JP4744253B2 - Auto focus camera - Google Patents

Description

  The present invention relates to an autofocus camera such as an electronic camera having an autofocus function.

In an electronic camera that captures an image of a subject and outputs the image signal, the image pickup signal is output while moving a focus lens that affects focus adjustment in the image pickup optical system, and a high frequency component is extracted from the output image signal. A focus evaluation value for the focus is calculated. Then, a “contrast AF method” is employed in which the focus lens is driven from the infinity to the close direction of the subject and the focus evaluation value is maximized to drive the focus lens to focus. An example of an autofocus camera using such an imaging signal is disclosed in Patent Document 1.
On the other hand, as an autofocus method using a focus evaluation value for focusing calculated by extracting a high frequency component from an output imaging signal, a focus evaluation value is obtained as a result of moving the focus lens. If it increases, it keeps driving in the same direction, and conversely, if the focus evaluation value decreases as the focus lens moves, it drives in the opposite direction to perform direction discrimination by searching for the peak of the evaluation value. There is a "servo system" and it is used in electronic cameras. An example of an automatic focus adjustment device that determines a search direction based on a change in focus evaluation value is disclosed in Patent Document 2. JP-A-6-339059

  In the “Contrast AF method”, the focus lens is driven from infinity to find the focus position regardless of the position of the focus lens or subject at the start of autofocus. In such a case, it takes more time to focus than the “mountain climbing servo method”.

  In the “mountain climbing servo method”, the driving direction of the focus lens must be determined as a preparatory operation for searching for the in-focus position. Since this determination requires time, it is necessary to focus before the “contrast AF method”. It may take time.

  The present invention has been made in view of such circumstances, and provides an autofocus camera capable of achieving high-speed autofocus by changing the focus lens drive control during autofocus according to the shooting situation. With the goal.

In order to solve the above problems, the present invention provides, as a first invention, an autofocus camera that performs an autofocus operation by detecting a high frequency component level of an image signal obtained from an image sensor as a focus evaluation value. A lens, a zoom lens, a zoom position detection means for detecting the position of the zoom lens, a lens characteristic storage means for storing the relationship between the position of the focus lens, the position of the zoom lens and the distance between the subject, 1 adjustment means and 2nd adjustment means,
The first adjusting means includes a moving means that moves the focus lens along the optical axis and sets the movement completion position as an autofocus start position, and a moving direction of the focus lens by the moving means from the autofocus start position. First search means for moving in a reverse direction in a predetermined step and obtaining a focus evaluation value for each step;
First focusing means for moving the focus lens to a focus position in accordance with the relationship between the focus lens position and the focus evaluation value obtained by the first search means,
The second adjusting means includes a direction determining means for determining a moving direction of the focus lens in which a focus evaluation value increases, and moves the focus lens in a moving direction determined by the direction determining means in predetermined steps. Second search means for obtaining a focus evaluation value for each, and second focus for moving the focus lens to a focus position in accordance with the relationship between the focus lens position and the focus evaluation value obtained by the second search means. Means, and
A movable range acquisition unit that acquires, using the lens characteristic storage unit, a movable range of the focus lens that is capable of autofocus control at the position of the zoom lens detected by the zoom position detection unit; and the movable range acquisition unit When the movable range acquired by the step is narrower than a predetermined value, the first adjustment unit is used to perform an autofocus operation, otherwise the first adjustment unit is used to perform the autofocus operation. It is characterized by comprising.

  Furthermore, it further comprises macro setting means for setting whether or not to include a macro area as an autofocus operation, and the lens characteristic storage means stores that the movable range changes according to the setting state of the macro setting means. It is characterized by.

Furthermore, as a second invention, in an autofocus camera that performs an autofocus operation by detecting a high frequency component level of an image pickup signal obtained from an image sensor as a focus evaluation value, a focus lens and a macro region as an autofocus operation are provided. Macro setting means for setting whether to include, first adjustment means, and second adjustment means,
The first adjusting means includes a moving means that moves the focus lens along the optical axis and sets the movement completion position as an autofocus start position, and a moving direction of the focus lens by the moving means from the autofocus start position. A first search means for moving in the reverse direction at a predetermined step and obtaining a focus evaluation value for each step, and the focus according to the relationship between the focus lens position and the focus evaluation value obtained by the first search means. First focusing means for moving the lens to the in-focus position,
The second adjusting means includes a direction determining means for determining a moving direction of the focus lens in which a focus evaluation value increases, and moves the focus lens in a moving direction determined by the direction determining means in predetermined steps. Second search means for obtaining a focus evaluation value for each, and second focus for moving the focus lens to a focus position in accordance with the relationship between the focus lens position and the focus evaluation value obtained by the second search means. Means, and
If the macro setting unit is set to include a macro area as an autofocus operation, the second adjustment unit is used to perform the autofocus operation; otherwise, the first adjustment unit is used to perform the autofocus operation. And a second discriminating means for performing.

  According to the present invention, the size of the movable range of the focus lens 1f that can be moved to focus on a subject existing within the assumed range is detected directly or indirectly, and the autofocus control is changed according to the detection result. Therefore, when the movable range is narrow, auto focus control without performing direction discrimination is performed, and when not, auto focus control is performed by omitting the search of the range where no subject exists by direction discrimination. Therefore, the time until the in-focus position is detected is shortened, and the autofocus speed can be increased.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a functional block diagram of an electronic still camera which is a first embodiment of the present invention. With reference to FIG. 1, incident light incident through the zoom lens 1 z and the focus lens 1 f is photoelectrically converted by the image sensor 2 to generate an image signal. The generated imaging signal is converted into a digital signal by the A / D converter 3 and then given to the signal processing circuit 4.

  The signal processing circuit 4 performs well-known automatic exposure correction and automatic white balance correction on the given digital image pickup signal, sequentially forms image data for each field (one screen) of the image pickup signal, and supplies the image data to the DRAM 5. The automatic exposure correction not only adjusts the gain of the imaging signal in the signal processing circuit 4, but also adjusts using a diaphragm mechanism (not shown), but a detailed description is omitted.

  The DRAM 5 sequentially stores the input field unit image data from the next to the next, and supplies the stored image data for each field to the processing circuit 6 and the gate circuit 8.

  The processing circuit 6 performs known signal processing such as color separation processing on the image data for one field read out from the DRAM 5, compresses the image data by software, and stores the compressed image data in the subsequent flash memory 7. The compressed image data stored in the flash memory 7 is read by a signal processing circuit (not shown), subjected to expansion processing, and displayed on a liquid crystal monitor (not shown).

  On the other hand, the image data for each field stored in the DRAM 5 is also supplied to the gate circuit 8. A focus motor 13 including a gate circuit 8 and a luminance signal generation circuit 9 at a subsequent stage, an HPF (high pass filter) 10, a digital integrator 11, a CPU 12, and a stepping motor has a circuit configuration provided for an autofocus operation. .

  For electronic still cameras, regardless of whether the release switch is on or off, the type that always performs autofocus operation using these circuit configurations 8-13, and the first time after the release switch is turned on at the time of shooting Although there is a type that performs an autofocus operation using these circuit configurations 8-13, an embodiment of the present invention is an electronic still camera of a type that performs an autofocus operation after a release switch is turned on. .

  When the release switch is turned on (or half-pressed) by the user, the image data of one field unit stored one after another from the signal processing circuit 4 to the DRAM 5 is sequentially given to the gate circuit 8 as well.

  The gate circuit 8 extracts the image data in the focus area set at the center of the imaging screen and gives it to the luminance signal generation circuit 9. Image data in the focus area on the imaging screen set by the gate circuit 8 is extracted and provided to the luminance signal generation circuit 9. The luminance signal generation circuit 9 generates a luminance signal from the given image data and supplies it to the HPF 10.

  The HPF 10 extracts a high frequency component from the luminance signal and gives it to the digital integrator 11, and the digital integrator 11 integrates the high frequency component for one screen (one field period) and gives it to the CPU 12 as a focus evaluation value.

  The CPU 12 drives the focus motor 13 to move the positional relationship of the focus lens 1f with respect to the image sensor 2 according to an autofocus program described later. The focus motor 13 is composed of a stepping motor, and the CPU 12 recognizes the position of the focus lens 1f according to the number of drive steps. The zoom lens 1 z is provided with a zoom encoder 14, which transmits the position information of the zoom lens 1 z to the CPU 12.

The lens characteristic storage circuit 15 stores the relationship between the position of the focus lens 1f, the position of the zoom lens 1z, and the distance to the subject, and detects a searchable range described later in response to a request from the CPU 12. Information necessary for the output is output to the CPU 12. The macro setting switch 16 is a switch for setting in the CPU 12 whether or not to include a macro area as an autofocus operation, and will be described in detail later.
The zoom lens 1z is driven manually or by a motor, but illustration and detailed description are omitted.

FIG. 2 is a flowchart for explaining the autofocus operation centered on the CPU 12 that executes the autofocus program of the electronic still camera shown in FIG.
In an electronic still camera, an auto focus (AF) process is started when a shutter button (not shown) is half-pressed. First, the position of the zoom lens 1z is detected using the zoom encoder 14 (S1), and it is detected by the macro setting switch 16 whether or not the macro area is set to be included as an autofocus operation (S3). Then, the lens characteristic storage circuit 15 is used based on the position of the zoom lens 1z obtained in step S1 and information on whether or not the macro area is set as the autofocus operation obtained in step S3. Then, the possible range of the focus lens 1f is acquired (S5). Details are as follows.

  FIG. 3 illustrates the relationship between the position of the focus lens 1f, the position of the zoom lens 1z, and the distance to the subject stored in the lens characteristic storage circuit 15. Even if the position of the zoom lens 1z is changed, the focus lens 1f must be moved along the tracking curve in order to make the distance to the subject, that is, the in-focus position constant. The lens characteristic storage circuit 15 is used not only in step S5 but also when changing the position of the zoom lens 1z. Curve A is a tracking curve when the subject is in an infinite state, curve B is a tracking curve when the subject is at the closest point of the normal focus area not including the macro area, and curve C is a macro area. It is a tracking curve when it exists in the in-focus limit position. A region sandwiched between the curves A and B is a normal region in focus control, and a region sandwiched between the curves B and C is a macro region in focus control. Although there are a plurality of tracking curves for each distance from the subject, illustration is omitted. The lens characteristic storage circuit 15 stores, as numerical data and / or mathematical expressions, a tracking curve that represents the relationship between the position of the focus lens 1f, the position of the zoom lens 1z, and the distance to the subject shown in FIG. Note that the number of stored tracking curves is finite, and if no tracking curve is stored at the distance to the required subject, the CPU 12 performs interpolation processing using two stored adjacent tracking curves. The target tracking curve is obtained.

  As shown in FIG. 3, in an optical system that generally includes a zoom lens, autofocus control is possible, that is, the movable range of the focus lens 1f that can be moved to focus on a subject that exists within the assumed range is an arrow. As indicated by a1 and arrow a2, the zoom lens 1z becomes wider as it is on the telephoto side. Further, as shown by the sum of the arrows a1 and a3 and the sum of the arrows a2 and a4, if the macro region is included in the assumed range, the position of any zoom lens 1z becomes wide. In step S5, the above-described lens characteristic storage is performed based on the position of the zoom lens 1z obtained in step S1 and information on whether or not the macro region is set as the autofocus operation obtained in step S3. The possible range of the focus lens 1 f is acquired using the circuit 15. Note that “acquiring” includes obtaining by referring to data or obtaining with some calculation.

  Next, it is determined whether or not the possible range of the acquired focus lens 1f is narrow (S7). In this embodiment, the movable range when the zoom lens 1z is located at the tele end is also included in the maximum movable range, and whether or not it is smaller than a predetermined ratio (for example, 40%) of the maximum movable range. Determine with. Note that the predetermined value serving as a reference for determining whether or not it is narrow in step S7 is determined in consideration of the characteristics of the optical system, the purpose of use of the electronic still camera, etc. in order to enjoy the effects of the present invention.

  If it is determined in step S7 that it is narrow, the focus lens 1f is moved along the optical axis to the infinity position that is the autofocus start position (S9), and the direction opposite to the moving direction before the infinity position is reversed. A search is performed to obtain a focus evaluation value at each step in the closest direction, and a process of detecting the position of the focus lens 1f having the maximum focus evaluation value as a focus position is performed (S11). The search in step S11 is the entire movable range of the focus lens 1f that can be moved to focus on the subject existing in the assumed range acquired in step S5 in order to detect the position where the focus evaluation value is maximized. Search for.

  Then, it is determined whether or not the in-focus position is detected as a result of the search in step S11 (S13). If the in-focus position is detected, the focus lens 1f is moved to the in-focus position (S15), and auto The focus process ends. In step S13, if the in-focus position is detected, as an error process, the in-focus position of the focus lens 1f is forcibly set to a subject distance 2m (S17), and the auto-focus process is terminated. Note that the position of the subject distance 2m in step S17 is a position that the designer of the electronic still camera thinks that the probability that the subject exists is high, and is merely an example and can be arbitrarily set. Further, as error processing in step S17, it may be notified by a display or sound that the in-focus position cannot be detected by the autofocus function, and the user may be prompted to manually adjust the focus.

  On the other hand, if it is determined in step S7 that the possible range of the focus lens 1f acquired in step S5 is not narrow, the direction of the focus lens 1f is determined (S19). The direction discrimination is to discriminate the moving direction of the focus lens 1f in which the focus evaluation value increases. In this embodiment, first, the focus evaluation value increases as a result of moving the focus lens 1f to the infinity side by a small amount. In this case, the same direction is set as the moving direction. On the other hand, when the focus evaluation value decreases with a slight movement of the focus lens 1f, the reverse direction, that is, the closest side is determined as the moving direction. Then, the focus lens 1f is moved in a predetermined step in the movement direction determined in step S19, and a search for obtaining a focus evaluation value for each step is performed, and the position of the focus lens 1f at which the focus evaluation value reaches a peak (maximum value) is determined. Processing for detecting the in-focus position is performed (S21). The search in step S21 ends when a position where the focus evaluation value reaches a peak (maximum value) is detected. Therefore, it is not necessary to search the entire movable range of the focus lens 1f that can be moved to focus on the subject existing in the assumed range acquired in step S5.

  Then, it is determined whether or not the in-focus position is detected as a result of the search in step S21 (S13). If the in-focus position is detected, the focus lens 1f is moved to the in-focus position (S15), and auto The focus process ends. In step S13, if the in-focus position is detected, the above error processing is performed (S17), and the autofocus processing is terminated.

  According to the present embodiment, since the autofocus control is changed according to the movable range of the focus lens 1f that can be moved to focus on the subject existing within the assumed range, when the movable range is narrow, Auto focus control without direction discrimination is performed, and if not, auto focus control is performed by omitting the search of the range where the subject does not exist by direction discrimination, so the time until focus position detection is short regardless of the size of the movable range. Can achieve high speed autofocus.

  Note that the focus start position in step S9 may be the closest position (the position of the tracking curve C shown in FIG. 3 when a macro region is included) instead of the infinity position, and the search direction in step S11 may be the infinity direction. Further, the focus start position is not set to the end of the movable range of the focus lens 1f, but the focus start position near the position of the focus lens 1f at the start of autofocus according to the magnitude of the focus evaluation value at the start of autofocus. It is good.

  In addition, instead of detecting the position where the focus evaluation value is maximized as the focus position detection in the search in step S11, a position where the focus evaluation value reaches a peak (maximum value) may be detected. In this case, it is not necessary to search the entire movable range of the focus lens 1f that can be moved to focus on the subject existing within the assumed range acquired in step S5.

  Alternatively, step S3 may be omitted, and the possible range of the focus lens 1f using the lens characteristic storage circuit 15 in step S5 may be acquired using only the position of the zoom lens 1z as a parameter.

  In addition, since there is an optical system in which the possible range of the focus lens 1f in the macro area is wider than that in the normal area, including the macro area as the autofocus operation may be performed as the autofocus operation only in the macro area. .

  Next, a second embodiment will be described. The functional block diagram of the electronic still camera is the same as that of the first embodiment shown in FIG. 1, and the description thereof is omitted. FIG. 4 is a flowchart showing the operation of the second embodiment. The step S3 of detecting whether or not the macro setting switch 16 is set so as to include a macro area as an autofocus operation with respect to the flowchart of FIG. 2 showing the operation of the first embodiment, and a lens characteristic storage circuit Step S5 for acquiring the possible range of the focus lens 1f using 15 is eliminated, and instead of the determination in Step S7, it is determined whether or not the position of the zoom lens 1z detected in Step S1 is wider than the predetermined position. A step S31 for determination is provided.

  As shown in FIG. 3, in an optical system that generally includes a zoom lens, autofocus control is possible, that is, the movable range of the focus lens 1f that can be moved to focus on a subject that exists within the assumed range is zoomed. The larger the position of the lens 1z is on the tele side, the wider. Accordingly, even if the movable range of the focus lens 1f is not acquired, it is determined whether or not the movable range of the focus lens 1f is narrow if it is determined whether or not the position of the zoom lens 1z is wider than the predetermined position. be able to.

  If it is determined in step 31 that the position of the zoom lens 1z is wider than the predetermined position, steps S9 and S11 are executed assuming that the movable range of the focus lens 1f is narrow. Otherwise, the movable range of the focus lens 1f. Are not narrow, steps S19 and S21 are executed. The predetermined value in step S31 is determined in consideration of the characteristics of the optical system, the purpose of use of the electronic still camera, etc. in order to enjoy the effects of the present invention. In FIG. 4, other steps are the same as those in FIG. 2, and the description thereof is omitted.

  According to the present embodiment, the auto focus control is changed by discriminating the size of the movable range of the focus lens 1f that can be moved to focus on the subject existing within the assumed range according to the position of the zoom lens 1z. The configuration is simpler than that of the first embodiment.

  Next, a third embodiment will be described. The functional block diagram of the electronic still camera is the same as that of the first embodiment shown in FIG. 1, and the description thereof is omitted. FIG. 5 is a flowchart showing the operation of the third embodiment. In contrast to the flowchart of FIG. 2 showing the operation of the first embodiment, step S1 for detecting the position of the zoom lens 1z using the zoom encoder 14 and the possible range of the focus lens 1f using the lens characteristic storage circuit 15 are shown. The step S5 to be acquired is eliminated, and instead of the determination in the step S7, a step S41 for determining whether or not the result detected in the step S3 is set so as to include the macro area as the autofocus operation is provided.

  As shown in FIG. 3, in an optical system that generally includes a zoom lens, autofocus control is possible, that is, the movable range of the focus lens 1f that can be moved to focus on a subject that exists within the assumed range is an auto range. If the macro region is included as the focus operation, the zoom lens 1z becomes wide at any position. Therefore, it is possible to determine whether or not the movable range of the focus lens 1f is narrow if it is determined whether or not the macro region is included as an autofocus operation without acquiring the movable range of the focus lens 1f. Can do.

  If it is determined in step 41 that the macro region is not set as an autofocus operation, steps S9 and S11 are executed assuming that the movable range of the focus lens 1f is narrow, and otherwise the movable range of the focus lens 1f. Are not narrow, steps S19 and S21 are executed. In FIG. 5, the other steps are the same as those in FIG. 2, and the description thereof is omitted.

  As in the first embodiment, since there is an optical system in which the possible range of the focus lens 1f in the macro area is wider than the normal area, including the macro area as an autofocus operation means that only the macro area is A focus operation may be performed.

  According to the present embodiment, it is determined whether or not the movable range of the focus lens 1f that can be moved to focus on a subject existing within an assumed range is set to include a macro region as an autofocus operation. Since the autofocus control is changed, the configuration is simpler than that of the first embodiment.

It is a functional block diagram of an electronic still camera showing an embodiment of the present invention. It is a flowchart which shows operation | movement of the 1st Example of this invention. It is explanatory drawing explaining operation | movement of the Example of this invention. It is a flowchart which shows operation | movement of the 2nd Example of this invention. It is a flowchart which shows operation | movement of the 3rd Example of this invention.

Explanation of symbols

1z Zoom lens 1f Focus lens 2 Image sensor 3 A / D converter 4 Signal processing circuit 5 DRAM
6 Processing Circuit 8 Gate Circuit 9 Luminance Signal Generation Circuit 10 HPF (High Pass Filter)
11 Digital integrator 12 CPU
13 Focus motor 14 Zoom encoder 15 Lens characteristic storage circuit 16 Macro setting switch

Claims (3)

In an autofocus camera that performs an autofocus operation by detecting a high frequency component level of an image pickup signal obtained from an image sensor as a focus evaluation value,
A focus lens,
A zoom lens,
Zoom position detecting means for detecting the position of the zoom lens;
Lens characteristic storage means for storing the relationship between the position of the focus lens, the position of the zoom lens, and the distance to the subject;
First adjusting means;
A second adjusting means;
Comprising
The first adjusting means includes
Moving means for moving the focus lens along the optical axis and setting the movement completion position to an autofocus start position;
First search means for moving the focus lens in a direction opposite to the moving direction by the moving means from the autofocus start position in a predetermined step, and obtaining a focus evaluation value for each step;
First focusing means for moving the focus lens to a focus position according to the relationship between the focus lens position and the focus evaluation value obtained by the first search means;
Comprising
The second adjusting means includes
Direction discriminating means for discriminating the moving direction of the focus lens in which the focus evaluation value increases;
Second search means for moving the focus lens in a predetermined step in the movement direction determined by the direction determination means to obtain a focus evaluation value for each step;
Second focus means for moving the focus lens to a focus position in accordance with the relationship between the focus lens position obtained by the second search means and a focus evaluation value, and further, the zoom position detection A movable range acquisition unit that acquires a movable range of the focus lens that is capable of autofocus control at the position of the zoom lens detected by the unit using the lens characteristic storage unit;
When the movable range acquired by the movable range acquisition unit is narrower than a predetermined value, the first adjustment unit is used to perform an autofocus operation. Otherwise, the second adjustment unit is used to perform the autofocus operation. First discriminating means to perform;
An autofocus camera comprising: Macro setting means for setting whether or not to include a macro area as an autofocus operation;
3. The autofocus camera according to claim 2, wherein the lens characteristic storage means stores that the movable range changes in accordance with a setting state of the macro setting means. In an autofocus camera that performs an autofocus operation by detecting a high frequency component level of an image pickup signal obtained from an image sensor as a focus evaluation value,
A focus lens,
Macro setting means for setting whether or not to include a macro area as an autofocus operation;
First adjusting means;
A second adjusting means;
Comprising
The first adjusting means includes
Moving means for moving the focus lens along the optical axis and setting the movement completion position to an autofocus start position;
First search means for moving the focus lens in a direction opposite to the moving direction by the moving means from the autofocus start position in a predetermined step, and obtaining a focus evaluation value for each step;
First focusing means for moving the focus lens to a focus position according to the relationship between the focus lens position and the focus evaluation value obtained by the first search means;
Comprising
The second adjusting means includes
Direction discriminating means for discriminating the moving direction of the focus lens in which the focus evaluation value increases;
Second search means for moving the focus lens in a predetermined step in the movement direction determined by the direction determination means to obtain a focus evaluation value for each step;
Second focusing means for moving the focus lens to a focus position in accordance with the relationship between the focus lens position and the focus evaluation value obtained by the second search means, and further, the macro setting means by performed autofocus operation using the second adjusting means if configured to include the macro area as the autofocus operation, a second determination to perform autofocus operation using the first adjusting means otherwise Means,
An autofocus camera comprising:

Images