JPH0341407A - Focus detector - Google Patents

Abstract

PURPOSE:To enable high-accuracy focus detection even at plural points in a photographing range as to a low-brightness object by using plural focus detection systems which have unequal optical characteristics such as stopping aperture area and an interval between aperture centers and an auxiliary illuminating system. CONSTITUTION:The focus detector consisting of a visual field mask 31, a field lens 32, a diaphragm 33, a secondary image forming lens 34, and a sensor is provided with a 1st focus detection system consisting of stopping apertures 33-1a and 33-1b, lenses 34-1a and 34-1b, and sensors 35-1a and 35-1b and a 2nd focus detection system consisting of stopping apertures 33-1c and 33-1d, lenses 34-1c and 33-1d, and sensors 35-1c and 35-1d corresponding to orthogonal directions of the center part of an image pickup screen so that a part of a detected object image is shared. Thus, the 1st and 2nd focus detection systems which have unequal optical characteristics are used, a pattern in a specific shape is projected on the object from the auxiliary illuminating system, and the light quantity distribution of the pattern image is detected to enable high- accuracy detection even when the brightness of the object is low.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a focus detection device suitable for photographic cameras, video cameras, etc. In particular, the pupil of an objective lens is divided into a plurality of regions, and the focus detection device is configured to pass through each region. A focus detection device suitable for detecting the in-focus state of an objective lens by forming a light amount distribution regarding a plurality of subject images (object images) using a light flux and determining the relative positional relationship of these multiple light amount distributions. It is related to.

(Prior Art) Conventionally, there is a so-called image shift method as a light-receiving focus detection method that utilizes a light beam passing through an objective lens.

This image shift method has been proposed, for example, in Japanese Patent Laid-Open No. 59-107311 and Japanese Patent Laid-Open No. 59-107313.

FIG. 8 is a schematic diagram of an optical system of a focus detection device using a conventional image shift method.

In the figure, 61 is an objective lens, and 62 is a field mask, which are arranged in the vicinity of the intended image formation plane of the objective lens 61.

Reference numeral 63 denotes a field lens, which is arranged near the intended image plane. 64 is a secondary optical system, which includes two lenses 64-1.64 arranged symmetrically with respect to the optical axis of objective lens 61.
64-2. Reference numeral 65 denotes a light receiving means, which has two light receiving element arrays 65-1 and 65-2 arranged behind the two lenses 64-1 and 64-2. 66 is an aperture which connects the two lenses 64-
1.64-2 and has two openings 66-1.66-2 arranged in front thereof. 67 is the exit pupil of the objective lens 61, which is divided into two areas 67-1.
．． 67-2.

Note that the field lens 63 has an opening 661.66-2.
It has the function of forming an image on the areas 67-1 and 67-2 of the exit pupil 67, and the light flux transmitted through each area 67-1, 67-2 is focused on the light receiving element array 65-1, 65-2. Each of them forms a light amount distribution.

In the focus detection device shown in FIG. 8, when the imaging point of the objective lens 61 is in front of the intended imaging plane, object images are formed on the two light-receiving element rows 65-1 and 65-2, respectively. When the light intensity distributions of the objective lens 61 become close to each other and the image forming point of the objective lens 61 is located behind the planned image forming plane,
The light quantity distributions formed on the two light receiving element rows 65-1 and 65-2 are separated from each other. Moreover, since the amount of deviation in the light intensity distribution formed on the two light-receiving element arrays 65-1 and 65-2 has a certain functional relationship with the amount of defocus of the objective lens 61, the amount of deviation can be calculated using an appropriate calculation means. Once calculated, the direction and amount of defocus of the objective lens 61 can be detected.

The focus detection device shown in FIG. 8 performs distance measurement for a subject located approximately in the center of a subject range photographed by an objective lens.

In contrast, the present applicant had previously filed a patent application for a focus detection device capable of detecting focus at distance measuring points other than the center of the shooting range.
It is proposed in No. 2-279835.

FIG. 9 is a schematic diagram of the optical system of a focus detection device for multiple distance measuring points proposed in Japanese Patent Application No. 62-279835. In the figure, 71 is a field mask, 72 is a field lens, and 7
3 is an aperture having two open lowers 3-1°73-2, 74
denotes a secondary optical system consisting of two lenses 74-1 and 74-2, and 75 denotes a sensor, respectively. Note that the objective lens 61 shown in FIG. 8 is omitted.

In the figure, a field mask 71 has a plurality of open lower parts 1a to 71e corresponding to a plurality of fields of view to be measured, and a light flux regulated by this field mask 71 is formed by a secondary optical system 74. A plurality of pairs of sensor rows 75a1 and 75a2, 75b1 and 75b2 .
75c1 and 75c2.75d1 and 75d2, and 75
e1 and 75e2 are provided as sensors 75.

In the figure, distance measurement is performed in a total of five areas: the center of the photographic screen and four areas on both sides thereof. The ability to detect focus in a plurality of areas in a photographic screen with such a simple configuration is very important when applied to cameras.

The focus detection device shown in Fig. 9 can detect objects whose light intensity distribution changes in this direction because the direction in which the two light intensity distributions on the sensor move relative to each other depending on the focus state of the objective lens is the vertical direction. Distance measurement is possible only for objects whose light intensity distribution changes only in the perpendicular direction, such as black and white edge patterns with vertical lines as boundaries. .

For this reason, the applicant proposed in Japanese Patent Application No. 63-274940 that it is possible to measure distances even for objects whose light intensity distribution changes only in one direction, vertically or horizontally, near the center of the photographing range. We have proposed a focus detection device that can measure distances at multiple points other than the vicinity of the center of the photographic range.

FIG. 10 is a schematic diagram of the main parts of the focus detection device proposed in Japanese Patent Application No. 63-274940.

In the figure, reference numeral 31 denotes a field of view mask, which intersects approximately the center of the photographic field by an objective lens (photographing lens) not shown, and has, for example, a cross-shaped opening 31-1 and vertically elongated openings 3 at the periphery on both sides.
1-2.31-3. 32 is a field lens, and the three openings 31-1.3 of the field mask 31
It consists of three regions 32-1.32-2.32-3 each having a predetermined optical characteristic corresponding to 1-2.degree. 31-3. 33 is a diaphragm, and the center part has a total of four openings 33-1a, one pair each on the top, bottom, left and right.

33-1b, 33-1c, 33-1d, and a pair of two openings 33-2a on the left and right peripheral portions.

33-2b and openings 33-3a and 33-3b are provided, respectively. Each region 32-1.32-2.32-3 of the field lens 32 has a pair of apertures 33-1.33-2.33-3 as an exit pupil of a photographing lens (not shown). It has the effect of forming an image nearby. 34 is a secondary optical system, which has a total of four pairs of secondary imaging lenses. That is, there are eight secondary imaging lenses 34-1a, 34-1b, and 34-1c in total.

34-1d, 34-2a, 34-2b, 34-3a, 3
4-3b, which are arranged behind each opening of the diaphragm 33 in correspondence with each other.

35 is a light receiving element array (sensor), which has four pairs of sensor arrays as a whole. That is, eight sensor rows 35-1a, 35-1b, 35-1c, 35-1d, 3
5-2a, 35-2b.

It consists of 35-3a and 35-3b, and is arranged so as to correspond to the secondary imaging lens and receive its image.

FIG. 11 is an explanatory diagram showing an image area formed on the surface of the sensor 35 in FIG. 10. Regions 36Ia, 36-1b,
36-1c and 36-1d are the image areas of the central aperture 31-1 of the field mask 31, and the light flux that has passed through the central part 32-1 of the field lens 32 is directed to the aperture 33-1 of the diaphragm 33.
a.

After being regulated by 33-1b, 33-1c, and 33-1d,
Secondary imaging lens 34-1a behind it.

Sensor 3 by 34-1b, 34-1c, 34-1d
The state in which they are formed on five sides is shown. Also, 36
-2a and 36-2b are openings 3 around the visual field mask 31;
1-2, and the light beam transmitted through the peripheral portion 32-2 of the field lens 32 is transmitted through the aperture 33-2a of the diaphragm 33.
, 33-2b, the sensor 35 is regulated by the secondary imaging lenses 34-2a, 34-2b behind them.
The state formed above is shown. Similarly, 36-3a,
36-3b is the image area of the peripheral opening 31-3 of the field mask 31, and the peripheral part 32-3 of the field lens 32.
The luminous flux transmitted through the apertures 33-3a and 33-3 of the diaphragm 33
3b and then formed on the surface of the sensor 35 by the secondary imaging lenses 343a and 34-3b behind it.

(Problems to be Solved by the Invention) The focus detection device shown in FIG. To enable distance measurement, four apertures were provided in the center of the diaphragm: top, bottom, left and right. In addition, in order to perform highly accurate focus detection, it is necessary to ensure that the light beam incident on the focus detection device is not blocked by the objective lens, but in order to satisfy this condition, the power of the field lens and objects not shown are required. Each aperture of the diaphragm must be located within a certain area determined by the size of the exit pupil of the lens. Therefore, compared to a conventional focus detection device having only two apertures as shown in FIG. 8, each aperture in a focus detection device having four apertures as shown in FIG. The amount of light that can be directed to the system's sensors is reduced. As a result, the low-brightness limit value of object brightness at which each focus detection system can operate increases, causing problems such as focus detection becoming impossible for dark objects and focus detection accuracy decreasing. there were.

The present invention uses a plurality of focus detection systems and auxiliary illumination systems with each element set appropriately. In this case, a pattern of a predetermined shape is projected toward the subject from the camera body or an auxiliary illumination system installed in a strobe, etc., a pattern is formed on the subject surface, and the light intensity distribution of the pattern image is detected. Accordingly, it is an object of the present invention to provide a focus detection device that can perform highly accurate focus detection at a plurality of points within a photographing range, regardless of the brightness of a subject.

(Means for Solving the Problems) The focus detection device of the present invention includes at least a first lens on the image plane side of the objective lens. In addition to arranging the second two focus detection systems,
An auxiliary illumination system is provided that projects a pattern in which the light intensity distribution changes in the dimensional direction toward the subject side, and when the focus detection system is used to determine the in-focus state of the objective lens, the focus detection system is a secondary optical system that forms a plurality of light intensity distributions regarding a subject image using light fluxes that have passed through different areas of the pupil; an aperture that limits the amount of light incident on the secondary optical system; and a relative relationship between the plurality of light intensity distributions. and a light receiving means for detecting the positional relationship between the first and second positions. The second focus detection systems have at least a part of the light intensity distribution regions of the subject images in common with each other, and the directions of change in the light intensity distribution of the subject images that cannot be detected are different from each other,
And the first one. The apertures of the second focus detection system are characterized in that their optical characteristics are different from each other.

(Example) Fig. 1 is a schematic diagram of the main parts of the first embodiment of the present invention, Fig. 2 is an explanatory diagram of the aperture shown in Fig. 1, and Fig. 3 is an application of the focus detection device of the present invention to a single-lens reflex camera. FIG. 2 is a schematic diagram of an example when

This embodiment is characterized in that the optical characteristics of the aperture are significantly different from those of the conventional focus detection device shown in FIG.

Next, each element of the present invention will be sequentially explained with reference to FIGS. 1 to 3.

31 in the figure is a field mask and an objective lens (photographing lens)
37, for example, a cross-shaped opening 31-1 and vertically elongated openings 31-1 at the periphery of both sides.
2.31-3. 32 is a field lens, which has three openings 31-1, 31- of the field mask 31;
It consists of three regions 32-1.32-2.32-3, each having a predetermined optical characteristic, corresponding to 2.313.

33 is a diaphragm, and the center part has a total of four openings 33-, one pair each on the top, bottom, left and right sides, which are inscribed in a nearly perfect circular area 52-1.
1a, 33-1b, 33-1c, and 33-1d, and the left and right peripheral portions are approximately perfect circular areas 52-2, 52-3, respectively.
A pair of two openings 33-2a and 33-2b inscribed in
and openings 33-3a and 33-3b are provided, respectively. Each area 32-1 of the field lens 32.
32-2, 32-3 are the apertures 33-1, 33-2 and 33-3, which are paired with the aperture 33, respectively, and the photographing lens 37.
It has the effect of forming an image near the exit pupil of the lens. 34 is a secondary optical system, which has a total of four pairs of secondary imaging lenses.

That is, there are eight secondary imaging lenses 341a, 34- in total.
1b, 34-1c, 34-1d.

34-2a 34-2b, 34-3a, 34-3
b, and are arranged behind each opening of the diaphragm 33 in correspondence with each opening.

35 is a light receiving element array (sensor), and has four pairs of sensor arrays as a whole. That is, eight sensor rows 35-1a, 35-1b, 35-1c, 35-1d,
35-2a, 35-2b.

It consists of 35-3a and 35-3b, and is arranged so as to correspond to the secondary imaging lens and receive its image.

In this embodiment, each element 31-2, 32-2, 33-2.
34-2a, 34-2b, 35-2a, 35-2b or each element 31-3.32-3.33-3a, 33-3b,
34-3a, 343b, 35-3a, and 35-3b constitute one focus detection system (third focus detection system).

In FIG. 3, reference numeral 101 is a projection lens, which projects a pattern as shown in FIG. 6 when the subject is dark or has low contrast.

37 is a photographing lens (objective lens), 38 is a quick return mirror, 39 is a focus plate, 40 is a pentaprism, 4
1 is an eyepiece lens, 42 is a film surface, and 43 is a submirror. Reference numeral 31 denotes a field mask, which is arranged at a position optically approximately equivalent to the film surface 42. 44 is an infrared cut filter arranged behind the visual field mask 31.

32 is a field lens, 45.46 is the 1st degree and the 2nd degree, respectively.
Total reflection mirror 47 is a light shielding mask, 33 is an aperture, 34
is a secondary optical system, which is formed integrally with a prism member 49, which will be described later. 49 is a prism member having a reflective surface 49-1, 35 is one sensor, and cover glass 5
0-1 and a light receiving surface 50-2.

In the figure, everything from the field mask 31 to the sensor 35 corresponds to the focus detection device shown in FIG.

In this embodiment, the opening 31-1 and the field lens 32-
1. Diaphragm apertures 33-1a, 33-1b, secondary imaging lenses 34-1a, 34-1b, sensors 35-1a, 35-1
5 aperture 31-1, field lens 32-1, aperture aperture 33-1c, 33-1d, secondary imaging lens 34-1c,
34-1d, sensor 35-1c.

35-1d constitutes a second focus detection system.

The distance measurement principle of the focus detection device according to the first embodiment of the present invention shown in FIG. ing.

Then, the first one corresponds to the direction orthogonal to the center of the photographic screen. A part of the subject whose distance is measured by the second focus detection system is common to all shots.

Next, the optical characteristics of the aperture 33 in this embodiment will be explained.

In FIG. 2, the [1 radial eclipse of the objective lens is larger in the periphery of the aperture 33 than in the center, so the region 52-1
The diameter of the region 52-2 and 52-3 is set smaller than the diameter of the region 52-2.52-3. Since the vignetting of the objective lens in the periphery mainly occurs in the left-right direction in FIG.
It is also possible to provide it within 2° 6 52'-3. By doing so, it becomes possible to introduce a larger amount of light.

In the first embodiment of the present invention shown in FIG.
-1 a, 33-1 b force spreads left and right 133-
Its area is set larger than that of 1c and 33-1d. The focus detection systems corresponding to the upper and lower apertures 33-1a and 33-1b and the focus detection systems corresponding to the right apertures 1-133-Ic and 33-1d are treated equally, and both focus detection systems can operate. Based on the concept of equalizing the limits on the low luminance side of a subject, the central aperture of the diaphragm 33 may be equally divided into four parts as shown in FIG. 12, for example.

However, when doing this, compared to a conventional focus detection device with only two aperture openings as shown in Figure 8, the light -qf incident on the focus detection system is reduced to less than half, making it easier to photograph dark objects. If the subject is particularly dark, focus detection may become impossible or the accuracy of focus detection may decrease.
It is necessary to operate the auxiliary illumination system and project a pattern onto the subject to ensure brightness and contrast, but even at this time, there is a significant disadvantage in terms of brightness compared to conventional focus detection devices.

On the other hand, if the aperture aperture of the diaphragm according to the present invention as shown in FIG. Aperture aperture 33-1a of the focus detection system that is easier to detect
, 33-1b are set large, the decrease in light amount is alleviated, and the low luminance limit is prevented from becoming extremely high.
It becomes possible to do so.

In this example, the projection pattern of the auxiliary illumination system is the sixth
We used the case of horizontal stripes as shown in the figure, but this means that the projection pattern of the auxiliary illumination system to be used in the two left and right peripheral fields of view other than the center of the focus detection device shown in Figure 1 is a similar horizontal stripe. This is because it was taken into consideration.

In other words, if the direction of change in the light intensity distribution of the projection pattern of the auxiliary illumination system used in the three fields of view is the same, it becomes possible to illuminate the three fields of view by simultaneously projecting one pattern, and the auxiliary illumination system This is very advantageous in simplifying the configuration.

In addition, in the present invention, the shape of the diaphragm 33 that changes the optical characteristics due to the diaphragm aperture at the center of the diaphragm 33 can be modified in various ways other than that shown in FIG.

FIGS. 5(8), CB) and ((:) are schematic diagrams of the second, third and fourth embodiments, respectively, showing the shape of the aperture opening at the center of the aperture 33 according to the present invention.

In the second embodiment shown in FIG. 5(A), the center aperture of the diaphragm corresponds to the center aperture of the diaphragm of the first embodiment shown in FIG. This is applied when wM is as shown in FIG. The projection patterns of existing auxiliary illumination systems built into strobes, etc., used in ordinary focus detection devices as shown in Figure 8, often have vertical stripes. This is effective when maintaining the integrity of

The feature of the third embodiment shown in FIG. 5(B) is that among the four apertures at the center of the diaphragm, the center distances a and b between two paired apertures have a relationship of a>b. It is well known that the distance between the centers of the two diaphragm apertures forming a pair corresponds to the so-called base line length in focus detection, and that the longer the distance, the higher the accuracy of focus detection.

In this embodiment, by increasing the base line length of the focus detection system that is easier to detect the projection pattern of the auxiliary illumination system, the focus detection accuracy is prevented from decreasing at low brightness and low contrast.

The fourth embodiment shown in FIG. 5(C) is characterized by four aperture openings L.
1, that is, the aperture widths c and d in the direction in which the image shifts depending on the focal state of the objective lens have a relationship of c<d. In other words, the aperture width in the viewing direction corresponds to the F number in the same direction, and within the range where the influence of diffraction can be ignored, the larger it is (the narrower the aperture width), the more the image formed on the sensor will be in the viewing direction. Contrast becomes higher.

This embodiment attempts to prevent a decrease in focusing accuracy at low brightness and low contrast by increasing the F number in the field of view of the focus detection system, which makes it easier to detect the projection pattern of the auxiliary illumination system. .

In addition, 3rd. The fourth embodiment is for the case where the projection pattern of the auxiliary illumination system mainly has a light amount distribution change in the vertical direction. However, when the same pattern has a light amount distribution change mainly in the horizontal direction, the aperture aperture is set to 90. The relationship that only needs to be rotated and replaced is exactly the same as the relationship shown in FIG. 2 and FIG. 5(A). Also, in the above explanation, the area, baseline length, F
Although each specification related to the aperture opening L1, such as the number, has been described individually, the object of the present invention can be achieved even if two or more of these specifications are unequal at the same time.

(Effects of the Invention) According to the present invention, by sharing the field of view in the photographing range,
In a focus detection device that has a plurality of focus detection systems that perform focus detection in at least two directions of a subject with different light intensity distribution changes, the optical characteristics of the diaphragm, such as the area of the diaphragm aperture, the distance between the centers of the apertures, the aperture width, etc. By making the optical characteristics unequal among multiple focus detection systems, it is possible to reduce the rate of non-detection of focus detection for low-brightness subjects, and to alleviate the decline in focus detection accuracy for low-brightness subjects. be able to. In particular, when an auxiliary illumination system is used, the consistency with the projection pattern is taken into account, so a focus detection device that can perform good focus detection even for objects at a longer distance can be used. .

[Brief explanation of drawings]

zi diagram is a schematic diagram of the main parts of the first embodiment of the present invention, FIG. 2 is an explanatory diagram of the aperture of FIG. 1, and FIG. 3 is a schematic diagram of an embodiment when the present invention is applied to a single-lens reflex camera. 4th. FIG. 5 is an explanatory diagram of another embodiment of the aperture according to the present invention, and FIG. FIG. 7 is an explanatory diagram of a projection pattern according to the present invention, and FIG. 9th. 1st
FIG. 0 is a schematic diagram of the main parts of a conventional automatic focus detection device, FIG. 11 is an explanatory diagram of a part of FIG. 10, and FIG. 12 is an explanatory diagram of a conventional aperture. 3 In the figure, 31 is a field mask, 32 is a field lens, 3
3 is an aperture, 34 is a secondary optical system, 35 is a sensor, 37 is an objective lens, 44 is an infrared cut filter, 101 is a light projection lens, and 102 is a pattern.

Claims (1)

[Claims] (1) At least a first and a second lens on the image plane side of the objective lens.
When determining the in-focus state of the objective lens using the focus detection system, an auxiliary illumination system is provided that projects a pattern in which the light intensity distribution changes in a one-dimensional direction toward the subject. , the focus detection system includes a secondary optical system that forms a plurality of light intensity distributions regarding the subject image using light fluxes that have passed through different regions of the pupil of the objective lens, and an aperture that limits the amount of light that enters the secondary optical system. and a light receiving means for detecting the relative positional relationship of the plurality of light quantity distributions,
The first and second focus detection systems have at least a part of the light intensity distribution area of the subject image in common with each other, and the directions of change in the light intensity distribution of the subject image that cannot be detected are different from each other. , and a focus detection device characterized in that the apertures of the first and second focus detection systems have different optical characteristics. (2) The apertures of the first and second focus detection systems are different from each other in at least one of three factors: the aperture area, the distance between aperture centers, and the aperture width in the same direction as the detection direction of the light amount distribution of the subject image. Claim 1 characterized in that the optical characteristics are different by tightening the optical properties.
The focus detection device described. (3) The focal point of the larger of the angles formed by the direction of change in the light amount distribution of the object image that cannot be detected among the first and second focus detection systems and the direction of change in the light amount distribution of the pattern projected by the auxiliary illumination system. In the detection system, the aperture area of the aperture of the focus detection system is made larger than other apertures, or the distance between aperture centers is made larger than other apertures, or in the same direction as the detection direction of the light amount distribution of the subject image. 2. The focus detection device according to claim 1, wherein at least one of the following aperture widths is made narrower than other aperture widths. (4) The focus detection device has a third focus detection system that detects the light intensity distribution of the subject image in substantially the same direction as the direction of change in the light intensity distribution of the pattern projected by the auxiliary illumination system. The focus detection device according to claim 1.