JPH0713699B2 - Projection system for automatic focus detection - Google Patents

Description

The present invention relates to a light projecting 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 light projecting system. Focus detection while expanding the subject distance in passive and active automatic focus detection, which is suitable for focus detection of the imaging system by receiving the pattern image that is projected from the subject and reflected from the subject side. The present invention relates to a light projecting system for automatic focus detection with improved accuracy.

(Prior Art) Conventionally, in a photographic camera, a cine camera, a video camera, etc., two types of focus detection methods have been used.

One is a passive method proposed in, for example, JP-A-54-159259 and the other is, for example, JP-A-57-154206.
This is the active method proposed in Japanese Patent Publication.

Among them, the active method is a method for performing focus detection by projecting, for example, an infrared light flux from the camera side to the subject side and receiving a reflected light flux from the subject, 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 with high accuracy. However, when the subject is far away, there is a drawback that the amount of reflected light flux decreases and focus detection accuracy decreases.

The passive method is a method in which focus detection is performed by detecting the image formation state of a subject image by the imaging 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 is an advantage that can be done. However, there is a drawback in that the focus detection accuracy decreases when the subject side is dark or the contrast of the subject is low.

One method for improving this drawback is proposed in, for example, Japanese Patent Publication No. Sho 49-19810. In this publication, focus detection is performed by projecting a pattern image of a fixed pattern from the camera side to the subject side by a light projecting system, and detecting a reflection pattern image from the subject on the camera side.

However, in this method, when the projected light amount is small, the reaching distance of the pattern image is limited. Therefore, a projecting system with a large light amount has been demanded.

Generally, when a pattern image is projected by a light projecting system and a reflected pattern image reflected from the subject side is received, the subject distance changes unless the light is projected through the photographing system, that is, unless the light is projected by TTL. Lux is coming.

As a result, if it is not TTL, there is an inconvenience that the distance range in which the pattern image can be projected is limited. For example, you can project the light flux on a distant subject by narrowing it down to increase the illuminance, and then project a pattern image on the subject for parallax to project on a subject at a short distance. As a result, focus detection may become difficult as a result.

(Problems to be Solved by the Invention) According to the present invention, each element of a light projecting system having a pattern image of a fixed pattern is appropriately arranged, and a pattern image is efficiently formed on a subject in a range from a long distance to a close distance. The projection system for automatic focus detection suitable for both the passive system and the active system in which the distance measurement range can be expanded by projecting the image onto the object and the distance measurement can be performed well even in a dark place or a low contrast object. For the purpose of providing.

(Means for Solving Problems) A focus image of a photographing system is detected by projecting a pattern image of a fixed 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 this case, the light projecting lens is integrally formed by a plurality of lens portions each having a plurality of focal positions whose optical axes are displaced from each other in the optical axis direction.

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

(Embodiment) FIG. 1 is a schematic view of an optical system of an embodiment when the present invention is applied to a part of a photographing system.

In the figure, 1 is a photographing system, 2 is a light projecting lens, 3 is a pattern support, for example, a negative having a stripe pattern of varying width, 4 is a light source, 5 is an image plane, and 6 is an active system. A light receiving lens, 7 is a light receiving element, and 8 is a focus detection unit in the case of the passive type. In practice, either the active method or the passive method is adopted.

2 (A) and 2 (B) respectively show a projection lens 2 according to the present invention.
FIG. 3 is an explanatory view of a lens cross section of one example.

The light projecting lens 2 in the present embodiment has two lens portions, a long distance lens portion 23 having an optical axis 21 and a short distance lens portion 24 having an optical axis 22 different from the optical axis 21. ing.

The lens unit 23 and the lens unit 24 are configured to have substantially the same focal length, that is, the same refractive power. For example, the same lens is divided into two parallel to the optical axis, and the respective optical axes are parallelly decentered.

Of these, the projection lens 2 of FIG. 2 (A) has a shape in which a short-distance lens portion 24 is extended toward the object side as compared with a long-distance lens portion 23. The projection lens 2 shown in FIG. 2B has a shape in which only the object-side lens surface 24a of the short-distance lens portion 24, that is, the first lens surface is extended to the object side. FIG. 3 shows a perspective view of the projection lens 2 of FIG. 2 (B) held on the holding plate 30.

In this embodiment, two lens units 23 and 24 having substantially the same focal length are used.
One of the lens parts is extended so that the focus positions of the two lens parts 23 and 24 are different from each other. Specifically, the focus position of the lens part 23 is closer to the lens part than the focus position of the lens part 24. Set to position. As a result, in this embodiment, as shown in FIG. 1, the two lens portions 23 and 24 of the light projecting lens 2 respectively project the pattern 3 illuminated by the light source 4 in two directions in which the object distance is different. For example, the lens unit 23 forms a focused pattern image on a long-distance subject in the direction indicated by the solid line, and the lens unit 24 is the lens unit.
A focused pattern image is formed on a short-distance subject in a direction indicated by a dotted line different from the subject distance range defined by 23. This improves the unclearness of the pattern image due to the change in the object distance when the focal positions of the two lens units 23 and 24 are made the same.

Generally, high illuminance is required when the subject is far away,
In this embodiment, the effective projection area of the lens portion 23 is larger than that of the lens portion 24.

In this way, by projecting the pattern 3 at both the long distance and the short distance and sharing the object distance range, it is possible to always form a clear pattern image for the object from the long distance to the short distance.

Then, the reflection pattern image reflected from the subject side is guided to the light receiving element 7 through the image capturing system 1 or by the light receiving lens 6 provided in the vicinity of the image capturing system 1, and the output signal from the light receiving element 7 or the detection unit 8 is output. The distance is measured to the object or the focus of the photographing system 1 is detected by using the focusing lens group, and the focusing lens group in the photographing system 1 is moved by a driving mechanism (not shown) for focusing.

As described above, in this embodiment, even if the focal length of the light projecting lens is increased, the irradiation light beam diameter is decreased, and the irradiation intensity is increased, it is possible to perform irradiation with less parallax.

Generally, in the light projecting lens according to the present embodiment, the curvature of the first lens surface is larger than that of the second lens surface in terms of aberration correction, and the aberration due to the change of the wall thickness, especially the variation of the spherical aberration is small, and therefore, FIG. As shown in (B), the first lens surface 24a is extended to the object side, and the second lens surface 24b is slightly lowered to the image surface side to eliminate a step in the meridional section of the entire lens and to make the overall lens shape smooth. With this configuration, the loss of the light amount generated from the step portion is prevented, and the pattern image is projected efficiently.

In the present embodiment, even if the subject is present at an intermediate distance, both projected pattern images overlap so that the pattern images are projected well over the entire shooting distance. Fig. 2 (B)
In the projection lens 2 shown in FIG.
May be composed of the same lens surface, and one of the lens surfaces 23a and 24a may be configured such that the optical axes thereof are shifted.
The optical axes may be shifted either parallel or tilted.

In the present embodiment, the light projecting lens is composed of a single lens composed of two lens parts, but it is composed of a plurality of lenses and also of a plurality of lens parts, and the focal positions of the plurality of lens parts are made different from each other. For example, long distance, medium distance,
You may comprise so that it may become a lens part for short distances.

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

(Effects of the Invention) According to the present invention, by configuring the lens shape of the light projecting lens as described above, the projection range of the pattern image is efficiently expanded to the near side and becomes clear in the range from the long distance to the short distance. It is possible to achieve a highly accurate projection system for automatic focus detection, which enables the projection of a pattern image and expands the distance range capable of distance measurement.

[Brief description of drawings]

FIG. 1 is a schematic view of an optical system of one embodiment when the present invention is applied to a part of an image pickup system, and FIGS. 2A and 2B are respectively a first diagram.
FIG. 2B is a sectional view of the light projecting lens shown in FIG.
FIG. In the figure, 1 is a photographing system, 2 is a projection lens, 3 is a pattern, 4 is a light source, 5 is an image plane, 6 is a light receiving lens, 7 is a light receiving element, and 8 is a light receiving element.
Is a focus detection unit, 21 and 22 are optical axes, and 23 and 24 are lens parts.

Claims (2)

[Claims] 1. When a focus image of a photographing system is detected by projecting a pattern image of a fixed pattern to a subject side by a light projecting lens and receiving the pattern image reflected from the subject side by a light receiving system, the projecting light is used. A projection system for automatic focus detection, characterized in that a plurality of lens positions in which the optical axes are displaced from each other are integrally formed by a lens section that differs in the optical axis direction. 2. The light projection system for automatic focus detection according to claim 1, wherein each of the plurality of lens portions is composed of a lens having a substantially equal focal length.