JPH01200212A - Projection system for focus detecting light - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a light projection system for focus detection suitable for photographic cameras, cine cameras, video cameras, etc., and particularly relates to a light projection system for projecting a pattern image toward a subject by the light projection system. By receiving the pattern image reflected from the subject side by the light-receiving system, it is possible to increase the subject distance in passive and active focus detection methods suitable for focus detection in photographing systems. The present invention relates to a light projection system for focus detection that aims to improve the focus detection area.

(Prior 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 focus by emitting, for example, an infrared beam from the camera side toward the subject and receiving the reflected beam from the subject, 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 with high accuracy even when 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 to being able to do it. 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. 810. 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 camera side.

However, photographic systems, particularly those of eye reflex cameras, are equipped with photographic lenses of various focal lengths.

Therefore, in the method using a pattern as proposed in the same publication, unless the so-called full TTL method is used, in which both pattern light emission and light reception are carried out through the entire photographic lens system, when the focal length of the photographic lens changes, The distance measurement target range of the pattern changes.

For example, if a telephoto lens with a long focal length is used, it will illuminate areas outside the range of the object to be measured, resulting in a significant drop in illumination efficiency.

On the other hand, the all-TTL method does not have the above-mentioned drawbacks, but instead requires a light projection system that projects the pattern to be installed inside the camera body, which results in a larger camera and multiplexing of the light beams within the photographic lens. Ghosts occur due to reflection, which deteriorates the optical performance of pattern images during light projection and light reception, and becomes a cause of deterioration of focus detection accuracy.

(Problems to be Solved by the Invention) The present invention appropriately arranges each element of a light projection system having a certain pattern, and even without TTL light projection, the light projection system can be adjusted according to changes in the focal length of the photographing system. By limiting the illumination range of the pattern, that is, by limiting the illuminance of the pattern, the pattern image is efficiently projected onto the subject over a wide range from the telephoto end to the wide-angle end, thereby expanding the range of distance measurement. Furthermore, it is an object of the present invention to provide a light projecting system for focus detection suitable for both passive and active methods, which is capable of good distance measurement even in dark places and objects with low contrast.

(Means for solving the problem) The light flux from the light source is focused with a condenser lens, illuminates a pattern in the form of a fixed area, and the pattern image is projected onto the subject side with a projection lens, so that it is reflected from the subject side. The condenser lens is configured to be movable on the optical axis between the light source and the pattern when detecting the focus of the photographing system by receiving the pattern image by the light receiving system.

(Embodiment) FIGS. 1A and 1B are schematic diagrams of an optical system according to an embodiment of the present invention. 11A shows the image taken when the photographing system (not shown) has a short focal length at the wide-angle end, and FIG. 11B shows the photographic system when the focal length is at the telephoto end, which has a long focal length.

In the figure, reference numeral 1 indicates a light projecting lens, and reference numeral 2 indicates a pattern in which a certain pattern of charts is formed, for example, a chart having the pattern shown in FIG. 3 is a condenser lens, which in this embodiment is composed of a Fresnel lens. Reference numeral 4 denotes a light source, such as an LED, and a condensing section 4a for condensing the diverging light beam is provided in front.

In this embodiment, the light beam from the light source 4 is focused by the condenser 4a and the condenser lens 3 to illuminate the pattern 2. Then, the pattern 2 is projected by the projection lens 1 toward a subject (not shown). At this time, the distance to the subject is set to be approximately 2 to 4 meters.

Further, the condenser lens 3 is configured to be movable on the optical axis between the pattern 2 and the light source 4.

In particular, in this embodiment, when the photographing system is on the wide-angle side (when the focal length is short), the condenser lens 3 is moved to the pattern 2 side in conjunction with the photographing system as shown in FIG.
The illumination range of the pattern 2 by the light beam from A4 is made to be wide as the range of the outer circumferential circle 3a shown by the solid line in FIG. In this way, the pattern image is set to be irradiated widely onto the subject surface. In addition, when the photographing system is on the telephoto side (when the focal length is long), the condenser lens 3 is moved to the light source 4 side as shown in FIG. The range is made narrow like the range of the inner circumferential circle 3b indicated by the broken line in FIG. As a result, the pattern image is set to be irradiated narrowly onto the subject surface.

In this embodiment, the refractive power of the condenser lens 3 is set so as not to cause vignetting due to the projection lens 1, and the effective diameter of the projection lens 1 is appropriately set, so that the light flux emitted from the light source 4 is captured by the condenser lens 3. The angle is made to be the same on the wide-angle side and the telephoto full, that is, the amount of projected light is made to be the same. On the telephoto side, the illumination range of the pattern is narrowed to increase the illuminance on the pattern surface, thereby increasing the projection distance of the pattern image by the projection lens 1.

As described above, in this embodiment, by moving the condenser lens along the optical axis as the focal length of the photographing system changes, the pattern is efficiently illuminated and the range of object distance that can be measured is increased.

FIG. 3 is a perspective view of an optical system according to another embodiment of the present invention.

In the figure, 31 is a cylindrical condenser lens, 5
is for photography.

The optical axis L1 of the light projection system having the condenser lens 31 and the light projection lens 1 and the optical axis L2 of the photographing system 5 are arranged at a slight angle. The condenser lens 31 does not have refractive power in a plane direction including the optical axis L1 of the light projection system and the optical axis L2 of the photographing system 5. Therefore, even if the condenser lens 31 is moved in the direction of the optical axis L1, the illumination range of the pattern 2 in the vertical direction does not change, and therefore the illuminance of the pattern image on the subject surface at the telephoto side can be adjusted without affecting the balax. It is possible to raise it.

FIG. 4 is an explanatory diagram showing the illumination state of pattern 2 in the embodiment shown in FIG. When the condenser lens 31 is moved to the vicinity of pattern 2 (on the wide-angle side), the refractive power of the condenser lens 31 does not contribute much to the illumination of pattern 2, so the illumination range of pattern 2 is
The outer circumferential circle 4a is indicated by the solid line in the figure.

On the other hand, when on the telephoto side, the condenser lens 31 becomes the light source 4.
Since the pattern 2 is moved to the side, the illumination range of the pattern 2 by the light beam from the light source 4 is affected by the refractive power of the condenser lens 31, and becomes a vertically long ellipse 4b as shown by the broken line in FIG.

In this way, by moving the condenser lens 31 as the focal length of the photographing system changes and limiting the illumination range of pattern 2, light can be distributed even on close objects, and the projection distance of the pattern image on the telephoto side can be increased. Furthermore, it is possible to measure distances with high accuracy even for objects with low reflectance.

In the embodiment shown in FIG. 1, the Fresnel surface of the condenser lens 3 may be reversed and provided on the pattern side. However, in this case, it is necessary to avoid placing the lens too close to the pattern so that Fresnel shadows do not appear on the subject surface.

Further, in each of the above embodiments, the condenser lens may be constructed of a toric lens having a weak refractive power in the vertical direction.

(Effects of the Invention) According to the present invention, a movable condenser lens is arranged between the pattern and the light source, and the illumination range of the pattern is changed as the focal length of the photographing system changes, so that the illuminance on the pattern surface can be adjusted. By making it variable, it illuminates a wide range when the imaging system is on the wide-angle side, and conversely illuminates a narrow range when it is set to telephoto (III). It is possible to achieve a light projection system for focus detection that is capable of highly accurate distance measurement with an expanded distance/pressure range.

In particular, the present invention has the advantage that, by arranging a movable condenser lens behind the pattern, it is possible to perform highly accurate distance measurement while preventing deterioration of the optical performance of the projected pattern image due to movement of the condenser lens. .

[Brief explanation of the drawing]

1A and 1B are schematic diagrams of an optical system according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the illumination range of the pattern shown in FIG. 1, and FIG. FIG. 4 is a perspective view of the optical system of the embodiment, and is an explanatory diagram of the illumination range of the pattern shown in FIG. 3. In the figure, 1 is a projection lens, 2 is a pattern, 3°31 is a condenser lens, 4 is a light source, and 5 is a photographing system. Method 1 Figure (A) (B)

Claims (4)

[Claims] (1) Concentrate the luminous flux from the light source with a condenser lens,
When detecting the focus of the photographing system by illuminating a fixed pattern, projecting the pattern image onto the subject side using a projecting lens, and receiving the pattern image reflected from the subject side using the light receiving system, the condenser is used. 1. A light projection system for focus detection, characterized in that a lens is configured to be movable on an optical axis between the light source and the pattern. (2) The condenser lens is moved so that it is located on the pattern side when the focal length of the imaging system is short, and so that it is located on the light source side when the focal length is long. Light projection system for focus detection. (3) The light projection system for focus detection according to claim 1 or 2, wherein the condenser lens is a Fresnel lens. (4) The condenser lens is a toric lens or a cylindrical lens having a gentle refractive power in a plane direction including the optical axis of the light projection lens and the optical axis of the photographing system. Light projection system for focus detection.