JPH05236328A - Image pickup device - Google Patents

Abstract

PURPOSE:To accurately decide in-focus direction by stopping the drive of a focus control lens for several field times at the position where the lens has the largest movement before and behind its optical axis when the lens is minutely driven. CONSTITUTION:A microcomputer 9 gives a driving instruction to a focus motor driver 10 with use of the sharpness signal that is transmitted through a band- pass filter 8 and drives a focus lens 4. When the microcomputer 9 decides that the in-focus direction should be fixed, it is decided whether the sharpness signal set at the position of the lens 4 exceeds a prescribed threshold level or not. If so, the driving width of the lens 4 is set within the depth of field that is calculated from the relevant stop value. If not, the driving width of the lens 4 is set larger than the depth of field. Thus, the sharpness signal is surely changed when the lens 4 is driven in the large driving width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus such as a video camera equipped with an automatic focus (AF) device for automatically focusing on a subject.

[0002]

2. Description of the Related Art In recent years, the development of image pickup devices such as video cameras and electronic cameras has been remarkable, and in particular, in order to improve the functions and operability thereof, automatic focusing devices and the like have come to be standardly equipped.

Looking at the automatic focus adjustment device, the sharpness of the screen is detected from the video signal obtained by photoelectrically converting the object image by an image pickup device or the like, and the focus lens (focus point) is set so as to maximize it. A method in which the position of an adjusting lens) is controlled to perform focus adjustment is becoming mainstream.

As the evaluation of the sharpness, in general, the intensity of the high frequency component of the video signal extracted by the band pass filter (BPF) or the blur width of the video signal extracted by the differentiating circuit (the edge of the subject image) The width of the part) The detection intensity is used.

This is because when a normal subject image is taken,
When the focus is out of focus, the level of the high frequency component is small and the blur width is large, and as the focus comes in, the level of the high frequency component is large and the blur width is small, and the level of the high frequency component is completely in focus. Is the maximum and the blur width is the minimum.

Therefore, when the sharpness is low, the focus lens is driven in the direction in which the sharpness becomes high as fast as possible, decelerates as the sharpness increases, and stops at the peak of the sharpness peak with high accuracy. To be controlled. This method is generally used for mountain climbing autofocus (mountain climbing A
F) method.

By adopting such an automatic focus adjusting device, the operability has been dramatically improved, especially in a video camera for taking a moving image, and the automatic focus adjusting function has become an essential function in recent years. Is becoming

In the hill-climbing AF method, when the focus lens is moved, the focus direction of the focus lens is detected by the level change of the sharpness signal of the subject image.

Therefore, in this method, unless the focus lens is moved once, it is unknown whether the focus position is before or after the current position, and the focus lens is driven in the wrong direction (non-focus direction). As a result, it takes longer to focus.

On the other hand, a method is known in which the focus lens is finely driven back and forth at the current position, and the driving direction of the focus lens is determined according to the change state of the level of the sharpness signal at that time (Japanese Patent Laid-Open No. HEI 2). -140074). According to this method, it is possible to determine the driving direction of the focus lens for performing the focusing operation and to determine whether or not to restart the focus lens when the focusing point shifts due to the movement of the subject after focusing. Being able to do it quickly reduces the time to focus.

[0011]

However, in the above-mentioned conventional example, when the focus direction is determined, the degree of change in the level of the sharpness signal is small when the blur width is large, and therefore there is a possibility of making an erroneous determination. It was

In the vicinity of the in-focus point, the amount of change in the high frequency component in the video signal is small with respect to the minute drive of the focus lens. Therefore, for example, when shooting under a fluorescent lamp, flicker or the like occurs. Due to the influence, the output value from the image pickup device (CCD) is shaken, the driving direction of the focus lens is erroneous, and the focus lens is stopped during the focusing operation.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image pickup apparatus capable of accurately determining a focusing direction.

[0014]

In order to achieve the above-mentioned object, the present invention provides a focus adjusting means for adjusting the focus by detecting a sharpness signal corresponding to the degree of focusing from a video signal by the detecting means. In the image pickup apparatus, the focus adjustment means includes a determination means for determining a focusing direction by minutely driving a focus adjustment lens that is a part of the image pickup lens and has a focus adjustment function. When the lens is finely driven, a control means is provided for controlling the focus adjusting lens so as to be stopped for a few fields at a position which moves the most in the front and rear on the optical axis.

Further, in order to achieve the same object, the number of fields for stopping the focus adjusting lens is changed according to the magnitude of the sharpness signal, and the detection of the sharpness signal is performed by the fine adjustment of the focus adjusting lens. It is desirable to perform the determination before and after driving and during the stop period, and further to determine the focusing direction by using the sum or average value of the detected sharpness signals for several fields.

[0016]

When the focus adjusting lens is slightly driven, the focus adjusting lens is stopped by being controlled by the control means for several fields at a position where the focus adjusting lens is moved most in the front and rear directions on the optical axis.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a block diagram showing the configuration of a video camera as an image pickup apparatus according to the first embodiment of the present invention. In FIG. 1, 1 is a first fixed lens, 2 is a conversion lens, and 1 is a conversion lens. Reference numeral 3 is a second fixed lens, and 4 is a focus lens (focus adjustment lens) for performing focus adjustment and correction of the focal plane by zooming.

The light passing through each of these lenses 1 to 4 is focused on the image pickup device 5 and converted into an electric signal. After the signal is amplified by the amplifier 6, the camera process circuit 7
Sent to. After the luminance signal is separated in the camera process circuit 7, the sharpness signal is detected by passing through the bandpass filter 8, and the sharpness signal is sent to the microcomputer (microcomputer) 9. The microcomputer 9 issues a drive command to the focus motor driver 10 according to the sharpness signal to drive the focus motor 11 and move the focus lens 4. When the microcomputer 9 determines that the in-focus direction needs to be determined, the microcomputer 9 issues a minute drive command to the focus motor driver 10. At this time, the microcomputer 9 changes the width of the minute drive according to the sharpness signal. The amount of movement of the focus lens 4 is monitored by the encoder 12 and accurate minute driving is performed.

In FIG. 1, reference numeral 13 is a variable magnification mode driver, and 14 is a variable magnification motor. When the microcomputer 9 issues a variable magnification drive command to the variable magnification motor driver 13, the variable magnification motor 14 is driven. , The variable power lens 2 is driven.

Next, the control procedure of the focusing direction determination routine executed by the microcomputer 9 in the image pickup apparatus of the present invention will be described with reference to the flowchart of FIG. When the microcomputer 9 determines that the focus direction determination is necessary, the focus direction determination routine shown in FIG. 2 is entered. Then, first, in step 1, the sharpness signal at the current position of the focus lens 4 is captured, and then the process proceeds to step 2 to check whether the sharpness signal captured in step 1 exceeds a predetermined threshold level. judge.

If the threshold level is exceeded, the routine proceeds to step 3, where the focus lens 4 is finely driven as in the general case. That is, the drive width (swing width) of the focus lens 4 is set within the depth of field calculated from the aperture value at that time. This is so that the user of the video camera can use the focus lens 4 without feeling uncomfortable while the focus lens 4 is slightly driven.

On the other hand, when the sharpness signal is smaller than the threshold level in step 2, the process proceeds to step 4 and the drive width of the focus lens 4 is set larger than the depth of field. By driving the focus lens with such a large drive width, it is possible to surely obtain a change in the sharpness signal.

In this way, after the drive width of the focus lens 4 is determined in step 3 or step 4, the process proceeds to the next step 5, in which the focus lens 4 is actually moved to capture the sharpness signal. As a place for taking in the sharpness signal, it is moved to the near side or the infinite side by the driving width of the focus lens 4 determined in steps 3 and 4 with respect to the place taken in in step 1 above. Further, for the focus direction determination, the sum or average value of the sharpness signals captured for several fields at each place is used.

When the acquisition of the sharpness signal at each position is completed, the process proceeds to step 6, where the focus lens 4 is returned to the original position and the sharpness signal is acquired. Then, in the next step 7, the direction in which the focus lens 4 should be driven next is calculated based on the data of the sharpness signal so far, and the driving direction is determined. After that, the control according to the hill-climbing AF method is performed according to the driving direction determined in step 7.

FIG. 3 is a diagram showing how the level of the sharpness signal changes with respect to the drive width of the focus lens 4 before and after the threshold level of the sharpness signal. As is clear from this figure, when the level of the sharpness signal is lower than the threshold level, that is, when it is regarded as a large blur state, the drive width of the focus lens 4 is increased to change the level of the sharpness signal. Can be increased. Further, the change in the angle of view at this time does not give the photographer any discomfort due to the large-blur state.

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to FIGS. In addition, in the present embodiment, the configuration of the image pickup apparatus is the same as that of the above-described first embodiment shown in FIG.

FIG. 4 is a flowchart showing a control procedure of a focusing direction determination routine executed by the microcomputer 9 in the image pickup apparatus according to the second embodiment of the present invention. When the microcomputer 9 determines that the focus direction determination is required, the focus direction determination routine shown in FIG. 4 is entered. First, in step 1, after the sharpness signal (high-frequency component level of the video signal), that is, data at the current position of the focus lens 4, that is, data, is fetched, the process proceeds to the next step 2, and the number of fetches designated in advance is repeated. It is determined whether or not the data has been fetched (for several fields).

Then, when the data for the predetermined number of fetches at the current position of the focus lens 4 is fetched, the process proceeds to step 3 and the focus lens 4 is moved to the close side. This amount of movement generally changes depending on the depth of field. Next, in step 4, it is determined whether or not the focus lens 4 has moved by a predetermined movement amount (to a designated position). If the focus lens 4 has moved to the designated position, in step 5, the focus lens 4 is moved at that position. Stop.

Then, after capturing the sharpness signal again,
In the next step 7, it is judged whether or not the data has been fetched the number of times designated in advance. When the data has been captured for the predetermined number of captures, the process proceeds to step 8 and the focus lens 4 is moved in the infinite direction. This amount of movement is twice the amount moved in steps 3 and 4, that is, the focus lens 4 is moved to a position on the infinite side with respect to the original position. After that, the routine proceeds to step 10, where it is judged whether or not the focus lens 4 has moved to the designated position, and if it has moved to the designated position, the routine proceeds to the next step 10 to stop the focus lens 4. Then, at this position, the sharp signal is captured again. Then, the process proceeds to the next step 12, and it is judged whether or not the data of the number of times of capturing designated in advance has been fetched. When the data of the predetermined number of times of capturing has been fetched, the process proceeds to the next step 13 and the focus lens 4 is moved. Drive to the near side and return to the original position.

After that, the process proceeds to step 14, and it is judged whether or not the focus lens 4 has returned to the original position. If it returns to the original position, the process proceeds to step 15 to stop the focus lens 4 at that position. Next, in step 16, the sharpness signal (data) is captured again. Then, in the next step 17, it is determined whether or not the data of the predetermined number of times of capturing is acquired, and when the data of the predetermined number of times of capturing is acquired, the process proceeds to step 18 and the driving direction of the focus lens 4 is changed. After the driving direction is determined by calculation, the focus direction determination routine is ended.

The answer to step 2 is negative (No).
If the answer to step 4 is negative (No), the procedure returns to step 3, if the answer to step 7 is negative (No), the procedure returns to step 6, and step 9 If the answer is negative (No), step 8
If the answer in step 12 is negative (No), the procedure returns to step 11. If the answer in step 14 is negative (No), the procedure returns to step 13 and the answer in step 17 is negative. In the case of (No), the process returns to step 16.

FIG. 5 shows the position of the focus lens 4 when the focus lens 4 is slightly driven near the in-focus point according to the present embodiment, the change state of the sharpness signal level, and the flicker state of the fluorescent lamp with the same time axis. FIG. The television system used here is NTSC, and the flicker is assumed to be 50 Hz. in this case,
The flicker of the fluorescent lamp shown in FIG. 5A is restored in three fields. Therefore, in this case, the number of times of data acquisition is designated as 3 and the subject is on the close side.

As shown in FIG. 5 (c), although the sharpness signal varies, it is understood that the overall level is different between the near side and the infinite side. Accurate in-focus direction determination can be performed by obtaining and comparing the sums of these signals for three fields.

Further, when the flicker of the fluorescent lamp is 60 Hz, it is considered that the flicker is synchronized with the NTSC television system, so that the influence of the flicker can be removed by taking in the data only for three fields. .. Further, by taking the sum or the average value of the sharpness signals, it is possible to remove the influence of various noises.

A stepping motor is mainly used as a drive motor for the focus lens 4, but any motor including a DC motor can be used as long as the stopping accuracy is stable to some extent. Is.

[0037]

As described above, according to the image pickup apparatus of the present invention, a focus adjustment lens is provided when a certain threshold level is set for the magnitude of the sharpness signal and the sharpness signal is lower than that. Since the erroneous determination of the in-focus direction is eliminated, the in-focus direction can be surely determined even in the case of a large blur, and the time until focusing can be shortened.

Further, when the focus adjustment lens is driven minutely, the focus adjustment lens is stopped once before and after the current focus adjustment lens position, and data is taken in a plurality of times, so that it is not affected by noise or flicker. In addition, it is possible to accurately determine the focusing direction.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an image pickup apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure of a focus direction determination routine in the same apparatus.

FIG. 3 is a diagram showing a level change state of a sharpness signal with respect to a drive width of a focus lens before and after a threshold level of the sharpness signal in the same apparatus.

FIG. 4 is a flowchart showing a control procedure of a focusing direction determination routine in the image pickup apparatus according to the second embodiment of the present invention.

FIG. 5 is a diagram showing the focus lens position, the change state of the level of the sharpness signal, and the flicker state of the fluorescent lamp when the focus lens is slightly driven near the in-focus point by the same device, with the same time axis.

[Explanation of symbols]

 4 Focusing Lens (Focus Lens) 8 Detecting Means (Band Pass Filter) 9 Control Means and Judging Means (Microcomputer)

Claims (4)

[Claims] 1. A focus adjusting means for adjusting a focus by detecting a sharpness signal corresponding to a focus degree from a video signal by a detecting means, the focus adjusting means being a part of an imaging lens. In an image pickup apparatus having a determination means for determining a focus direction by minutely driving a focus adjustment lens having a focus adjustment function, when the focus adjustment lens is finely driven, it is the largest before and after on the optical axis. An image pickup apparatus comprising: a control unit that controls the focus adjustment lens to stop for several fields at a moved position. 2. The image pickup apparatus according to claim 1, wherein the number of fields for stopping the focus adjustment lens is changed according to the magnitude of the sharpness signal. 3. The sharpness signal is detected by the detecting means before and after the minute drive of the focus adjusting lens and during the stop period of the focus adjusting lens by the control means. Item 1. The image pickup device according to item 1. 4. The determination of the focusing direction by the determination means is
The image pickup apparatus according to claim 1, wherein the sharpness signal detected by the detector is summed or averaged.