JPH1020184A - Focus detection device and its calibration method - Google Patents

Abstract

(57) Abstract: The present invention relates to a focus detection device mounted on a camera or other optical equipment and a method of calibrating the focus detection device. The purpose is to remove. For a plurality of focus detection areas set on a shooting screen, focus detection means for detecting focus detection data, and fetching focus detection data from the focus detection means in response to an external operation input; An offset storage unit 2 that stores a difference between reference focus detection data and other focus detection data as an offset value, and a focus detected by the focus detection unit 1 using the offset value stored in the offset storage unit 2. And calibration means 3 for calibrating the detection data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device mounted on a camera or other optical equipment and a calibration method thereof, and more particularly, to a focus detection device which allows an operator to appropriately calibrate focus detection data. It relates to the calibration method.

[0002]

2. Description of the Related Art Conventionally, for a plurality of focus detection areas,
2. Description of the Related Art A focus detection device that detects a defocus amount and other focus detection data is known. In this type of focus detection device,
Due to the effects of various aberrations of the photographing optical system, focus detection data detected in individual focus detection areas are not uniform,
Some detection variations occur.

[0003] Therefore, in some photographing optical systems, a storage section for lens information is provided inside the lens barrel, and correction data unique to each type of the photographing optical system is stored in this storage section. The focus detection device reads the correction data from the photographing optical system and calibrates the focus detection data. Therefore, in the conventional focus detection device, it was possible to appropriately remove the detection variation generated for each type of the imaging optical system.

[0004]

Incidentally, the correction data stored in the lens information of the photographing optical system is often determined based on the calculation of the optical path, the measurement of the sample, and the like.
Therefore, the value of the correction data is based on the assumption that the imaging optical system is manufactured as designed. Therefore, if the lens group constituting the imaging optical system is decentered or tilted,
The focus detection data cannot be completely calibrated. As a result, detection variations remain between the plurality of focus detection areas.

[0005] The detection variation caused by the individual difference of the photographing optical system varies in a complicated and various manner depending on which constituent lens is displaced and how. For this reason, there is a problem that this type of detection variation cannot be strictly removed from the focus detection data. Further, when the mounting position of the lens group constituting the photographing optical system changes over time, there is a problem that the detection variation caused by the individual difference of the photographing optical system further increases.

If the variation in detection due to such individual differences becomes larger than a certain level, the focusing accuracy is reduced and the best image plane cannot be obtained. Therefore, strict calibration for such detection variations has been strongly desired. In view of the above, it is an object of the present invention to provide a focus detection device capable of easily removing, from focus detection data, detection variations caused by individual differences in an imaging optical system.

According to a second aspect of the present invention, in addition to the object of the first aspect, there is provided a focus detection apparatus capable of accurately removing detection variations due to individual differences in the photographing optical system from focus detection data. The purpose is to provide. A third object of the present invention is to provide a focus detecting device suitable for a case where a plurality of photographing optical systems are exchanged and used, in addition to the object of the first aspect.

According to a fourth aspect of the present invention, in addition to the object of the first aspect, the focus detection is suitable when the operator intentionally corrects the focus detection data to perform a unique focus adjustment. It is intended to provide a device. A fifth object of the present invention is to provide a calibration method for simply and accurately calibrating the focus detecting device according to the first aspect.

[0009]

FIG. 1 is a block diagram showing the principle corresponding to the first to third aspects of the present invention. Claim 1
The focus detection means 1 detects focus detection data for a plurality of focus detection areas set on a shooting screen, and the focus detection data from the focus detection means 1 according to an external operation input. Offset storage means 2 for storing, as an offset value, a difference between the focus detection data to be taken in and reference and other focus detection data, and the focus detection means 1 detects the difference by using the offset value stored in the offset storage means 2. Calibration means 3 for calibrating the focus detection data.

According to a second aspect of the present invention, in the focus detecting apparatus according to the first aspect, the offset storage means 2 uses the focus detection data in a focus detection area at the center of the photographing screen as a reference. According to a third aspect of the present invention, in the focus detection device according to the first aspect, the offset storage unit 2 stores the offset value in association with the ID data of the imaging optical system at the time of storage, and
Is characterized by selecting the offset value corresponding to the ID data of the photographing optical system at the time of calibration, and calibrating the focus detection data detected by the focus detection unit 1.

FIG. 2 is a block diagram showing the principle corresponding to the fourth aspect of the present invention. According to a fourth aspect of the present invention, there is provided the focus detection device according to the first aspect, further comprising an initialization unit configured to initialize an offset value stored in the offset storage unit 2 in response to an initialization input from outside. Configure. FIG. 3 is a flowchart corresponding to the invention described in claim 5.

According to a fifth aspect of the present invention, there is provided a calibration method for calibrating the focus detection device according to the first aspect,
A step of directing the photographing optical system to a “plane perpendicular to the photographing optical axis” or “a photographing target used as a reference when intentionally correcting focus detection data” (S1, S3 in FIG. 3); (S2, S4 in FIG. 3).

(Operation) In the focus detecting apparatus according to the first aspect, the offset storage means 2 fetches focus detecting data at a plurality of locations in response to an external operation input. The offset storage means 2 stores, among these focus detection data,
The difference (offset value) between the reference focus detection data and the other focus detection data is calculated.

The offset value calculated in this way is an actually measured value indicating the variation in the detection of the focus detection data, and directly reflects the individual difference of the photographing optical system actually used. The calibrating unit 3 uses these offset values to calibrate the focus detection data, thereby removing detection variations caused by individual differences in the imaging optical system. In the focus detection apparatus according to the second aspect, focus detection data at the center of the photographing screen is used as reference focus detection data.

Normally, off-axis focus detection data sharply reflects the effects of off-axis aberrations (such as image surface distortion) of the photographing optical system, and therefore, large variations occur in detection due to individual differences in the photographing optical system. Cheap. For the same reason, the detection variation is likely to greatly change over time outside the optical axis. On the other hand, the focus detection data in the vicinity of the optical axis is not affected by off-axis aberrations and the like, so that detection variations due to individual differences in the imaging optical system are small. Further, for the same reason, the variation of the detection variation with time is small near the optical axis.

Accordingly, when the focus detection data at the center of the photographing screen (near the optical axis) is used as a reference as in the present invention, the reference itself does not change much, and the offset value is a relatively stable value. Therefore, it is possible to accurately calibrate the focus detection data for a long period from the time when the offset value is stored.

In the focus detecting device according to the third aspect, the offset storing means 2 stores the I / O of the photographing optical system when storing.
The offset value is stored in association with the D data. The calibration unit 3 calibrates the focus detection data using the offset value corresponding to the ID data of the imaging optical system at the time of calibration. Therefore, according to the ID data of the photographing optical system,
The focus detection data can be properly calibrated.

In the focus detecting device according to a fourth aspect, the initialization means initializes the offset value stored in the offset storage means 2 in response to an external initialization input.
Therefore, the operator can immediately erase the offset value after temporarily executing the calibration of the unique focus detection data. In the calibration method according to the fifth aspect, first, the photographing optical system is directed to the “plane perpendicular to the photographing optical axis” or “the photographing target used as a reference when intentionally correcting the focus detection data”.

Next, by giving an operation input to the offset storage means 2, the detected variation at this point is stored as an offset value. Here, when the photographing optical system is directed to a “plane perpendicular to the photographing optical axis”, normal calibration based on the plane is performed. On the other hand, when the photographing optical system is directed to “the photographing target used as a reference when intentionally correcting the focus detection data”, the operator can perform his own calibration.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a diagram showing an embodiment corresponding to claims 1 to 5. In FIG. 4, a lens barrel 12 is attached to the front of a camera body 11, and a lens barrel 1 is provided.
An imaging optical system 13 is disposed inside the camera 2.

A mirror 14 is provided on the optical axis of the photographing optical system 13.
And the sub-mirror 15 are arranged in order.
The focus detection unit 16 is arranged in the reflection direction of. The photoelectric output of the focus detector 16 is connected to a microprocessor 18 via an A / D converter 17. The PWM (pulse width modulation) output of the microprocessor 18 is connected to a motor 19 via a drive circuit, and the driving force of the motor 19 is transmitted to a lens driving mechanism 20 in the lens barrel 12.
The lens drive mechanism 20 extends the focus adjusting lens group of the photographing optical system 13 forward and backward.

An encoder 21 for detecting the number of revolutions is provided on the drive shaft of the motor 19, and the pulse output of the encoder 21 is connected to the microprocessor 18. The microprocessor 18 includes a release button 22 and a setting button 2
3, the release button 24 and the storage unit 25 are connected respectively. The setting button 23 is an operation member operated when capturing an offset value used for calibrating the defocus amount.

The release button 24 is an operation member operated when initializing these offset values. The communication terminal of the microprocessor 18 is connected to a lens data storage unit 26 via a lens mount unit. FIG.
3 is an exploded perspective view showing an internal configuration of the focus detection unit 16. FIG.

In FIG. 5, a lens holder 51 is provided on the upper surface of the focus detecting section 16.
1 is fitted with a condenser lens 52. A light-shielding plate 53 is arranged on the upper surface of the condenser lens 52, and field masks 53a to 53e are perforated on the light-shielding plate 53 in accordance with the arrangement of the focus detection areas. An infrared cut filter 54 that blocks infrared light is disposed on the upper surface of the light shielding plate 53.

A mirror 55 is obliquely disposed immediately below the condenser lens 52, and the diaphragm plate 57, the lens plate 58 and the image sensor 5 are arranged along the reflection axis of the mirror 55.
9 are arranged in order. The photoelectric output of the image sensor 59 is transmitted to the microprocessor 18 via the A / D converter 17.
Connected to. Further, aperture masks 57a to 57e each having a pair of openings are formed in the aperture plate 57 in accordance with the arrangement of the focus detection area.
In FIG. 8, separator lenses 58a to 58e composed of a pair of imaging lenses are integrally formed in accordance with the arrangement of the focus detection area.

On the light receiving surface of the image sensor 59,
Light receiving portions 59a to 59e each including a pair of light receiving element rows are formed in accordance with the arrangement of the focus detection areas. As for the correspondence between the first to third aspects of the present invention and the present embodiment, the focus detection unit 1 corresponds to the focus detection unit 16 and the “focus calculation function of the microprocessor 18”, and the offset storage unit 2 The calibration section 3 corresponds to the storage section 25 and the “offset calculation function of the microprocessor 18”, and the calibration section 3 corresponds to the “calibration function of the microprocessor 18”.

Regarding the correspondence between the invention described in claim 4 and the present embodiment, in addition to the above-described correspondence, the initialization means corresponds to “the function of initializing the offset value by the microprocessor 18”. FIG. 6 is a flowchart illustrating the operation of the present embodiment. Hereinafter, the operation of the present embodiment will be described with reference to these drawings.

First, the transmitted light of the photographing optical system 13 passes through the transmitting portion of the mirror 14, is reflected by the sub-mirror 15, and forms an image near the light shielding plate 53 in the focus detecting unit 16. The light shielding plate 53 shields light other than the focus detection area via the field masks 53a to 53e. The light beam that has passed through the light shielding plate 53 in this manner is condensed by the condenser lens 52 and the mirror 5.
Through 5, it reaches the diaphragm plate 57.

In the aperture plate 57, the light beam is individually pupil-divided via the aperture masks 57a to 57e. These split light beams are individually tilted and imaged via the separator lenses 58a to 58e to form a plurality of pairs of light images on the light receiving surface of the image sensor 59. In this state, when the setting button 23 is pressed (S1 in FIG. 6), the microprocessor 18 first performs data communication with the lens data storage unit 26,
The ID data of the photographing optical system 13 is acquired (S2 in FIG. 6).

Next, the microprocessor 18 sequentially takes in the photoelectric output from the image sensor 59. The microprocessor 18 performs a well-known correlation operation on the photoelectric output to obtain defocus amounts Da to D for each focus detection area.
e is calculated (S3 in FIG. 6). Here, the microprocessor 18 calculates offset values M1 to M4 between the central defocus amount Dc and other defocus amounts as follows (S4 in FIG. 6).

M1 = Da−Dc (1) M2 = Db−Dc (2) M3 = Dd−Dc (3) M4 = De−Dc (4) Microprocessor 18 Are the offset values M1 to M
4 is associated with the ID data of the photographing optical system 13 and the storage unit 2
5 (S4 in FIG. 6).

By the above operation, the offset values M1 to M
4 is completed. In this case, when the operator operates the setting button 23 in a state where the imaging optical system 13 faces the “plane perpendicular to the imaging optical axis”, the offset values M1 to M4 based on the plane are stored. . On the other hand, the release button 22
Is pressed halfway (S6 in FIG. 6), the microprocessor 1
8 first performs data communication with the lens data storage unit 26 to acquire ID data of the photographing optical system 13 (FIG. 6).
S7).

Here, the microprocessor 18 reads out the offset value corresponding to the ID data from the storage unit 25 (S8 in FIG. 6). Next, the microprocessor 18
Captures the photoelectric output from the image sensor 59 sequentially.
The microprocessor 18 performs a known correlation operation on the photoelectric output, and calculates defocus amounts Da to De for each focus detection area (S9 in FIG. 6).

Here, the microprocessor 18 subtracts the offset values M1 to M4 from the defocus amounts Da to De, respectively, to obtain Da '= Da-M1 (5) Db' = Db-M2. .. (6) Dc ′ = Dc (7) Dd ′ = Dd−M3 (8) De ′ = De−M4 (9) and the defocus amount Da after calibration 'To De' (S10 in FIG. 6).

The microprocessor 18 executes a known focus control based on the defocus amounts Da 'to De' after the calibration (S11 in FIG. 6). With the above operation, the calibration of the defocus amount is executed. Further, the release button 24
Is pressed (S12 in FIG. 6), the microprocessor 18
Initializes the offset value stored in the storage unit 25 (S13 in FIG. 6).

With the operation described above, the focus detection data of the present embodiment is calibrated based on the offset value reflecting the individual difference of the photographing optical system 13. Therefore, it is possible to accurately calibrate a detection variation caused by an individual difference of the imaging optical system 13. In addition, by updating the storage of the offset value in a timely manner, it is possible to reliably remove the secular change of the detection variation.

Further, since the offset value is calculated based on the focus detection data at the center of the photographing screen, a relatively stable offset value can be obtained. Therefore, the focus detection data can be accurately calibrated over a long period of time from the time when the offset value is stored.

Since the offset value is selected according to the ID data of the photographing optical system 13, data calibration suitable for the photographing optical system 13 can be performed. In the above-described embodiment, the offset value is stored in a state where the imaging optical system 13 is directed to the “plane perpendicular to the imaging optical axis”. However, the present invention is not limited to such a calibration method. is not.
For example, the offset value may be stored in a state where the imaging optical system 13 is directed to “an imaging target that is used as a reference when intentionally correcting focus detection data”. In such a calibration method, the operator can independently calibrate the focus detection data based on a photographing intention or the like.

[0039]

As described above, according to the first aspect of the invention, the focus detection data is calibrated by using the offset value directly reflecting the individual difference of the photographing optical system. Therefore, it is possible to reliably and easily remove the detection variation caused by the individual difference of the imaging optical system from the focus detection data.

Further, by updating the storage of the offset value as needed, it is possible to reliably and easily remove the secular change of the detection variation. In the invention according to claim 2,
The offset value is calculated based on the focus detection data at the center of the shooting screen. Since the focus detection data at the center of the photographing screen (near the optical axis) is not affected by off-axis aberration, it has an accurate and stable value over a long period of time. According to the second aspect of the present invention, since such an accurate and stable value is used as a reference, a relatively stable offset value can be obtained.

Therefore, the focus detection data can be accurately calibrated over a long period of time from the time when the offset value is stored. According to the third aspect of the present invention, the ID of the photographing optical system is
An offset value is selected according to the data and used for calibrating the focus detection data.

Therefore, when a plurality of photographing optical systems are exchanged, data calibration suitable for the photographing optical system being mounted can be performed. According to the fourth aspect of the present invention, since the initialization means is provided, even when the operator temporarily executes the calibration of the unique focus detection data, the offset value can be quickly erased.

In the calibration method according to the fifth aspect, the photographing optical system is directed to the “plane perpendicular to the photographing optical axis” or “the photographing target used as a reference when intentionally correcting the focus detection data”. In this state, the offset value is stored. Therefore, when the photographing optical system is directed to a “plane perpendicular to the photographing optical axis”, normal calibration based on the plane can be performed.

On the other hand, when the photographing optical system is directed to "the photographing target which is used as a reference when intentionally correcting the focus detection data", the operator can perform his own calibration. As described above, in the camera system to which the present invention is applied, the operator can easily and appropriately calibrate the focus detection data.

[Brief description of the drawings]

FIG. 1 is a principle block diagram corresponding to the first to third aspects of the present invention.

FIG. 2 is a principle block diagram corresponding to the invention described in claim 4;

FIG. 3 is a flowchart corresponding to the invention described in claim 5;

FIG. 4 is a diagram showing an embodiment corresponding to claims 1 to 5;

FIG. 5 is an exploded perspective view showing the internal configuration of the focus detection unit 16.

FIG. 6 is a flowchart illustrating the operation of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Focus detection means 2 Offset storage means 3 Calibration means 11 Camera body 12 Lens barrel 13 Imaging optical system 14 Mirror 15 Submirror 16 Focus detection unit 17 A / D conversion unit 18 Microprocessor 19 Motor 20 Lens drive mechanism 21 Encoder 22 Release button 23 Setting button 24 Release button 25 Storage unit 26 Lens data storage unit 51 Lens holder unit 52 Condenser lens 53 Light shielding plate 53a-e Field mask 54 Infrared cut filter 55 Mirror 57 Aperture plate 57a-e Aperture mask 58 Lens plate 58a-e Separator Lens 59 Image sensor 59a-e Light receiving unit

Claims (5)

[Claims] 1. A focus detection means for detecting focus detection data for a plurality of focus detection areas set on a shooting screen, and fetching focus detection data from the focus detection means in response to an external operation input; Offset storage means for storing a difference between reference focus detection data and other focus detection data as an offset value; and focus detection detected by the focus detection means using the offset value stored in the offset storage means. A focus detection device, comprising: calibration means for calibrating data. 2. The focus detection device according to claim 1, wherein said offset storage means uses focus detection data in a focus detection area at a center of a photographing screen as a reference. 3. The focus detection device according to claim 1, wherein the offset storage means is associated with ID data of a photographing optical system at the time of storage.
Storing the offset value, wherein the calibration means selects the offset value corresponding to the ID data of the imaging optical system at the time of calibration, and calibrates the focus detection data detected by the focus detection means. Focus detection device. 4. The focus detection device according to claim 1, further comprising an initialization unit for initializing an offset value stored in said offset storage unit in response to an external initialization input. Focus detection device. 5. A calibration method for calibrating a focus detection device according to claim 1, wherein a “plane perpendicular to the photographing optical axis” or “when the focus detection data is intentionally corrected”. A calibration method comprising: directing a photographing optical system to a “photographing object to be a reference”, and providing the operation input to the offset storage means.