Focus control device and camera

Focus control device and photographing device

Technical field

The present invention relates to a focus control device and a photographing device that divide the distance of a subject into a plurality of distance measurement areas, and scan each distance measurement area sequentially to shorten the distance measurement time.

Background technique

In many photographing devices such as digital cameras, an autofocus (hereinafter, AF (Auto Focus)) method called the TV-AF method is adopted. In this method, the focus position is moved within a certain range, and the subject distance is calculated from the value of the AF evaluation signal at each point in the range (for example, refer to Japanese Patent Application Laid-Open No. 3-68280). The AF evaluation signal is calculated by extracting signal components of a predetermined frequency band using a BPF (Band Pass Filter), and the more the focus is on the subject, the larger the output signal.

For example, in the case where the range from infinity to 50cm is used as the distance measurement range, as shown in Figure 10, the AF evaluation signal focused on the focus position at infinity is obtained, and the focus position is gradually brought closer to 50cm while obtaining the AF evaluation signal. AF evaluation signal at distance. Subsequently, the AF evaluation signal at each distance obtained is compared, and the focus position is moved to the subject distance A (the subject distance corresponding to the apex of the peak of the AF evaluation value signal) determined as the best focus position. A method for AF control.

In addition, since it is generally difficult to continuously obtain the AF evaluation signal while adjusting the focus position, for example, the AF evaluation signal is sampled every distance corresponding to the depth of field to be photographed to obtain the AF evaluation signal in many cases.

However, in the above-mentioned existing technology, in the case of a digital camera with a long focal length and a wide range of focus movement, or a digital camera with a shallow depth of field that needs to refine the focus movement, the range of the measurement will be obtained. The number of samples of the data (AF evaluation signal) needs to be sampled very much, so there is a problem that it takes time to acquire the data and the AF time is prolonged.

Summary of the invention

The present invention has been completed in view of the above problems, and its object is to provide that even when the number of samples of the autofocus evaluation signal required for the ranging range is large, the accuracy of the autofocus evaluation signal can be reduced without reducing the accuracy of the autofocus evaluation signal. , A focus control device and a photographing device that seek to increase the speed of auto-focusing and shorten the time of auto-focusing.

In order to achieve the above object, the first technical solution of the present invention provides a focus control device that detects the focus position of the focus optical system by scanning while driving the focus optical system; it is characterized in that it includes : Selecting device to select the driving range for scanning; in-focus state acquisition device to scan the selected drive range to obtain the in-focus state of the above-mentioned focusing optical system; judging device to use the above-mentioned in-focus state to obtain It is determined whether to scan another driving range; and the position determining device determines the driving position of the focusing optical system based on the acquisition of the in-focus position.

In addition, the second technical solution of the present invention provides a focus control device that detects the focus position of the focus optical system by scanning while driving the focus optical system; it is characterized by comprising: a selection device , Select the drive range for scanning; the focus state acquisition device scans the selected drive range to obtain the focus state of the above-mentioned focusing optical system; the focus judgment device uses the above-mentioned focus state to obtain Judging whether there is in-focus; updating the device to sequentially change the driving range to be scanned; and the judging device, according to the result of the above-mentioned in-focus judgment, judging whether to scan other driving ranges.

As described above, according to the present invention, the distance of the subject is divided into a plurality of driving ranges, and the driving range to be scanned is selected at the same time; the selected driving range is scanned to obtain the in-focus state of the focusing optical system; To determine whether to scan other driving ranges; appropriately change the driving range to be scanned, and at the same time determine the in-focus position based on the acquisition of the in-focus state, so in the case of rapid discovery of the object, there is no need Scan other drive ranges. As a result, it is possible to achieve an increase in the autofocus speed without reducing the accuracy of the autofocus evaluation signal even when the number of samples of the autofocus evaluation signal necessary for the ranging range is large. The focus control device and the imaging device equipped with the focus control device to shorten the time of automatic focusing. In addition, according to the present invention, the distance of the subject is divided into a plurality of driving ranges, and the driving range to be scanned is selected at the same time; scanning the selected driving range To obtain the in-focus state of the focusing optical system; use the in-focus state to determine whether there is in-focus; sequentially update the driving range to be scanned; determine whether the update of the driving range is performed according to the result of the in-focus judgment , So in the case of rapid discovery of the subject, there is no need to scan other driving ranges. As a result, it is possible to realize a focus control device with a shortened auto-focusing time and an imaging device equipped with a focus control device in the same way as above. In addition, by judging whether to scan other driving ranges according to the update history of the driving range, scanning can be more appropriate. The driving range.

In addition, even when there are multiple AF positions, the drive range is divided into multiple, and the selected drive range is scanned at the same time to obtain the in-focus position of the focusing optical system, and it is determined based on the in-focus state. Scanning is ended when the in-focus state is obtained, so similar to the above, it is possible to shorten the auto-focusing time by improving the auto-focusing speed.

In addition, by changing the order of changing the driving range in accordance with the shooting conditions or shooting mode, and changing the number of divisions of the driving range in accordance with the focus distance or aperture value during shooting, similar to the above, it can be shortened by improving the autofocus speed. Auto focus time.

The other objectives and advantages of the present invention in addition to the above will be known to those skilled in the art through the following description of the preferred embodiments of the present invention. In the description, reference will be made to the drawings constituting a part of the description and showing examples of the present invention. However, this example is not an exhaustive list of various embodiments of the present invention, and therefore, the scope of the present invention should be determined with reference to the claims following the description.

Description of the drawings

FIG. 1 is a block diagram showing a schematic configuration of a digital camera equipped with an autofocus device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example in which the distance measurement area is divided into a plurality of objects according to the distance of the subject.

FIG. 3 is a flowchart showing the AF operation when the ranging area is divided.

Fig. 4 is a flowchart showing a process for determining update of a ranging area.

FIG. 5 is a diagram showing an example of the relationship between the range of the distance measurement area and the AF evaluation value.

6 is a diagram showing the positions of AF frames when nine AF frames are set according to the second embodiment of the present invention.

Fig. 7 is a flowchart showing a ranging area update determination process when there are multiple AF frames.

FIG. 8 is a diagram showing an example of the relationship between the focal length and the number of divisions of the distance measurement area according to the third embodiment of the present invention.

9A and 9B are diagrams showing an example of the relationship between the F number and the number of divisions of the ranging area. Fig. 9A is an example of the division of the ranging area at F5.6, and Fig. 9B is an example of the division of the ranging area at F4.

FIG. 10 is a diagram showing an example of the relationship between the subject distance and the AF evaluation value.

detailed description

First, the outline of the embodiment of the present invention will be explained. The embodiment of the present invention is to divide the distance of the subject into multiple distance measurement areas in a digital camera or other photographing device with an autofocus function, and select and scan from the multiple distance measurement areas at the same time (corresponding to the distance of the object) To drive the action of the optical system for focus adjustment) the distance measurement area, and scan the selected distance measurement area to obtain the AF evaluation value. At the same time, based on the update judgment, the distance measurement area to be scanned is appropriately updated, and based on the AF evaluation value. Decide the focus position to shorten the AF time in order to improve the AF speed.

Hereinafter, the embodiments of the present invention will be described in detail based on the drawings.

[First Embodiment] In the first embodiment of the present invention, an embodiment when the autofocus device of the present invention is applied to a digital camera will be described. Fig. 1 is a block diagram showing a schematic configuration of a digital camera with an autofocus function according to a first embodiment of the present invention. The digital camera is equipped with optical system 1, focusing lens 2, imaging element 3, preprocessing circuit 4, A/D converter 5, memory controller 6, memory 7, recording medium 8, switch SW1·9, switch SW2·10, control Unit 11, distance measurement area setting device 12, distance measurement area selection device 13, AF evaluation value calculation circuit 14, area update determination device 15, focus position determination device 16, and focus lens drive circuit 17.

The optical system 1 makes the image of the subject incident on the imaging element 3 via the focusing lens 2. The focus lens 2 is driven within the selected distance measurement range. The imaging element 3 photoelectrically converts the image of the object into an electric signal. The preprocessing circuit 4 includes a CDS circuit that eliminates output noise, and a nonlinear amplifier circuit that performs nonlinear amplification before A/D conversion. The A/D converter 5 converts the analog signal output from the preprocessing circuit 4 into a digital signal. The memory controller 6 stores the digital signal output from the A/D converter 5 in the memory 7. The memory 7 stores the above-mentioned digital signal. The recording medium 8 records images. The switch SW1·9 is a switch that is pressed when the focus lens 2 is driven. The switch SW2·10 is a switch that is pressed when shooting is performed.

The control unit 11 controls various operations including AF operations by controlling various components of the digital camera, and executes the processing shown in the flowcharts described below based on programs stored in the digital camera or programs provided from outside. . The distance measurement area setting device 12 divides (sets) the distance measurement area into a plurality of pieces. The ranging area selection device 13 determines the order of the ranging areas to be scanned. The AF evaluation value calculation circuit 14 calculates an AF evaluation value by extracting mid- and high-frequency signal components of the signal acquired by the imaging element 3. The area update determination device 15 determines whether to update the ranging area based on the AF evaluation value. The in-focus determination device 16 determines the in-focus position based on repeatedly performing the update of the distance measurement area and the acquisition of the value of the AF evaluation described above. The focus lens driving circuit 17 drives the focus lens 2 to the in-focus position.

The digital camera in the first embodiment performs the following processing: during shooting, the light (image of the subject) formed on the imaging element 3 through the optical system 1 and the focus lens 2 is photoelectrically converted by the imaging element 3, and passes through The signal digitized by the preprocessing circuit 4 and the A/D converter 5 with a CDS circuit that eliminates output noise and a nonlinear amplifier circuit that performs nonlinear amplification before A/D conversion are stored in the memory 7 via the memory controller 6 After the digitized signal stored in the memory 7 is converted into an image by a signal processing circuit not shown, it is recorded on the recording medium 8 as an image.

Next, the operation of the digital camera in the first embodiment constructed as described above will be described in detail with reference to FIGS. 1 to 5.

The operation of AF will be described. The AF operation is controlled by the control unit 11. First, if the photographer presses the switch SW1·9, the focus lens driving circuit 17 drives the focus lens 2, so that the distance of the subject is divided into a plurality of distance measurement areas by the distance measurement area setting device 12, and the distance measurement is performed by the distance measurement area setting device 12. The distance measurement range (distance measurement area) selected by the distance area selection device 13 is scanned, and a signal is acquired by the imaging element 3. The signal obtained by the imaging element 3 is converted into an AF evaluation value (AF evaluation signal value) at each scanning point by extracting the middle and high frequency signal components by the AF evaluation value calculation circuit 14 using BPF.

Next, the area update judgment device 15 judges whether to perform distance measurement in other distance measurement areas based on the AF evaluation value at each scan point. After repeating the update of the distance measurement area by the area update determination device 15 and the acquisition of the AF evaluation value by the AF evaluation value calculation circuit 14, the focus determination device 16 determines the focus pair based on the AF evaluation value after the scan is completed. In the collimated position, the focus lens 2 is driven to the in-focus position by the focus lens driving circuit 17. In this state, the photographer presses the switch SW2·10 to perform photography.

The AF action will be described in further detail. In the first embodiment, it is assumed that a single focus lens is used as a premise and that there is only one AF frame (range measurement position) as an area displayed on the screen of a digital camera. In addition, it is assumed that the range of the measurement distance is from infinity to, for example, 50 cm. The distance measurement area is divided into three by the distance measurement area setting device 12 as shown in FIG. 2. FIG. 2 is a diagram showing the relationship between the subject and the distance measurement area. It is an example in which the distance measurement area 1 is 2 m to infinity, the distance measurement area 2 is 1 m to 2 m, and the distance measurement area 3 is 50 cm to 1 m. The method of dividing the distance measurement area may be arbitrarily determined according to the distance measurement speed, which subject is prioritized, or shooting conditions. In addition, the number of divisions of the ranging area can be changed according to the focal length during shooting and the aperture value during shooting. In this case, the longer the focal length, the larger the number of divisions of the distance measurement area, and the smaller the aperture, the smaller the number of divisions of the distance measurement area.

Next, the ranging area selection device 13 determines the order of the ranging areas to be scanned. In this example, the order is, for example, ranging area 1 ranging area 2 ranging area 3. In this case, as shown in Figure 2 means to start scanning from a place far away from the subject. In addition, it is also possible to start scanning from a place close to the subject as ranging area 3 ranging area 2 ranging area 1, or it can be performed as ranging area 2 ranging area 1 ranging area 3 scanning. Since the purpose of dividing the distance measurement area is to shorten the AF time by quickly finding the subject and ending the scan there, it is desirable to start scanning from the distance measurement area where the subject has a high probability of existence.

Therefore, the scanning order may be changed according to the shooting mode as follows. For example, by configuring to scan from far to near when shooting in landscape photography mode, and to scan from near to far when shooting in portrait mode, it can be faster Focus on the subject that the photographer wants to shoot.

Next, based on the flowchart of FIG. 3, a flowchart of processing until the AF evaluation value obtained by sequentially scanning the distance measurement areas divided as described above, and finally determining the in-focus position will be described. The processing shown in this flowchart is executed by the control unit 11 controlling each component of the digital camera of FIG. 1 based on a program.

In step S1, the distance measurement area setting device 12 sets a distance measurement area for scanning. In the case where the update order of the ranging area is ranging area 1 ranging area 2 ranging area 3, ranging area 1 is set first. Next, in step S2, by scanning the distance measurement area set by the distance measurement area setting device 12, the AF evaluation value calculation circuit 14 obtains an AF evaluation value. The AF evaluation value can be calculated by applying BPF filter processing to the captured signal, and after extracting the mid and high frequency components of the captured signal, the maximum amplitude in the AF frame is used as the AF evaluation value, or In the AF frame, the maximum value is extracted along the X-axis direction of the BPF filter, and the result obtained by integrating the maximum value in the direction perpendicular to the X-axis direction of the BPF (Y-axis direction) is used as the evaluation value of AF .

Next, in step S3, the area update determination device 15 performs a distance measurement area update determination process based on the AF evaluation value acquired by the AF evaluation value calculation circuit 14 described above. This ranging area update determination processing determines whether to update the ranging area. In the ranging area update determination processing, specifically, for example, it is determined whether to update the ranging area based on the difference in the level of the AF evaluation value and the increase in the AF evaluation value at the end of the ranging area.

The details of the distance measurement area update determination processing in step S3 described above will be described based on the flowchart of FIG. 4. The processing shown in this flowchart is executed by the control unit 11 controlling each component of the digital camera of FIG. 1 based on a program.

In step 11, first, the area update judgment device 15 calculates the difference Afdiff1=Afmax-Afmin between the maximum value Afmax and the minimum value Afmin of all the AF evaluation values of the range-measuring areas scanned so far. Next, in step 12, the area update judging means 15 judges whether the Afdiff1 calculated above is greater than the threshold TH1. In the case of the difference Afdiff1>TH1, when the topping processing of the AF evaluation value signal (finding the apex of the peak of the AF evaluation signal) is completed, the area update judging device 15 judges as OK (the ranging area is not updated). In the case of Afdiff1>TH1, the area update determination device 15 determines that it is NG (updated ranging area).

As for the rise of the AF evaluation value at the end of the distance measurement area, for example, as shown in FIG. 5, it is determined whether the AF evaluation value on the close side in the distance measurement area 1 is rising. That is, in step 13, the area update judging means 15 calculates the difference Afdiff2=Afsikin-Afsikin-1 between the closest AF evaluation value Afsikin in the ranging area 1 and the previous AF evaluation value Afsikin-1, and in step S14 Compare the calculation result with TH2. When the calculation result is greater than the threshold TH2, the area update determination device 15 determines that the AF evaluation value at the end of the distance measurement area is rising. When the peak of the mountain of the AF evaluation signal in FIG. 5 is in another distance measurement area, It is judged as NG (the ranging area is updated), and when the calculation result is smaller than the threshold TH2, it is judged as OK (the ranging area is not updated).

In addition, the threshold TH1 in the above-mentioned ranging area update determination does not need to be a fixed value, and may be changed according to the number of ranging areas scanned so far. That is, the more the distance measurement area is observed (the number of divisions of the distance measurement area increases), the greater the difference between the apex and the lowest point of the peak of the AF evaluation signal should easily appear, so the threshold value can be larger. In addition, because the smaller the ranging area, the more difficult it is for the peak height difference of the AF evaluation signal to appear, and sometimes it is desirable to obtain a smaller threshold value. In this way, by changing the ranging area update determination condition according to the update history of the ranging area, a more appropriate ranging area update determination can be made.

Furthermore, it is also possible to change the parameters (range-finding area update judgment conditions) in accordance with the shooting mode. For example, when the subject is dark and it can be estimated that the S/N of the AF evaluation value is not good, as in the night scene photography mode, the update of the ranging area can be made as easy as possible, and observation can be made in a wide range. (Calculate) the distance of the subject.

In the case where the above-mentioned two ranging area update conditions of step S12 and step S14 are both OK, the area update judging means 15 decides not to update the ranging area in step S15; otherwise, it decides to execute in step S16 The ranging area is updated.

Return to Figure 3 again. In step S4, the area update determination device 15 uses the result of performing the distance measurement area update determination processing of FIG. 4 to determine whether to update the distance measurement area. When the area update determining device 15 determines that the ranging area is updated, in step S5, it is determined whether the above processing for all the ranging areas has been completed, and when it is determined that the ranging area is not to be updated, the process proceeds to step S5. S6 in-focus position determination processing. In the case where the area update determination device 15 determines that the ranging area is updated, in step S5, if the above processing for all the ranging areas is not completed, the next ranging area is set in the above step S1. After the above-mentioned processing of the distance measurement area of is completed, the process proceeds to the in-focus position determination processing of step S6.

In the in-focus position determination processing in step S6, first, the in-focus determination device 16 calculates the in-focus position after determining the in-focus position. Judgment of the in-focus state, for example, based on the AF evaluation values of all the range-measuring areas scanned so far, in the same way as the above-mentioned range-measuring area update determination process, Afdiff1 (=Afmax-Afmin) is obtained, and Afdiff1 Compare with the threshold TH3. If Afdiff1>TH3 is established, the focus determination device 16 determines that it is in focus, and if Afdiff1>TH3 is not established, it is determined that it is out of focus. In the case where focus is possible, the maximum value of the AF evaluation value is taken as the focus position. In addition, the judgment condition of the in-focus state can be changed according to the update history of the ranging area. In addition, if it is determined that the focus can be focused, the ranging area update is ended.

By changing the setting of the threshold value TH1 in the distance-measuring area update determination processing and the threshold value TH3 in the in-focus position determination processing, it is possible to set the method of updating the distance-measuring area to be easy or difficult. For example, if the threshold TH1 is greater than the threshold TH3, it is not considered OK (the ranging area is not updated) unless the height difference of the peak of the AF evaluation signal becomes larger accordingly, so the updating of the ranging area becomes easy. In addition, it is also possible to set the judgment of updating the ranging area to be exactly the same judgment as the judgment of the in-focus state.

As explained above, according to the first embodiment, the distance of the subject is divided into a plurality of distance measurement areas, the distance measurement area to be scanned is selected at the same time, and the selected distance measurement area is scanned to obtain the AF evaluation value, and the AF evaluation value is used To determine whether the ranging area to be scanned is updated, update the ranging area to be scanned appropriately, and determine the focus position based on the acquisition of the AF evaluation value, so if the subject is quickly found, there is no It is necessary to scan other ranging areas, so the focusing time can be shortened accordingly. In addition, the focusing performance of AF will not decrease even in this case.

Therefore, even when the number of samples of the AF evaluation signal necessary for the ranging range is large, it is possible to achieve an autofocus device that shortens the AF time by improving the AF speed without reducing the AF accuracy, and the autofocus device equipped with the autofocus Device of the digital camera.

[Second Embodiment] In the second embodiment of the present invention, the implementation in the case where the autofocus device of the present invention is applied to a digital camera and there are multiple AF frames (range measurement positions) on the screen of the digital camera will be described. form. The difference between the second embodiment and the first embodiment is that the range-finding area update determination processing is changed because there are multiple AF frames. In the second embodiment, a case where there are nine AF frames as shown in FIG. 6 will be described. In addition, the configuration of the digital camera in the second embodiment is the same as that in the first embodiment (refer to FIG. 1), so the description is omitted.

Next, referring to FIG. 1, FIG. 6 and FIG. 7, the operation of the digital camera in the second embodiment constructed as described above will be described in detail.

The flow of the AF operation processing in the second embodiment is the same as the flowchart of FIG. 3 in the first embodiment, and there is only a difference in the ranging area update determination processing part of step S3. In the second embodiment, this ranging area update determination processing part will be described. In addition, the update sequence of the ranging area is set to update from far to near.

In addition, the determination of the peak state of the AF evaluation signal in each AF frame in the second embodiment is the same as the flowchart of FIG. 4 in the first embodiment. In the second embodiment, it is in step S14. In the case of No, the state of the peak of the AF evaluation signal is expressed as (the apex of the peak (peak top) in the ranging area), and in the case of Yes in step S14, it is expressed as (in other ranging areas If there is a peak in the middle), if it is No in step S12, it is expressed as × (there is no peak in the ranging area).

Next, based on the flowchart of FIG. 7, the flow of the above-mentioned ranging area update determination processing part will be described. The processing shown in this flowchart is executed by the control unit controlling each component of the digital camera of FIG. 1 based on a program.

In step 21, the area update judging device 15 checks the status of the AF evaluation values of the 3 AF frames in the middle among the 9 AF frames in the upper, middle and lower parts of FIG. 6, and only if all of them are , proceed to step S26: It is determined that the ranging area is not to be updated. The reason for not checking all the AF frames in the upper, middle and lower parts is because the AF frame in the middle is given priority. Even if there is a close subject in the upper or lower AF frame, the focus will not be pulled there (e.g. This makes it impossible to focus in the upper or lower AF frame if there is a main subject in the middle AF frame). In addition, the reason for checking the three AF frames in the center instead of the center point is to prevent the mis-measurement of AF when the main subject is not in the center of the hollow scene.

In the case of "No in step S21 (when the middle part is not all ), in step S22, the area update determination means 15 determines whether the update of the ranging area is the second or later. If it is not the second or later, the area update judging means 15 judges that the ranging area is updated in step S27. The reason for judging whether the update of the ranging area is the second or later is that when the ranging area is finely divided, there is a possibility that only the bottom of the peak of the AF evaluation signal is scanned. Therefore, in order to avoid the fact that there is a peak, Only the bottom of the peak is observed and the × judgment is performed, and the update judgment of the distance measurement area is performed after checking as many distance measurement areas as possible.

In the case of "Yes in step S22 (the update of the ranging area is the second or later), in step S23, the area update judging means 15 checks the status of the AF evaluation value of the AF frame in the middle, and judges Is there a delta in the middle. In the case where there is a Δ in the middle, the area update determination device 15 interprets that the peak of the AF evaluation signal is present in another distance measurement area, and in step S27, it is determined that the distance measurement area is updated. When there is no Δ in the middle part, the area update judging device 15 checks the state of the AF evaluation value of the AF frame in the middle part in step S24, and judges whether the middle part is all x.

When the area update determination device 15 is not all x, since there is a in a certain frame, it is determined in step S26 that the ranging area is not to be updated. In the case where the area update judgment device 15 is all x, the AF evaluation value status of the upper and lower AF frames is checked in step S25 because the focus cannot be performed in the middle part, and whether there is a in the upper and lower parts. When the area update determination device 15 has a Δ in the upper and lower parts, it is determined in step S27 that the ranging area is updated because the subject exists in the other upper and lower areas. In the case where there is no Δ in the upper and lower parts of the area update determination device 15, it is determined in step S26 that the ranging area is not to be updated.

Although this example shows an example of the ranging area update determination processing when there are multiple AF frames. However, it is not limited to this, and all the AF frames may always be used for the ranging area update determination, and the middle AF frame among the plurality of AF frames may not be prioritized.

As described above, according to the second embodiment, even when there are multiple AF frames, the ranging area can be divided into multiple, and the selected ranging area can be scanned at the same time to obtain the AF evaluation value based on the AF evaluation value. When it is determined that the in-focus state has been obtained, the scan ends. Therefore, it is possible to realize an autofocus device that shortens the AF time by improving the AF speed, and a digital camera equipped with the autofocus device.

[Third Embodiment] In the third embodiment of the present invention, an embodiment in the case where the autofocus device of the present invention is applied to a digital camera equipped with a focusing lens in addition to a zoom lens will be described. The third embodiment is different from the first embodiment in that the optical system includes a variable power lens. In addition, the configuration of the digital camera other than the zoom lens in the third embodiment is the same as that in the first embodiment (refer to FIG. 1), so the description is omitted.

Hereinafter, the operation of the digital camera in the third embodiment constructed as described above will be described in detail while referring to FIG. 1, FIG. 8, FIG. 9A, and FIG. 9B.

The number of scanning points related to the AF time is determined by the amount of movement of the focus lens 2 necessary to scan the distance measurement range and how fine the scanning distance measurement range is. Generally, as the focal length becomes longer, the amount of movement of the focus lens 2 increases. On the other hand, how fine the scanning range is determined by Fδ (F is the F number, and δ is the allowable diameter of circle of confusion) equivalent to the focal depth. Now, if the F number does not change due to the focal length, since the movement amount of the focus lens 2 increases when the focal length becomes longer, the AF time is correspondingly extended by the increase amount. Therefore, it is desirable to optimize the number of divisions of the distance measurement area as shown in FIG. 8 according to each focal length.

In addition, when the fineness of scanning is changed in accordance with the F number, the division method of the ranging area can also be changed in accordance with the F number. For example, in the case of a digital camera with two aperture values of F4 and F5.6, compared to the case of shooting at F4, the depth of focus is deeper when shooting at F5.6, so the AF evaluation is obtained more roughly. The value does not matter. Specifically, if the amount of movement of the focus lens 2 when shooting with F5.6 is set to 2 times the amount of movement within the scanning point of the focus lens 2 when shooting with F4, then when shooting with F5.6 The number of scanning points in all areas of the ranging range becomes approximately half. Therefore, if the number of scanning points for each range-finding area is always set to be constant, the number of divisions of the range-finding area when shooting with F4 compared to when shooting with F5.6 becomes as shown in Figures 9A and 9B. 2 times.

Although in this example, the number of divisions of the ranging area has been described, the order of updating the ranging area may be changed according to the shooting conditions. For example, when the brightness level is high during shooting, it is determined that the shooting is taking place outdoors, and scanning is performed from the distance measurement area to the close distance measurement area according to the method of prioritizing distant objects. In addition, when the brightness level is low during shooting, it is judged that the shooting is taking place indoors, and scanning is performed from the near distance measurement area to the far distance measurement area according to the method of prioritizing close objects.

In addition, the update order of the ranging area may be changed according to the shooting mode. For example, in the case of setting to the mode of shooting landscapes, the distance measurement area can be preferably scanned. In the case of setting to the mode of shooting people, priority is given to the near area or the measurement that contains many people. Just scan from the area. In addition, when the flash setting is performed, it is determined that a person is being photographed, and the close area or the distance measuring area containing many people may be scanned with priority.

As described above, according to the third embodiment, by changing the number of divisions of the ranging area, the number of scanning points, or the updating sequence of the ranging area in accordance with the focal length or aperture value at the time of shooting, it is possible to achieve an increase in the AF speed. An autofocus device that shortens the AF time, and a digital camera equipped with the autofocus device.

[Other implementation forms] In addition, the purpose of the present invention can also be achieved by providing a storage medium recording software program codes for realizing the functions of the above implementation forms to a system or device, and the computer (or CPU of the system or device) , MPU, etc.), read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium will realize the functions of the above-mentioned embodiment, and the storage medium storing the program code will constitute the present invention.

In addition, as the storage medium for supplying the program code, for example, a flexible (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAW, a DVD-ROM can be used. RW, DVD+RW, magnetic tape, non-volatile memory card and ROM, etc.

In addition, it includes not only the case where the functions of the above-mentioned embodiment are realized by executing the program code read out by the computer, but also the part of the actual processing performed by the OS (operating system) running on the computer according to the instructions of the program code. Or all, the case where the functions of the aforementioned implementation form are realized by this process.

Furthermore, it also includes when the program code read from the storage medium is written into the memory provided on the function expansion board inserted into the computer and/or the function expansion unit connected to the computer, according to the instructions of the program code, the function The CPU or the like provided on the expansion board and/or the function expansion unit performs part or all of the actual processing, and the function of the aforementioned embodiment is realized by the processing.

The present invention is not limited to the above-mentioned embodiments, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to disclose the scope of the present invention, the following claims are attached.