JP2003107339A - Device and method for automatically detecting focus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a focus with high accuracy by changing intervals between two diaphragm apertures belonging to a diaphragm mask and the areas of the two apertures corresponding to the change of an open F value of a photographing lens in an AF mechanism of a phase form. SOLUTION: In the method for automatically detecting the focus, by which luminous flux from the photographing lens is divided into two, one luminous flux and another luminous flux are introduced to a photoelectric transducer through a first aperture and a second aperture respectively, and the phase difference between two images is detected to perform a focusing, as the open F value of the photographing lens becomes large (namely, as the lens gets dark), the interval between the two apertures is made smaller and the area of each of the apertures is made smaller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus detection (autofocus) device and an automatic focus detection method that employ a phase difference detection method.

[0002]

2. Description of the Related Art A phase difference detection method has been conventionally known as one of methods for realizing autofocus in a camera.

As shown in the outline of FIG. 9, the phase difference detection method divides the light beam from the photographing lens into two light beams (light beams A and B in FIG. 9), and photoelectric conversion elements (line sensor, etc.). An image is formed on each of the two light receiving portions 3a and 3b of 3) and the phase difference between the images is detected, so that the amount of focus deviation and the direction of deviation can be known. Then, by controlling the movement of the photographing lens group so as to correct this shift, it is possible to focus automatically.

Now, let us consider a case where the open F value of the taking lens changes in a camera having a zoom function, a single-lens reflex camera in which the lens can be exchanged, or the like. in this case,
A diaphragm mask 1 that guides two light beams to each photoelectric conversion element is arranged in accordance with the maximum open F value. That is,
Even in the case of a bright photographic lens having a small open F value, the light flux entering the photographic lens at a position away from the photographic optical axis cannot be effectively used.

The reason why it is preferable to perform the focus detection by using the light flux entering the photographing lens at a position as far from the photographing optical axis as possible is as follows. That is, the amount of movement of the light beam along the surface of the line sensor with respect to a constant focus shift is larger as the light beam is farther from the photographing optical axis. That is,
This is because the sensitivity to the focal shift increases as the luminous flux moves away from the photographing optical axis.

As a means for avoiding the above-mentioned inconvenience, the applicant of the present application has already used the luminous flux entering the taking lens at the position farthest from the taking optical axis in correspondence with the change of the open F value of the taking lens. We have developed a technology to detect phase differences and have completed patent applications (application number: Japanese Patent Application No. 8-223554, publication number: Japanese Patent Application Laid-Open No. 10-62681).

The technique disclosed in the above patent application is 2
The distance between the two diaphragm openings for projecting a light beam to each photoelectric conversion element is changed according to the open F value of the taking lens. That is, the interval between the two aperture openings is widened for a bright photographic lens with a small open F value, and conversely, the interval between the two aperture openings is narrowed for a dark photographic lens with a large open F value. In this way
The outermost light flux at each open F value (the light flux entering the photographic lens at the farthest position from the photographic optical axis) is effectively used to improve focus detection accuracy.

However, in the above application, the aperture area itself of the diaphragm does not change even if the open F value changes. That is, even if the open F value changes, the light amount itself guided to the photoelectric conversion element does not change. However, considering that a brighter lens has a shallow depth of field, and therefore high focus detection accuracy is required, accurate focus detection should be secured at a large open F value even at low brightness. However, no special consideration has been given to this point.

[0009]

[Means, Actions and Effects for Solving the Problems]
The present invention was made in view of the above conventional circumstances, and changes the interval and area of two aperture openings that guide light to the photoelectric conversion element of the focus detection module according to the change of the open F value of the taking lens, The focus detection is performed with higher accuracy.

That is, according to the present invention, the luminous flux from the photographing lens is divided into two, and one luminous flux is guided to the photoelectric conversion element through the first diaphragm opening and the other luminous flux is guided to the photoelectric conversion element through the second diaphragm opening. In automatic focus detection for detecting the phase difference between images and focusing, it is necessary to reduce the distance between the two aperture openings and reduce the area of each aperture opening as the open F value of the taking lens increases. It has a feature.

In the present invention, the smaller the open F value (that is, the brighter the photographic lens), the larger the distance between the aperture openings. Therefore, at each open F value, the outermost luminous flux (that is, the photographic image) is maximized. By using the luminous flux located at the maximum distance from the optical axis, it is possible to perform focus detection with high accuracy.

Further, the smaller the open F value, the larger the area between the aperture openings. Therefore, for a bright lens with a shallow depth of field, even if the diaphragm aperture is large and the brightness is low, a lot of light can be taken in and highly accurate focus detection can be realized.

Further, the present invention is characterized in that the aperture areas of the two diaphragm apertures are reduced when the contrast of the subject is insufficient for automatic focus detection. In general, the smaller the aperture area of the aperture, the clearer the image on the sensor and the higher the contrast. Therefore, by performing such control, highly accurate focus detection can be performed.

Further, when the contrast of the subject is insufficient for automatic focus detection, it is preferable to reduce the aperture area of the two aperture openings and reduce the distance between the two aperture openings. This is because the defocus amount (focus shift amount) that can be detected is increased by narrowing the distance between the aperture openings, so that focus detection can be performed even in a greatly blurred state.

[0015]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a sectional view of an essential part of a single-lens reflex camera according to an embodiment of the present invention. The light flux A that has passed through the lens barrel 11 attached to the front side of the camera body 10 passes through the half mirror 12 and the sub mirror.
It is reflected by 13 and reaches the AF module 20.

The light flux entering the AF module 20 passes through a condenser lens 21, a reflection mirror 22, a diaphragm mask 23, and a re-imaging lens 24 in this order, and is imaged on a CCD 25. At this time, as described with reference to FIG. 9, in order to perform focus detection by the phase difference method, the light flux is divided into two before entering the diaphragm mask 23.

One Example of Aperture Mask (FIG. 2) FIG. 2 is a schematic view for explaining an example of the aperture mask 23 in the AF module 20 shown in FIG. The diaphragm mask includes a fixed mask plate 230 and two movable mask pieces 232a and 232b. The fixed mask plate 230 is a single plate member and has two oval fixed openings 231a and 231b formed at regular intervals. Two movable mask pieces 232a, b
Is held so as to be slidable in the vicinity of the fixed mask plate 230 in the direction perpendicular to the photographing optical axis (that is, parallel to the surface of the fixed mask plate 230). The movable mask pieces 232a and 232b have oval openings 233a and 233a, respectively.
b is formed.

In the diaphragm mask constructed as described above, the fixed mask plate side fixed openings 231a and 231b and the movable mask half-side openings 233a and 233b are formed by overlapping. Two diaphragm apertures are constructed.
Then, with respect to the fixed mask plate 230, the movable mask piece 232
The relative movement of a and b changes the overlap amount (that is, the opening area of each aperture opening). Further, at the same time as the aperture area of the aperture openings changes, the distance between both aperture openings (that is, the distance between the centers of gravity of both aperture openings) also changes.

2 (B-1) to 2 (B-3) show the fixed mask plate 230 and the movable mask pieces 232a, 232b as viewed from the front side, and FIG. 2 (A-1). 2 (A-3) is a perspective view for easy understanding of the relationship between the two. Further, in each of FIGS. 2B-1 to 2B-3, the aperture opening formed by the overlap is shown by hatching, and the fixed mask plate 230 and the movable mask piece 232a are shown. , B are also shown as viewed from the lateral direction to explain the overlapping state of the openings.

FIGS. 2A-1 and 2B-1 show a state where the two movable mask pieces 232a, 232b are closest to each other.
In this state, the two aperture openings are closest to each other and have the smallest area.

FIGS. 2A-2 and 2B-2 show a state in which the two movable mask pieces 232a and 232b are slightly apart from each other. Compared with the case of FIGS. 2A-1 and 2B-1, the apertures of both diaphragms are slightly separated from each other and their areas are slightly larger.

2A-3 and 2B-3 show a state in which the two movable mask pieces 232a and 232b are the farthest apart. The distance between both diaphragm openings (that is, the distance between the centers of gravity of both diaphragm openings) is the largest, and the area is also the largest.

Second Example of Aperture Mask (FIGS. 3 and 4) FIG. 3 shows a second example of the aperture mask. This diaphragm mask includes a fixed mask plate 330 and two movable mask pieces 332.
It is composed of a and b. The fixed mask plate 330 is a single plate member and has two fixed openings 331a and 331b formed at regular intervals. The fixed openings a and b are
It has an irregular shape in which the top and bottom widths increase with increasing distance from each other. Two movable mask pieces 332a, 332b
Are held slidably in the vicinity of the fixed mask plate 330 in the direction perpendicular to the photographing optical axis (that is, parallel to the surface of the fixed mask plate 330). The movable mask pieces 232a and 232b have arcuate notches 333a and 333b, respectively.
Are formed.

In the diaphragm mask constructed as described above, the fixed opening portions 331a and 331b on the fixed mask plate side form two diaphragm openings. Then, the movable mask pieces 332a and 332b move relative to the fixed mask plate 330, so that the movable mask pieces partially mask the aperture openings, whereby the aperture area of each aperture opening changes. At the same time as the aperture area of the aperture openings changes, the distance between the aperture openings (that is, the distance between the centers of gravity of the aperture openings) also changes.

FIGS. 4A to 4C show a fixed mask plate 330.
FIG. 6 is a perspective view showing a relative relationship between movable mask pieces 332a and 332b. In each figure, the diaphragm aperture is shown with diagonal lines.

FIG. 4A shows two movable mask pieces 332a,
b shows the closest state. In this state, 2
The two apertures are closest to each other and have the smallest area.

FIG. 4B shows two movable mask pieces 332a,
It shows a state in which b is slightly apart. Compared with the case of FIG. 4 (A), both aperture openings are slightly separated and the area is slightly larger.

FIG. 4C shows two movable mask pieces 332a,
b shows the farthest state. The distance between both diaphragm openings is the largest, and the area is also the largest.

Third Example of Aperture Mask (FIGS. 5 and 6) FIG. 5 shows a third example of the aperture mask. This diaphragm mask includes a fixed mask plate 430, two liquid crystal mask plates 440,
It is constructed by stacking 450. Fixed mask plate 430
Is a single plate member and includes two fixed openings 431a,
b are formed at regular intervals. The interval and area of these two fixed openings are changed by turning on / off the power to the liquid crystal mask plates 440 and 450.

The liquid crystal mask plate 440 has two light transmitting portions 441a and 441b in the ON state of energization, and the other portions have a light shielding property. Further, in the power-off state, the entire liquid crystal mask plate 440 becomes transparent. However, in the power-off state, it is sufficient if at least the portions of the fixed mask plate 430 that overlap the fixed openings 431a and 431 are translucent.

The two light-transmitting portions 441a and 441 appearing on the liquid crystal mask plate 440 when the power is turned on have a narrower interval (center interval) than in the case of the fixed openings 431a and 431 formed in the fixed mask plate 430. And the area is small.

Similarly to the case of the liquid crystal mask plate 440, the liquid crystal mask plate 450 is switched between the light-transmitting property and the light-shielding property by turning on / off the power. However, the interval and area of the two light transmitting portions 451a and 451b are both set to be smaller than those in the case of the liquid crystal mask plate 440.

In the diaphragm mask constructed as described above, the interval and the area of the two diaphragm openings can be controlled by selecting the combination of ON / OFF of energization of the liquid crystal mask plates 440 and 450.

FIG. 6 illustrates this, and FIG.
FIG. 6A is a central cross-sectional view of the stacked plates, and FIG.
(B) is a front view. In FIG. 6 (A), both liquid crystal mask plates 440 and 450 are in a power-on state.

When both of the liquid crystal mask plates 440 and 450 are in the power-off state, both diaphragm openings are represented by α in FIG. 6B, and their intervals and areas are maximized. LCD mask plate
When the liquid crystal mask plate 440 is in the power-on state and the liquid crystal mask plate 440 is in the power-off state, both diaphragm openings are represented by β in FIG. 6 (B), and their intervals and areas have intermediate values. At least when the liquid crystal mask plate 450 is in the power-on state, both diaphragm openings are represented by γ in FIG. 6B, and the distance and the area between them are minimized.

Although the two liquid crystal mask plates are used in the examples shown in FIGS. 5 and 6, the distance between the centers of the two light-transmitting portions and the area of the two light-transmitting portions when the power is on are different from each other.
It is also possible to use more than one liquid crystal mask, and by increasing the number of liquid crystal masks, it becomes possible to adjust the aperture in multiple stages.

Description of Flowchart Next, an example of autofocus control in a camera equipped with the automatic focus detection device of the present invention will be described with reference to a block diagram and a flow chart.

FIG. 7 is a block diagram for explaining the autofocus control according to the present invention. Each of the interchangeable lenses 1 to 3 selectively attached to the camera body stores the data (including the open F value) peculiar to the lens in a memory (ROM) arranged therein. . on the other hand,
In the memory inside the camera body, "open F-number of shooting lens"
And “appropriate aperture spacing and area for each open F value” are stored in advance. Note that the specific storage content differs depending on the aperture mask actually used in the AF device.

In the flow chart of FIG. 8, an example of using the liquid crystal type aperture mask described in FIGS. 5 and 6 will be described.

When the AF control is started, first, the opening F of the relevant interchangeable lens is released from the memory inside the interchangeable lens.
Read the value (# 10) and open F stored in the camera body.
The appropriate mask spacing is determined by checking the appropriate aperture opening spacing with respect to the value (when the mask spacing is determined, the aperture area is also determined). Corresponding to the determined mask interval,
The on / off of the liquid crystal is controlled (# 11).

When the open F value is equal to or less than A (the brightest case), the liquid crystal mask plates 440 and 450 are both turned off, and the distance between the two aperture openings and the aperture area are both maximum (FIG. 6 ( Α) in B). When the open F value is greater than A and less than or equal to B (in the case of intermediate brightness), the liquid crystal mask plate 440 is in the energized on state and the liquid crystal mask plate 450 is in the energized off state. Both areas have intermediate values (β in FIG. 6B). When the open F value is larger than B (when it is the darkest), the liquid crystal mask plate 44
Both 0 and 450 are turned on, and the distance between the two aperture openings and the aperture area are both minimized (γ in FIG. 6B).

When the interchangeable lens is a zoom lens and the open F value changes according to zooming,
The liquid crystal is also controlled to be turned on and off in response to the change in the open F value (# 12).

When the aperture opening interval according to the open F value is determined, the actual autofocus control is executed (# 13 →
# 14 → # 15).

At # 16, it is determined whether the contrast of the subject is sufficient for detecting the phase difference. If there is sufficient contrast, it is determined whether the defocus amount absolute value obtained by the AF calculation is less than or equal to a predetermined value and it can be determined that the subject is in focus.
(# 17) If the focus can be determined, a series of AF control is ended (# 18). If the absolute value of the defocus amount is larger than the predetermined value and it cannot be determined that the lens is in focus, the lens is actually driven for focusing (# 19), and focus detection is continued after the driving is completed. Return to 12 and continue the series of AF control.

If it is determined in # 16 that the contrast is insufficient, lens scanning processing is performed (# 20).
Although this process itself is a known technique, it will be briefly described as follows. For example, consider a case where a distant subject is to be photographed immediately after a subject in the vicinity is photographed.
At that point in time when the camera is pointed at a distant subject, the focus is greatly deviated, so the contrast of the subject is too low, and therefore the phase difference cannot be detected.
(That is, I cannot focus). In this case,
The lens is moved in a predetermined pattern, and the phase difference is detected at the time when the contrast is detected to the extent that the phase difference can be detected. This is called a lens scan process, which is a generally known technique.

When a sufficient contrast is detected by the lens scanning process, the process proceeds to # 19 to perform the above-described lens driving process (# 21 → # 19). If sufficient contrast cannot be obtained even by the lens scan process, the interval between the aperture openings is narrowed to reduce the aperture area and then the lens scan process is performed (# 21 → # 22 →
# 20).

When sufficient contrast cannot be obtained even by the lens scanning process, the reason why the distance between the aperture openings is made smaller and the aperture area is made smaller is generally that the smaller the aperture area, the smaller the image on the sensor. Is clear and the contrast can be improved. Further, by narrowing the aperture interval, the range of defocus amount (focus shift amount) that can be detected becomes large, and focus detection can be performed with a smaller lens scanning operation.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of a camera according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a first example of a diaphragm mask adopted in the camera of FIG.

FIG. 3 is an explanatory diagram showing a second example of a diaphragm mask employed in the camera of FIG.

FIG. 4 is an explanatory diagram showing a second example of a diaphragm mask employed in the camera of FIG.

5 is an explanatory diagram showing a third example of a diaphragm mask employed in the camera of FIG.

6 is an explanatory diagram showing a third example of a diaphragm mask employed in the camera of FIG.

FIG. 7 is a functional block diagram for executing AF control according to the present invention.

FIG. 8 is a flowchart illustrating AF control according to the present invention.

FIG. 9 is a schematic diagram illustrating an out-of-focus method of a phase difference detection method.

[Explanation of symbols]

1 Aperture mask 2 Re-imaging lens 3 Photoelectric conversion element 10 camera body 11 lens barrel 12 half mirror 13 sub mirror 20 AF module 21 Condenser lens 22 reflective mirror 23 Aperture mask 24 Reimaging lens 25 CCD 230 Fixed mask plate 231a, b Fixed opening 232a, b movable mask pieces 233a, b opening 330 Fixed mask plate 331a, b Fixed opening 332a, b movable mask pieces 333a, b Notch 430 Fixed mask plate 431a, b Fixed opening 440 LCD mask plate 441a, b Translucent part 450 LCD mask plate 451a, b Translucent part

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tsutomu Honda             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture             Osaka International Building Minolta Co., Ltd. (72) Inventor Keiji Tamai             2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture             Osaka International Building Minolta Co., Ltd. F-term (reference) 2H011 BA23 BB01 DA00                 2H051 AA01 BA04 CB06 CD11 CD28                       CD29

Claims (6)

[Claims] 1. A light flux from a photographing lens is divided into two,
In the automatic focus detection device that guides one of the light fluxes through the first aperture opening and the other light flux through the second aperture opening to the photoelectric conversion element to detect the phase difference between the two images for focusing, A fixed mask plate which is provided in advance and has two openings for giving the above two aperture openings, and a fixed mask plate which is slidably arranged in the vicinity of the fixed mask plate in a direction perpendicular to the photographing optical axis, and the opening amount of each opening. A diaphragm mask composed of two movable mask pieces for changing the aperture ratio, and as the open F value of the taking lens increases, the distance between the two diaphragm apertures becomes smaller and the area of each diaphragm aperture becomes smaller. An automatic focus detection device, further comprising: a control unit that controls the sliding movement of the movable mask piece. 2. The light flux from the photographing lens is divided into two,
In the automatic focus detection device that guides one of the light fluxes through the first aperture opening and the other light flux through the second aperture opening to the photoelectric conversion element to detect the phase difference between the two images for focusing, A fixed mask plate having two openings provided in advance to provide the two aperture openings, and a liquid crystal mask plate having two light-transmitting portions whose light-transmitting areas can be switched by turning on and off electricity. In the aperture mask, each light-transmitting portion covers the entire area of one opening of the fixed mask when the power is turned off, and a part of the opening is shielded by turning the power on so that both openings of the fixed mask are shielded. As the aperture mask for reducing the space and the area of each aperture is increased, and as the aperture F-number of the taking lens increases, the space between the two apertures becomes smaller and the area of each aperture becomes smaller. In, characterized by comprising a control means for controlling an energization state to the liquid crystal mask plate, automatic focus detection device. 3. The aperture mask is composed of one fixed plate and a plurality of liquid crystal mask plates, and the two light-transmitting parts of each liquid crystal mask plate have mutually the intervals and areas in the ON state. 3. The automatic focus detection device according to claim 2, wherein the distance and the area of the two diaphragm apertures can be changed by differently combining the ON / OFF states of energization to each liquid crystal mask. 4. The light flux from the taking lens is divided into two,
In the automatic focus detection method, in which one light flux is guided through the first aperture opening and the other light flux is passed through the second aperture opening to the photoelectric conversion element to detect the phase difference between the two images for focusing, An automatic focus detection method, wherein the distance between the two aperture openings is reduced and the area of each aperture opening is reduced as the open F value increases. 5. The light flux from the photographing lens is divided into two,
In the automatic focus detection method in which one light flux is guided through the first aperture opening and the other light flux is passed through the second aperture opening to the photoelectric conversion element, the phase difference between the two images is detected for focusing. Is insufficient to perform automatic focus detection, the aperture areas of the two aperture openings are reduced. 6. When the contrast of an object is insufficient for automatic focus detection, the aperture areas of the two aperture openings are reduced and the distance between the two aperture openings is reduced. The automatic focus detection method according to claim 5.