JPS58186708A - Automatic focus detector - Google Patents

Abstract

PURPOSE:To assure accuracy thoroughly without decreasing the performance in detecting the focus of a remote object and without saturating a photodetector at excessive quantity of light in the focus detection of a desired near distance, by limiting the quantity of incident light to the photodetecting means according to the distance of the object. CONSTITUTION:A photodetector consists of plural photodetector groups 7 and plural micro-lens groups 8, and decreases the lightness of the micro-lenses in the parts of the groups 8 where the lenses receive the reflected light from the object of a near distance. In other words, an F value is increased to avoid saturation of the photodetector. The saturation of the photodetector is prevented by decreasing the area for photodetection, using a density filter or increasing the F value of the micro-lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active automatic focus detection device that measures the distance to an object by detecting the reflected light of a light beam projected toward the object using a light receiving means.

For conventional active automatic focus detection devices, various methods have been proposed to use bright optical systems, increase the amount of projected light, and increase the sensitivity of the light receiving means so that the object distance can be measured as far as possible. When attempting to measure the distance of a nearby object using a similar device, the amount of light incident on the light receiving means exceeded the saturation level of the light receiving means, making it unusable.

SUMMARY OF THE INVENTION An object of the present invention is to obtain an automatic focus detection device that can measure the distance of a wide range of objects, from objects at a long distance to objects at a short distance, with a simple configuration.

Figure 1 shows an example of an active automatic focusing device based on the principle of triangulation, in which 1 is a light source 2 is a projection lens that converges the light from the light source onto an object, and 3 is a projection lens that is projected from a projection means 1.2. A light-receiving lens is arranged at a predetermined baseline spacing BL in the lateral direction to receive the reflected light beam that is reflected by an object, and 4 is a light-receiving element that receives the light beam converged by the light-receiving lens 3. be.

The angle between the projected light beam and the reflected light beam is determined by the position of the object, and the light is focused on the light receiving element 4 according to the angle. At this time, the correspondence between the position of the object and the condensing position of the reflected light beam on the light receiving element 4 is established and utilized in the automatic focusing device.

In this case, as the distance of the object increases to ,02,1), the position of the light beam reflected from the object on the light receiving element 4 becomes (
1,,d2. Changes to d. If the position of the light beam reflected from an object at an infinite distance is set to 0 on the light-receiving element 4, the reflected light beam of a near object will be located in the direction where d increases, that is, on the left side. ' As mentioned above, each position of the light receiving element 4 corresponds to a predetermined object distance, and in order to determine the position of the light beam reflected from the object on the light receiving element 4, multiple photoelectric elements are arranged and output according to the position. Different body sensor devices (P
SD) is used as the light receiving element 4. The light receiving element 4 receives more rays of reflected light from an object as the distance from the object becomes shorter.When a beam of light is projected toward an object in the form of a parallel beam, if the object is a diffusing surface, the beam of reflected light is If the reflectance is equal, it is inversely proportional to the square of the distance between objects. Therefore, the light receiving section that receives the reflected light from the object at Lm receives four times as much light as the light receiving section that receives the reflected light from the object at 2 m.

FIG. 2 shows the shape of the light-receiving surface of the light-receiving element 4 in an embodiment of the present invention. The light receiving section that receives reflected light from a distant object is shown on the right, and the light receiving section that receives reflected light from a nearby object is shown on the left. 0 corresponds to an object at infinity. As mentioned above, even if the same amount of light is irradiated, the amount of light reflected from the object is
The amount of light changes significantly depending on the distance, and in particular, the amount of reflected light from a nearby object may saturate the light receiving element, leading to a decrease in distance detection accuracy. Therefore, if the light-receiving area of the light-receiving section that receives reflected light from a nearby object is made smaller than the light-receiving area of the light-receiving section that receives reflected light from a distant object, it is possible to eliminate the adverse effects of excessive reflected light.

The change in area may be curved or stepwise, and the area of the opening may be changed without changing the area of the light receiving element.

FIG. 3 shows an embodiment in which an optical density filter 5 is used in front of the light-receiving surface of the light-receiving element 4 to reduce reflected light from an object instead of changing the light-receiving area of the light-receiving element 4. The density is determined at a position on the surface of the light receiving element corresponding to the distance, and by making the near distance side darker and lowering the transmittance, the light receiving element 4 is prevented from becoming saturated. Various concentration distributions can be considered as shown in FIG. In FIG. 4, the curve (b) shows that the density changes with the square of the position d of the light-receiving element 4. The curve (0) shows that the density gradient can be produced in a linear manner, and the curve (2) shows that the density can be changed in a stepwise manner. In this embodiment, the filter 5 is stacked on the window member 6 of the light receiving element 4, but this does not mean that the window member may be constructed of a density filter.

FIG. 5 shows an embodiment of an automatic focus detection device in which the light receiving element is composed of a plurality of light receiving element groups 7 and a plurality of microlens groups 8, and the part of the microlens group 8 that receives reflected light from a nearby object. Reduce the brightness of the microlens. In other words, the F value is increased to prevent the light receiving element from becoming saturated.

As shown in Figures 2 to 5, the light-receiving area can be made smaller.
Although an example has been shown in which a filter is used or the F value of a microlens is increased to prevent the light-receiving element from becoming saturated, a combination of these methods may be used. In the embodiment, a system in which the light projecting means 1.2 and the light receiving element 4 are fixed based on the principle of triangulation is shown, but a system in which the optical axes of the light projecting means 1.2 and/or the light receiving means 3, 4 are swung may be used. When adjusting the focus on an object closer than a predetermined distance, a suitable density filter or aperture limiting member may be configured to be placed within the optical axis in conjunction with the means for photographing the optical axis.

In addition, in the so-called TTL type device that uses a photographic lens to project and/or receive light, such as the device disclosed in Japanese Patent Application Laid-Open No. 54-155832, a light amount limiting member is provided in conjunction with the focal position of the photographic lens. That's fine.

As described above, according to the present invention, it is possible to ensure sufficient accuracy for desired short-distance focus detection without saturating the light-receiving element with an excessive amount of light without deteriorating the focus detection performance of a long-distance object. I can do it.

Furthermore, by using the present invention, there is no need to increase the dynamic range of the focus detection circuit more than necessary, and processing becomes simpler.

[Brief explanation of the drawing]

Figure 1 shows the same principle as an active autofocus device. Figure 2 is a plan view of the light-receiving surface shape of the light-receiving element. Figure 3 is an enlarged cross-sectional view of the photodetector. Figure 4 is a density distribution diagram of the density filter. FIG. 5 is an enlarged cross-sectional view of a light receiving element with a microlens. Explanation of symbols for main parts Light receiving means...4 Applicant: Nippon Kogaku Kogyo Co., Ltd. Takao Watanabe, a person with good memories 37-

Claims (1)

[Claims] 1. Detecting the reflected light of a luminous flux projected toward an object using a light receiving means. An automatic focus detection device characterized by: 2. The automatic focus detection device according to claim 1, wherein the amount of light incident on the light receiving means is limited by a density filter. 3. The automatic focus detection device according to claim 1, wherein the amount of light incident on the light receiving means is limited by reducing the light receiving area of the light receiving element.