6 have no effect on focus detection based on changes in the position of the image sensor 13.

As described above, in the modulation method, it is particularly important to compare the high frequency components when the image sensor 13 swings most toward the front focus side and when it swings the most toward the rear focus side.

According to the present application, the phase of the vibration of the relay lens 6 is exactly the same at both sampling timings (high level period of gate pulse) on the front pin side and the rear pin side, so when comparing high frequency components, the vibration of the relay lens 6 The direction of movement does not matter.

In this way, by managing the phase of the vibration of the relay lens 6 that is not used for automatic focus adjustment, even in camera systems where the oscillator for optical path modulation is duplicated on the lens side and the camera side, modulation is possible. Automatic focus adjustment can be performed without any problem.

In this embodiment, the vibration period of the relay lens 6 has been explained as the vibration period of the image sensor 13, but the position of the relay lens 6 cannot always be at the same position during sampling (during the gate pulse period). If the vibration period of the relay lens 6 is set to an even fraction of the vibration period of the image sensor 13, the same effect can be obtained.Also, if the vibration period of the relay lens 6 is % of that of the image sensor 13, relay lens 6
Sampling (gate pulse for ranging gate) is performed at the timing when the actual position of the relay lens 6 is located at the center of vibration, but if the vibration frequency of the relay lens 6 is sufficiently high (if it becomes so, the displacement during sampling can be ignored). can.

In the above-described embodiment, the information mf on the vibration frequency of the relay lens is sent to the lens-side microcomputer 11.
is calculated from the reference signal frequency f by the camera-side microcomputer 17 and then transmitted.However, the information about the reference signal frequency f is sent to the lens side, and the lens-side microcomputer 11 calculates m f t. It can also be supplied to the relay lens drive section 10.

FIG. 6 shows a second embodiment of the present invention, in which charts having the same meanings as in the first embodiment are given the same symbols.

Further, the configuration of the camera system may be the same as that shown in FIG. In FIG. 6, reference numeral 501 represents the sampling timing at which optical information is accumulated in the case of performing a photographing method (hereinafter referred to as high-speed shutter mode) in which the time for accumulating optical information in the image sensor is shortened. Similar to the gate pulse 206 for capturing the video signal corresponding to the distance measurement area, sampling is performed only when the pulse 501 is at a high level.

Normally, in the case of high-speed shutter mode, optical information is accumulated once every vertical period within a predetermined period of time.

In this embodiment, it is assumed that the accumulation is performed immediately before the end of each vertical synchronization period. That is, when a shutter is used, the video signal accumulated during the accumulation time by the shutter is read out and gated, and information corresponding to the degree of focus is compared with the period of the vertical synchronization signal to perform an automatic focus adjustment operation. Therefore, in order to efficiently detect a change in information according to the degree of focus, the shutter must be released when the image sensor 13 swings to the front focus side or back focus side to the maximum, that is, at the apex of characteristic 202 in FIG. need to operate.

Therefore, as shown in Figure (C), characteristic 2 of Figure (a)
02, that is, just before the end of the vertical synchronization period, the shutter is operated to perform storage.

On the other hand, in the case of photography without using a high-speed shutter, the optical information storage time is approximately equal to one vertical phase period, so unnecessary changes in focus due to vibration of the relay lens 6 are integrated and become noticeable.

However, in high-speed shutter mode, the accumulation time is inherently short, so the amount of focus change during accumulation is small in terms of time, but since the image information is not integrated, the relay lens
A problem arises in that a change in focus due to vibration appears directly in the video signal.

In other words, when each phase relationship as shown in FIG. The operation is performed at the peak of the characteristic 202 representing the displacement of the element 13, and the accumulation is performed.
The timing of reaching the apex is when the relay lens 6 crosses the center position 301 of its movement range, that is, the timing when the displacement speed of the relay lens 6 becomes maximum. This is disadvantageous because even with a high-speed shutter, fluctuations within the accumulation period become large and accuracy decreases.

Therefore, if the phase is controlled so that the displacement is the smallest in the vertical feedback part where the shutter operates (i.e. near the apex on the front focus side or rear focus side) as shown in Figure 6, high-speed shutter mode Even if there is, it can be made less susceptible to the influence of the vibration of the relay lens 6. In FIG. 6, the phase of the displacement 202 of the image sensor is different from that in FIG. This is because it is necessary to obtain image information for the front and rear bins accordingly.

Also, sampling of high frequency components (gate pulse 206)
The timing is the same as that of FIG. 4 because the target is one field of the screen shot in high-speed shutter mode.

In addition, in these embodiments, the case where the vibration of the image sensor 13 is used for automatic focus adjustment has been explained, but as long as the phase relationship of the vibrations described above is maintained, it is possible to vibrate not only the image sensor but also any element. The present invention can also be applied to.

That is, even if the automatic focus adjustment operation is performed by vibration of the relay lens 6 and the image sensor side is driven synchronously with the timing and phase relationship established in each of the above-mentioned embodiments, the present invention cannot be implemented. It's not a hindrance.

According to , with the development of interchangeable lens systems as part of the development of video cameras and other video equipment, for example, camera systems are equipped with redundant optical path modulation elements that periodically change the optical path length on each of the lens side and camera side. Even in such a case, by synchronizing and driving the elements used for automatic focus adjustment and the elements not used, it is possible to reliably prevent malfunctions and decreases in focus detection accuracy due to interference with each other. Therefore, automatic focus adjustment can be performed accurately without causing hysteresis errors caused by stopping unused elements.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a camera system to which the automatic focus adjustment device of the present invention is applied, and FIG. 2 is a block diagram of main parts showing the configuration of a focus detection system in the camera system of FIG. 1. FIG. 3 is a timing chart for explaining the operation of the automatic focus adjustment device of the present invention when applied to a camera system, and FIG. 4 is a timing chart for explaining another embodiment of the automatic focus adjustment device of the present invention. 5 is a timing chart for explaining the operation of the modulation method used in the automatic focus adjustment device of the present invention, and FIG. 6 is the amount of high frequency components in the video signal representing the position and degree of focus of the focusing lens. FIG. Patent applicant Canon Co., Ltd.

Claims (3)

[Claims] (1) An automatic camera system comprising a plurality of focus modulation means for periodically changing the focus state, further comprising a control means for controlling drive cycles of the plurality of focus modulation means to a predetermined relationship. Focusing device. (2) The automatic focus adjustment device according to claim (1), wherein the control means drives the plurality of focus modulation means in synchronization with each other in a predetermined relationship. (3) In claim (1) or (2), in the camera system, the lens unit and the camera unit are removable, and the plurality of focus modulation means are arranged in the lens unit and the camera unit, respectively. An automatic focus adjustment device characterized by: