JP2001100088A - Multispot automatic focus detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multispot focus detecting device which suppresses an increase in memory capacity needed for sensor system unevenness correction even when the number of focus detection areas is increased. SOLUTION: The multispot focus detecting device which has focus detection areas distributed at the center part and peripheral part of a focus detection picture plane is equipped with a focus detection sensor which has multiple pixels and photodetects a couple of optical images formed by a focus detection optical system, a correcting means which corrects variance of the focus detection sensor output when a uniform luminance plane is observed, and a memory means which stores correction data that the correcting means refers to when corrected; and the correcting means has different correcting modes between the center part and peripheral part of the focus detection picture plane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an automatic focus detection device, and more particularly, to a multi-point automatic focus detection device for a camera having a plurality of ranging points.

[0002]

2. Description of the Related Art In recent years, many autofocus cameras having a plurality of distance measuring points in a shooting screen have been provided. Many single-lens reflex cameras using the so-called phase difference detection method have a focus detection area of five points including the central part of the screen and three points at the left and right, and two points at the top and bottom, but a distance measurement exceeding five points Some have dots. In such an autofocus camera, the ranging points tend to increase more and more in order to improve the usability, and there is a possibility that ranging points will be arranged throughout the entire screen in the future.

In a focus detection device of a TTL phase difference detection system using a light beam passing through a photographing lens, a photoelectric conversion element array having a plurality of pixels such as a CCD element is generally used as a focus detection sensor. These photoelectric conversion element arrays are formed on the same semiconductor substrate, but not all elements have the same photoelectric conversion characteristics, and there are considerable offset variations and sensitivity variations between pixels. Furthermore, in a focus detection optical system that guides light to the focus detection sensor, the illuminance distribution on the focus detection sensor is not uniform even when observing a uniform luminance surface due to restrictions on optical design and other factors, and the illuminance distribution is reduced particularly at the periphery. It is known that light is easily generated.

Since the automatic focus detection device performs focus detection based on an output signal from a focus detection sensor, it is needless to say that the sensor output must be flat when a uniform luminance surface is observed. Therefore, when a uniform luminance surface is observed, it is common practice to perform electrical correction so as to make the sensor output flat, and to perform focus detection based on the corrected sensor data.

FIGS. 17A to 17D schematically show non-uniformity relating to sensor variation and vignetting, which are problems of the focus detection system described above, and how to correct it. . Because of the TTL phase difference detection method, the focus detection sensor has a pair of photoelectric conversion element rows on the left and right, and L and R attached on the drawing indicate left and right photoelectric conversion element rows, respectively. The horizontal axis indicates the order of arrangement of the photoelectric conversion element rows (pixel rows), and the vertical axis indicates the output signal for each pixel, and illustrates an example in which the higher the illuminance on the light receiving surface, the higher the output level.

FIG. 17 (a) shows an example of the effect of peripheral dimming of the focus detection optical system when it is assumed that there is no variation in the sensor itself, and FIG. 17 (b) shows the sensitivity variation between pixels of the sensor. An example is shown. FIG. 17C is a composite of FIGS. 17A and 17B, and illustrates a sensor output when observing a uniform luminance surface. Then, the correction is performed as shown in FIG. 17C to obtain flat sensor data as shown in FIG. 17D. This correction is referred to as “illuminance correction”.

FIG. 17E shows an example of the relationship between the integration time of the sensor and the output level. Time T for all pixels of the sensor
When the integration operation of 1 is performed, the pixel indicating the maximum output among all the pixels is set to a, and the others are set to b. The illuminance correction is performed when the time T1 is integrated by observing a uniform luminance surface.
The correction is performed so that the output levels of all the pixels are adjusted to D1, and the inclination with respect to the time axis is corrected. For example, the following correction formulas are known.

D ′ (i) = {H (i) / k + 1} * D (i) Equation (1) Here, the meanings of the symbols are as follows. D '(i): corrected sensor data, H (i): correction value to be written at the time of manufacturing the device (for example, 4 bits per pixel), k: constant determined by variation in optical system and sensor sensitivity, D (i); Sensor data before correction.

In addition, "offset correction" for correcting an offset error for each pixel as non-uniformity correction.
Is also known. This is for correcting variations in the sensor output level in a very short time immediately after the start of integration of about 100 μs, and has no time dependency.

FIG. 18 shows an example of a sensor output in a short time immediately after the start of integration. In the figure, c indicates the lowest integrated value of all the pixels, and d indicates the integrated values of the other pixels. c as the common offset value,
Assuming that the output D4 of d is a pixel-specific offset value, the output after offset correction is given by the following equation.

D ″ (i) = D (i) −D3−D4 (i) Equation (2) Here, the meanings of the symbols are as follows: D ″ (i): corrected sensor data, D (I): sensor data before correction D4 (i): offset value unique to each pixel.

As a technique in which the illuminance correction and the offset correction are applied to a camera having a plurality of focus detection areas, Japanese Patent Laid-Open No. Hei 6 (1996) -1994 discloses a technique for correcting the illuminance so that the outputs of all the focus detection areas become uniform. For example, Japanese Patent Application Laid-Open No. 331885 and Japanese Patent Application Laid-Open No. H8-75996 which divide a sensor output into a plurality of blocks for offset correction and store each offset value are known.

[0013]

However, in order to perform the illuminance correction and the offset correction described above,
A storage unit for storing the illuminance correction value and the offset correction value for each sensor pixel is required. Generally, a non-volatile memory is used as the storage means. However, since the capacity of one non-volatile memory has a limit value, when the number of pixels increases, a large number of non-volatile memories must be used. .

For example, assume a multi-point focus detection device having 150 pixels in one focus detection area and 15 focus detection areas. Now, if 4-bit correction data for one pixel is given for illuminance correction, 9000 bits are required (150 * 15 * 4 = 9000), and if 2-bit correction data for one pixel is given for offset correction, the same applies. Thus, 4500 bits are required. If they are added together, 13500 bits of correction data are required. Even if the focus detection area is limited to five locations, a total of 4500 bits are required. However, since a large-capacity nonvolatile memory is not supplied in one chip, it is necessary to use a large number of such memories. When a large number of nonvolatile memories are used, it is difficult to reduce the size of the device. Further, the time required for the writing process to the nonvolatile memory in the manufacturing stage of the device incorporating the multipoint focus detection device also increases.

The present invention has been made in view of the above technical problem, and an object of the present invention is to increase the memory capacity required for correcting the sensor system non-uniformity even if the number of focus detection areas is increased. It is an object of the present invention to provide a multi-point focus detection device that is suppressed.

[0016]

In order to solve the above-mentioned technical problem, a multi-point focus detection apparatus according to claim 1 of the present invention comprises a plurality of focus detection areas distributed in a central portion and a peripheral portion of a focus detection screen. A focus detection sensor having a plurality of pixels and receiving a pair of optical images formed by a focus detection optical system, and the focus detection when observing a uniform luminance surface Correction means for correcting variations in sensor output, and memory means for storing correction data referred to by the correction means at the time of correction, wherein the correction means
The correction mode is different between the central part and the peripheral part of the focus detection screen.

According to a second aspect of the present invention, there is provided a multi-point automatic focus detecting apparatus according to the first aspect, wherein the correcting means comprises the focus detecting optical system. The present invention is characterized in that peripheral dimming on the light receiving surface of the sensor and sensitivity variation between pixels of the focus detection sensor itself are corrected.

Further, according to a third aspect of the present invention, in the multi-point automatic focus detecting device according to the first or second aspect, the correction data is:
1 corresponding to the focus detection area near the center of the focus detection screen
One of the two correction data or the average value of the correction data of all the detection areas of the focus detection sensor.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a focus control unit 1 which is a multipoint automatic focus detection device according to an embodiment of the present invention. The focus detection unit 2 includes a focus detection optical system and a focus detection sensor, and is connected to the focus calculation unit 3. The focus calculation unit 3 includes a focus detection unit 2 and a ranging point selection unit 4
And the non-uniformity correction unit 5. The non-uniformity correction unit 5 is connected to the non-uniformity correction data storage unit 6 in addition to the focus calculation unit 3.

In FIG. 1, a focus detection unit 2 outputs an image signal necessary for focus detection, and a focus calculation unit 3 inputs data from the focus detection unit 2 and the non-uniformity correction unit 5 and Focus detection calculation is performed for a plurality of distance measurement areas based on the data. The ranging point selection section 4 selects one of the plurality of focus detection areas output from the focus calculation section 3 and outputs the ranging result to the outside. The non-uniformity correction unit 5
Before the focus detection unit 3 performs the above calculation, the focus detection unit 2
To correct the non-uniformity caused by the The non-uniformity correction data storage unit 6 stores correction data referred to when performing correction by the non-uniformity correction unit 5.

FIG. 2 is a cross-sectional view of a single-lens reflex camera to which the multipoint automatic focus detection device of the present invention is applied as one embodiment. Hereinafter, main components along the optical path of the camera will be described. A focus detection unit 21 is disposed below the mirror box of the camera body 20, and a part of the subject light beam that has passed through the photographing lens 22 is reflected upward by a main mirror 23 in the camera body 20, and the remaining light beam is transmitted. I do. The light beam reflected by the main mirror 23 is guided to the finder eyepiece 24 via the pentaprism and enters the observer's eye. On the other hand, the light beam transmitted through the main mirror 23 is reflected below the mirror box by the sub-mirror 25 and reaches the focus detection unit 21.

The focus detecting section 21 includes a field mask 27 for limiting the luminous flux of the object passing through the photographing lens 22, an infrared cut filter 28 for removing infrared light components, a condenser lens 29 as a condenser lens, Total reflection mirror 30
And a pupil mask 31 for splitting the incident light beam into pairs, and a photoelectric conversion element group P of the area sensor 33 for each of the split light beams.
It comprises a re-imaging lens 32 for re-imaging, and an area sensor 33 including a photoelectric conversion element group and its processing circuit.

In this single-lens reflex camera, at the time of photographing, the main mirror 23 and the sub-mirror 25 are retracted to the upper surface of the mirror box as shown by a broken line in the figure (mirror up), and the focal plane shutter 34 is opened for a predetermined time to make a photographic film 35. Exposure.

FIGS. 3A and 3B schematically show a focus detection optical system. FIG. 3A shows the state of a light beam from the taking lens 22 to the photoelectric conversion element group P of the area sensor 33 (the total reflection mirror 30 is omitted). A dashed line G in the figure is a primary imaging plane which is a conjugate plane with the film surface, and a light flux indicated by a straight line group is transmitted from one exit pupil Ha of the photographing lens 22 to the photoelectric conversion element group P
Up to the re-imaging R1 formed above, the other light flux indicated by a straight line group from the other exit pupil Hb of the taking lens 22 to the re-imaging R2 on the photoelectric conversion element group P is actually A pair of subject images is formed on the photoelectric conversion element group P of the area sensor 33. FIG.
It is a perspective view of (a).

As shown in FIG. 3A, in the optical path of the focus detecting optical system, a field mask 27 for defining a field of view, a condenser lens 29, and an opening arranged substantially symmetrically with respect to the optical axis O of the photographing lens. And a pupil mask 31 for splitting the light beam into pairs.
Reimaging lenses 32a and 32b are provided behind 1a and 31b, respectively. Exit pupil H of taking lens 22
a, Hb pass through the field mask 27, the condenser lens 29, the openings 31a, 31b of the pupil mask 31,
And re-imaging lenses 32a and 32b, respectively,
An image is formed again on the photoelectric conversion element group P in the areas 33a and 33b of the area sensor 33.

Now, when the taking lens 22 is "focused", that is, when the subject image I is formed on the primary imaging plane G, the subject images I become I1 and I2 in FIG. When the photographing lens 22 is “front-focused”, that is, when the subject image F is formed in front of the image plane G, the subject image F is shown in FIG.
F1 and F2. Further, when the photographing lens 22 is “back-focused”, that is, when the subject image R is formed behind the image forming plane G, the subject images R become R1 and R2 in FIG.

Therefore, by measuring the relative distance between the first image and the second image, it is possible to detect the focus adjustment state of the photographing lens 22. Specifically, the light intensity distribution of the first image and the light intensity distribution of the second image are obtained from the subject image signal from the area sensor 33, and the above-mentioned two image interval is measured.

FIG. 4 is a block diagram showing functions of the electric control system of the camera shown in FIG. The controller 40 functions as an overall control unit of the camera, and includes a CP
U (central processing unit) 41, ROM (read only memory) 42, RAM (read / write memory) 43, ADC
(A / D converter) 44 and EEPROM (rewritable nonvolatile memory) 45. Controller 4
0 controls a series of operations of this camera according to the camera sequence program stored in the ROM 42. EE
Adjustment values for focus detection and photometry and correction data for correcting non-uniformity of the focus detection system are written in the PROM 45 as unique information for each camera body during this camera manufacturing stage. Temporary data such as the number of film frames to be stored when the battery is replaced is also written.

The controller 40 includes the area sensor 3
3, lens driving unit 46, encoder 47, photometric unit 49,
The shutter drive unit 50, the aperture drive unit 51, and the film drive unit 52 are connected so as to be able to communicate with each other, and the operation switches 1RSW and 2RSW are also connected.

The lens driving section 46 is connected to a motor ML 48 as a driving source, and drives the focusing lens 22 a in the taking lens 22 in response to the control of the controller 40. The encoder 47 has a focusing lens 2
A pulse train is generated in response to the movement of 2a, and the controller 40 counts this pulse train and controls lens driving.

The photometric unit 49 includes an SPD (silicon photodiode) having a field of view corresponding to the photographing area of the camera, and outputs field luminance information. The output of the photometric unit 49 is converted into a digital value by the ADC 44 by the controller 40 and then stored in the RAM 43. The shutter driving unit 50 and the aperture driving unit 51
And operates the focal plane shutter 34 and the aperture mechanism (not shown) to control the film exposure amount. The film driving unit 52 performs an automatic loading, winding, and rewinding operation of the film according to a control signal from the controller 40.

1RSW (fast release switch)
And 2RSW (second release switch) are switches having a two-step stroke interlocked with the release button of the camera.
Only the RSW is turned on, and the 2RSW is also turned on in response to the subsequent second-step pressing operation. The controller 40 is a ROM
1RSW according to the camera sequence stored in
Performs photometry and focus adjustment in response to
A film exposure operation is started in response to ON, and after the exposure is completed, the film is fed.

FIG. 5 shows an internal circuit block of the area sensor 33. Pixel units 301 are regularly and two-dimensionally arranged in the pixel unit 300, which is a photoelectric conversion element group of the area sensor 33. The accumulation control unit 313
The integration operation of all the pixel units 301 is controlled according to a control signal from the controller 40. One output Vo of a specific pixel unit 301 is output from the output buffer 31 by the vertical shift register 308 and the horizontal shift register 309.
Input to 0. Output SDATA of output buffer 310
Is input to the ADC 44 inside the controller 40, converted into a digital value, and stored in the RAM 43.

Another output Vm of the pixel unit is formed by connecting a predetermined number of Vm to each other and connecting the switches MSL1 to MSL1 to MSL1.
The data is input to the output buffer 312 via the MSLn. The Vm signal line M in one area 311 on the area sensor has a level corresponding to the peak value Vp of the outputs Vmn of the plurality of pixel units 301. Therefore, the switch MS
When L1 to MSLn are sequentially turned on exclusively, the peak level Vp in each area 311 can be monitored by the output MDATA of the buffer 312. This MD
ATA is the same as SDATA,
The signal is input to the DC 44 and converted into a digital value.

FIG. 6 shows a circuit configuration inside the pixel unit 301. The pixel unit 301 includes a photodiode 302, a capacitor 303, an amplifier 304, switches 305 and 306, and an NMOS transistor 307, which are connected as shown. The photodiode 302 serving as a photoelectric conversion element generates a signal charge according to the amount of incident light, and the signal charge is accumulated in the capacitor 303 by the amplifier 304. The output of the amplifier 304 is connected to the switch 305 and the vertical shift register 30 controlled by the signal Xn of the horizontal shift register 309, respectively.
8 is connected to the output Vo via a series body with a switch 306 controlled by the signal Yn.

The output of the amplifier 304 is also input to a source follower circuit formed by an NMOS transistor 307, and the output of the source follower is connected to a monitor terminal Vm. It is assumed that the output level of the integrating circuit including the amplifier 304 and the capacitor 303 increases as the accumulation of the signal charge progresses. The monitor output Vm is
Since a predetermined plurality of pixel units are connected in common, as a result, they are governed by the maximum output level among them.

FIG. 7 shows areas 1 to n which are focus detection areas arranged in the photographing screen of the camera. The above-described monitor area selection switches MSL1 to MSLn are associated with the above-described areas 1 to n. By turning on the switch MSLm, the peak level Vpm in the area m can be monitored. If, for example, multiple monitor area selection switches are turned on at the same time,
You can monitor peak levels in multiple areas,
If all the monitor area selection switches are turned on collectively, the peak level in the entire area of the area sensor 33 can be monitored.

FIG. 8 is a timing chart showing the outline of the accumulation operation control of the area sensor 33, and exemplifies only the areas 5 to 7 in order to simplify the explanation.
The controller 40 outputs the integration start signal INTS to start the accumulation operation of the area sensor 33, and monitors the monitor level for each area. At this time, the area in which the level rises fastest is preferentially referred to. Then, when each monitor level reaches a predetermined appropriate accumulation level, the controller 40 outputs an integration end signal to end the accumulation operation for each area. In the illustrated example, the accumulation operation is completed in the order of the areas 6, 5, and 7.

At this time, as shown in FIGS. 9A and 9B, the accumulation of two areas 33a and 33b of the area sensor, for example, a5 and b5 corresponding to area 5, are simultaneously terminated. In addition, for one area m defined by am and bm, FIGS. 10A and 10B show a one-dimensional array of corresponding photodiodes. Photodiode row a forming one area sensor 33a
m is L (1), L (2), L (3),..., L (6
4), and the photodiode array bm forming the other area sensor 33b has R (1), R (2), R
(3),..., R (64), and the subject image signal can also be processed one-dimensionally.

When the accumulation control is completed, the controller 40
Outputs a read clock signal CLK. The accumulation control unit 313 of the area sensor 33 controls the horizontal shift register 309 and the vertical shift register 308 in accordance with the read clock signal CLK to sequentially output sensor data as a subject image signal from the signal output terminal SDATA.
This sensor data is stored in the ADC 44 inside the controller 40.
And converts the data into digital data.
2 Thus, the controller 40 can read out only the sensor data of the specific focus detection area.

FIG. 11 is a flowchart showing a main routine which is a schematic operation sequence of the controller 40 for controlling the camera. When the operation of the camera is started, first, as initialization of each part of the camera system, each mechanism is driven to an initial position to set a photographable state (S
1). Next, the luminance of the field is measured by the photometric unit 49, and the control condition at the time of exposure is calculated in consideration of the film sensitivity information (S
2), sensor data of area sensor 33 and EEPROM
The focus state of the taking lens 22 is detected based on the 45 correction data (S3), and it is determined whether the release button (not shown) is operated and the 1RSW is turned on (S4). 1RS
If it is determined that W is not turned on, the process returns to S2, and 1
Wait for RSW to turn on. If it is determined that the 1RSW is turned on, it is determined whether the photographing lens 22 is already in focus (S5). If not, the lens driving unit 46 drives the lens (S6).

Subsequently, it is determined whether or not the 2RSW is turned on (S7). If the 2RSW is turned on, the main mirror 23 and the sub mirror 25 are retracted (S9).
If the ON of 2RSW is not detected in S7, 1RSW
Is turned on again (S8). If 1RSW is on, the process returns to S7 to wait for 2RSW on, and if 1RSW is not on, returns to S2. Subsequent to the mirror retraction, the aperture driving unit 51 and the shutter driving unit 50 control the aperture mechanism and the focal plane shutter 34 to the set values set in S3 to perform exposure of the film 35 (S10). The mirror is returned to its original position (S11), and the focal plane shutter 34 is charged (S1).
2). Thereafter, the film 35 is moved by the film driving unit 52.
Is advanced by one frame (S13), and the process returns to S2.

FIG. 12 is a flowchart showing a distance measuring routine in which the operation of the distance measuring (S3) of the main routine shown in FIG. 11 is developed. When the distance measurement routine starts, FIG.
The integral control of the area sensor 33 is performed in the manner described with reference to (S20). Subsequently, it is determined whether or not the integration operation in all the focus detection areas has been completed, and the process returns to S20 to continue the control until the integration operation in all the areas has been completed (S21).

When the integration operation of all areas is completed, the sensor data of the area sensor 33 is AD-converted and stored in the RAM 43 (S22). Subsequently, illuminance correction is performed on the data stored in the RAM 43 (S23), and offset correction is further performed (S24). Details of these illuminance correction and offset correction will be described later. A known correlation operation is performed based on the corrected sensor data of all the focus detection regions, and a focus detection region where a main subject is likely to be present is selected from these correlation operation results, for example, by selecting closest data. (S25), the defocus amount of the photographing lens 22 in the selected focus detection area is calculated (S26).

Subsequently, the aberration of the photographing lens 22 is corrected by a known calculation (S27). Here, the aberration indicates a change amount in which the defocus amount changes according to the focal length of the photographing lens 22. It is determined whether the obtained defocus amount is within a predetermined value, and it is determined whether the photographing lens 22 is already focused on the subject. If the camera is in the in-focus state, this routine ends (S29). If out of focus, the amount of drive required to focus the taking lens 22 is calculated and converted into the number of pulses of the encoder 47 (S30),
This routine ends and returns to the main routine.

Here, the correction in S23 and S24 will be described in detail. In the present embodiment, for the sake of convenience, a plurality of focus detection areas distributed in the shooting screen are defined as areas near the center (for example,
Areas 7 to 9, 12 to 14, 17 to 19 in FIG. 7 and peripheral areas (areas 1 to 5, 6, 10, 11, 15, 15, 1 in FIG. 7).
6, 20 to 25). Then, illuminance correction and offset correction similar to those described in the related art are performed on the sensor data in the vicinity of the center, but such correction is not performed on the sensor data in the peripheral region. This is because, in general, the resolving power of the photographing lens 22 is lower at the peripheral portion than at the central portion, and thus, even if set in this way, the suitability of focusing on a photographic print does not matter much. Thus, in the present embodiment, the size of the sensor-related correction data can be significantly reduced.

FIG. 13 is a flowchart showing an illuminance correction routine in which the operation of the illuminance correction (S23) of the distance measurement routine shown in FIG. 12 is developed. When the illuminance correction routine is started, first, the area to be corrected is the peripheral area (for example,
Areas 1 to 5, 6, 10, 11, 15, 16, 2 in FIG.
0 to 25), and if it is in the vicinity, this routine is terminated without doing anything (S50). If it is not the peripheral area, the correction value H (i) described in the equation (1) is stored in the EEPROM.
45 to the RAM 43 (S51), and the initial value of the variable i is set as the head pixel number of the sensor data in the correction area (S52). After that, the sensor data D (i) is stored in the RAM 4
3 (S53), and the corrected sensor data D '(i) is obtained according to the equation (1) (S54). It is determined whether or not the variable i is the last pixel number of the focus detection area. If the variable i is the last pixel number, this routine ends and the process returns to the main routine (S55). If it is not the last pixel number, the variable i is increased by one and the process returns to S54, and the correction operation is repeated (S56).

FIG. 14 is a flowchart showing an offset correction routine in which the operation of offset correction (S24) of the distance measurement routine shown in FIG. 12 is developed. When the offset correction routine is started, first, the area to be corrected is the peripheral area (for example, areas 1 to 5, 6, 10, 1 in FIG. 7).
1, 15, 16 and 20 to 25), and if it is in the vicinity, the routine ends without doing anything (S60).
If it is not the peripheral area, the common offset correction value D3 and the correction value D4 (i) unique to each pixel described in Expression (2) are copied from the EEPROM 45 to the RAM 43 (S6).
1) The initial value of the variable i is set as the head pixel number of the sensor data in the correction area (S62). Then, the sensor data D
(I) is copied to the work area of the RAM 43 (S63),
The corrected sensor data D ″ (i) is obtained according to the equation (2) (S64). It is determined whether the variable i is the last pixel number of the focus detection area.
This routine ends and returns to the main routine (S6)
5). If it is not the last pixel number, the variable i is increased by one and the process returns to S64, and the correction operation is repeated (S66).

As described above, according to this embodiment, since the illuminance correction and the offset correction for the sensor data are omitted in the peripheral area, the size of the focus detection sensor related correction data can be reduced, and The non-volatile memory is not required, and the manufacturing cost of the camera and the man-hour for writing adjustment data in the production process can be reduced.

Next, a second embodiment of the present invention will be described. In the second embodiment, only the illuminance correction routine of the first embodiment shown in FIG. 13 is modified. In the first embodiment, the illuminance correction and the offset correction for the sensor data in the peripheral area are omitted, but in the second embodiment, one appropriate correction data is given to the sensor data in the peripheral area. Other than the illumination correction routine, the first
Since the configuration is the same as that of the embodiment, the duplicate description will be omitted, and the illuminance correction routine of the second embodiment will be described.

FIG. 15 is a flowchart showing an illuminance correction routine according to the second embodiment. When the illuminance correction routine is started, first, the area to be corrected is the peripheral area (for example, the areas 1 to 5, 6, 10, 11, 15, 1 and 1 in FIG. 7).
6, 20 to 25), and if it is in the vicinity, S7
Go to 7 (S70). If it is not the peripheral area, the correction value H (i) described in the equation (1) is stored in the RAM from the EEPROM 45.
43 (S71), and the initial value of the variable i is set as the head pixel number of the sensor data in the correction area (S72). Thereafter, the sensor data D (i) is copied to the work area of the RAM 43 (S73), and the corrected sensor data D '(i) is obtained according to the equation (1) (S74). It is determined whether or not the variable i is the last pixel number of the focus detection area. If the variable i is the last pixel number, this routine ends and the process returns to the main routine (S75). If it is not the last pixel number, the variable i
Is incremented by one, the process returns to S54, and the correction operation is repeated (S7
6). If it is determined in S70 that the area is the peripheral area, the illuminance correction value H (i) for the peripheral area is copied from the EEPROM 45 to the RAM 43, and the process proceeds to S72 (S77).

Here, the illuminance correction value H (i) for the peripheral portion in the present embodiment will be described in detail with reference to FIG. FIGS. 16A to 16C illustrate a memory space of the EEPROM 45 related to sensor correction. FIG.
(A) shows all the focus detection areas (areas 1 to 2 in FIG. 7).
This is the case where correction values are given to all the pixels in 5), which is the memory space required in the prior art. FIG. 16B shows the first
This is a memory space corresponding to the embodiment, and stores correction values only for the central region. FIG. 16C shows a memory space corresponding to the second embodiment, which has only one peripheral correction value in addition to the correction of the central area. This one peripheral correction value is the peripheral correction value H (i) of the second embodiment.
It is nothing less than.

Specifically, for example, one correction value for one central area is given as the peripheral correction value. In this case, sensitivity variation cannot be corrected, but in terms of illuminance correction, it is possible to correct for peripheral dimming. Alternatively, an average correction value for all pixels of the focus detection sensor may be obtained as a peripheral correction value, and one of the correction values may be given as a representative value.

Regarding the offset correction, one representative value may be given as a peripheral correction value in the same manner as in the illuminance correction, or may be omitted as in the first embodiment. According to the second embodiment, the illuminance correction for the sensor data is not omitted in the peripheral area and is simplified by a set of correction data, so that an increase in the size of the focus detection sensor-related correction data can be prevented. In addition, a large-capacity nonvolatile memory is not required, and the cost of manufacturing the camera and the number of steps for writing adjustment data in the production process can be reduced. In addition, since the correction is performed on the peripheral detection area although it is insufficient, it is possible to prevent the focus detection accuracy from deteriorating.

In the above-described embodiment, the TTL in which the multipoint automatic focus detection device of the present invention is applied to a single-lens reflex camera
Although the phase difference detection method is illustrated, an external light type phase difference detection method applied to a lens shutter camera or the like may be used. Furthermore, although an example in which an area sensor is used as a focus detection sensor is shown, a plurality of line sensors may be arranged in parallel. In the case of such a deformation, the point is to determine where the peripheral part and the central part are separated, but it may be appropriately set according to the specifications of the focus detection optical system and the focus detection sensor to be used.

The above-described embodiment of the present invention includes the following configuration. (1) In a multi-point automatic focus detection device having a plurality of focus detection areas, a focus detection sensor having a plurality of pixels for covering the plurality of focus detection areas, and at least approximately a center of the focus detection sensor with respect to a uniform luminance plane. Uniformizing means for performing an equalization correction on the output from the focus detection area of the unit, and performing a correction different from that of the center part on the output from the peripheral focus detection area, and a correction referred to by the uniformization means A multi-point automatic focus detection device comprising: a memory unit for storing data. (2) The uniformizing means is illuminance correction for correcting peripheral dimming of a focus detection optical system that guides light to the focus detection sensor and variation between pixels of the focus detection sensor. 2. The multi-point automatic focus detection device according to item 1. (3) The multi-point automatic focus detection apparatus according to (1), wherein the uniformization means is an offset correction for correcting an offset error between pixels of the focus detection sensor. (4) The equalizing means does not perform the equalization correction on the focus detection area in the peripheral portion. (1)
2. The multi-point automatic focus detection device according to item 1. (5) The multi-point automatic focus detection device according to (1), wherein the correction data stored in the memory means and used in the correction of the peripheral focus detection area is predetermined correction data. (6) The predetermined correction data is either correction data corresponding to the focus detection area near the center or average correction data of all the focus detection areas of the focus detection sensor. The multi-point automatic focus detection device according to (1).

[0057]

As described above, according to the present invention,
Non-uniformity correction due to the focus detection optical system and focus detection sensor is omitted or simplified in the peripheral detection area, so even if the number of focus detection areas is increased, the memory capacity required for sensor system non-uniformity correction increases. Thus, it is possible to provide a multipoint focus detection device in which the number of focus points is reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of a configuration according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of a single-lens reflex camera to which the multipoint automatic focus detection device according to the embodiment is applied;

3A is an explanatory view showing an optical path of a phase difference type focus detection optical system, FIG. 3B is a perspective view of FIG.

FIG. 4 is a block diagram showing an electrical configuration of the camera in FIG. 2;

FIG. 5 is a block diagram showing an internal configuration of an area sensor according to the embodiment;

6 is a block diagram showing a configuration of a unit pixel of the area sensor shown in FIG.

FIG. 7 is an explanatory diagram showing a relationship between a photographing screen of a camera and a focus detection area;

FIG. 8 is a timing chart showing an example of the integral control operation of the area sensor;

FIG. 9A shows one light receiving area of an area sensor;
(B) is an explanatory view showing the other light receiving area of the area sensor,

10A is a light receiving section of an area sensor constituting one focus detection area inside FIG. 9A, and FIG.
(B) Explanatory diagram showing a light receiving section of an area sensor constituting one internal focus detection area,

11 is a flowchart showing a main routine of a CPU 41 of the camera in FIG. 2;

12 is a flowchart showing a subroutine developed from a distance measurement routine of FIG. 11;

FIG. 13 is a flowchart showing a subroutine of the first embodiment in which the illuminance correction routine of FIG. 11 is developed;

FIG. 14 is a flowchart showing a subroutine developed from the offset correction routine of FIG. 11;

FIG. 15 is a flowchart showing a subroutine of a second embodiment in which the illuminance correction routine of FIG. 11 is developed;

16 is an example of a memory space required for correction data in an EEPROM 45 of the camera in FIG. 2;
(B) shows the prior art, and (c) shows the first embodiment.
Indicates a second embodiment.

17A illustrates an example of an illuminance distribution on an area sensor, FIG. 17B illustrates an example of sensitivity variation of the area sensor itself, and FIG. 17C illustrates a combination of (a) and (b). (D) is the sensor output after performing illuminance correction and sensitivity variation correction (e).
Is a graph for explaining the sensitivity variation of the area sensor,

FIG. 18 is a graph for explaining offset variation of an area sensor.

[Explanation of symbols]

 1 focus control unit, 2 focus detection unit, 3 focus calculation unit, 4 ranging point selection unit, 5 non-uniformity correction unit, 6 non-uniformity correction data storage unit.

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Claims (4)

[Claims] 1. A multi-point automatic focus detection device having a plurality of focus detection areas distributed in a central portion and a peripheral portion of a focus detection screen, comprising a plurality of pixels, and a pair formed by a focus detection optical system. A focus detection sensor that receives the optical image of the above, correction means for correcting variations in the output of the focus detection sensor when observing a uniform luminance surface, and memory means for storing correction data that the correction means refers to at the time of correction. The multi-point automatic focus detection device, wherein the correction means has different correction modes between a central portion and a peripheral portion of the focus detection screen. 2. The method according to claim 1, wherein the correction unit corrects a peripheral dimming on the light receiving surface of the focus detection sensor due to the focus detection optical system and a variation in sensitivity between pixels of the focus detection sensor itself. The multipoint automatic focus detection device according to claim 1. 3. The correction data used in the peripheral portion is one correction data corresponding to a focus detection area near the center of the focus detection screen, an average value of correction data of all the detection areas of the focus detection sensor, or zero. 3. The multi-point automatic focus detection device according to claim 1, wherein the correction data is any one of the following correction data. 4. The multi-point automatic focus detection device according to claim 1, wherein the correction unit omits correction for a peripheral portion of the focus detection screen.