JPS63235907A - Focus detector - Google Patents

Abstract

PURPOSE:To enable high-accuracy focus detection by bending an optical path through a reflecting mirror, arranging one element of a detecting means on this optical path, and moving the reflecting mirror in the same moving direction with the focus adjusting lens of a photographic system for the focus detection of the photographic system. CONSTITUTION:The reflecting mirror 6 is introduced as part of a photodetecting means, the optical axis L2 of a photodetection lens 5 is bent, and the photodetection part 7 which is one element for focus detection is arranged on the bent optical path on a substrate 8. Thus, the focus group 1a of the photographic system 1 and the reflecting mirror 6 are both moved in the same direction. Consequently, a focus detector is obtained which is simplified in mechanism and capable of high-accuracy focus detection while maintaining the size of the whole camera with good balance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a focus detection device suitable for photographic cameras, video cameras, etc., and in particular detects focus by utilizing the correlation between the image formation positions of subject images. It can be used in two detection methods: the so-called light receiving type and the so-called active type, in which the focus of the photographing system is detected by projecting a light beam toward the subject using a light projecting means and receiving the reflected light beam from the subject using a light receiving means. The present invention relates to a focus detection device.

(Prior Art) Recently, active focus detection devices have been widely used not only in lens shutter cameras but also in single-lens reflex cameras, video cameras, and the like. Among these, an optical system having an active focus detection device using the principle of triangular distance measurement is disclosed in Japanese Patent Application Laid-Open No. 58-88, for example.
This method has been proposed in JP-A No. 0608, Japanese Unexamined Patent Publication No. 59-201007, and the like.

FIGS. 4 and 5 are schematic diagrams of typical active focus detection optical systems that utilize the principle of conventional triangular distance measurement. Fourth
In the figure, a light beam from a light source 42 is projected to a subject 43 through a light projecting lens 41, and a light beam reflected from the subject 43 is received by a light receiving lens 44 and a light receiving section 45 consisting of a plurality of light receiving elements. .

The distance to the subject 43 is measured by detecting the position of the reflected light beam formed on the light receiving section 45. This focus detection method does not require a drive mechanism, but since it uses multiple light receiving elements, the signal processing of the light receiving means and the accompanying electric circuit tend to become complicated. An encoder is required to accommodate the focusing lens of the photographing system.

In FIG. 5, a light beam from a light source 56 is projected onto a subject 52 through a part of a photographing system 51, and the reflected light beam from the subject 52 is received by a light receiving section 54 consisting of two light receiving elements Y. There is. At this time, the light receiving section 54 is linked with the focusing lens group 55 to scan in the direction of the arrow so that the outputs from the two light receiving elements are equal, or the output difference is below a certain value, so that the imaging system Focus detection is being performed.

In addition, in passive focus detection, there is a method of detecting focus by using two light receiving means, moving the light receiving element of one of the light receiving means, and detecting the correlation between the imaging positions obtained from the two light receiving means. . These focus detection methods require relatively simple signal processing and electrical circuitry, but require the light receiving section 54 to be moved in a predetermined relationship according to the amount of extension of the focusing lens group 55. For this reason, the interlocking structure of the cam mechanism, drive method, etc. becomes complicated, which tends to make highly accurate focus detection difficult.

(Problems to be Solved by the Invention) The present invention aims to simplify the drive mechanism of the light emitting means, light receiving means, etc. for focus detection, and increases the It is an object of the present invention to provide a focus detection device using triangular distance measurement that enables accurate focus detection and maintains the size of the entire optical system in a well-balanced manner.

A further object of the present invention is to obtain a patent application filed in 1983 by the applicant.
The object of the present invention is to provide a focus detection device that further improves the focus detection device according to No. 0-31033 and enables high-grained focus detection from an object at infinity to an object at a short distance.

(Means for Solving the Problem) The optical path of at least one of the plurality of detection means for focus detection arranged at a predetermined baseline length is bent via a reflecting mirror, and the optical path of the folded [110] one element of the plurality of detection means is placed at [-, and the reflector is moved in the same direction as the moving force direction of the focusing lens of the imaging system to detect the focus of the imaging system. be.

(Embodiment) FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention. In the figure, 1 is a photographing system, 1a is a focusing lens group (hereinafter referred to as "focus group") of the photographing system 1, and 2 is an imaging plane, such as a photographic film surface or a video imaging surface.

L3 is the optical axis of the photographing system 1, and 0 is the object to be photographed. 3
4 is a light projecting lens, and 4 is a light projecting light source, such as a light emitting diode that emits invisible near-infrared light. Ll is the projection optical axis, 5
The light-receiving lens is provided as far away from the light-emitting lens 3 as the base line length. 6 is a reflecting mirror, and L2 is a receiving optical axis, which is bent by the reflecting mirror 6 at a substantially right angle. Reference numeral 7 denotes a light-receiving section, which has, for example, two light-receiving areas in the vertical direction with the light-receiving optical axis L2 as a boundary. Reference numeral 8 denotes a substrate on which the light receiving section 7 is mounted. 7a
8a is a mirror image of the light receiving section 7 by the reflecting mirror 6, and 8a is a mirror image of the substrate 8 by the reflecting mirror 6. Reference numeral 9 denotes a driving means that moves the reflecting mirror 6 and the focus group 1a in the same direction, for example, from the position shown by the dotted line to the position shown by the solid line in response to the output signal from the light receiving section 7.

In this embodiment, an infrared beam from a light source 4 is projected onto an object 0 via a projection lens 3. Then, the reflected light beam from the object 0 is condensed by a light receiving lens 5, and is received by a light receiving section 7 via a reflecting mirror 6.

At this time, the reflecting mirror 6 is moved by the driving means 9 to the focus group 1a.
At the same time, it is moved in a direction parallel to the optical axis L2 in the direction indicated by the arrow Y1. Thereby, the light-receiving optical axis L2 is tilted as shown by L2a, so that it intersects with the optical axis L1 of the light projecting lens 3 on the object 0.

At this time, the reflecting mirror 6 is located at the principal point of the light-receiving part 7b and the light-receiving lens 5, as shown in FIG. The line L2a that connects the lines L2a and L2a extends out to the extent that it intersects the projection optical axis L1 on the object 0.

In this way, when the light emitting optical axis L1 and the receiving light @ll L2a intersect, it is determined that the photographing system 1 is in focus, and the focus group 1a, which was being moved at the same time, is stopped.

In this embodiment, the reflecting mirror 6 is introduced as a part of the light receiving means, the optical axis L2 of the light receiving lens 5 is bent, and the light receiving part 7, which is an element for focus detection, is placed on the substrate 8 on the bent optical path. With this arrangement, both the focus group 1a of the photographing system 1 and the reflecting mirror 6 are moved in the same direction. As a result, in this embodiment, focus detection can be performed using a movement mechanism that is extremely simplified compared to the conventional movement mechanism that moves the light source in a direction perpendicular to the movement direction of the focus group, for example, in the direction of arrow Yl' in the figure. It is possible.

Furthermore, in this embodiment, the optical axis L2 of the light receiving means is bent by the reflecting mirror 6 in a direction away from the light emitting optical axis L1, thereby simplifying the movement mechanism when moving the focus group 1a and the reflecting mirror 6 in conjunction with each other. ing.

In this embodiment, the focus group 1a and the reflecting mirror 6 are moved integrally by appropriately setting the optical arrangement of the focus group and the light receiving lens.

This eliminates the need for a means for adjusting the difference in the amount of movement between the two, thereby simplifying the movement mechanism. Next, the optical arrangement relationship of this embodiment will be explained.

FIG. 3 is an explanatory diagram of the optical arrangement of the light projecting means and the light receiving means when the reflecting mirror 6 of FIG. 1 is omitted and the light receiving section 7 is arranged on the optical axis R2 and unfolded. The focal length of the R1 light receiving lens 5, which is the distance from the front principal point position of the light receiving lens 5 to the object 0, is f5. If the scanning distance of the light receiving unit 7 for focusing from an object at infinity to an object at a finite distance is a, then according to the principle of triangular distance measurement, R/D=f5/a, and from this, a=D-f5/R...・・・・・・ （
1).

Next, the distance from the front focus F1 of the focus group 1a to the object 0 is X, the distance from the rear principal point F2 of the focus group 1a to the imaging point is Xo, and the focal length of the focus group 1a is fl.
If a, then X' = -f, a' /X (2).

The amount of edge extension when focusing is performed by extending the focus group is -X°. Therefore, if each element is configured so that the moving amount a of the light receiving section 7 shown in FIG. It becomes possible to move the reflecting mirror 6 integrally. The conditions at this time are (1
) and (2), D −f5 /R=fla' /X...-(3). If the front focal position F1 of the focus group 1a and the front principal point position of the light-receiving lens 5 are configured to match, then R=X and equation (3) becomes D-f5=f,,'...
...... (4).

Therefore, in this embodiment, when focusing on an object at infinity, the front focal position of the focus group and the front principal point position of the light receiving lens are made to match, so that X=R is approximately satisfied, and from this state, the focus group The reflecting mirror 6 is moved integrally. According to this method, focus detection with sufficient granularity is possible even if the object distance changes.

In this embodiment, the degree of coincidence between the front focal position of the focus group and the front principal point of the light-receiving lens does not need to be exactly matched as long as focus detection is possible within the depth of focus of the imaging system. can be achieved.

In the embodiment shown in FIG. 1, the arrangement of the light projecting means and the light receiving means may be exchanged so that the reflecting mirror 6 and the focus group 1a are moved in the same direction. Further, either the light projecting means or the light receiving means may be configured to project light or receive light through a part of the photographing system 1.

Furthermore, this embodiment can also be applied to a so-called passive focus detection device that performs focus detection by detecting the correlation between the imaging positions of two subject images without using a light projection means. In this case, two light receiving means are used as the plurality of detection means, the optical path in which one of the light receiving means is arranged is bent through a reflecting mirror, the light receiving element is arranged on this bent optical path, and the reflecting mirror is placed in the focus group. It may be moved in the same direction.

(Effects of the Invention) According to the present invention, the refractive power arrangement of the focus group of the photographing system is appropriately set, and a reflecting mirror is arranged in the optical path of at least one of the light projecting means or the light receiving means, and the focus group and focus detection By integrally moving one element of the camera to perform focus detection, we have created a focus detection device that maintains the overall size of the camera in a well-balanced manner and is capable of highly accurate focus detection with a simplified mechanism. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, and FIG. 3 is an explanatory diagram of a part of FIG. 1, and FIGS. 4 and 5 are schematic diagrams of the optical system of a conventional active focus detection device. In the figure, 1 is the photographing system, 1a is the focus group, 2 is the imaging plane, and 3
is a light projecting lens, 4 is a light source, 5 is a light receiving lens, 6 is a reflecting mirror, 7 is a light receiving section, 8 is a substrate, 9 is a driving means, 0 is an object, L
l, L2. L3 is the optical axis, and D is the baseline length.

Claims (1)

[Claims] The optical path of at least one of the plurality of detection means for focus detection arranged at a predetermined baseline length apart is bent via a reflecting mirror, and one element of the plurality of detection means is placed on this bent optical path. A focus detection device, characterized in that the reflector is moved in the same direction as a moving direction of a focusing lens of the imaging system to detect the focus of the imaging system.