JP2003107333A - Focusing device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focusing device and a focusing method which are excellent in both responsiveness and accuracy. SOLUTION: This focusing device for an image pickup device has a distance measuring means 13 for detecting a distance up to an object, lens driving means 34 and 35 for driving a photographing lens 22 of the image pickup device according to results of the distance measuring means 13, a focus detecting means for detecting a focus of the object by using an imaging sensor 21 of the image pickup device, a correcting means for correcting the lens driving means 34 and 35 in accordance with focus detection results of the focus detecting means, and a deciding means for deciding the effectiveness of the correcting means.

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, and more particularly to a focus adjustment apparatus for a digital still camera.

[0002]

2. Description of the Related Art In recent years, digital still cameras, which are rapidly becoming popular, have a conventional silver-salt camera that forms a subject image on a film surface and chemically records the image, whereas a CCD sensor or the like. The image captured in (1) is electrically digitally recorded on a recording medium such as a memory card.

FIG. 7 is a front view of a compact type digital camera, which comprises a camera body 1, a taking lens 2, a release button 3, a finder 4, an active AF light projecting window 5, an active AF light receiving window 6 and a main switch 7. There is. The appearance of this digital camera is not much different from that of a camera using a conventional silver salt film.

The automatic focus adjustment mechanism (A
There are two types of "auto focus" (hereinafter abbreviated as AF)), "active AF" and "video AF". FIG. 8 shows the principle of "active AF". Infrared light projected from an infrared LED (hereinafter abbreviated as “IRED”) 11 is projected onto the subjects 15a and 15b through a projection lens 12 and a projection window 5, and reflected light thereof is received by a light receiving window 6,
An image is formed on the light receiving sensor 13 through the light receiving lens 14.

As the light receiving sensor, a "light incident position detecting element: PSD (Positions-Sens) for detecting the positional displacement of the spot light imaged on the sensor and outputting it by voltage.
Suitable detectors ”are suitable.

When the subject 15a is distant, the spot light of the reflected light 16a forms an image on the image forming portion 17a on the light receiving sensor 13. When the subject 15b comes close,
The spot light of the reflected light 16b is received by the light receiving sensor 13
An image is formed on the image forming portion 17b above. Therefore, if the position of the spot light that forms an image can be detected, the distance to the subject can be detected, and the subject can be focused by driving the taking lens 2 accordingly. This method is called “active AF” because infrared light is actively projected.

Next, FIG. 9 shows the principle of "video AF". With a video camera or digital camera, the subject 23
Image is formed on the image sensor 21 via the taking lens 22. The photoelectric conversion signal is electrically stored in a magnetic tape or a semiconductor memory. Video AF is a method of detecting the focus of a subject from this photoelectric conversion signal without providing a dedicated member for focus detection.

The photoelectric conversion signal contains a spatial frequency component of the subject 23. Focusing on the high frequency component,
There is a large amount of high frequency components when the subject is in focus, and the high frequency components decrease as the subject goes out of focus. Utilizing this property, the high frequency component 24 of the photoelectric conversion signal of the subject is extracted while moving the taking lens from the closest distance to the infinite direction as shown in FIG. And FIG.
When the peak position 25 is searched for as in 0 (b) and (c), the lens position 26 at that time is the most focused lens position.

Since this photoelectric conversion signal is sometimes called a "video signal", this AF method is called a "video AF". In the case of a subject having a low contrast in the video AF method, naturally the high frequency component is also scarce. The change of the component becomes, for example, the high frequency component 27 of FIG. 11A or the high frequency component 28 of FIG. 11B when the contrast is lower. In such a case, it becomes difficult to detect the peak, and the reliability of focus adjustment becomes low.

In the video AF method, the focus is detected by the image sensor itself, so that the most focused object image is finally formed on the sensor surface. Therefore, the accuracy is high, and even if the image sensor fluctuates in the optical axis direction for some reason,
The AF method is not affected by this. However, since the image is taken while moving the lens finely, it takes a long time to move the lens. Further, if the contrast of the subject, that is, the high frequency component is low, focus detection becomes substantially difficult.

On the other hand, in the active AF method, the detection time of the focus (actually, the object distance) is short because there is no moving part. In addition, since infrared light is actively projected, it is a method that allows focus adjustment without depending on the contrast of the subject. However, since the detection system and the image pickup system are separated, the accuracy is inferior to that of the video AF method, and it is not possible to cope with the above-mentioned fluctuation of the image pickup sensor.
Even in the manufacturing process, a process for improving accuracy is required, which results in an increase in cost.

Since the active AF does not detect the focus but the object distance, the detecting operation is called "distance measuring". Further, the AF for performing focus detection or distance measurement by a detection system other than the image pickup optical system is also referred to as "outside measurement AF". The same external AF as described above, which utilizes reflected light of the natural illumination light of the subject without projecting infrared light, may be called "passive AF" in the sense of being passive.

The image sensor of the digital camera is CC
It is made of semiconductor such as D sensor. For this reason, the size of a silver salt film is currently extremely expensive,
Smaller sizes are used than conventional silver salt films.
In that case, when the image size becomes smaller, the out-of-focus becomes larger when it is stretched, and higher focus accuracy than in the past is required.

From the viewpoint of focusing, the video A is more accurate.
Although F is preferable, it can be said that active AF is preferable in terms of responsiveness. Therefore, a so-called "hybrid AF method", which has both focus adjustment accuracy and responsiveness by combining both methods, has been proposed by the applicant as an AF method for digital cameras (Japanese Patent Laid-Open No. 5-64056). . That is, first, focus adjustment is performed by external active AF, and driving of the taking lens is performed. Since the focus accuracy of the digital camera is not certain in this state, the final focus adjustment is performed next by using the video AF centering on the lens position.

[0015]

By adopting the hybrid AF as described above, it becomes possible to perform the AF in which the focus is guaranteed in a considerably shorter time than the conventional video AF. However, as compared with the case where only the active AF is used, it takes extra time by adding the video AF. Then, there is a problem that the active AF alone does not reach the light operation feeling of the silver halide camera.

In view of such circumstances, it is an object of the present invention to provide a focus adjusting device and method which are excellent in both responsiveness and accuracy.

[0017]

A focus adjusting apparatus of the present invention is a focus adjusting apparatus in an image pickup apparatus, wherein distance measuring means for detecting a distance to an object and image pickup apparatus of the image pickup apparatus according to the result of the distance measuring means. Lens driving means for driving a photographing lens, focus detecting means for detecting the focus of an object using the image sensor of the image pickup device, and correction for the lens driving means according to the focus detection result of the focus detecting means It is characterized in that it has a correction means for carrying out the above, and a judgment means for judging the effectiveness of the correction means.

Further, in the focus adjusting apparatus of the present invention, the control means invalidates the correction of the correction means according to an operation on a predetermined operation member of the image pickup apparatus.

Further, in the focus adjusting device of the present invention, the control means invalidates the correction of the correction means according to a change in the ambient temperature of the image pickup device.

Further, in the focus adjusting apparatus of the present invention, the control means invalidates the correction of the correction means according to the elapsed time after the correction is executed.

Further, the focus adjusting method of the present invention is a focus adjusting method in an image pickup apparatus, wherein a distance measuring step for detecting a distance to an object and a photographing lens of the image pickup apparatus are driven according to the result of the distance measuring step. Lens driving step, a focus detecting step of detecting a focus of a subject using an image sensor of the image pickup device, and a correcting step of correcting the lens driving means according to a focus detection result of the focus detecting step. And a determination step of determining the effectiveness of the correction step.

Further, in the focus adjusting method of the present invention, in the control step, the correction in the correction step is invalidated in response to an operation on a predetermined operation member of the image pickup apparatus.

Further, in the focus adjusting method of the present invention, in the control step, the correction in the correction step is invalidated according to a change in ambient temperature of the image pickup device.

Further, in the focus adjusting method of the present invention, in the control step, the correction in the correction step is invalidated according to an elapsed time after execution of the correction.

According to the present invention, in order to solve the above problem, focus adjustment is first performed by active AF, and final focus adjustment is performed on video AF centering on the lens position.
And, especially, the detection result of the video AF is the active AF.
Feedback to the lens adjustment mechanism. During the period when the feedback result is effective, that is, when the ambient temperature does not change much or the time does not pass for a long time, the focus adjustment is completed only by the active AF, and the response is similar to that of the silver halide camera and the accuracy is high. To achieve high AF.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings, by using the same reference numerals for members substantially the same as or corresponding to those of the conventional example. (First Embodiment) FIG. 1 is an electric block diagram of a digital still camera according to an embodiment of the present invention, particularly, the compact type camera shown in FIG. Microcontroller for camera control (hereinafter abbreviated as "MCU") 3
Reference numeral 1 denotes a release button switch 3, a main switch 7, an IRED 11 for active AF and its drive circuit 33, and a light incident position detection element (PSD) 1 for detecting a subject distance.
3, a temperature sensor 18, a photographing lens drive motor 34, a drive circuit 35 thereof, and a lens position detection member 36 are connected. The lens position detection member 36 uses a potentiometer in this embodiment, but may use an encoder.

In the camera control MCU 31, a ROM storing a program for executing a camera operation, a RAM for storing variables, an EEPROM (electrical erasing / writing) for storing the above-mentioned correction data and other parameters. Possible memory) is built in. MC for camera control
The U 31 is connected to the imaging control MCU 304 via the communication line 120, and this MCU 304 controls the imaging operation of a digital image according to the instruction of the camera control MCU 31. The imaging control MCU 304 controls various devices related to imaging according to a program stored in advance in the flash memory 306.

By the release operation by pressing the release button switch 3, the instruction from the camera control MCU 31 is received,
The subject image formed on the image sensor 21 (for example, CCD or CMOS area sensor) is photoelectrically converted, the image signal is A / D converted by the A / D converter 302, and color interpolation processing is performed by the image signal processing IC 303. After performing the filtering process, the data is temporarily stored in the DRAM 308 via the data bus 311. The digital image data stored in the DRAM 308 is displayed on the color monitor 305 as needed. Digital image data is JPEG
The data is compressed by the IC 307 and written in the removable memory card 313 via the memory card interface (abbreviated as I / F) 310. Further, the image data is transferred to the serial bus 312 via the serial I / F 309.
The image data can also be output to, and the image data can be easily distributed on the network.

Now, FIG. 2 is a flowchart of the operation of the digital camera according to the first embodiment of the present invention.
Also, description will be made with reference to a diagram for explaining control of the photographing lens in FIG.

In the flow chart of FIG. 2, when the release button 3 of the camera is turned on, step S100 is executed,
In step S101, distance measurement is first performed by external AF (active AF in this embodiment). In this state, the taking lens 22 of the camera is at the initial position where the subject on the infinity side is in focus as shown in FIG. The position of the taking lens 22 located on the range ring 41 can be detected by the potentiometer 36. In the figure, the image sensor 21 is shown in a state of being slightly rearwardly displaced with respect to the original focus surface 42 due to an error in a manufacturing process or an environmental change such as temperature or posture difference. Since the taking lens 22 is located on the infinite side of the range ring 41 here,
For example, an image of a subject located 3 m away from the camera is formed at a position 43 behind the focusing surface 42 as shown in the figure.

In the next step S102, it is determined whether or not the distance can be measured by the external AF. Active A
In F, it often happens that distance measurement becomes impossible, but the same outside measurement A
Even in the case of F, in passive AF, distance measurement may be impossible when the subject brightness is low or when the contrast of the subject is poor.

If the distance can be measured, the process shifts to step S103 to control the taking lens 22 based on the result of the external AF. This state will be described with reference to FIG. That is, the taking lens 22 is moved to the 3 m scale position of the distance ring 41. As a result, the image of the subject located at a distance of 3 m is formed at the same position 44 as the focus surface 42. However, since the image sensor 21 is now slightly displaced rearward with respect to the original focus surface 42, a focused image cannot be obtained even if the focus adjustment of the taking lens 22 is correct. In the present invention, this deviation amount is corrected so that correct focus adjustment can be performed.

In FIG. 2, in the next step S104, it is determined whether or not the "distance ring correction" is valid. Since "distance ring correction" is not yet effective, the next step S105
Then, fine adjustment of the focus is performed using the above-mentioned video AF.
That is, by directly detecting the image signal from the image sensor 21 as shown in FIG. 8C, the lens is moved to the position where the focus is most achieved. At this time, the subject image can be formed at the position 45, exactly on the sensor surface of the image sensor 21.

There are cases where the video AF cannot be performed because the contrast of the subject is low. In this case, step S
In 106, it is discriminated, and if impossible, step S1.
The procedure moves to 09 to complete the focus adjustment. If fine adjustment of the focus by the video AF is possible, step S1
In step 07, the "distance ring" of the external measurement AF is corrected and the "distance ring correction" is validated.

As a result of the fine adjustment by the video AF, the distance ring position where the subject at a distance of 3 m brings the image sensor 21 into focus is deviated from the original 3 m scale. Figure 9
By moving the distance ring 41 in accordance with it as in (a), the scale of the distance ring 41 can be corrected to the correct lens position.

The focus position due to the relative relationship between the image pickup sensor 21 and the taking lens 22 described here changes with time of the camera in the long term, and changes with posture difference and temperature in the short term. The predetermined relationship is maintained for a short period of time or when there is no attitude difference or temperature change, during which the "distance ring correction" is valid. In this way, the focus control by the external AF and the fine adjustment by the video AF are completed, and the focus adjustment is ended in step S109.

When the distance measurement cannot be performed by the external AF for some reason, the process proceeds from step S102 to step S108, and the focus adjustment is performed by the normal video AF over the entire lens drivable range. Focus adjustment in the case of taking an image again in this state will be described.

When the focus adjustment is requested again while the "distance ring correction" is effective, if the distance measurement can be performed by the external measurement AF, the focus adjustment by the external measurement AF is performed in step S103. For example, when focus adjustment is performed again on a subject at a distance of 3 m, the taking lens 22 is driven from the initial position shown in FIG. 9B to FIG. 9C. Since the "distance ring correction" is now effective, if the photographing lens 22 is moved so as to match the scale of the distance ring 3m, the focus 46 of the subject at the distance 3m is properly formed on the image sensor 21. When the "distance ring correction" is effective, fine adjustment by the video AF is not necessary, and therefore, without taking extra time for the control, the process shifts from step S104 to step S109 to finish the focus adjustment.

When the main switch 7 of the camera is turned off, "distance ring valid" is invalidated in step S111 via step S110, and the power-off sequence is executed in the next step S112. Therefore, in a situation where the main switch is turned off, it is assumed that time elapses until the next AF, and this "distance ring correction" is invalidated. As described above, when the focus correction by the video AF is effective, it is not necessary to execute the video AF again, and the focus can be adjusted at a higher speed.

(Second Embodiment) FIG. 5 shows a second embodiment of the present invention.
5 is a flowchart illustrating an operation in the embodiment of FIG. In this embodiment, attention is paid to the shift of the focus adjustment mechanism and the image sensor due to the temperature change. After the distance ring correction is performed, if there is not much temperature change, the correction is validated. Note that the description of the same parts as those in FIG. 2 will be omitted.

After the external AF can be measured by pressing the release button, and the focus of the taking lens 22 is adjusted based on the result (step S203), whether or not the "distance ring correction" is effective in step S204. To determine. If it is not effective yet, fine focus adjustment is performed using the video AF in the next step S205. When the contrast of the subject is low and the video AF cannot be performed, the process proceeds from step S206 to step S212 to complete the focus adjustment.

If the focus can be finely adjusted by the video AF, the process proceeds to step S207, the "distance ring" of the external measurement AF is corrected, and the "distance ring correction" is validated. At the same time, information about the temperature at that time is stored in step S208. This temperature information is detected based on the output of the temperature sensor 18 of FIG.

When the focus adjustment is requested again in the next photographing, the focus adjustment by the external measurement AF is first performed in step S203 (when the distance measurement by the external measurement AF is possible). Since the "distance ring correction" is valid now, the process proceeds from step S204 to step S210, the current temperature information is detected, and it is compared with the temperature information stored in step S208. If this change is less than the given value,
The focus fluctuation due to the temperature change from the time when the distance ring correction is performed by the video AF is considered to be small, and the process directly proceeds to step S212 to end the focus adjusting operation.

If the temperature change is large, it is assumed that the focus change caused by it is not negligible, and step S21 is performed.
At 1, the "distance ring correction" is invalidated, and the fine adjustment of focus by the video AF after step S205 is tried.

In the second embodiment described above, when the temperature change is small and the focus fluctuation caused by it is negligible, the focus adjustment can be performed at high speed without performing the video AF again.

(Third Embodiment) FIG. 6 shows a third embodiment of the present invention.
5 is a flowchart illustrating an operation in the embodiment of FIG. In this embodiment, the elapsed time after the execution of the distance ring correction is actually measured, and the correction is validated when there is not much time elapsed. Here, characteristic steps of the second embodiment will be described.

In step S308, the time when the "distance ring correction" is executed is stored. A dedicated timer may be provided for measuring the time, but since it is functionally sufficient to know the relative time, a simple timer function built in the camera control MCU may be used.

After the focus adjustment by the external measurement AF, the current time is compared with the time stored in step S308 in step S310, and if the elapsed time is shorter than a predetermined time (for example, 10 minutes), the focus does not fluctuate much. If not, the process proceeds to step S312 to end the focus adjustment. If the elapsed time is large, it is determined that the distance ring correction is not effective, and the fine adjustment of the focus by the video AF after step S305 is executed.

In the above description, the "active AF" of the type that projects infrared rays has been described as the external AF, but the same effect can be obtained by applying the so-called "passive AF". Further, it goes without saying that the configuration of the present invention is not limited to the specific description in the above-described embodiment, and various embodiments can be considered depending on the specifications of the camera, the assumed user group, and the like.

Here, each functional block and processing procedure shown in the above various embodiments may be configured by hardware, or may be a CPU or MPU, ROM and R.
It may be configured by a microcomputer system including an AM and the like, and its operation may be realized according to a work program stored in a ROM or a RAM. Further, a program of software for realizing the function of each function block is supplied to the RAM so as to realize the function of the function block, and each function block is operated according to the program, so that the function block is also included in the scope of the present invention. include.

In this case, the software program itself realizes the functions of the above-described respective embodiments, and the program itself and means for supplying the program to the computer, for example, the recording medium storing the program. It constitutes the invention. As a storage medium for storing such a program, in addition to ROM and RAM, for example, a flexible disk, a hard disk,
Optical disc, magneto-optical disc, CD-ROM, CD-
I, CD-R, CD-RW, DVD, zip, magnetic tape, or a non-volatile memory card can be used.

Further, not only the functions of the above-described embodiment are realized by executing the supplied program by the computer, but also the OS (operating system) or other application software running the program on the computer. Needless to say, such a program is included in the embodiment of the present invention even when the functions of the above-described embodiment are jointly realized.

Further, after the supplied program is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, it is stored in the function expansion board or function expansion unit based on the instruction of the program. It goes without saying that the present invention also includes a case where the CPU or the like performs a part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

[0054]

As described above, according to the present invention, when the focus adjustment is first performed by the external AF, and the final focus adjustment is performed by the video AF, the detection result of the video AF is detected by the external AF. It is fed back to the lens adjustment mechanism. By performing the focus adjustment only by the external measurement AF during the period or under the condition that the feedback result is effective, it is possible to realize the highly accurate AF with the same responsiveness as the conventional silver halide camera.

[Brief description of drawings]

FIG. 1 is an electrical block diagram of a digital still camera of the present invention.

FIG. 2 is a flowchart illustrating an operation according to the first exemplary embodiment of the present invention.

FIG. 3 is a diagram illustrating a focus adjustment method of the present invention.

FIG. 4 is a diagram illustrating a focus adjustment method of the present invention.

FIG. 5 is a flowchart illustrating an operation according to the second exemplary embodiment of the present invention.

FIG. 6 is a flowchart illustrating an operation according to the third exemplary embodiment of the present invention.

FIG. 7 is a front view of a digital still camera.

FIG. 8 is a diagram for explaining the principle of active AF.

FIG. 9 is a diagram for explaining the principle of video AF.

FIG. 10 is a diagram for explaining the principle of video AF.

FIG. 11 is a diagram for explaining the principle of video AF.

[Explanation of symbols]

1 Digital still camera body 2 Shooting lens 3 Release button 4 finder 5 Infrared light projection window 6 Infrared light receiving window 7 Main switch 11 Infrared LED 12 Projector lens 13 PSD 14 Light receiving lens 18 Temperature detection sensor 21 Image sensor 31 MCU for camera control 33 IRED drive circuit 34 Photographic lens drive motor 35 Motor drive circuit 36 Lens position detection member 120 MCU communication line 301 image sensor 302 A / D converter 303 Image signal processing IC 304 Digital MCU 306 Flash memory 308 DRAM 311 data bus

Claims (8)

[Claims] 1. A focus adjusting device in an image pickup apparatus, comprising: distance measuring means for detecting a distance to a subject; lens driving means for driving a taking lens of the image pickup apparatus according to a result of the distance measuring means; Focus detection means for detecting the focus of an object using the image sensor of the apparatus, correction means for correcting the lens drive means according to the focus detection result of the focus detection means, and effectiveness of the correction means A focus adjustment device comprising: a determination unit that determines. 2. The focus adjustment device according to claim 1, wherein the control unit invalidates the correction of the correction unit according to an operation on a predetermined operation member of the image pickup apparatus. 3. The focus adjustment apparatus according to claim 1, wherein the control unit invalidates the correction of the correction unit according to a change in ambient temperature of the image pickup apparatus. 4. The focus adjusting apparatus according to claim 1, wherein the control unit invalidates the correction of the correction unit according to an elapsed time after execution of the correction. 5. A focus adjustment method in an image pickup apparatus, comprising: a distance measuring step of detecting a distance to a subject; a lens driving step of driving a photographing lens of the image pickup apparatus according to a result of the distance measuring step; A focus detection step of detecting the focus of an object using an image sensor of the apparatus, a correction step of correcting the lens driving means according to the focus detection result of the focus detection step, and the effectiveness of the correction step. And a determination step of determining. 6. The focus adjusting method according to claim 5, wherein, in the control step, the correction in the correction step is invalidated in response to an operation on a predetermined operation member of the image pickup apparatus. 7. The focus adjusting method according to claim 5, wherein, in the control step, the correction in the correction step is invalidated according to a change in ambient temperature of the image pickup apparatus. 8. The focus adjusting method according to claim 5, wherein, in the control step, the correction in the correction step is invalidated according to an elapsed time after execution of the correction.