JPS58108506A - Focus detector - Google Patents

Abstract

PURPOSE:To remove optical influences on front and back photodetectors and also to remove influences on a finder image by arranging the front and back photodetectors on the same surface symmetrically centering a surface equivalent to a film surface. CONSTITUTION:In case of supposing surfaces 20, 22 having the same area in front and in rear of a face 18 equivalent to the exposed surface of a film against a photographing lens 16, the quantity of incident light to the surfaces 20, 22 is different when an image is formed on a face other than the face 18, so that the surfaces of two optical sensor arrays are arranged and contrasts of luminous flux from the directions of arrows 30, 32 are compared to detect the surface of image formation. Photoelectric elements 46, 48 are embedded in a focusing plate 38 so that an exposure equivalent surface 42 in the focusing plate 38 is put between the elements 46, 48. Photoelectric element groups 50, 52 are formed on glass plates 54, 56. Outputs from the plural photoelectric elements are led into the terminal parts 54a, 56a of the glass plates 54, 56 and transmitted to an external processing circuit. The glass plates 54, 56 are used as the focusing plate by combining them.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device suitable for a focus adjustment device of a single-lens reflex camera.

Conventionally, as shown in FIG. 1, a pair of photoelectric conversion means 6 and 8 for receiving an image by the photographic lens are arranged at two positions before and after a surface equivalent to the film surface 4 behind the photographic lens 2.
The photographing lens 2
A focus adjustment device has been proposed in which the focus is adjusted by moving the .

The photoelectric conversion means 6 and 8 of this device have light receiving surfaces perpendicular to the optical axis 10 of the photographic lens 2. Therefore, in this type of focus detection device, photoelectric conversion elements are placed on two surfaces, front and rear of the surface equivalent to photographic film, but since the front light-receiving element interferes with the image reception of the rear light-receiving element, as shown in Figure 1. As shown in Figure 2, the optical path splitting means BS is used to further divide the surface corresponding to the photographic film into two mutually conjugate surfaces, and the photoelectric conversion means is arranged in front of one surface and behind the other surface. It is necessary to have a suitable configuration. If another photoelectric conversion means is placed at the position of the focusing plate 12, the finder image will include the shadow of the photoelectric conversion means. For this reason, the arrangement in which the photoelectric conversion section of the focusing device is disposed at the position of the focusing plate 12 as shown in FIG. 1 is not actually adopted. However, if the photoelectric conversion unit could be placed at the focus plate position, the double-reflection mirror 14 mechanism, which requires strict positioning accuracy, would be unnecessary, and the focus detection device could be applied to conventional cameras with replaceable focus plates and viewfinders. You will be able to do this.

The present invention provides a focus plate with a group of photoelectric conversion elements, which are components of a focus detection device, and which are optically arranged one behind the other, without the front side optically interfering with the rear side. The present invention proposes a focus detection device with a novel configuration that is arranged so as not to interfere with the viewfinder image even when the focus detection device is placed in the viewfinder. The main feature of the focus detection device according to the present invention is that photoelectric conversion elements are arranged in the center of the focus plate as follows. That is, each of the photoelectric conversion elements forming a pair is positioned in front of and behind the surface equivalent to the film exposure surface of the reticle, the light receiving surface is parallel to the optical axis of the photographic lens, and the directions of the light receiving surfaces are opposite to each other. It is characterized by its placement.

In this configuration, it is desired that the photoelectric conversion element be as thin as possible, so an amorphous silicon photodiode is used as the photoelectric conversion element. This photodiode can be made, for example, 1 μm thick. As described above, according to the present invention, the photoelectric conversion section has a structure in which a small photodiode is embedded in the reticle in parallel with the optical axis, so that the shadow caused by the photodiode is not a problem for observing the viewfinder image. No.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a diagram for explaining the focus detection principle of the focus detection device of the present invention. In FIG. 2, two surfaces 20.degree. 22 having the same area are assumed to exist before and after the exposure side surface 18, which is equivalent to the film exposure surface for the photographing lens 16. These surfaces 20.22 lie in the same plane parallel to the optical axis 24,
The exposure planes are symmetrical to each other with respect to one day. Suppose now that the image of the light spot 26 on the optical axis is focused on a point 2 on the exposure side. Considering the light passing through the surface 20 and heading toward the point 28 and the light passing through the point 2 and heading toward the surface 22, the amounts of light incident on each surface 20 and 22 are equal to each other. Assuming that the two surfaces 20 and 22 are placed on or near the optical axis, when an image is formed on the exposure side surface 18,
Face 20. The amount of light incident on each of 2 and 2 is approximately equal. On the other hand, when an image is formed at a position other than the side surface 18, such as during exposure, the amounts of light incident on the two surfaces 20 and 22 are different. Therefore, the focal state can be detected by arranging a photoelectric element at each position of the surface 20.22 so as to receive light from the direction of the arrow 30.32 and monitoring the photoelectric conversion output thereof. In other words, the photographic lens 1 is placed at a position where the outputs of the two photoelectric elements forming a pair before and after the side surface 18 are equal for exposure, etc.
6 is adjusted. Furthermore, if two photosensor arrays made up of a plurality of photoelectric elements are placed perpendicular to the plane of the paper at the positions of planes 20 and 22 and the contrast of the images received by each sensor array is detected, the image formation of the subject can be It is possible to detect whether the position is before or after the exposure equivalent surface of 1 day. When the subject image is formed in front of the exposure equivalent plane 1 day, the contrast detected by the sensor array arranged at the position of the plane 20 is greater than the contrast detected by the other sensor array. When the imaging coincides with the exposure equivalent plane 18, the contrast detected by both sensors is equal. Furthermore, when the image formation is located behind the exposure equivalent plane 18, the contrast detected by the sensor array at the position of the plane 22 becomes larger.

FIG. 3 is a diagram showing one embodiment of the present invention, in which one photoelectric element is used.
1 shows a cross section arranged within the focus plate of an eye reflex camera. In FIG. 3, a reflecting mirror 36, a focus plate 3, and a pentaprism 40 are arranged behind the photographing lens 34, as is well known. The surface indicated by the dotted line 42 within the third focus plate corresponds to the exposure equivalent surface equivalent to film exposure surface number 4. A pair of photoelectric elements 46 and 49 are embedded within the focus plate so as to sandwich this equal side surface 42. These photoelectric elements are made of amorphous silicon semiconductor and have a thickness of about 1 μm. A focusing plate in which such a photoelectric element is embedded consists of elements as shown in FIG. Fourth
In the figure, photoelectric element groups 50, 52 are formed on glass substrates 54, 56, respectively. The light-receiving surface of the photoelectric element 50, 52 is the surface that comes into contact with the glass substrate. Focus plate element 5
8.60 is made of a plastic material as a transparent plate, or the exposed side surface shown by the dotted line 62 is the surface of two plates pasted together. In the latter case, one of the surfaces of the lamination 9 is made into a matte surface. The outputs of the plurality of photoelectric elements arranged in a row on each glass substrate are transmitted to the end portion 54a of the glass substrate via a transparent conductor formed on the glass substrate.

56a, and further supplied to an external signal processing circuit from these ends. The reticle elements 5, 60 and glass substrates 54, 56 are bonded together to form a reticle as shown in FIG. Note that when the glass substrates 54 and 56 are pasted together, although strictly speaking the light receiving surfaces of the photodiodes 50 and 52 are not located on the same plane, they can be considered as actually located on the same plane. The above is the configuration of the main parts of the focus detection device of the present invention. Next, an example of a circuit configuration including a photoelectric element and related elements provided on a glass substrate will be described.

FIG. 6 shows a first example of a circuit constructed on the aforementioned glass substrate. In FIG. 6, the photodiodes 64 to 3 have the same light-receiving area and are arranged in a row in numerical order as shown in FIG. 4 (the figure is divided into two rows to make the circuit configuration easier to understand). arranged on top. Further, diode magnets 4 to 82 are arranged on a glass substrate other than the photodiode. The area occupied by these diodes is much smaller than that of a photodiode. The focus detection operation of the focus detection circuit shown in FIG.
6 boat USF3039824.

FIG. 7 shows a second example of a circuit configured on a glass substrate. In FIG. 1, photodiodes 88 to 94 are arranged in a row on a glass substrate and combined with an externally provided scanning circuit to form a photosensor array. ,...
... FIG. 8 shows an example of a detection signal processing circuit when the focus detection circuit shown in FIG. 6 is used. In FIG. 8, block 9
6.98 is a focus detection circuit shown in FIG. 6, which is arranged before and after the exposure equivalent plane. Terminal 83 in the circuit of FIG.
The terminals 112 and l14 corresponding to 84 are connected to the voltage output terminal of the bias circuit 116, and a reverse bias voltage is applied to the photodiodes 100 and 102. The photodiodes within the 9th block are similarly reverse biased. A current inversion circuit 118 whose input terminal is connected to the terminal 108 corresponding to the terminal 85 in the electrical diagram is connected to the circuit 9.
6 sinks current through terminal 108, it outputs a current equal to this current value to logarithmic compression circuit 120. Now, focusing on the photodiodes 100 and 102, the contrast detection operation will be explained. If the light incident on photodiode 102 is brighter than that on photodiode 100, a current corresponding to the difference in photocurrent generated by both photodiodes will flow through terminal 1.
09, photodiode 102 via diode 104
flows into. On the other hand, when brighter light is incident on the photodiode 100, a current corresponding to the difference in photocurrent flows from the photodiode 100 to the diode 106. Terminal 11
Flows through 0.

In this way, when there is a difference in the brightness of the incident light to the photodiodes 100 and 102, a current corresponding to the absolute value of the difference is input to the logarithmic compression circuit. Logarithmic compression circuit 1
At 20, a voltage proportional to the logarithm of the input current is output.

As a result of this operation, the output voltage of the logarithmic compression circuit 120 is a signal corresponding to the sum of the contrasts of the images on the light receiving surfaces of the pair of photodiodes 100 and 102 and a pair of photodiodes (not shown). Focus detection circuit 98. Current reversal circuit 122
, the logarithmic compression circuit 124 has the same configuration as the circuit described above, and outputs a contrast signal of the image on the photoelectric element arranged behind the exposure equivalent plane. Comparison circuit 126 compares the output voltages from logarithmic compression circuits 120 and 124,
A signal is given to the lens drive circuit 128 to drive the photographing lens 130 in a direction in which these two output voltages are balanced. Further, the display circuit 132 displays the direction in which the photographing lens 130 should be moved for manual focus adjustment in accordance with the output of the comparison circuit 126, for example, in a finder.

In the embodiment described above, the light-receiving element is arranged on the focus plate, but of course it is also possible to arrange it in the same place as the conventional detection element as shown in FIG.

As described in detail above, the present invention takes advantage of the fact that a photodiode can be constructed with an extremely small thickness on a glass plate, and uses a photodiode for focus detection to detect light at two positions, front and back on the side, such as when exposing a film. Since the surfaces are arranged in opposite directions to each other on the same plane parallel to the optical axis of the photographing lens, when a photodiode with this configuration is incorporated into a focus plate, the photodiode with a thickness of 1 μm aligns the light-receiving surface with the optical axis. Since the photodiode is arranged parallel to the camera and only its thickness can be seen from the viewing direction, the photodiode does not create shadows that interfere with the viewfinder image, making it a practical focus detection method. As a result, it is possible to obtain a new focusing plate incorporating a photoelectric element for -
A transparent part is provided in the center of the eye reflex mirror 14, a double-reflection mirror 14 is attached later, and a light receiving element is placed on a surface equivalent to the film exposure surface, which is different from the finder focal plane formed in this way using a beam splitting means BS. This eliminates the need for extra parts and extra structures and processing required for positioning accuracy, and it is possible to construct a focus detection system that does not cause loss of light from the finder circular image. In other words, in the conventional focus detection method, the light-receiving element obstructs the optical path, so in order to not obstruct the photographing optical path or the viewfinder optical path, it was necessary to make some modification to the camera configuration different from that of a normal camera. Accordingly, the focus detection system can be configured using the current camera structure without such modifications.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the optical configuration and arrangement of a conventional focus detection means in a single-lens reflex camera, FIG. 2 is a diagram for explaining the focus detection principle of the focus detection device of the present invention, and FIG. 4A is an exploded view of the focus plate in FIG. 3, FIG. 4 is a sectional view thereof, and FIG. The completed view of the reticle in Fig. 4 is shown in Fig. 4.
A circuit diagram showing an example of a photoelectric conversion circuit provided on the glass substrate in the figure, FIG. 7 is a circuit diagram showing another example in place of the circuit in FIG. 6, and FIG. 8 processes the output signal of the circuit in FIG. 6. FIG. 2 is a diagram illustrating an example of a circuit. 2...Photographing lens, 5...Conventional focus detection device, 3
8... focus plate, 46. 4B, 50. 52. ,
, photodiode, 54.56... glass substrate, 58
．． 60...Plastic focus plate. Agent: Patent Attorney Kosuke Mai Figure 2

Claims (3)

[Claims] (1) Symmetrically across a surface equivalent to the film surface of the camera, so that the light-receiving surfaces are opposite to each other, parallel to the optical axis of the photographing lens, and on the same plane.
A focus detection device characterized by arranging a pair of light receiving elements. (2) A surface equivalent to the exposure surface of the camera is the focal plane of the finder of a single-lens reflex camera, and the light receiving element is embedded in the focusing plate with the light receiving surface perpendicular to the focal plane. A focus detection device according to claim 1, characterized in that: (3) The focus detection device according to claim 1 or 2, wherein the light receiving element is an amorphous silicon diode formed on a glass substrate, and the surface of the substrate is parallel to the optical axis of the photographing lens.