JPH057321A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To reduce the influence of back-lash at the time of judging the direction of initial movement, and to shorten focusing time so as to improve a quick photographing property. CONSTITUTION:In an imager AF by a hill climbing system, the driving direction of a focusing lens 1 immediately before stoppage at the time when focusing drive is stopped before the focusing operation of this time is stored previously in a RAM 8 as, for instance, '0' in the case of forward movement and '1' in the case of backward movement. The focusing drive is started after making the direction of the initial movement of the focusing lens 1 at the time of starting the focusing drive of this time coincide with the drive of the last time stored in the above-mentioned RAM 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device, and more specifically, to detecting a focusing state based on the transition of a component (hereinafter referred to as contrast information) relating to the sharpness of a subject image being output from an image sensor. To an automatic focusing device.

[0002]

2. Description of the Related Art As one of conventional automatic focusing methods, an image pickup apparatus using an image pickup device is provided with a video signal when an optical system (hereinafter referred to as a focusing lens) capable of focusing driving is extended or retracted. Based on this, the contrast information of the subject showing the degree of focusing is obtained, the peak value of the value is obtained, and the position showing this peak value is determined as the focus position,
There was a system that drives a focusing lens at that position.
This focusing method is called "mountain climbing method".
NHK Technical Research Report (1940, Volume 17, No. 1,
No. 86, pages 21-37).

In this automatic mountain climbing system,
It is not known in which direction the focusing lens should be driven at the start of the focusing operation, that is, whether the peak value of the contrast information of the subject is in the extending direction or the extending direction of the focusing lens. Therefore, as shown in FIG. 3, if the focusing lens positioned at the point A is extended to the point B, for example, if the contrast value increases, the peak value should be detected by continuously driving in the same direction. On the other hand, as shown in FIG. 4, if the contrast value decreases when the focusing lens located at the point A is extended to the point B, then the peak value cannot be detected unless it is driven in the opposite direction. Then, the minute movement operation in an arbitrary direction for determining the driving direction of the focusing lens as described above will be referred to as "initial movement direction determination" hereinafter.

[0004]

By the way, in the determination of the initial direction in the above-mentioned hill climbing method, the lens driving amount and the driving direction have a great influence on the focusing time and the focusing accuracy. Specifically, the larger the lens drive amount is at the time of determining the initial movement direction, the more accurately the initial movement direction can be determined without being affected by noise. However, if the lens drive amount is set too large, it suffices that the peak point of the contrast information exists in the drive direction, but in the opposite direction, the focusing time becomes too long.

That is, when the peak value of the contrast information of the object is opposite to the driving direction for determining the initial moving direction, the driving amount in the initial moving direction must be returned at least, and in addition to this, the transmission system of the lens driving mechanism is required. The existing backlash must also be returned. Therefore, the focusing time becomes long and the quick-shooting property is lacking.

Therefore, in order to shorten the focusing time and improve the quick-shooting property, if the lens driving amount at the time of determining the initial moving direction is reduced, then the focusing driving is started before the lens driving for determining the initial moving direction is started. When the drive is stopped, the driving direction of the optical system immediately before the stop (hereinafter referred to as the previous drive direction) becomes a big problem.

That is, if the lens driving direction for determining the initial movement direction is the same as the previous driving direction, the backlash does not exist, and there is no problem. However, if the drive is the reverse drive that is the reverse of the previous drive direction, the actual drive amount of the lens will be smaller than that in the forward drive due to the backlash, and the accuracy of the initial movement direction determination will be reduced. This backlash is greater than the lens drive amount for determining the initial movement direction in the worst case due to variations over time due to lot-to-lot variation in mass-produced products, changes in environmental temperature, wear, etc. Sometimes it is not possible to determine the direction.

Therefore, if the maximum amount of backlash is assumed in advance and is added to the normal lens drive amount for determining the initial movement direction, the above problem is solved. However, with such means, when the initial drive direction determination operation is forward drive without backlash, or in the reverse drive in a lot with little backlash, the lens drive amount at the time of initial drive direction determination becomes too large and the focusing time is long. Will be longer and lack of quick-shooting performance.

Therefore, an object of the present invention is to solve the above problems and reduce the influence of backlash at the time of determining the initial movement direction.
An object of the present invention is to provide an automatic focusing device which shortens the focusing time and improves the quick shooting property.

[0010]

SUMMARY OF THE INVENTION An automatic focusing device according to the present invention provides an image pickup device for obtaining a video signal corresponding to a subject image by an optical system capable of focus driving, and a sequential displacement to the optical system. And a driving means for driving the driving means based on the transition of the component relating to the sharpness of the subject image in the output video signal of the image sensor, which sequentially changes corresponding to the sequential displacement of the optical system by the driving means. Immediately before the stop when the focus drive is stopped before the start of drive control means for controlling the focus drive of the optical system and at least until the focus drive of the optical system is started by the drive means Drive direction history means for making the drive direction of the optical system recognizable, and the initial movement direction of the optical system at the time of starting focusing drive coincides with the direction recognized by the drive direction history means. Let Characterized in that way the.

[0011]

Embodiments Embodiments in which the present invention is applied to an electronic still camera will be described below. FIG. 1 is a block diagram of an electronic still camera incorporating an automatic focusing device according to an embodiment of the present invention, which mainly includes a focusing lens 1, an image sensor 2, an image signal amplification and a sample hold process. Imaging processing circuit 3
, Output terminal unit 4, and B. extracting the contrast information from the image pickup signal. P. An F (band pass filter) circuit 5,
A / D for analog / digital conversion of contrast information
A conversion circuit 6, an arithmetic processing circuit 7 that calculates and processes this digital data, and a RAM 8 that temporarily stores data and the like.
A ROM 9 for storing programs and the like, a motor 11 for driving the focusing lens 1, a motor drive circuit 10 for the motor 11, and a video recording / reproducing system (not shown).

In the operation of the image pickup apparatus having the above structure, first, the subject light is taken in through the focusing lens 1 and is formed as a subject image on the light receiving surface of the image pickup element 2. The output signal from the image pickup device 2 is sampled and held in the image pickup processing circuit 3, and is output as an image pickup signal to the output terminal section 4 and B.
P. It is output to the F circuit 5. Then, the signal is output from the output terminal portion 4 to the recording / reproducing system circuit.

The above B. P. In the F circuit 5, a predetermined high frequency component is extracted as a contrast value, and further converted into a digital value by the A / D conversion circuit 6, and the arithmetic processing circuit 7
It is taken into the RAM 8 via the. This arithmetic processing circuit 7
Is executed by a program stored in the ROM 9, and has a built-in means for recognizing the peak point of the contrast value, a driving direction history means at the final stage of lens driving, a focus determination means, and the like. A control unit for driving the motor 11 via the motor drive circuit 10 to move the focusing lens 1 to a predetermined position during the detection operation and the focusing operation is incorporated.

The arithmetic processing circuit 7, the motor drive circuit 10 and the motor 11 constitute drive means for sequentially displacing the optical system including the focusing lens 1. P. By the F circuit 5, the A / D conversion circuit 6, the arithmetic processing circuit 7, and the ROM 9, the sharpness of the subject image in the output video signal of the image pickup device is sequentially changed corresponding to the sequential displacement of the optical system by the driving means. Drive control means for controlling the focusing drive of the optical system by the drive means based on the transition of the component relating to the degree, that is, the contrast information, and further, by the arithmetic processing circuit 7 and the RAM 8, at least the optical system by the drive means. Until the focusing drive of (1) is started, the driving direction history means for making it possible to recognize the driving direction of the optical system immediately before the stop when the focusing drive is stopped before the start, that is, the driving direction history means , Respectively configured.

The focusing operation of this embodiment thus constructed will be described with reference to the flow chart of FIG. First, the prerequisites for this flow will be described below.

(1) Forward rotation of the focusing lens 1 directed toward the closest point from ∞, and vice versa.
The case in which it is revolved toward is called reverse.
Further, (2) 0 is stored in the RAM 8 shown in FIG. 1 if the previous driving direction is forward rotation, and 1 is stored if the previous driving direction is reverse rotation. In other words, a driving direction history means is formed which allows the previous driving direction to be recognized.

When this process starts in FIG. 2,
First, the previous drive direction data stored in the RAM 8 which is the drive direction history means is moved to the variable m (step S40).
2) Check whether the variable m is 0 (step S4)
03). If the variable m is 0, the previous driving direction is the forward rotation direction, so the contrast value of the current subject is input to the variable C0 (step S404), and the focusing lens is normally rotated only by an arbitrary driving amount (step S405). The contrast value of the subject after this normal rotation is input to the variable C1 this time (step S406).

That is, the RAM 8 as the driving direction history means
Since the previous driving direction stored in the normal rotation direction is the forward rotation direction, the initial movement direction of the focusing lens 1 when starting the focusing operation is also the forward rotation direction, and the contrast value C before and after this forward rotation movement is
0 and C1 are compared (step S407), and if C0 <C1, the initial movement direction of the focusing lens 1 is in the ascending region on the hill climbing curve, that is, this normal rotation direction is toward the peak value of the contrast information, The lens normal rotation AF is executed as it is (step S408).

Returning to step S407, if C0 <C1 is not satisfied, it means that the vehicle has passed the peak point of the mountain climbing curve and entered the descending region, so step S415.
Then, the lens driving direction is reversed and the lens reverse AF is executed.

Returning to step S403, the previous driving direction data stored in the driving direction history means is not 0 but 1
If so, it means that the previous drive direction was the reverse direction. Therefore, the lens is reversed in accordance with the initial movement direction of the focusing lens when the focusing drive is started (step S412), and the contrast value of the subject after the reverse rotation is input to the variable C1 (step S413). Then, the contrast values C0 and C1 obtained before and after this reverse rotation drive are set in step S414.
If C0 <C1, it is in the ascending region of the hill climbing curve, so the driving direction is the same, that is, the lens reverse AF is performed (step S41
5). On the other hand, if C0 <C1 is not established, it means that the vehicle is in the descending region of the hill climbing curve, and therefore, the processing proceeds to step S408, and the lens driving, that is, the lens forward rotation AF, which is the reverse of the direction determining operation (step S412), is performed.

In this way, the above steps S408, S
When the focusing operation by 415 is completed, it is checked whether the driving direction immediately before stopping the lens driving at the focused point is the forward rotation direction (step S409). If this is the forward rotation direction, 0 is substituted for the variable m (step S410), and if it is the reverse rotation direction, 1 is substituted for m (step S416), and this flow is ended.

According to the flow of FIG. 2, step S4
Since the initial movement direction of the optical system at the time of starting the focusing drive is made to coincide with the direction recognized by the driving direction history means in 05 and S412, it is not affected by the backlash and therefore the quick-shooting property can be improved. Note that the above step S
The lens drive amount in the direction determination operation of 405 and S412 may be set arbitrarily according to the camera system.

Some focusing systems do not initially set the focusing lens to the ∞ position or the like when the power is turned on. In this case, since the previous driving direction is undefined, 1/0 of the variable m is calculated in step S403 of FIG.
Since it is not possible to judge that, this flow may cause a malfunction on the contrary. Therefore, if the system is constructed so that the optical system is always reset immediately after the power of the automatic focusing device is turned on, the previous driving direction is always input to the variable m, and thus the flow of FIG. 2 is established. To do.

As another means in this case, for example, in the first initial movement direction determination operation immediately after the power is turned on, the initial movement direction is driven beyond the maximum possible backlash amount, and the processing flow of FIG. It may be executed.

In the above embodiment, the previous driving direction data is stored in the RAM 8 (see FIG. 1).
If the memory is stored in, for example, an E ² PROM instead of the RAM 8, the memory contents will not be lost even if the power is turned off. Therefore, even if the power is turned on again, the step S4 in FIG.
No malfunction occurs at 03.

In the above embodiments, the present invention is applied to an electronic still camera. However, the present invention is not limited to this, and can be widely applied to a video movie camera or a silver halide camera. is there.

[0027]

As described above, according to the present invention, the initial movement direction of the optical system at the time of starting the focusing drive is made to coincide with the direction recognized by the drive direction history means. The effect of backlash can be reduced, and the focusing time can be shortened to improve the quick shooting performance.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an electronic still camera including an automatic focusing device according to an embodiment of the present invention.

FIG. 2 is a flowchart of the focusing operation in FIG.

FIG. 3 is a diagram in which a contrast value is plotted with respect to a lens position in an ascending region.

FIG. 4 is a diagram in which a contrast value is plotted with respect to a lens position in a descending region.

[Explanation of symbols]

1 ... Focusing lens (optical system capable of focusing drive) 2 ... Image sensor 5 ... B. P. F circuit (drive control means) 6 ... A / D conversion circuit (drive control means) 7 ... Arithmetic processing circuit (drive means, drive control means, drive direction history means) 8 ... RAM (drive direction history means) 9 ...... ROM (drive control means) 10 ... motor drive circuit (drive means) 11 ... motor (drive means)

Claims (1)

Claim: What is claimed is: 1. An imaging device for obtaining a video signal corresponding to a subject image by an optical system capable of focus driving, a driving means for sequentially displacing the optical system, and the driving means. The focus drive of the optical system is controlled by the drive means based on the transition of the component relating to the sharpness of the subject image in the output video signal of the image pickup device which sequentially changes in accordance with the sequential displacement of the optical system. And a drive control means for controlling the driving direction of the optical system immediately before stop when the focus drive is stopped before the start of the focus drive of the optical system by the drive means. And a driving direction history unit for adjusting the initial movement direction of the optical system at the time of starting the focusing drive to the direction recognized by the driving direction history unit. Self Focusing device.