JPH06100717B2 - Focus detection device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device preferably used for a single-lens reflex camera, and in particular, as a focus detection method in addition to a passive method by external light, a light from a light projecting unit is used. The present invention relates to a focus detection device having an active method of illuminating a subject with light as auxiliary light.

2. Description of the Related Art In cameras, as a focus detection method for detecting the focus adjustment state of a taking lens, a passive method that relies only on external light and an active method that illuminates an object with light emitted from a light projecting unit are known. There is. Although there are different types of active systems, the one that excels in terms of high illumination rate is the T that projects light from behind through the shooting lens.
TL active method, an example of which is JP-A-54-155832.
JP-A-57-22216.

Problems to be Solved by the Invention Conventionally, in the case of a focus detection device for a camera, the focus detection area is defined near the center of the shooting screen regardless of whether it is a passive system or an active system, and a subject is placed at a position other than the center of the shooting screen. When taking a picture, in order to take a picture in focus on the subject, shake the camera once to detect the focus with the subject in the focus detection area, then return the camera to its original composition. It had to be photographed and had the drawback of being difficult to use. It is suggested from Japanese Patent Laid-Open No. 146028/1984 that focus detection should be performed on a plurality of areas within a photographic screen as one measure to solve this problem. That is, the publication discloses that in an active distance measuring device that measures the distance to a subject based on the principle of triangulation, distance measurement is performed for each subject located in a plurality of areas within the shooting screen. A proposal has been made to select the closest distance information from a plurality of subject distance information obtained by. Here, the closest distance information is selected from the multiple-object distance information because the main object is often at a short distance.
From this, it can be understood that this proposal is intended for the range finder that measures the distance to the subject, but aside from the method of evaluating the information obtained for a plurality of areas in the shooting screen, By applying the strategy to the focus detection device,
It is easily conceivable that the above-mentioned drawbacks of the conventional focus detection device will be solved.

However, when focus detection is performed on a plurality of areas within the photographic screen as described above, no consideration has been given to how to perform the active-type light projection for illuminating the subject as described above.

The present invention relates to a passive focus detection device that performs focus detection for a plurality of areas, and a rational control device for the active projection device that illuminates an object by a projection device when the amount of light in the shooting screen is insufficient. The purpose is to obtain.

Means for Solving Problems Here, consideration will be given to what subject situations the passive method and the active method are used in.

First, the passive method detects the light of the outside world (subject and background) to detect the focus adjustment state, and is therefore usually used in a bright daytime environment. At this time, as in the case of a snapshot, the person is the main subject and it is relatively large in the center of the shooting screen. Photos with various compositions such as photographs are possible.

On the other hand, the active method is used auxiliary when the surroundings are dark and focus detection by the passive method by external light cannot be performed, that is, at nighttime or indoor shooting. Therefore, it is unlikely that a photograph mainly of a landscape will be taken, and it is considered that there are many photographs mainly of a person or a still life. Therefore, it is considered that the subject is often placed at a relatively short distance, so that the magnification of the subject in the field of view becomes large, and even if the focus is adjusted in one specific region, the subject is moved from that region. Is very unlikely to come off.

Therefore, when using the active method, because of the above-mentioned circumstances, focus detection is performed only on a specific area in which a subject is most likely to exist in the scene, and focus detection is not performed on a plurality of areas. However, the probability of correct focus detection is high.

In addition, as a focus detection method of the active method, especially when adopting the TTL active method that irradiates light from behind through the taking lens, it is possible to improve the focus detection accuracy of harmful light due to inter-surface reflection of the lenses forming the taking lens. Another problem is that the impact cannot be ignored. That is, when focus detection is performed on a plurality of areas at the same time, it is necessary to arrange a plurality of focus detection sensors corresponding to the respective focus detection areas. Part of the light is reflected by the lens surface that constitutes the shooting lens and enters the focus detection sensor as harmful light, resulting in a large change in the output of the focus detection sensor.
Correct focus detection based on the output becomes difficult. T.
In the focus detection device of the TL active method, by setting so that the light projecting optical axis and the light receiving optical axis are not point-symmetric with respect to the intersection of the principal plane and the taking lens optical axis on the principal plane of the taking lens, A proposal for avoiding the influence of such harmful light due to reflection between lens surfaces (hereinafter, simply referred to as harmful light) is also made in JP-A-57-22210, but if there are a plurality of focus detection sensors, all It is difficult to satisfy the proposed positional relationship for the focus detection sensor, and the correct focus detection will not be performed due to harmful light after all.

The harmful light in the photographing lens will be described in detail below. FIG. 6 is a diagram showing an example of a focus detection optical system, and FIG.
Figure is a view of Figure 6 viewed from 90 ° different directions,
Lo is a taking lens, F is a focal plane, and a focus detecting optical system Ao is arranged behind it. Q and P are masks arranged in front of the lenses, and C is a one-dimensional light receiving element such as CCD. FIG. 8 is an example of a projection optical path diagram for explaining harmful light generated by the inter-surface reflection of the photographing lens. For convenience of explanation, the projection optical system is omitted in the figure,
Only the rays are shown. A light beam projected from a point O on the planned focal plane on the optical axis of the taking lens is reflected by each lens surface constituting the taking lens and returns to the incident direction with a spread as shown in the figure. Come on. Drawing the light rays reflected on all surfaces becomes complicated, so in Fig. 8 (A), the light rays returning after being reflected on surfaces 1, 2, and 6 are shown as a typical example (single reflection). . FIG. 8 (B) shows an example in which the light is reflected many times (three times) and then returns in the incident direction.
The case where the number of faces is one to six is shown as an example.

FIG. 9 (A) shows the spread of harmful light on the first mask Q surface in FIG.
It is shown that it spreads in the range of point symmetry with respect to C). Here, each circle corresponds to the spread of harmful light reflected on the surface of each lens forming the taking lens. Here, only the spread of harmful light generated by one reflection is shown, but the same is true for the case where the harmful light is reflected three times or more, and spreads in a range of point symmetry with respect to the optical axis. FIG. 9B shows the spread of harmful light on the P surface of the second mask (aperture mask). The harmful light that reaches the second mask passes through the first mask.
Figure 10 shows how harmful light changes with different types of taking lenses. Similar to FIG. 9 (B),
The state on the surface of the second mask P is shown. The upper row shows the case where the taking-out position of the taking lens is ∞, and the lower row shows the case where it is closest. As can be seen from the figure, the focal length f
= 50mm, standard lens with open F value F = 1.7 (lens structure:
Deformed Gauss type), f = 35 to 105 mm, F = 3.5 to 4.5
The state of harmful light has changed with the zoom lens of. It depends on the difference of these optical systems. Further, in the zoom lens, the state of harmful light is different between the telephoto end (L) and the wide end (S). This is because the optical system of the taking lens changes due to zooming. Further, the reason why it changes depending on the difference in the amount of feeding is also for the same reason.

In addition, as for the above description of harmful light, as shown in FIG. 11, the angle θ between the projection optical axis and the shooting lens optical axis is 5.5 °, the aperture diameter in front of the projecting lens is 4 mmφ, and the focal length of the projection lens is 12 mm
The light source is a light emitting diode (light emitting diameter 40 μmφ) with a spherical glass ball (0.5 mmφ). Further, it is assumed that the optical axis of the projection optical system is set in a plane orthogonal to the arrangement direction of the diaphragm masks P, including the optical axis of the photographing lens.

In order to achieve the above-mentioned object, the present invention was made based on the consideration of the difference between active and passive as described above, and it is possible to detect the focus state of each area by dividing the photographing screen into a plurality of areas. The focus detection light receiving element is arranged corresponding to each area so that the focus adjustment is performed based on the focus detection signals output from the plurality of focus detection light receiving elements in the passive AF, while in the active AF, It is characterized in that the focus adjustment is performed using only the focus detection signal output from the specific light receiving element for focus detection.

EXAMPLE FIG. 1 shows a single-lens reflex camera equipped with the focus detection device of the present invention. In the figure, 100 is a camera body, 101 is an interchangeable taking lens, 102 is a reflex mirror, and the taking lens 101 is refracted, The transmitted light is reflected in the direction of the finder optical system, and a part of the light is transmitted and guided to the focus detection optical system 104. 103 is a total reflection mirror for that purpose. Reference numeral 105 denotes an optical member arranged near the planned focal plane of the taking lens 101, and a wavelength at which light of a wavelength emitted from a light emitting diode 107 arranged above a pentaprism is reflected in the central portion and visible light is transmitted. Selective semi-transmissive part 105a
Is installed at an angle of about 45 ° with respect to the optical axis. A prism 106 having a shape as shown in the figure is arranged on the side surface of the optical member 105, and deflects the light beam emitted from the light emitting diode 107 and introduces it into the optical member 105. Reference numeral 108 denotes a reflecting mirror arranged in the optical path of the light beam emitted from the light emitting diode 107, and acts to deflect the light beam emitted from the light emitting diode 107 downward. Above reflector
108 and eyepiece lens 113, which is one of the viewfinder components
A first light-projecting lens 109 is arranged between and, and this lens collimates the light rays emitted from the light-emitting diode 107. A first light projecting mask 110 is provided between the first light projecting lens 109 and the eyepiece lens 113 and immediately before the first light projecting lens 109. This mask is for narrowing the projected light flux. The eyepiece lens 113 also serves as a path for light rays emitted from the light emitting diode 107. Reference numeral 111 is a second lens arranged below the eyepiece lens 113.
The light projecting lens of the first projecting lens 109 focuses the light rays collimated by the first light projecting lens 109 to form an image near the planned image forming surface of the photographing lens 101. Reference numeral 112 denotes a second light projecting mask provided immediately before the second light projecting lens 111.

With this configuration, the light rays emitted from the light emitting diode 107 are condensed by the light projecting lenses 109 and 111 and the light projecting masks 110 and 112 and pass through the optical axis of the taking lens on the planned focal plane of the taking lens. The light is projected at a slight angle. This angle is a sufficiently small value, for example, F = when converted to an F value so that the projection light is not vignetted by the lens barrel or diaphragm even when a dark photographing lens having a large F value is used.
It is set to about 4 to 5.6. Component 1 described above
05 to 113 form the first projection optical system.

Reference numeral 114 denotes a second light emitting diode, which is arranged in the upper front part of the pentaprism 118. Reference numeral 115 denotes a prism, which acts to bend the light beam emitted from the light emitting diode 114 toward the front of the camera. Reference numeral 116 denotes a light projecting lens arranged on the surface of the prism 115 from which the light rays are emitted, and collects the light rays emitted from the light emitting diode 114 and projects the light rays toward the subject. Reference numeral 117 denotes a panel provided in front of the light projecting lens 116, and a wedge-shaped convex portion 117a is formed in a part of the panel. The wedge-shaped convex portion 117a serves to illuminate an object at a short distance by deflecting a part of the light beam emitted from the light projecting lens 16 downward (in the optical axis direction of the photographing lens in the figure). The constituent members 114 to 117 described above form a second light projecting optical system.

FIG. 2 is a detailed view of the focus detection optical diameter 104. 200 in the figure
Is a taking lens, and a and a ′ represent regions on the pupil plane of the taking lens 200 through which the focus detection photon flux passes.
Reference numeral 201 denotes a focus detection area mask arranged immediately after the planned focal plane, which has a rectangular opening 201a. 20
Reference numeral 2 denotes a condenser lens arranged immediately after the focus detection area mask 201, which forms an image of the aperture mask openings A and A'on a and a'on the exit pupil plane of the taking lens 200. That is, the aperture mask openings A and A'regulate the focus detection light flux area. 203 is a condenser lens 202
Is a diaphragm mask having the openings A and A'arranged behind it, and immediately after that, imaging lenses 204 and 205 are arranged at positions for receiving the light flux that has passed through the diaphragm mask openings A and A '. The image forming lenses 204 and 205 convert the image formed on the planned focal plane of the taking lens 200 into the focus detecting line sensors 207 and 20.
Reimages on 8,209. 206 is a substrate,
Focus detection line sensors 207, 208, and 209 are arranged on the surface. The focus detection line sensor is composed of a one-dimensional light receiving element such as a CCD (hereinafter, referred to as a focus detection light receiving element), and is arranged in parallel in the short side direction of the focus detection area mask opening 201a by the imaging lenses 204 and 205. Receive the formed image.

FIG. 4 shows the relationship between the photographing screen and the light receiving area of the light receiving element for focus detection. 400 shows the whole shooting screen, 401,4
Three areas indicated by 02 and 403 are light receiving areas, which correspond to the light receiving areas of the focus detection line sensors 209, 208 and 207, respectively.

FIG. 3 shows a case where a subject is irradiated from the back of the taking lens through the taking lens and the reflected light is imaged on the surface of the light receiving element for focus detection through the taking lens. The relationship between the harmful light generated on the detection light receiving element surface and the reflected light from the subject is shown. As described in FIG. 1, the light emitting diode 10
The light beam emitted from 7 passes through the optical axis of the taking lens on the planned focal plane of the taking lens and is projected with a slight inclination with respect to the optical axis of the taking lens. The harmful light that is emitted is the aperture mask aperture A, A ′.
It looks like Fig. 10 on the surface. 50 / 1.7 or 35-10
In 5 / 3.5-4.5 (L), harmful light is blocked by the aperture mask and does not enter the light receiving element for focus detection.
In 3.5-4.5 (S), the light enters the focus detection light receiving element through the edge of the aperture mask. The harmful light passing through this diaphragm mask is displayed on the surface of the light receiving element for focus detection as 300, 300 in FIG.
As in 301, when O is the optical axis of the photographing lens, an image is formed at a position displaced from the optical axis in the short side direction of the focus detection area opening 201a. On the other hand, if the light reflected from the subject returns, when the focus of the photographing lens is near the in-focus state, it forms an image like 302, 303 on the surface of the central focus detection light receiving element 208. In order to widen the focus detection area, when the focus detection area opening 201a is enlarged (especially when the width in the short side direction is widened) or the number of light receiving elements for focus detection is increased, the above-mentioned harmful light influences. It becomes even more noticeable.

In consideration of such a point, the present invention limits the light receiving element for focus detection to a specific one (for example, the center 208) when light is projected through the taking lens, so that there is no influence of the harmful light. Focus detection is performed. Since the harmful light changes depending on each photographing lens, the light receiving element for focus detection used when light is projected through the photographing lens may be changed according to the photographing lens.

Next, an example of the focus detection device of the present invention will be described based on the block diagram shown in FIG. In the figure, reference numeral 500 denotes a first focus detection light receiving element, which corresponds to 207 in FIG. 501 is a second light receiving element for focus detection, which corresponds to 208 in FIG. 502
Is a third light receiving element for focus detection and corresponds to 209 in FIG. Reference numerals 503, 504, and 505 denote analog signal-digital signal (A / D) conversion circuits and CCD drive circuits, which perform A / D conversion of the signals output from the focus detection light receiving elements 500, 501, 502, and output the focus detection light receiving elements. To 500,501,502,
Outputs a signal for driving. Reference numerals 506, 507 and 508 denote storage circuits connected to the output terminals of the A / D conversion and CCD drive circuits 503, 504 and 505, respectively, and temporarily store the signals output from the A / D conversion and CCD drive circuits 503, 504 and 505. 509 is a select circuit, which selectively outputs the data output from the storage circuits 506, 507 and 508 to the algorithm processor based on the signal output from the system controller 518.
Output to 510. The algorithm processor 510 processes the input data according to an algorithm and calculates the defocus amount of the taking lens. 511 is a select circuit, which outputs the signal output from the algorithm processor 510 to the signal output from the system controller 518. Based on the above, it selectively outputs to the motor drive circuit 512 and the minimum value detection circuit 513. The motor drive circuit 512 is the select circuit 5
The photographing lens drive motor is controlled based on the information value obtained from the algorithm processor 510 via 11. The minimum value detection circuit 513 detects the minimum value (corresponding to the shortest shooting distance) of the signals output in time series from the algorithm processor 510 via the selection circuit 511, and the motor drive circuit 512. Output to. 514 is a trigger circuit, which generates a focus detection start signal in response to ON / OFF of a shutter button or an additional switch,
The signal is applied to A / D conversion, CCD drive circuits 503, 504, 505, gate circuit 515, and system controller 518. The gate circuit 515 opens and closes the gate according to the signal output from the photometric circuit 517, opens the gate only when the photometric output output from the photometric circuit 517 is darker than a predetermined level, and trigger circuit 514. Output signal to the light emitting circuit 516. The light emitting circuit 516 is the light emitting diode 1 of FIG.
It is composed of 07 and a circuit for controlling the lighting thereof. The integrated signal output from the focus detection light-receiving element 501 by turning on the light emitting diode by the signal output from the trigger circuit 514 through the gate circuit 515 (subject At this time, the light is turned off according to the integrated output of the reflected light). 517 is a photometric circuit for measuring the brightness of the subject, and when the value is darker than a predetermined level, outputs a signal to the gate circuit 515 to open the gate. The system controller 518 starts its operation by the focus detection start signal output from the trigger circuit 514, and outputs a signal to the select circuits 509 and 511 based on the signal output from the photometric circuit 517.
That is, when the brightness of the subject is lower than a predetermined level, the photometry circuit 517 causes the system controller 518
To the algorithm processor 510, and the output signal of the memory circuit 507 is output to the algorithm processor 510.
Select circuit 511 to switch 09 and output the output signal of algorithm processor 510 to motor drive circuit 512.
Switch. When the brightness of the subject is higher than a predetermined level, the photometry circuit 517 outputs a signal to that effect to the system controller 518, and the storage circuit 5
The select circuit 509 is sequentially switched so as to output the output signals of 06, 507, 508 to the algorithm processor 510 in time series, and the result processed by the algorithm processor 510 is output to the minimum value detection circuit 513 in time series. Switch 511 sequentially.

Next, the focus detection operation in the above configuration will be described.

First, a case where the brightness of the subject is darker than a predetermined level will be described.

When the user touches the shutter button etc. at first, the trigger circuit 514 generates the focus detection start signal, and this signal is A / D.
It is applied to the conversion / CCD driving circuits 503, 504, 505, the gate circuit 515, and the system controller 518.

When the brightness of the subject is dark, the gate circuit 515 is in the open state due to the signal output from the measurement optical circuit 517, so the output signal from the trigger circuit 514 is the gate circuit 515.
Is applied to the light emitting circuit 516 via the light emitting diode, and the light emitting diode starts emitting light. On the other hand, from the trigger circuit 514 to the signal line 514
A / D conversion, CCD drive circuit 503, 504,5
05 starts its operation, and the focus detection light receiving elements 500, 501, 502 start the integration operation of the light reflected from the subject. When the integration result output from the focus detection light receiving element 501 reaches a constant value, a signal is output from the focus detection light receiving element 501 to the light emitting circuit 516, so that the light emitting diode stops emitting light. Then, the integrated signals output from the light receiving elements 500, 501, 502 for focus detection are A / D converted and A / D converted by the CCD drive circuits 503, 504, 505, and then stored in the storage circuits 506, 507, 508. When the storage is completed, a signal is output from the system controller 518 to the select circuit 509, and the output of the storage circuit 507 is connected to the algorithm processor 510, so that the output of the focus detection light receiving element 501 is the algorithm processor 510.
Will be output to. Algorithm processor 51
0 calculates the defocus direction and the defocus amount according to a predetermined algorithm, and outputs the result to the select circuit 511 via the signal line 510b. The select circuit 511 uses the signal line 510 according to a control command from the system controller 518.
The signal input through b is output to the motor drive circuit 512. As a result, the motor drive circuit 512 adjusts the focus of the photographing lens based on the defocus amount and the defocus direction calculated by the algorithm processor 510.

In this way, focus detection is performed based only on the output of the focus detection light receiving element 501 in a specific area.

Next, a case where the brightness of the subject is brighter than a predetermined level will be described.

In this case, since the gate circuit 515 is closed by the signal output from the photometric circuit 517, the light emitting diode does not emit light. Photodetector for focus detection 50
When the integrated output of 0,501,502 reaches a certain value, A / D conversion, CC
D drive circuits 503, 504, 505 complete the integration operation,
After A / D conversion, output to storage circuits 506, 507, 508. When storage is completed, the system controller 518 selects the select circuit 5
The signal is output to 09, and first, the information stored in the storage circuit 506 is output to the algorithm processor 510 via the signal line 506a. This signal is converted into the defocus direction and the defocus amount by the algorithm processor 510, and then the select circuit 511 is passed through the signal line 510a.
Is output to. The select circuit 511 first connects the signal line 510a of the algorithm processor 510 to the minimum value detection circuit 513 in response to a signal from the system controller 518, so the output of the algorithm processor is output to the minimum value detection circuit 513. It Similarly, the information stored in the memory circuit 507 is input to the select circuit 509 through the signal line 507a, and the system controller 518
Depending on the signal output by the algorithm processor 51
After being input to 0 and processed, it is input from the signal line 510b to the minimum value detection circuit 513 via the select circuit 511, compared with the previous value (output from the storage circuit 506), and smaller (known as a closer distance). Value) is selected. Finally, the information stored in the storage circuit 508 is output through the signal line 508, and similarly, the minimum value detection circuit 513 compares the previous values and selects the smaller value. In this way, of the focus detection light receiving elements 500, 501, 502, the signal outputting the shortest distance is finally adopted.

Depending on the intention of the photographer, even if the photograph is taken at night or indoors, a photograph in which the main subject is arranged at the edge of the screen or a photograph in which the magnification of the subject is small may be photographed. Therefore, even in the case of the active method, it may be possible to switch the focus adjustment to a plurality of areas. In that case,
As described above, the focus detection by the light passing through the taking lens may have an adverse effect due to the reflection between the lens surfaces. Therefore, as shown in FIG. 1, the second light is projected without passing through the taking lens. The projection optical system (114 to 117 in FIG. 1) may be used. In that case, the control method of the system controller may be switched according to the switching between the second projection optical system and the first projection optical system described in the above embodiment.

Effect of the Invention The focus detection device according to the present invention, as described above, the focus adjustment is performed for a plurality of regions in the passive mode,
When the active method is used, focus adjustment is performed on a specific area. Therefore, in any object situation, it is possible to obtain an irradiation member for irradiating the object necessary for the active method and an irradiation angle corresponding to a plurality of areas without lowering the probability that the focus adjustment is correctly performed on the object. Since the light projecting member and the like can be downsized, the camera can be downsized, and since the amount of light emission can be small, the power consumption of the irradiation member can be reduced.

[Brief description of drawings]

FIG. 1 is a view showing a camera having a focus detection device of the present invention, FIG. 2 is a view showing a focus detection optical system of the camera of FIG. 1, and FIG. 3 is a plan view showing an arrangement of a focus detection light receiving element. ,
FIG. 4 is a diagram showing a photographing screen, FIG. 5 is a block diagram showing a focus detecting device as one embodiment of the present invention, and FIGS.
FIG. 11 is a view relating to harmful light, FIG. 6 is a side view showing a focus detection optical system which generates harmful light, and FIG.
FIG. 8 (A) and (B) are side views showing a situation in which harmful light is generated, and FIG. 9 (A) shows the spread of harmful light on the first mask surface as viewed from different directions. Figure, Figure (B) Figure showing the spread of harmful light on the second mask surface, Figure 10 shows how harmful light changes with different types of photographic lenses, and Figure 11 shows the above. It is a figure which shows the concrete structure of the focus detection optical system used for the measurement of harmful light. 101 ... Shooting lens 207, 208, 209, 500, 501, 502 ... Focus detection light receiving element 400 ... Shooting screen 401, 402, 403 ... Divided area

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location 9119-2K G03B 3/00 A

Claims (1)

[Claims] 1. A light-receiving element for focus detection is arranged corresponding to each area so that a focus state of each area can be detected by dividing a photographing screen into a plurality of areas. The focus adjustment is performed based on the focus detection signal output from the element, while the focus adjustment is performed using only the focus detection signal output from the specific light receiving element for focus detection during active AF. Focus detection device.