JPH05107463A - Focus detecting device - Google Patents

Abstract

PURPOSE:To detect a focus rapidly and surely in an active focus detecting device for detecting the focus through projection of an auxiliary light to a subject from a specified lighting device even when a defocusing amount is large. CONSTITUTION:A focus detecting device is provided with a pattern projecting means 101 for projecting either a first pattern or a second pattern which is denser than the first pattern to a subject, a focus detecting means 102, a lens driving means 103 and a control means 104 which selects the first pattern as a projection pattern of the pattern projecting means 101, operates the focus detecting means 102 and the lens driving means 103 and then, selects the second pattern and operates the focus detecting means 102 and the lens driving means 103.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active focus detecting device for detecting focus by projecting auxiliary light from a predetermined illuminating device onto an object.

[0002]

2. Description of the Related Art Generally, an interchangeable lens type camera is compatible with many types of interchangeable lenses. Therefore, there is a so-called passive type focus detecting device for performing focus detection using light from the outside that has passed through a photographing lens. It is the mainstream.

However, such a passive type focus detection device has a drawback that focus detection becomes difficult or impossible when the external environment is dark or when the contrast of a subject is low. Focus detection is performed by projecting auxiliary light such as external light.
An active focus detection device as disclosed in JP-A-1-138222 has been developed.

FIG. 8 shows a camera equipped with the active focus detection device disclosed in this publication. In this camera, the object light passing through the taking lens 801 passes through the light transmitting portion of the main mirror 802. The light passes through, is reflected downward by the sub mirror 803, and is incident on the focus detection unit 804.

On the other hand, a strobe 807 is mounted on an accessory shoe 806 formed on the upper surface of the camera body 805. Inside the strobe 807, a projection light source 808,
A focus detection projection optical system 811 including a projection pattern unit 809 and a projection lens 810 is formed.

With such a camera, when the external environment is dark,
When the contrast of the subject is low, for example, infrared light is emitted from the projection light source 808, and the projection pattern unit 80
9. A pattern having a contrast corresponding to the projection pattern of the projection pattern unit 809 is projected onto the subject through the projection lens 810, and the reflected light is reflected by the photographing lens 80.
The light is incident on the focus detection unit 804 using the well-known phase difference method via the first mirror 802 and the mirror 803, and the focus is detected.

FIG. 9 shows the principle of focus detection by the phase difference method. In the figure, reference numeral 901 is a planned image forming surface of the photographing lens 801 equivalent to the film surface, and reference numeral 90 is used.
Reference numeral 2 denotes a surface which is conjugate with the planned image forming surface with respect to the re-imaging optical system including the condenser lens 903 and the pair of re-imaging lenses 904 and 905.

The front focus image A, the focused focus image B, and the rear focus image C formed by the taking lens 801 are the condenser lens 9
03, by the pair of re-imaging lenses 904 and 905, the first image A1, B1, C1 and the second image A2, respectively.
The images are re-imaged as B2 and C2, but the interval between the first and second images changes depending on the focus adjustment state of the taking lens 801.

Therefore, by arranging the light receiving element 906 on the planned image forming plane 902 or in the vicinity thereof and obtaining the interval between the two images when the first and second images are best matched, based on the output thereof. The focus adjustment state of the taking lens 801 can be detected.

In the figure, reference numeral 907 is an optical axis of the photographing lens, and reference numeral 908 is an aperture mask for forming a pair of aperture openings immediately before the re-imaging lenses 904 and 905.

FIG. 10 shows the projection pattern section 809 described above.
1 shows an example of a projection pattern of the transparent pattern 1001.
The width q of 3 and the repetition period (p + q) are formed completely irregularly.

That is, in the case of focus detection by the phase difference method described above, when a plurality of opaque portions having the same width are provided, a plurality of sets of two projected pattern images formed by the re-imaging lenses 904 and 905 coincide with each other. Since a pair is detected and focus detection is erroneous, the opaque portion 1002
Width p, the width q of the transparent portion 1003 and the repetition period (p
+ Q) is completely irregularly formed.

The width p of the opaque portion 1002 is determined in consideration of the width of one pixel of the light receiving element 906 for focus detection in the focus detecting portion 804, which is, for example, a CCD.

That is, when the projection pattern image formed on the subject is formed on the light receiving element 906 of the focus detection unit 804, the width a of the projection pattern image formed is one pixel of the light receiving element 906. It must be larger than the width b of the minute.

On the other hand, if the width a of the projected pattern image becomes very large and there is only one boundary (hereinafter referred to as a pattern edge) between the transparent portion and the opaque portion on the light receiving element 906 column, information for focus detection calculation is obtained. Since the amount becomes small, it is easily affected by noise and the like, and it becomes difficult to detect a good focus. Therefore, it is desirable that at least two pattern edges are formed on the light receiving element 906 row.

Therefore, in the focus detection device disclosed in Japanese Patent Laid-Open No. 62-144123, as shown in FIG. 11, the projection pattern 1101 goes from the center to the periphery.
It is configured such that the density is reduced, and the pattern shape in the range of the distance measurement area is substantially constant no matter what focal length the photographing lens is used.

For example, in a long focus lens, reference numeral 1102
Is the range-finding area.
The range of 03 is the distance measuring area. Furthermore, JP-A-62-1
In the focus detection device of Japanese Patent No. 269126, instead of an irregular pattern, light fluxes having different widths are projected depending on the focal length of the photographing lens, and the ratio between the distance measurement area and the luminous flux width is constant even if the focal length of the photographing lens changes. It is supposed to be.

In the focus detection device of each of the above-mentioned publications, it is possible to effectively prevent a decrease in focus detection accuracy due to a difference in focal length of the taking lens.

[0019]

However, the above-described focus detection device has a problem that it is not possible to prevent the focus detection accuracy from being deteriorated due to the amount of focus shift at the time of distance measurement, that is, the so-called defocus amount. there were.

That is, in general, when the defocus amount is large, the projection pattern image re-formed on the surface of the light receiving element 906 for focus detection is blurred, the width of the projection pattern image is widened, and the pixels between the adjacent pixels in the light receiving element 906 are widened. Output difference becomes small and focus detection becomes difficult.

On the other hand, as described above, the projection pattern is determined so as to minimize it, but in the case of a long focus lens in which the image plane movement amount due to the movement of the photographing lens is large, when the defocus amount exceeds a certain value, Blurring of the projected pattern image makes focus detection difficult.

Therefore, in such a case, there is no choice but to scan the photographing lens until focus detection becomes possible.
There is a problem that it takes time to bring the image into focus when scanning is performed on the side opposite to the focus position.

The present invention has been made in order to solve the above-mentioned conventional problems. Even when the defocus amount is large,
An object of the present invention is to provide a focus detection device capable of performing focus detection quickly and reliably.

[0024]

FIG. 1 shows the structure of a focus detecting device according to a first aspect of the present invention. Reference numeral 101 is a first pattern and a pattern denser than the first pattern. The pattern projecting means projects one of the two patterns onto the subject.

Reference numeral 102 is the pattern projection means 10
The focus detection means receives the reflected light from the subject of the pattern projected from No. 1 through the photographing lens and detects the focus position of the photographing lens.

Reference numeral 103 is a lens driving means for driving the photographing lens to the focal position according to the output from the focus detecting means 102. Reference numeral 104 selects the first pattern as the projection pattern of the pattern projection means 101, operates the focus detection means 102 and the lens drive means 103, then selects the second pattern, and selects the focus. The control means operates the detection means 101 and the lens driving means 103.

A focus detecting apparatus according to a second aspect is the focus detecting apparatus according to the first aspect, wherein the pattern projecting means 101 includes a pattern forming member for forming the first pattern and the second pattern, the first pattern and the second pattern. Out of the pattern
The pattern forming member having a projection light source that projects one of the patterns selected by the control unit 104 onto the subject, and one side of the pattern forming member that forms the first pattern is a transparent portion, and the other side is a transparent portion. The side is an opaque part.

According to a third aspect of the present invention, in the second aspect, the pattern forming member is a transmissive electro-optical element. The focus detection device according to claim 4 is the focus detection device according to claim 3.
In the above, the transmissive electro-optical element is provided in the vicinity of a finder screen, and the projection light source has one of the first and second patterns formed by the transmissive electro-optical element as an object through the taking lens. Projected on
On the other hand, the light passing through the taking lens irradiates a third pattern formed by the transmissive electro-optical element, which is different from the first and second patterns, and the third pattern is applied to the finder optical system. It guides and displays in the finder.

[0029]

In the focus detecting device according to the first aspect, the control means 104 is provided.
The first pattern is selected as the projection pattern of the pattern projection unit 101 by the pattern projection unit 101, the first pattern is projected onto the subject by the pattern projection unit 101, and the reflected light from the subject is received through the photographing lens and focused. The detection unit 102 detects the in-focus position of the photographing lens, and the lens driving unit 103 drives the photographing lens to the focal position according to the output from the focus detection unit 102.

After that, the control means 104 selects the second pattern as the projection pattern of the pattern projection means 101, and the pattern projection means 101 projects this second pattern onto the subject, and the reflected light from the subject is generated. The light is received through the taking lens, the focus detection means 102 detects the in-focus position of the taking lens, and the lens driving means 10
3, the photographing lens is driven to the focus position according to the output from the focus detection unit 102.

According to a second aspect of the focus detection apparatus, in the first aspect, the pattern projecting means 101 includes a pattern forming member for forming the first pattern and the second pattern, and the first pattern and the second pattern. Of which, control means 1
And a projection light source for projecting any one of the patterns selected by 04 onto a subject, and the pattern forming member forming the first pattern has a transparent portion on one side and an opaque portion on the other side. To be done.

According to a third aspect of the focus detection apparatus, in the second aspect, the pattern forming member is formed of a transmissive electro-optical element. In the focus detection device of claim 4, claim 3
In the above, a transmissive electro-optical element is provided in the vicinity of the finder screen, and the projection light source projects one of the first and second patterns formed by the transmissive electro-optical element onto a subject through a taking lens. On the other hand, the light that has passed through the taking lens irradiates a third pattern, which is different from the first and second patterns, formed by the transmissive electro-optical element, and the third pattern is guided to the finder optical system. Internal display is performed.

[0033]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows a camera equipped with an embodiment of the focus detection device of the present invention. In this camera, the subject light that has passed through the taking lens 201 passes through the light transmitting portion of the main mirror 202 and is The light is reflected downward by the mirror 203 and is incident on the focus detection unit 204.

On the other hand, a strobe 207 is mounted on an accessory shoe 206 formed on the upper surface of the camera body 205, and a projection light source 208,
A focus detection projection optical system 211 including a projection pattern unit 209 and a projection lens 210 is formed.

In this embodiment, the projection pattern section 209
Is composed of a transmissive electro-optical element 212 such as an LCD or an EC (electrochromic element) capable of switching between the first pattern and the second pattern.

FIG. 3 shows a first pattern. The first pattern 301 is composed of a simple black-and-white pattern having a transparent portion 302 on one side and an opaque portion 303 on the other side. There is.

FIG. 4 shows a second pattern, and the second pattern 401 is constructed so that the density decreases from the central portion to the peripheral portion. Even if a lens is used, the pattern shape in the range of the distance measurement area is made substantially constant.

For example, in the case of the long focus lens, the range of reference numeral 402 is the distance measuring area, and in the case of the wide-angle lens, the reference numeral 403.
The range becomes the distance measurement area. This second pattern 401
Is the same as the above-described pattern shown in FIG. 11, which can minimize the influence of the focal length of the taking lens 201.

FIG. 5 is a block diagram of an embodiment of the focus detection device of the present invention. In FIG. 5, reference numeral 501 indicates a CPU that performs overall control of the focus detection apparatus of this embodiment.

This CPU reads the lens data such as the focal length and the open F value stored in the in-lens circuit 503 in the interchangeable lens 502, the exposure calculation is performed by the photometry circuit 504, and the focus is detected by the focus detection circuit 505. Calculate.

In the normal case, the focus detection circuit 5
The lens drive circuit 506 is operated based on the calculation result of 05, and focus adjustment is performed. On the other hand, when the external environment is dark, or when focus detection cannot be performed due to lack of contrast in the subject, the auxiliary light emitting circuit 507 in the strobe 807 is activated by the outputs of the photometry circuit 504 and the focus detection circuit 505.

The switching of the projection pattern at this time is performed by the projection pattern switching circuit 508. Figure 6
6 is a flowchart showing the operation of the above-described focus detection device in the auxiliary light emission mode, that is, during active AF.

That is, for example, when the external environment is dark, or when focus detection cannot be performed due to lack of contrast of the subject, this auxiliary light emission mode is operated. In this embodiment, when the auxiliary light emission mode is entered, first, step 60
1, the projection of the second pattern 401 shown in FIG. 4 onto the subject is performed.

At this time, if the defocus amount is not too large, focus detection by the second pattern 401 is possible, and it is determined in step 602 that focus detection is possible.

When it is determined that focus detection is possible, in step 603, the lens drive circuit 506 is operated based on the calculation result of the focus detection circuit 505 to perform focus adjustment, and in step 604, a normal photographing sequence is performed. Executed.

On the other hand, in step 602, when the focus detection is impossible because the defocus amount is large, in step 605, the projection pattern switching circuit 508 switches the projection pattern to the first pattern 301, as shown in FIG. The first pattern 301 shown is projected onto the subject.

Then, in step 606, it is determined whether or not focus detection by the first pattern 301 is possible. Since the first pattern 301 is a simple black-and-white pattern here, rough focus detection with low accuracy is possible in most cases even though the defocus amount is large.

A black and white pattern edge 3 is provided in the center of the visual field.
Since 04 exists, focus detection is possible regardless of the range of the distance measurement area due to the difference in the focal length of the taking lens 201.

When focus detection by the first pattern 301 is possible, in step 607, the lens drive circuit 506 is operated based on the calculation result of the focus detection circuit 505 to perform focus adjustment.

Thereafter, in step 608, the projection pattern switching circuit 508 switches the projection pattern to the second pattern 401, and the second pattern 401 shown in FIG. 4 is projected onto the subject.

Then, in step 609, it is determined whether or not focus detection by the second pattern 401 is possible. Note that here, the focal position of the taking lens 201 is
Since it is close to the in-focus position, focus detection can be performed by the second pattern 401. However, when focus detection is impossible due to, for example, the subject moving while the shooting lens 201 is being driven, the process returns to step 605. Returning to this, focus detection by the first pattern 301 is performed.

When the focus detection by the second pattern 401 is possible, in step 610, the lens drive circuit 506 is operated based on the calculation result of the focus detection circuit 505 to perform the focus adjustment with high precision, and in step 60.
In 4, the normal shooting sequence is executed.

On the other hand, although the possibility is low, in step 606, when the focus detection is not possible even by the first pattern 301, the projection pattern switching circuit 508 switches the projection pattern to the second pattern 401 and the second pattern 401.
The pattern 401 is projected onto the subject.

Then, after that, in step 612, the photographing lens 201 is scanned in a predetermined direction as in the conventional case, focus detection is performed, and when the focus position is detected in step 613, in step 614,
The movement of the photographing lens 201 is stopped, and in step 604, a normal photographing sequence is executed.

Thus, in the focus detecting apparatus configured as described above, for example, when the defocus amount is large and the normal second pattern 401 cannot detect the focus, the projection pattern is changed to the simple first pattern. Since focus detection is performed by switching to the pattern 301, focus detection can be performed quickly and reliably even when the defocus amount is large.

That is, in this focus detection device, even when the defocus amount is large, it is not necessary to scan the taking lens 201 until focus detection becomes possible as in the conventional case, and focus detection is performed quickly and reliably. be able to.

In the embodiment described above, step 6
In 01, first, the second pattern 401 is projected,
I explained an example of focus detection based on this,
The present invention is not limited to such an embodiment, and it goes without saying that, for example, step 601 may be omitted and the first pattern 301 of step 605 may be projected first.

Further, although the first pattern and the second pattern are formed by different transmissive electro-optical elements respectively, they are not limited to this and may be formed by the same element. Further, in the above-described embodiment, the projection pattern is set to the transmissive electro-optical element 2.
However, the present invention is not limited to such an embodiment. For example, the first pattern and the second pattern are formed by different members, and are controlled electromagnetically, for example. It goes without saying that the first pattern and the second pattern may be switched by a mechanical switching means.

Further, in order to reduce the influence of the change in the focal length of the taking lens 201, there is disclosed in JP-A-62-269126.
As disclosed in the publication, instead of an irregular pattern, a light beam having a different width is projected depending on the focal length of the photographing lens 201, and even if the focal length of the photographing lens 201 changes, the ratio between the distance measurement area and the luminous flux width. It is needless to say that the projection pattern unit 809 may be provided with a pattern switching mechanism for keeping constant.

Further, instead of such a simple switching of the width of the light beam, a slightly complicated pattern such as the second pattern is adjusted within the distance measuring area in accordance with the change in magnification due to the change in the focal length of the photographing lens. Of course, zooming may be performed so that the projection pattern is changed so that the magnification is always the same.

FIG. 7 shows another embodiment of the focus detecting apparatus of the present invention. In this embodiment, the projection pattern is projected onto the subject through the taking lens 201. That is, in this embodiment, the transmissive electro-optical element 703 forming the projection pattern portion is arranged between the pentaprism 701 and the finder screen 702.

On one side of the penta prism 701,
A projection light source 704 is provided. In such a focus detection device, one of the first and second patterns formed by the transmissive electro-optical element 703 is projected onto the subject by the emission of the projection light source 704 via the main mirror 202 and the taking lens 201. To be done.

The light transmitted through the taking lens 201 through the third pattern different from the first and second patterns formed by the transmissive electro-optical element 703 is composed of the pentaprism 701 and the eyepiece 705. Display in the viewfinder can be performed by guiding the viewfinder optical system.

The operation of the focus detection apparatus of this embodiment in the auxiliary light emission mode, that is, in the active AF mode is the same as that of the flowchart shown in FIG. 6, and therefore its detailed description is omitted.

In the focus detecting device of this embodiment, almost the same effect as the focus detecting device described above can be obtained, but in this embodiment, the transmissive electro-optical element 703 is used.
It can be easily used also as a superimposing display element for displaying photographing information and the like on the viewfinder field.

[0066]

As described above, in the focus detecting apparatus of the first aspect, rough focus detection is performed by the first pattern which is a simple pattern, and then the second pattern which is denser than the first pattern is performed. Since the focus detection is performed by the pattern, the focus detection can be performed quickly and surely even when the defocus amount is large.

In the focus detecting apparatus according to the second aspect, the pattern forming member forming the first pattern is formed with the transparent portion on one side and the opaque portion on the other side. Therefore, even when the defocus amount is large. It becomes possible to perform focus detection.

In the focus detecting device of the third aspect, since the pattern forming member is formed of the transmissive electro-optical element, it is possible to switch between the first pattern and the second pattern quickly and reliably. ..

In the focus detection device of the fourth aspect, since the transmissive electro-optical element is provided in the vicinity of the finder screen, the transmissive electro-optical element can also be used as a superimpose display element. There is.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a focus detection device of the present invention.

FIG. 2 is an explanatory diagram showing a camera provided with an embodiment of a focus detection device of the present invention.

FIG. 3 is an explanatory diagram showing a first pattern of a projection pattern portion of FIG.

FIG. 4 is an explanatory diagram showing a second pattern of the projection pattern portion of FIG.

5 is a block diagram showing a focus detection device of the camera of FIG. 2. FIG.

6 is a flowchart of the focus detection device of FIG.

FIG. 7 is an explanatory diagram showing a camera provided with another embodiment of the focus detection device of the present invention.

FIG. 8 is an explanatory diagram showing a conventional camera with an active focus detection device.

FIG. 9 is an explanatory diagram showing a principle of focus detection of a phase difference method.

FIG. 10 is an explanatory diagram showing a conventional projection pattern.

FIG. 11 is an explanatory diagram showing another example of a conventional projection pattern.

[Explanation of symbols]

 101 pattern projection means 102 focus detection means 103 lens drive means 104 control means 201 photographing lens 208 projection light sources 212, 703 transmissive electro-optical element 301 first pattern 401 second pattern 702 finder screen

Claims (4)

[Claims] 1. A pattern projection means for projecting one of a first pattern and a second pattern, which is a denser pattern than the first pattern, onto a subject, and the pattern projection means for projecting from the pattern projection means. Pattern of
Receives the reflected light from the subject through the shooting lens,
A focus detection unit that detects a focus position of the photographing lens, a lens driving unit that drives the photographing lens to the focal position according to an output from the focus detection unit, and a projection pattern of the pattern projection unit. A first pattern is selected to operate the focus detection means and the lens driving means, and then a second pattern is selected to control the focus detection means and the lens driving means. A focus detection device characterized by the above. 2. The pattern projecting means selects one of a pattern forming member that forms the first pattern and the second pattern and a pattern forming member that is selected by the control means from the first pattern and the second pattern. A projection light source that projects one of the patterns onto the subject, and the pattern forming member that forms the first pattern is characterized in that one side is a transparent portion and the other side is an opaque portion. The focus detection device according to claim 1. 3. The focus detection device according to claim 2, wherein the pattern forming member is a transmissive electro-optical element. 4. The transmissive electro-optical element is provided in the vicinity of a finder screen, and the projection light source is configured such that one of a first pattern and a second pattern formed by the transmissive electro-optical element is connected to the taking lens. On the other hand, the light that has been projected onto the subject through the photographing lens passes through the third pattern, which is different from the first and second patterns formed by the transmissive electro-optical element, and the third pattern is generated. 4. The focus detection device according to claim 3, wherein the pattern is guided to a finder optical system to display in the finder.