JPS63229439A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To reduce the range finding parallax between a finder system and a photography system by arranging a light emitting element or light receiving element at a position nearly equivalent to the primary image formation surface of the objective of a finder system. CONSTITUTION:A light receiving lens 10 and the light receiving element 11 are arranged across a photographic lens symmetrically with the objective 2 of the finder system 20. Namely, near infrared light emitted by the light emitting element 8 arranged at the position nearly equivalent to the primary image formation surface of the objective 2 is deflected by a half-mirror 9 provided on a finder optical path toward the objective 2 on the optical path and passed through a concave lens 2b and a convex lens 2a to illuminate a subject surface. Its reflected light from the subject surface passes through the light receiving lens 10 and is guided onto the position detection type light receiving element PSD 11 to form a spot image. An automatic focus adjusting device is therefore obtained which has a small visual field at the time of focus detection and facilitates the displacement of the range finding visual field of the finder system.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is suitable for a viewfinder system having a dedicated observation objective lens system independent of a photographic lens, a so-called external viewfinder system. This invention relates to an automatic focusing device.

(Prior Art) In simple active automatic focusing devices conventionally used in lens-shutter cameras and the like, a method of calculating the distance to a subject surface based on the principle of triangulation is often used. FIG. 2 is a schematic diagram of a distance measuring device using the principle of triangulation.

In the figure, reference numeral 21 denotes a light emitting element, such as an IRED (near infrared light emitting diode), which projects the luminous flux from the light emitting element 21 onto a subject plane 25 through a projection lens 22 . Reference numeral 24 denotes a light receiving element (PSD) which can detect the incident position and receives the reflected light beam from the subject surface 25 through the light receiving lens 23. At this time, distance measurement is performed by detecting the position of the imaging spot of the reflected light beam on the light receiving element 24, and focus detection is performed.

However, since the dedicated light projection lens is placed at a certain distance in space from the optical axis of the objective lens of the finder system, it has the disadvantage of causing parallax. ing. Furthermore, if the baseline length is increased to improve distance measurement accuracy, the light-receiving lens 23 must be placed far away from the light-emitting lens 22, which tends to increase the size of the camera. Ta.

In general, in cameras using an external viewfinder system, in order to suppress parallax in the finder system as much as possible, a finder light is provided close to the photographic lens, for example, directly above the photographic lens, and each focus point is placed on the left and right of this. Light emitting and light receiving lenses are arranged for detection. In this way, the focus detection means is placed at a position away from the photographic lens, and parallax becomes noticeable during focus detection.

Furthermore, conventionally, for convenience in observing the viewfinder field of view, a distance measurement field mark for indicating the distance measurement field of view has been provided within the finder field of view. However, if the parallax for focus detection is large, the distance measurement field mark of the finder will be positioned far away from the center of the field of view of the photographic lens, and the focus of the viewfinder observation field and the photographic screen will be adjusted. This has the disadvantage that the two positions do not match due to a deviation between the two positions.

Furthermore, in recent years, lens shutters and the like have been proposed in which the focal length of the photographing lens can be changed, and with this, there has been a demand for viewfinder systems that can also change the magnification. 8 If the J12 lens is a variable magnification system and a conventional finder system without an independent variable magnification function is used as part of the focus detection device, the diameter of the projected light spot on the subject is:
It does not change even if the focal length of the photographing lens changes.5Furthermore, there is a drawback that the distance measuring field of view is different between the photographing system and the light projecting system.

(Problems to be Solved by the Invention) The present invention has a simple configuration suitable for a camera equipped with a so-called external real image finder system, which has a dedicated objective lens that does not use a part of the photographic lens. An object of the present invention is to provide an automatic focusing device which has a small field of view during focus detection and which facilitates displacement of the distance measuring field of a finder system in response to changing the magnification of a photographing lens.

(Means for solving the problem) A light emitting element r or a light emitting element for focus detection is installed in a finder system having an objective lens system provided independently of the photographing lens at a position approximately equivalent to the primary image formation plane of the object image by the objective lens. This is because a light receiving element is arranged.

In particular, in the present invention, the magnification is changed by a finder-based objective lens system in response to the magnification change of the photographic lens.

(Embodiment) FIG. 1 is a schematic diagram of an embodiment of the present invention. In the figure, 1 is a photographing lens, which includes a front group lens 1a and a rear group lens 1.
It is composed of b. By changing the mutual positions of the front group lens 1a and the rear group lens 1b, the focal length of the entire system of the photographing lens 1 is changed, that is, the magnification is changed.

In this embodiment, the focal length of the photographic lens is changed from the wide-angle side to the telephoto side by displacing both lens groups 1a and lb along the arrows indicated by broken lines in the figure. 2
0 is a real image finder system. 2 is an objective lens system, which has a concave lens 2a and a convex lens 2b. 9
The half mirror 58 is a light emitting element and is arranged at a position substantially equivalent to the primary imaging plane of the objective lens 2. 3 is a condenser lens, 5 is a Porro prism, 6 is an eyepiece lens, and 7 is the position of the observation pupil. 10 is a light receiving lens, and 11 is a light receiving element. The finder light flux passes through the convex lens 2a and concave lens 2b of the objective lens system 2, and then enters the condenser lens 3.
A finder image is formed on the primary imaging plane 4 of the objective lens system 2 in a nearly telecentric state. At this time, the convex lens 2a and the concave lens 2b of the objective lens system 2 of the finder system change their positions in conjunction with the movement of the photographic lens 1 which is changing the magnification.

In other words, the viewfinder field of the finder optical system is changed in response to changes in the photographic field of view caused by changing the magnification of the photographic lens, and the ratio of the size of the finder field of view to the photographic field of the photographing system is kept constant.

In this embodiment, the finder optical system is set close to and directly above the photographic lens 1, so that although some parallax occurs in the vertical direction of the screen, no parallax occurs in the horizontal direction.

Next, a light projection system for focus detection in the embodiment shown in FIG. 1 will be explained. Near-infrared light emitted from a light emitting element 8 placed at a position substantially equivalent to the primary imaging plane of the objective lens 2 is deflected toward the objective lens 2 on the optical path by a half mirror 9 provided on the finder optical path. , passes through the concave lens 2b and the convex lens 2a, and is irradiated onto the subject surface.

The reflected light from the object surface passes through the light receiving lens 10 and is guided onto the position detection type light receiving element PSDII to form a spot image. Here, the light-receiving lens 10 and the light-receiving element 11 are arranged at positions symmetrical to the objective lens 2 of the finder system 20 with the photographing lens 1 in between, in order to ensure a long base line length for the purpose of increasing distance measurement accuracy.

In the embodiment described above, the finder objective lens 2, which functions as a light projecting lens, changes magnification in response to the magnification change of the photographic lens 1, so that the size of the distance measurement field in the observation screen is large when the photographic lens 1 is at the wide-angle focal length, and becomes small when the photographic lens 1 is at the telephoto focal length, and the ratio of the distance measuring field of view to the screen size is constant. The w1 shadow visual field and the finder visual field of the finder system match.

Incidentally, if a dichroic mirror having a property of transmitting visible light and reflecting near-infrared light is used as the deflection member 9, the amount of light can be effectively utilized.

Furthermore, if it is desired to change the diameter of the projected light spot on the object surface, a condensing lens (not shown) having an appropriate focal length may be provided at an intermediate position between the light emitting element IRED8 and the mirror 9.

Further, in this embodiment, the arrangement of the light emitting element and the light receiving element may be reversed.

(Effects of the Invention) According to the present invention, the distance measurement parallax between the finder system and the photographing system can be reduced by arranging the light emitting element or the light receiving element at a position substantially equivalent to the primary imaging plane of the objective lens of the finder system. By changing the magnification of the viewfinder's objective lens in accordance with the magnification of the photographic lens, the ratio of the distance measurement field of view to the size of the photographic screen is always constant. A matching device can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 is a schematic diagram of an optical system of a conventional active automatic focusing device. In the figure, 1 is the photographing lens system, 20 is the external finder system, 2 is the finder objective lens system, 3 is the condenser lens, 5 is the Porro prism, 6 is the eyepiece, 7 is the observation pupil, and 8 is the IRED etc. A light emitting element, 9 a deflection member, 10 a light receiving lens, and 11 a light receiving element such as a PSD.

Claims (3)

[Claims] (1) A light emitting element or a light receiving element for focus detection is arranged at a position approximately equivalent to the primary imaging plane of the object image formed by the objective lens of a finder system having an objective lens system provided independently of the photographic lens. automatic focusing device. (2) The automatic focusing device according to claim 1, wherein the objective lens system of the finder system changes the magnification in response to the magnification change of the photographing lens. (3) The light receiving element or the light emitting element for focus detection is provided at a position symmetrical to the objective lens system of the finder system with the photographing lens in between.
Automatic focusing device as described in Section 1.