JPH02101413A - Light projecting system for focus detection - Google Patents

Abstract

PURPOSE:To project a pattern image on an object having a wide extent with good image forming performance by constituting a projecting lens of lens sections which are elongated in the direction of the stripe of the striped pattern image and shifted from each other in apex position. CONSTITUTION:When the focus of a photographing system is detected by projecting a striped video camera image 2 on an object by means of a light projecting lens 1 and receiving the pattern image 2 reflected by the object by means of a light receiving system, the light projecting lens 1 is constituted of three lens sections 11, 12, and 13 respectively having optical axes 14, 15, and 15 and the pattern image 2 is respectively projected in different directions by means of the lens section 11-13. Therefore, the striped pattern image can be projected on an object having a wide extent with excellent image forming performance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a light projection system for automatic focus detection suitable for photographic cameras, cine cameras, video cameras, etc. Automatic focus that improves focus detection accuracy in passive and active automatic focus detection, which is suitable for detecting the focus of a photographing system by projecting light and receiving the pattern image reflected from the subject side. This relates to a light projection system for detection.

[Conventional technology]

BACKGROUND ART Conventionally, two types of focus detection methods have been used in photographic cameras, cine cameras, video cameras, and the like.

One is the passive method proposed in, for example, Japanese Patent Application Laid-open No. 54-159259, and the other is the passive method proposed in, for example, Japanese Patent Application Laid-Open No.
This is an active method proposed in Publication No. 7-154206 and the like.

Among these, the active method detects the focus by emitting, for example, an infrared beam from the camera side toward the subject and receiving the reflected beam from the subject, so it is accurate even when the subject is dark or the contrast of the subject is low. It has the advantage of being able to perform focus detection well. However, when the subject is far away, the amount of reflected light flux decreases, resulting in a decrease in focus detection accuracy.

The passive method detects the focus by detecting the imaging state of the subject image by the imaging system using a detection means installed in a part of the camera, and allows relatively high-precision focus detection even when the subject is far away. There are advantages. However, there is a drawback that focus detection accuracy decreases when the subject side is dark or when the contrast of the subject is low.

One method to improve this drawback is, for example,
This is proposed in Publication No. 10. In this publication, focus detection is performed by projecting a pattern image of a certain pattern from the camera side to the subject side using a light projection system and detecting the reflected pattern image from the subject.

On the other hand, in recent years, a focus detection method has been proposed that applies the two focus detection methods described above to measure distances at a plurality of points on a subject. Even in such cases, the method of detecting focus by projecting a fixed pattern image onto the subject using the projection system and detecting the reflected pattern image from the subject is of course effective. be.

However, with this conventional method, it is difficult to simultaneously project pattern images onto a plurality of points on a subject that serve as distance measurement points. In order to project pattern images onto multiple points at the same time, it is necessary to create a large pattern image in advance and focus it over a wide area, or to project a very fine pattern image over a wide angle of view with a short focal length. It is necessary to form an image over a wide range using an optical lens. In any case, in order to properly form a pattern image on the subject that will be the distance measurement point, the aberration of the projection lens must be well corrected over a wide angle of view. It is quite difficult to realize this. In addition to this, the above-described method for creating a large pattern image requires a large light source for illuminating the large pattern image, and there is also the problem that a compact configuration cannot be achieved. In addition, in the method described above in which a pattern image is formed over a wide area using a light projection lens with a very short focal length, it is difficult to make the aperture of the projection lens wide, so (The problem of not being able to
Another problem was that it was difficult to create very fine pattern images.

As a proposal to solve these problems, Japanese Patent Application Laid-Open No. 63-47710 proposes a system in which a plurality of illumination light sources are used to create the above-mentioned large pattern image. However, such a configuration cannot solve the above-mentioned problem of correcting aberrations of the light projecting lens.

Although the purpose is different, Japanese Patent Application Laid-Open No. 62-247312 proposes a light projection system in which a light projection lens is composed of a plurality of lens parts whose optical axes are shifted as means for illuminating a wide area on a subject. The publication proposes to project a pattern image onto both a distant subject and a close subject, in other words, to solve the problem caused by misalignment (parallax) between the optical axis of the light emitting system and the optical axis of the light receiving system. However, the method proposed here can be applied to projecting pattern images onto multiple distance measurement points.

However, even if it is possible to solve the problem caused by the above-mentioned variax by simply constructing the projecting lens from a plurality of lens parts with shifted optical axes, it is possible to solve the problem of the above-mentioned variax. It is quite difficult to form an image well.

[Problems to be Solved by the Invention] The present invention appropriately arranges each element of a light projection system having a striped pattern image,
The purpose of the present invention is to provide a light projection system that projects a pattern image over a wide range of objects with good imaging performance, and that is particularly suitable for an automatic focus detection method that measures distances at multiple points on the object.

[Means for solving problems]

In the present invention, a striped pattern image is projected by a projecting lens.
When the pattern image projected onto the subject side and reflected from the subject side is received by the light receiving system to detect the focus of the photographing system, the projecting lens is elongated in the direction of the stripes of the striped pattern image. It is composed of a plurality of lens parts that have different shapes and whose apex positions (optical axis positions) are shifted.

Other features of the invention are described in the Examples.

〔Example〕

FIG. 1 is a perspective view of a light projection system according to a first embodiment of the present invention.

In the figure, ■ represents a light projection lens, 2 represents a striped pattern extending in the horizontal direction, and 3 represents a light source such as an LED having a relatively large light emitting portion. Further 11. 1
2. 13 are three lens parts constituting the projection lens 1;
14. 15. 16 are lens portions 11 .
12. It represents 13 optical axes.

That is, as shown in FIG. 1, the projecting lens 1 includes a lens portion 11 having an optical axis 14, a lens portion 12 having an optical axis 15,
It has three lens parts, a lens part 13 having an optical axis 16. Then, the three lens parts 11 of the light projecting lens l.
12. 13, the pattern images 2 are projected in different directions.

FIG. 2 is a diagram showing the optical arrangement when the present invention is applied to a single-lens reflex camera equipped with a passive focus detection device. , pattern, and light source, respectively. Also, the optical axes 14 of the three lens parts of the light projection lens 1. 15. 1
6 is 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 submirror, 24 is a field of view mask, 25 is a condensing lens, 26 is a total reflection mirror, 27 is a pupil division mask,
28 is an imaging lens, 29 is a light receiving section, and 30 is a film surface.

In this embodiment, a part of the subject image formed in the vicinity of the field mask 24 disposed near the planned imaging plane of the photographing lens 21 is formed on the light receiving section 29 by the imaging lens 28, and
Passive focus detection is performed.

FIG. 3 is a perspective view of essential parts constituting the focus detection device of FIG. 2. In the figure, numerals 24 to 29 correspond to those in FIG. 2, respectively. In this embodiment, as shown in FIG. 3, a field mask 24 having three apertures in the direction perpendicular to the plane of the paper in FIG. 25 and an imaging lens 28 having two lens parts, two of the exit pupils of the photographic lens 1 are
The image is divided into two object images corresponding to two areas, and the images are formed on the light receiving section 29, and distance measurement is performed at three points corresponding to the three apertures of the field mask 24 using a phase difference detection method.

Figures 4 and 5 are diagrams showing the positional relationship between the pattern image projected onto the subject and the distance measurement field of view. Figure 4 shows the case where the photographing lens is a wide-angle lens, and Figure 5 This shows the case where the photographing lens is a telephoto lens. 4 and 5, 31.32° 33 represents the image of the pattern formed on the subject by the projection lens, and the lens portions, 11, 11, and 11 of the projection lens 1 in FIG.
12.13 represents the image of pattern 2. In addition, 34° 35 and 36 in Fig. 4 represent images obtained by projecting the three distance measurement fields of Fig. 3 onto the subject when the photographing lens l of Fig. 2 is a wide-angle lens. It shows an image of the three distance measurement fields of FIG. 3 projected onto a subject when the photographing lens 1 of FIG. 2 is a telephoto lens. Figures 4 and 5
As shown in the figure, in a single-lens reflex camera equipped with a focus detection device having a plurality of distance measuring points like this embodiment, a pattern is projected onto the area on the subject corresponding to the plurality of distance measuring points. Therefore, it is effective to form a projection lens with a plurality of lens parts to form images of a plurality of patterns on a subject, especially when a wide-angle lens is attached or a zoom lens is set on the wide-angle side.

In this embodiment, as shown in FIGS. 1, 4, and 5, the pattern is a striped pattern consisting of lines of different widths. This is because it is assumed that the light receiving section 29 is composed of a plurality of one-dimensional line sensors such as COD, as is normally used in a focus detection device as shown in FIG. This makes it easier to detect the contrast in the direction in which the images are arranged. In a focus detection device using a phase difference detection method like this embodiment, in order to make it easier to detect the contrast in the direction in which the sensors are arranged, it is possible to create a striped pattern in the direction perpendicular to the direction in which the sensors are arranged and project it onto the subject. It is often done.

FIG. 6 is a diagram for explaining the features of the embodiment.
It is a front view of the projection lens l shown in the figure.

11 in the figure. 12. 13 corresponds to the four lens sections shown in FIG. As shown in FIG. 6, the aperture of the projection lens is divided into a plurality of lens parts each having a long shape in the left direction of the figure, that is, in the direction of the stripes of the pattern.

Normally, in a light projection system for focus detection, the aperture of the light projection lens is made thick in order to make the pattern image reach a long distance, and the pattern image is focused in order to increase the contrast of the object to be measured. Good image performance and a compact configuration are required.In order to meet these requirements, aspherical surfaces have been introduced into the projection lens to effectively correct mainly axial aberrations. However, in the light projection system of a focus detection device that measures multiple distance measurement points as in this embodiment, in order to form a pattern image on a wide range of subjects, various off-axis aberrations must be compensated for over a wide field of view. There is also an increasing demand for good correction.It is difficult to satisfy the above conditions using normal methods in terms of aberration correction.

When using a projection lens with a normal approximately circular aperture,
It is difficult to satisfactorily correct axial aberrations such as field curvature and coma, and the pattern image produces blur depending on the shape of the aperture of the projection lens.

Therefore, the shape of each lens part of the light projecting lens forms a striped pattern so that the pattern image shows good imaging performance even when blurring depending on the shape of the aperture of the light projecting lens occurs. The stripes are long in the direction of the stripes and short in the direction perpendicular to the stripes. Therefore, according to the light projection system of this example, the blurring of the pattern image due to the aperture of the light projection lens mainly occurs in the direction of the stripes of the striped pattern, and rarely occurs in the direction perpendicular to the stripes. A focus detection device that performs focus detection using a striped pattern and vertical contrast can perform excellent focus detection.

[Other Examples]

FIG. 7 is a perspective view of a light projection system according to a second embodiment of the present invention.

In the figure, 41 represents a light projection lens, 42 represents a striped pattern, 43 represents a light source, and 51.5 represents a light source.
2.53.54 are the four lens parts of the projection lens 41, 5
5 represents the optical axes of the lens portions 51 and 52, and 56.degree. 57 represents the optical axes of the lens portions 53 and 54, respectively.

As shown in FIG. 7, the projecting lens 41 has four lens parts: a lens part 51 and a lens part 52 having an optical axis 55, a lens part 53 having an optical axis 56, and a lens part 54 having an optical axis 57. ing. The four lens portions 51 to 54 of the projection lens 41 project the pattern image 42 in different directions.

FIG. 8 shows a front view of the projection lens 41 of FIG. 7. In the figure, numerals 51 to 54 correspond to the four lens parts in FIG. 7. In this embodiment as well, each lens section, particularly the lens section 53, projects a pattern image onto an area other than the center of the subject. 54 is elongated in the horizontal direction of the figure, that is, in the direction of the stripes of the pattern, and exhibits the same effect as the first embodiment of the present invention.

In this embodiment, lens sections 53 and 54 for projecting a pattern image onto an area other than the center of the object are further arranged near the center, and the projection lens 41 is vertically symmetrical, so that the lens sections 53 and 54 are vertically symmetrical. The aperture is made sufficiently wide (while keeping the positional deviation of the aperture small from the optical axis to prevent deterioration in the imaging performance of pattern images projected onto areas other than the center of the subject, in particular.

FIG. 9 is a diagram showing another method of dividing the aperture of the projection lens. In the figure, 61 to 63 are three lens parts, 6
4 to 66 represent the optical axis positions of the respective lens portions. If the projection lens is divided into lens parts shaped like the one shown in this example, it will be long in the direction of the stripes of the striped pattern image.
Since the shape is short in the direction perpendicular to the stripes, it is possible to form a better pattern image compared to the shape shown in FIG.

FIG. 10 is a diagram showing another method of dividing the aperture of the projection lens. In the same figure, 71 to 76 are six lens parts, 7
7 is the lens portion 71 and the optical axis position of the lens portion 71; 78-
81 represents the optical axis positions of the lens portions 73 to 76, respectively. This embodiment develops the method of dividing the aperture of the light projecting lens shown in FIG. 7 to provide a structure having five optical axes. By adopting the configuration as shown in FIG. 10, it becomes possible to illuminate a wider area.

In the several embodiments described above, the optical axes of the lens parts constituting the projecting lens are all arranged in a straight line, but this is due to the distance measuring point of the focus detection device shown in FIGS. 2 and 3. are arranged on a - straight line, and the purpose is to illuminate this. Therefore, when it is necessary to illuminate a wide range that is not on the - straight line, the optical axis position of the lens portion may be appropriately set according to the illumination range.

Incidentally, the light projection system for automatic focus detection described above can be suitably applied to either a passive method or an active method.

(Effects of the Invention) As described above, according to the present invention, it is possible to achieve a light projection system for automatic focus detection with a compact configuration that projects a striped pattern image onto a wide range of subjects with good imaging performance. It has the effect of being able to

It is particularly suitable for a light projection system for automatic focus detection that measures distances at multiple points.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the first embodiment of the present invention, Fig. 2 is an optical arrangement diagram when applied to a single-lens reflex camera, Fig. 3 is a perspective view of a focus detection device that performs distance measurement at multiple points, 4 and 5 are explanatory diagrams 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.
The figure is a perspective view of the second embodiment of the present invention, FIG. 8 is a front view of the light projecting lens of the second embodiment of the present invention, and FIG.
The figure is a front view of a light projecting lens according to a third embodiment of the present invention. FIG. 10 is a front view of a projection lens according to a fourth embodiment of the present invention. 1 is a light projection lens, 2 is a pattern, 3 is a light source, 11 to 13 are lens parts of the light projection lens, 14 to 16 are optical axes of the lens parts, 21 is a photographing lens, 22 is a quick return mirror 23 is a submirror 24 25 is a field mask, 25 is a condensing lens, 26 is a total reflection mirror 27 is a pupil division mask, 28 is an imaging lens, 29 is a light receiving section,
30 is a film surface, 31 to 3 are projected images of the pattern, and 34 to 36 are projected images of the distance measuring field. Figure 3 3 Otsu 35″ 5b !i2

Claims (1)

[Claims] When a striped pattern image is projected onto the subject side by a light projecting lens, and the pattern image reflected from the subject side is received by a light receiving system to detect the focus adjustment state of the photographing system, the light projecting lens is A light projecting system for focus detection, comprising a plurality of lens parts each having a shape elongated in the direction of the stripes of the striped pattern image and having apex positions shifted.