JPH0820592B2 - Projection system for focus detection - Google Patents

Description

The present invention relates to a projection system for automatic focus detection suitable for a photographic camera, a cine camera, a video camera, etc., and particularly to a pattern image on the subject side by the projection system. Automatic focus with improved focus detection accuracy in passive and active automatic focus detection, which is suitable for focus detection of the photographic system by receiving the pattern image projected from the subject side The present invention relates to a projection system for detection.

[Conventional technology]

2. Description of the Related Art Conventionally, two types of focus detection methods are roughly used in photographic cameras, cine cameras, video cameras and the like.

One is a passive method proposed in Japanese Patent Laid-Open No. 54-159259, and the other is, for example, Japanese Patent Laid-Open No. 57-1542.
This is the active method proposed in Japanese Patent Publication No. 06 and the like.

Among them, the active method is a method for performing focus detection by projecting an infrared light flux from the camera side to the subject side and receiving a reflected light flux from the subject, which is accurate even when the subject side is dark or the contrast of the subject is low. It has the feature that it can perform focus detection well. However, when the subject is far away, there is a disadvantage that the amount of reflected light flux decreases and the focus detection accuracy decreases.

The passive method is a method in which focus detection is performed by detecting the image formation state of the subject image by the photographing system by a detection means provided in a part of the camera, and relatively high-precision focus detection is possible even when the subject is far away. There are advantages. However, when the subject side is dark or when the contrast of the subject is low, there is a disadvantage that the focus detection accuracy is reduced.

One method for improving this drawback is, for example, Japanese Patent Publication No. Sho 49-19810.
It has been proposed in the publication. In this publication, a pattern image of a fixed pattern is projected from the camera side to the subject side by a projection system,
Focus detection is performed by detecting the reflection pattern image from the subject.

On the other hand, in recent years, a focus detection method has been proposed in which the above-described two focus detection methods are applied to measure distances at a plurality of points on a subject. Even in such a case, the method of performing focus detection by projecting the above-described pattern image of a fixed pattern to the subject side by the light projecting system and detecting the reflection pattern image from the subject is naturally effective. is there.

However, according to this conventional method, it is difficult to project a pattern image to a plurality of points on a subject, which is a distance measuring point, at the same time. It is necessary to form an image on a wide range or to form a pattern image of a very fine pattern on a wide range by a light projecting lens having a short focal length and a wide angle surface. In any case, in order to form a good pattern image on the object that becomes the focus point, aberration of the projection lens must be corrected well over a wide angle of view. Is quite difficult to achieve. In addition to this,
In the method of creating the large pattern image described above, it is necessary to increase the size of the light source that illuminates this large pattern image.
There is also a problem that it cannot be made compact. Further, in the above-described method of forming a pattern image in a wide range by the projection lens having a very short focal length, it is difficult to increase the aperture of the projection lens, and it is possible to sufficiently increase the reach distance of the illumination light. There are also problems that it is not possible and that it is difficult to create a very fine pattern image.

As a proposal for solving these problems, Japanese Patent Application Laid-Open No. 63-47710 proposes a method in which a plurality of illumination light sources of the type for forming the large pattern image described above are used. However, with such a configuration, the problem of aberration correction of the light projecting lens cannot be solved.

By the way, although the purpose is different, Japanese Patent Application Laid-Open No. 62-247312 proposes a light projecting system in which a light projecting lens is composed of a plurality of lens parts whose optical axes are displaced as means for illuminating a wide range on a subject. In this publication, a pattern image is projected on a long-distance subject as well as a short-distance subject, that is, a problem due to misalignment (parametric) between the optical axis of the light projecting system and the optical axis of the light receiving system is solved. However, the one proposed here can be applied to the projection of a pattern image on a plurality of distance measuring points.

However, even if it is possible to solve the problem due to the above-mentioned parallax by simply constructing the light projecting lens from a plurality of lens units whose optical axes are shifted, the pattern image over a wide range corresponding to the plurality of distance measuring points described above is obtained. It is quite difficult to form a good image.

[Problems that the invention is trying to solve]

The present invention appropriately arranges each element of the light projecting system having a pattern image of a fixed pattern, projects the pattern image on a wide range of subjects with good imaging performance, and particularly performs distance measurement at a plurality of points on the subject. An object of the present invention is to provide a good projection system for an automatic focus detection method.

[Means for solving problems]

The present invention projects a pattern image of a predetermined pattern onto the subject side by a light projecting lens, and receives the pattern image reflected from the subject side by a light receiving system to detect the focus of a photographing system. In the first lens, the projection lens has a first optical axis for forming a pattern image in substantially the same direction as the optical axis of the photographing system, and has an opening not on the first optical axis. And a plurality of second optical axes forming a pattern image in a direction different from the optical axis of the photographing system.
Of the second lens portion having an opening on each of the optical axes.

Other features of the present invention are described in the embodiments.

〔Example〕

FIG. 1 is a perspective view of a light projecting system according to a first embodiment of the present invention. In the figure, 1 is a projection lens, 2 is a pattern having a linear pattern extending in the horizontal direction, and 3 is a light source such as an LED having a relatively large light emitting portion. Further 11,12,1
Reference numerals 3 and 14 denote the four lens portions of the light projecting lens 1, 15 denotes the optical axes of the lens portions 11 and 12, and 16 and 17 denote the optical axes of the lens portions 13 and 14, respectively.

As shown in FIG. 1, the light projecting lens 1 has four lens portions, a lens portion 11 and a lens portion 12 having an optical axis 15, a lens portion 13 having an optical axis 16, and a lens portion 14 having an optical axis 17. ing.

In the present embodiment, the light projecting lens 1 has an optical axis 15 for forming a pattern image in substantially the same direction as the optical axis of the photographing system, that is, a lens portion 11 and a lens portion 12 having an optical axis substantially parallel to the optical axis of the photographing system. , An optical axis that forms a pattern image in a direction different from the optical axis of the imaging system
16, that is, a lens group 13 having an optical axis that is inclined with respect to the optical axis of the photographing system and having an opening near the optical axis 16, and further forms a pattern image in a direction different from the optical axis of the photographing system. optical axis
A lens portion 14 having an opening 17 near the optical axis 17
The three optical axes 15 to 17 and the four lens portions 11 to 14 are included.

FIG. 2 is a diagram showing an optical arrangement in the case where the present invention is applied to a single-lens reflex camera equipped with a passive focus detection device. In FIG. 2, 1, 2, and 3 are the projections of FIG. It corresponds to each lens, pattern and light source. The optical axes 15, 16 and 17 of the four lens portions of the light projecting lens 1 are assumed to extend in the direction perpendicular to the paper surface. In FIG. 2, 21 is a photographing lens, 22 is a quick return mirror, 23 is a sub-mirror, 24 is a field mask, 25 is a converging lens, 26 is a total reflection mirror, 27 is a pupil division mask, 28 is an imaging lens, 29 Is the light receiving part,
30 is a film side. In the present embodiment, a part of the subject image formed near the visual field mask 24 arranged near the planned image forming surface of the taking lens 21 is formed on the light receiving unit 29 by the image forming lens 28, and the passive system is used. Focus detection.

FIG. 3 is a perspective view of a main part of a portion which constitutes the focus detection device of FIG. In the figure, reference numerals 24 to 29 correspond to those in FIG. 2, respectively. In this embodiment, as shown in FIG. 3, a visual field mask 24 having three openings is provided in a direction perpendicular to the paper surface of FIG. 2, and a subject image formed near each of the openings is focused by a condenser lens. 25 and an image forming lens 28 having two lens parts divides into two object images corresponding to two areas of the exit pupil of the taking lens 1, and forms an image on the light receiving part 29 by the phase difference detection method. The distance measurement is performed at three points corresponding to the three openings of the field mask 24.

4 and 5 are diagrams showing the positional relationship between the pattern image projected onto the subject and the distance measuring field of view. FIG. 4 shows the case where the taking lens is a wide-angle lens, and FIG. This shows the case where the taking lens is a telephoto lens. In FIGS. 4 and 5, reference numerals 31, 32, and 33 represent images of the pattern formed on the subject by the light projecting lens. The lens portion of the light projecting lens 1 in FIG. 13,14
The image of the pattern 2 is shown. Also, 34,3 in Fig. 4
Reference numerals 5 and 36 denote images obtained by projecting the three distance measuring fields of FIG. 3 onto the subject when the taking lens 1 of FIG. 2 is a wide-angle lens. FIG. 5 shows the taking lens 1 of FIG. 3 shows an image obtained by projecting the three distance measuring fields of FIG. As shown in FIGS. 4 and 5,
In a single-lens reflex camera equipped with a focus detection device having a plurality of focus detection points as in this embodiment, a projection lens is used to project a pattern onto an area on a subject corresponding to the plurality of focus detection points. It is effective to form a plurality of patterns of images on the subject by using a plurality of lens units, especially when a wide-angle lens is attached or when the zoom lens is set to the wide-angle side.

In this embodiment, as shown in FIGS. 1, 4, and 5, the pattern is a striped pattern in which filaments having different widths are collected. This is because it is assumed that the light receiving unit 29 is composed of a plurality of one-dimensional line sensors such as CCDs, as is normally used in the focus detection device as shown in FIG. This makes it easier to detect the contrast in the arrangement direction of. In the phase difference detection type focus detection apparatus as in the present embodiment, in order to easily detect the contrast in the sensor array direction, it is possible to create a striped pattern in the sensor array direction and the vertical direction and project it on the subject. It is often done.

FIG. 6 is a diagram for explaining the features of the embodiment, and is a diagram of the light projecting lens 1 of FIG. 1 seen from the front. 11,1 in the figure
2,13,14 are the four lens parts in FIG. 1, and 15,16,17 are the first
It corresponds to the three optical axes in the figure. As shown in FIG. 6, the present invention preferentially arranges a lens portion that forms a pattern image in a direction different from the optical axis of the taking lens near the optical axis.

Normally, the projection system for focus detection has a pattern image forming performance for increasing the aperture of the projection lens for reaching the pattern image to a long distance and for increasing the contrast of the object to be measured. Is required, and a compact structure is required. In order to satisfy these requirements, conventionally, an aspherical surface has been introduced into a light projecting lens to mainly correct axial aberration well. However, in the light projection system of the focus detection apparatus for measuring a plurality of distance measuring points as in the present embodiment, in order to form a pattern image on a wide range of subjects, off-axis various aberrations are favorably achieved over a wide angle of view. Further correction is also required. It is difficult in terms of aberration correction to satisfy the above conditions with a normal method. Now, in order to form a pattern image on a wider range of subjects, the pattern image is formed on the light projecting lens in substantially the same direction as the optical axis of the photographing lens. It is considered that a lens unit that forms a pattern image in a direction different from the optical axis of the taking lens is provided outside a lens unit that corresponds to a conventional light projecting lens. At this time, if the optical axis of the lens unit that forms the pattern image in a direction different from the optical axis of the taking lens is inside this lens unit, it becomes relatively easy to correct various aberrations. Since it is required to project a pattern image on a long-distance and wide-range subject, the projection lens usually has to have a large aperture and a short focal length, and the projection lens must be in a direction different from the optical axis of the shooting lens. The optical axis of the lens portion that forms the pattern image often exists inside the lens portion that forms the pattern image in the substantially same direction as the optical axis of the taking lens, and it is difficult to correct various aberrations. Therefore, when the optical axis of the lens unit that forms the pattern image in a direction different from the optical axis of the photographing lens exists near the optical axis of the lens unit that forms the pattern image in substantially the same direction as the optical axis of the photographing lens, A lens portion for projecting a pattern image in a direction different from the optical axis of the taking lens was preferentially arranged near the optical axis. At this time, the lens portion that forms the pattern image in substantially the same direction as the taking lens loses the opening near the optical axis, but this lens portion can be realized by mainly correcting axial aberration as in the past. Is possible. When the pattern is arranged substantially perpendicular to the optical axis of the taking lens and a plurality of images are projected on the subject, the position where the pattern is arranged for the lens unit that forms the pattern image in a direction different from the optical axis of the taking lens. Is a position with a considerably large angle of view. In such a case, it is usually difficult to correct various aberrations. Therefore, in this example, a lens unit that forms a pattern image in a direction different from the optical axis of the taking lens is preferentially arranged near the optical axis. I am trying.

[Other Examples]

FIG. 7 shows a sectional view of a light projecting system according to a second embodiment of the present invention. In the figure, 41 is a projection lens, 42 is an auxiliary lens, 43
Is a pattern, and 44 is a light source. In this embodiment, an auxiliary lens is arranged behind the light projecting lens to shorten the focal length of the light projecting optical system so that the pattern image can be projected onto a wider range of subjects.

FIG. 8 shows a front view of the light projecting lens 41 of FIG. In the figure, 51 to 54 correspond to the four lens portions in FIG. Also in this embodiment, the light projecting lens 41 has substantially the same shape as the light projecting lens 1 shown in FIG. 6, and the lens portion for forming the pattern image in a direction different from the optical axis of the taking lens is provided. It is placed preferentially near the optical axis.

When the projection optical system is composed of a plurality of lenses as in this embodiment, the projection optical system is a decentered optical system with respect to the lens unit that forms a pattern image in a direction different from the optical axis of the photographing lens. Become. In this example, the lens portion that forms the pattern image in a direction different from the optical axis of the taking lens is configured near the optical axis where the curvature becomes relatively gentle. It will be easier.

FIG. 9 is a diagram showing another method of dividing the aperture of the light projecting lens. In the figure, reference numerals 61 to 66 denote six lens portions, 67 denotes optical axis positions of the lens portions 61 and 62, and 68 to 71 denote optical axis positions of the lens portions 63 to 66, respectively. This embodiment is a development of the method of dividing the aperture of the projection lens shown in FIG.
The configuration has five optical axes. With the configuration shown in FIG. 9, it is possible to illuminate a wider area.

In some of the embodiments described above, all the optical axes of the lens parts constituting the light projecting lens are arranged in a straight line. This is the focus detection point of the focus detection device shown in FIGS. 2 and 3. However, they are arranged in a straight line, and the purpose is to illuminate them. Therefore, when it is necessary to illuminate a wide range that is not on a straight line, the optical axis position of the lens unit may be set appropriately according to the illumination range.

The projection system for automatic focus detection described above can be favorably applied to both the passive system and the active system.

〔The invention's effect〕

As described above, according to the present invention, it is possible to achieve a projecting system for automatic focus detection having a compact structure that projects a pattern image of a predetermined pattern on a wide range of subjects with good imaging performance. There is. In particular, it is suitable for a light projection system for automatic focus detection that measures distances at a plurality of points.

[Brief description of drawings]

FIG. 1 is a perspective view of a first embodiment of the present invention, FIG. 2 is an optical layout diagram when applied to a single-lens reflex camera, and FIG. 3 is a perspective view of a focus detection device for performing distance measurement at a plurality of points, 4 and 5 are explanatory views showing the positional relationship between the pattern image on the subject and the distance measuring field, FIG. 6 is a front view of the light projecting lens of the first embodiment of the present invention, and FIG. 7 is the present invention. FIG. 8 is a sectional view of a second embodiment, FIG. 8 is a front view of a light projecting lens of a second embodiment of the present invention, and FIG. 9 is a front view of a light projecting lens of a third embodiment of the present invention. 1 is a light projecting lens, 2 is a pattern, 3 is a light source, 11 to 14 are lens parts of the light projecting lens, 15 to 17 are optical axes of the lens part, 21 is a photographing lens, 22 is a QUIK clean turn mirror, and 23 is Sub-mirror, 24 field mask, 25 condenser lens, 26 total reflection mirror, 27 pupil division mask, 28 imaging lens, 29 light receiving part, 30 film surface, 31 to 3 pattern projection image, 34 to 36 are projection images of the distance measuring field.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-233610 (JP, A) JP-A-63-32508 (JP, A) JP-A-62-247312 (JP, A) Sankaihei 1- 64608 (JP, U)

Claims (1)

[Claims] 1. A light projection system for detecting a focus of a photographing system by projecting a pattern image of a predetermined pattern onto a subject side by a light projecting lens and receiving the pattern image reflected from the subject side by a light receiving system. In the first lens, the projection lens has a first optical axis for forming a pattern image in substantially the same direction as the optical axis of the photographing system, and has an opening not on the first optical axis. And a plurality of second optical axes forming a pattern image in a direction different from the optical axis of the imaging system, and a plurality of second optical axes each having an opening on the second optical axis. A light projecting system for focus detection, which is configured by a lens section.