JP3490747B2 - Automatic focusing device for still video camera - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjusting device provided in a still video camera for positioning a taking lens at a focus position.

[0002]

2. Description of the Related Art As a conventional still video camera, there is known a still video camera configured to use two image pickup devices provided for detecting an image also for automatic focus adjustment. In this automatic focus adjustment device, the in-focus state of the photographing lens is detected by the contrast method based on, for example, the light amount distribution on one screen obtained by each image sensor.
That is, the photographing lens is set at a position where the high frequency component of the light quantity change is the largest in the light quantity distribution (the spatial frequency is the highest).

[0003]

The optical path length from the taking lens of each image pickup device is the same, and the information obtained from these image pickup devices is common. Therefore, at the start of the automatic focus adjustment operation, it is unknown whether the taking lens is in front of or behind the in-focus position. Therefore, first, the photographing lens is moved in either the front-back direction to detect the change in the output signal of the image sensor, and the direction in which the photographing lens should be moved is determined based on the detection result. Therefore, conventionally, there has been a certain limit in speeding up the automatic focusing operation.

According to the present invention, when the automatic focusing operation is started,
The purpose is to detect the direction in which the taking lens should be moved, and thereby reduce the time required for automatic focus adjustment.

[0005]

An automatic focus adjusting device for a still video camera according to the present invention comprises first and second image pickup devices provided at positions having the same optical path length from a taking lens,
A focus changing lens provided to face an AF area formed in a part of the second image sensor, and first and second imaging
Taken by comparing the magnitude of AF signals obtained by the element
Detects the focus state of the lens and determines the moving direction of the shooting lens
By the moving direction determining means and the moving direction determining means
And a lens moving unit for moving the taking lens in the direction of the in-focus position according to the determined moving direction .

[0006]

The present invention will be described below with reference to illustrated embodiments. FIG. 1 is a block diagram of a still video camera to which an embodiment of the present invention is applied.

The system control circuit 10 is a microcomputer, which is based on an input signal from an operation unit 18 including a photometric switch and a release switch which are turned on and off in synchronization with the operation of a release button (not shown). Controls the entire still video camera.

The taking lens 11 is driven by a motor 12 to move along the optical axis X, and the motor 12 is driven by a motor drive circuit 13. The motor drive circuit 13 is controlled by the system control circuit 10, whereby the taking lens 11 is set at the in-focus position. The rotation amount of the motor 12 is detected by the encoder 19, and the detection signal is input to the system control circuit 10. The encoder 19 includes, for example, a disc having a slit attached to the rotation shaft of the motor 12 and a pair of photocouplers.

The light beam that has passed through the taking lens 11 is reflected by the beam splitters 15 and 16 of the prism 14 and guided to the first and second CCDs (image pickup devices) 21 and 22, respectively. These CCDs 21 and 22 are the taking lens 1
The optical path lengths from 1 are equal to each other, that is, optically equal positions. Therefore, the same image obtained via the taking lens 11 is formed on the first and second CCDs 21 and 22.

The light beam that has passed through the prism 14 is directly reflected by the first CC
Although incident on D21, it is incident on the second CCD 22 via a focus changing lens 71 (FIG. 2) described later. That is, a focus changing lens 71 is provided between the prism 14 and the second CCD 22.

The first and second CCDs 21 and 22 are driven and controlled by a CCD drive circuit (not shown), and by this control, a signal corresponding to the image formed on the CCDs 21 and 22 is correlated double sampling (CDS) circuit 23, 24
Is supplied to. The image signals input to the CDSs 23 and 24 are subjected to predetermined processing such as removal of reset noise,
The signals are converted into digital signals in the A / D converters 25 and 26 and stored in the first and second memories 27 and 28.

2 and 3 show the structure of the prism 14 and its vicinity. 2 is a view of the prism 14 seen from the direction of the taking lens 11, and FIG.
It is the figure which looked at from the upper part.

Between the second CCD 22 and the prism 14,
A transparent plate member 72 having a focus changing lens 71 is arranged. The transparent plate member 72 is, for example, a flat plate made of glass and having a refractive index of 1, and the focus changing lens 71 is a convex lens. The focus changing lens 71 is the prism 1 of the transparent plate member 72.
It is a surface on the fourth side and is formed at a position facing substantially the center of the CCD 22. That is, the AF area 22a is formed at the center position of the CCD 22, and as described later, the AF area 22a is formed.
The AF operation is performed using the pixel data in the area 22a.

FIG. 4 shows a ray of light passing through the transparent plate member 72. As shown in this figure, the focus changing lens 71
The light ray passing through is focused on the prism 14 side with respect to the light receiving surface of the second CCD 22 as compared with the light ray passing through other portions, and therefore, for example, a portion other than the AF area 22a is in focus. At this time, the AF area 22a is not in focus. Further, the focusing position of the light beam incident on the AF area 22a is higher than the focusing position of the light beam incident on the portion corresponding to the AF area 22a in the first CCD 21.
Close to 1. That is, the AF area 22a is the photographing lens 11
On the other hand, it is equivalent to being optically placed farther than the first CCD 21.

The AF area 22a is a circular area formed substantially at the center of the second CCD 22 as shown in FIG. 5, and is smaller than the outer shape L of the focus changing lens 71. A
In the F operation, the pixel data of the horizontal scanning line H2 that passes through almost the center of the AF area 22a is used. On the other hand, the first CCD 21
With regard to (2), the pixel data of the horizontal scanning line H1 passing through substantially the center of the portion B corresponding to the AF area 22a is used for the AF operation.

The AF operation in this embodiment will be described. The light amount of the portion corresponding to the horizontal scanning line H1 detected by the first CCD 21 and the light amount of the portion corresponding to the horizontal scanning line H2 detected by the second CCD 22 are compared. In FIG. 7, solid lines S1 and S2 indicate the input levels of light rays to the first and second CCDs 21 and 22, respectively, that is, the light amount distributions on the horizontal scanning lines H1 and H2. The output signals from the first and second CCDs 21 and 22 are subjected to predetermined fine product processing (high-frequency components are extracted) in the system control circuit 10, as described later,
As a result, an AF signal indicating the in-focus state of the taking lens 11 is obtained. Solid lines S3 and S4 indicate AF signals obtained from the first and second CCDs 21 and 22, respectively. As can be understood from the comparison of these AF signals, in this example, the peak value of the AF signal from the second CCD 22 is higher than the peak value of the AF signal from the first CCD 21, and therefore the AF area 22a of the second CCD 22 is the current value. It is close to the focal point at the position of the taking lens 11.
That is, in this state, in order to bring the taking lens 11 into focus with respect to the CCD 21, the taking lens 11 and the CC
It should be adjusted so that the optical path length (distance) to D21 and D22 becomes longer.

FIG. 8 is a flow chart of the photographing operation.
This operation control is performed by the system control circuit 10, and the power switch of this still video camera is turned on.
During the state, interrupt processing is performed at predetermined time intervals.

At step 91, it is judged at predetermined time intervals whether or not the photometric switch is turned on. The photometric switch is turned on by half-pressing the release button, whereby step 92 is executed and AF processing is performed. This will be described later with reference to FIG.

After the AF process, the AE is performed in step 93.
Processing is performed, and based on the photometric result, the CCD 21, 22
The charge accumulation time (exposure time) is determined by calculation.
In step 94, it is determined whether or not the release switch has been turned on, that is, whether or not the release button has been fully pressed. When the release switch is in the OFF state, steps 91 to 93 are executed again, but when the release switch is in the ON state, the process proceeds to step 95, the exposure operation is performed, and during the exposure time determined in step 93,
The CCDs 21 and 22 are exposed. Then, in step 96, signal processing and recording operation are performed. This will be described later with reference to FIG.

FIG. 9 is a flow chart of the AF operation executed in step 92 of FIG. Step 101
Then, the output signals of the first and second CCDs 21 and 22 are A
/ D conversion is performed, and these signals are read into the memories 27 and 28 in step 102. The signals of all pixels output from the CCDs 21 and 22 are stored in the memories 27 and 28, and in step 103, the AF area 22a (FIG. 5).
Alternatively, the pixel data of the horizontal scanning lines H1 and H2 passing through the AF area corresponding portion B (FIG. 6) are read from the memories 27 and 28.

In step 104, the first and second CCs
The output signals of D21 and D22 are subjected to fine product processing to obtain the AF signal. That is, the output signals of the CCDs 21 and 22 indicated by the solid lines S1 and S2 in FIG.
After being differentiated, it is integrated by taking the absolute value,
An AF signal as shown by the solid lines S3 and S4 is obtained.

In step 105, the first and second CCs
The moving direction of the taking lens 11 is determined based on the AF signal obtained from D21 and D22. In the example of FIG. 7, the second C
The AF signal (S
4) is larger, and in this case, the light receiving surfaces of the CCDs 21 and 22 are located in the range indicated by the symbol A in FIG. That is, the focal point of the taking lens 11 is located farther along the optical axis direction than the current position, and therefore, in this case, the taking lens 11 should be moved in the direction away from the prism 14. In FIG. 10, the convergent position means the AF obtained from the AF area 22a of the second CCD 22.
The position where the signal (S4) is equal to the AF signal obtained from the AF area corresponding portion B of the first CCD 21.

On the other hand, when the AF signal obtained from the AF area corresponding portion B of the first CCD 21 is larger, the CCD 2
The light-receiving surfaces 1 and 22 are located in the range indicated by the symbol E in FIG. That is, the focal point of the taking lens 11 is closer to the subject along the optical axis than the current position, and in this case, the taking lens 11 should move in the direction of approaching the prism 14.

In step 106, the taking lens 11
Starts moving in the direction determined in step 105. In step 107, the first and second CCD2
The magnitudes of the AF signals obtained from Nos. 1 and 22 are compared, and when these AF signals are not equal, the process returns to step 101 and the above-described operation is repeated. When it is determined in step 107 that the AF signals are substantially equal to each other, the taking lens 11 is considered to be in the converged position (FIG. 10), and the taking lens 11 is temporarily stopped in step 108. The distance D from the converging position to the focal point is the taking lens 11
Is calculated from the F number (aperture aperture value), f value (focal length), and the amount of extension, and is stored in advance in the table memory of the system control circuit 10. Step 1
At 09, this distance D is read out from the table memory, the taking lens 11 is moved by that distance D and stopped at the in-focus point, and the AF operation ends. The drive amount of the photographing lens 11 is detected via the encoder 19.

FIG. 9 is a flow chart of the operation of recording a still image on a recording medium such as a magnetic disk. In this recording operation, the release button is fully pressed (the release switch is turned off).
It becomes N state) and starts.

In step 111, the first and second CCs
The output signals of D21 and D22 are A / D converted, and step 1
At 12, these signals, that is, pixel signals for one screen are read into the memories 27 and 28, respectively.

During the recording operation, the images obtained by the taking lens 11 are focused on the light receiving surfaces of the CCDs 21 and 22, but the images are not focused in the AF area 22a of the second CCD 22. That is, the pixel signal obtained from the AF area 22a is a signal of an out-of-focus image. Therefore, in step 113, the pixel signal in the image circle I (the circle surrounding the circle of the AF area 22a) of this focus changing lens is the image signal obtained from the position II equivalent to the image circle of the focus changing lens of the first CCD 21. Is replaced by In other words, the pixel signal obtained from the first CCD 21 is directly input to the signal processing circuit (not shown), but regarding the pixel signal obtained from the second CCD 22, the AF area 22a has the image circle of the focus changing lens. The pixel signal obtained from the equivalent position II is complemented and input to the signal processing circuit. The pixel signal is subjected to predetermined processing in a signal processing circuit and recorded on a recording medium.

As described above, according to this embodiment, the second CC
Due to the action of the focus changing lens 71 provided in front of D22, the optical path length from the taking lens 11 to the AF area 22a and the AF area corresponding portion B is different. Therefore,
At the start of the AF operation, it can be easily determined whether the taking lens 11 is in front of or behind the in-focus position. That is, the taking lens 11 can be immediately moved toward the in-focus position, and the time required for the AF operation can be shortened.

FIG. 10 shows another example of the focus changing lens. As shown in this figure, the focus changing lens 73 may be a concave lens. In this case, the focus changing lens 73
The light ray passing through the prism 1 is compared with the light ray passing through the other portions with respect to the light receiving surface 22a of the second CCD 22.
Focus is on the opposite side of 4. That is, the AF area 22
The focus position of the light beam incident on a is farther from the taking lens 11 than the focus position of the light beam incident on the portion corresponding to the AF area 22a in the first CCD 21. Even if the focus changing lens 73 formed of a concave lens is used in this way, the same effect as described above can be obtained.

The positions where the focus changing lenses 71 and 73 are provided may be off the center of the light receiving surface of the CCD.

[0032]

As described above, according to the present invention, it is possible to detect the direction in which the photographing lens should be moved at the start of the automatic focus adjustment operation, and to shorten the time required for the automatic focus adjustment. can get.

[Brief description of drawings]

FIG. 1 is a block diagram of a still video camera to which an embodiment of the present invention is applied.

FIG. 2 is a diagram of a prism and its vicinity as viewed from a photographing lens side.

FIG. 3 is a view of a prism and its vicinity as viewed from above.

FIG. 4 is a diagram showing a focus changing lens of a convex lens.

FIG. 5 is a diagram showing a light receiving surface of a second CCD.

FIG. 6 is a diagram showing a light receiving surface of a first CCD.

FIG. 7 is a diagram showing light amounts and AF signals detected by first and second CCDs.

FIG. 8 is a flowchart of a shooting operation.

FIG. 9 is a flowchart of an AF operation.

FIG. 10 is a diagram showing a positional relationship between a lens surface of a photographing lens and a focal point.

FIG. 11 is a flowchart of a recording operation.

FIG. 12 is a diagram showing a focus changing lens of a concave lens.

[Explanation of symbols]

11 Shooting lens 21, 22 CCD (imaging device) 22a AF area 71, 72 Focus change lens B AF area corresponding part

Claims (2)

(57) [Claims] 1. A focus change provided to face an AF area formed in a part of a second image pickup device and a first image pickup device provided at a position of the same optical path length from a photographing lens. By the lens and the first and second imaging elements
By comparing the magnitude of the obtained AF signals,
Detects the focus state and determines the moving direction of the taking lens
Moving direction determining means and determined by this moving direction determining means
And a lens moving means for moving the taking lens in the direction of the in-focus position according to the moving direction . 2. Provided at the same optical path length from the taking lens
Of the first and second image pickup devices and the second image pickup device
Focus provided facing the AF area formed in part
Change lens and output signals of the first and second imaging elements
Focus for detecting the focus state of the taking lens based on the
According to the state detecting means and the output signal of this focusing state detecting means.
To move the shooting lens toward the in-focus position.
An image signal of one screen is obtained by complementing an image signal obtained from the moving means and a portion corresponding to the AF area of the first image sensor as an image signal in the AF area of the second image sensor. An image signal generation device for a still video camera, comprising: a generation unit.