JPS58111910A - Focus detector - Google Patents

Abstract

PURPOSE:To dispose photosensor arrays on a focal plate without any interference for practicable use upon subject images by disposing two pieces of two rows of photosensor arrays, which are formed extremely thin, back to back, and disposing the arraying directions of unit photodetectors in parallel with the optical axis of a photographic lens. CONSTITUTION:A photosensor array 12 of which the photodetecting plane is made parallel with the optical axis 10 of a photographic lens 2 is disposed in a focal plate 8. The focal plane 14 conjugate with the exposure plane 16 of a film is made transparent or matte. The focal plate consists of two pieces of focal plate elements 44, 46 of plastics and glass substrate 52, 54 vapor deposited with photosensor arrays 48, 50 having photodiodes, which are adhered to each other. The substrates 52, 54 are longer than the width D of the plate 14, and terminals connected to transparent electrodes are provided, in the end parts 52a, 54a thereof. The arrays 49, 50 are provided to the plate 14 so as to sandwich the optical axis of the photographic lens.

Description

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

Conventionally, a pair of photo sensor arrays have been installed at positions in front and behind a surface (referred to as the image surface) equivalent to the film surface on which the image taken by the photographing lens is exposed, in order to detect the contrast of the image. A focus detection device has been proposed which is configured to compare the contrast of images before and after exposure, etc., to detect the in-focus state.

The photosensor array in such a conventional focus detection device is disposed, for example, at the bottom of a mirror box of a single-lens reflex camera, and its light-receiving surface is perpendicular to the optical axis of the photographic lens. In this way, since the light-receiving surface of the photosensor array is perpendicular to the optical axis of the photographing lens, two photosensor arrays that are optically arranged one behind the other are also placed one behind the other in terms of their specific positional relationship. The optical path must be divided into two and placed at separate positions, and the configuration in which the photosensor array is placed on the focusing plate results in shadows caused by the photosensor array on the subject image focused on the focusing plate. It was not something that could be adopted because it would be difficult to use.

The present invention proposes a focus detection device with a novel configuration in which a photosensor array can be arranged on a focus plate without causing any practical problems to the subject image on the focus plate. If the photosensor array can be placed on the focusing plate, it is possible to prepare a pentaprism unit equipped with a focus detection device in a single-lens camera system in which the focusing plate and the pentaprism part are interchangeable, and the camera can be used. Users can purchase the units as needed.

In the present invention, two photo sensor arrays each having a plurality of extremely thin photodiodes arranged in a row are placed back to back so that the light receiving surfaces face oppositely to each other, and the arrangement direction of the unit light receiving elements of each array is aligned with the photographing lens. The present invention is characterized in that a focus detection element is provided, which is configured to extend vertically through a surface parallel to the optical axis and conjugate to the film exposure surface, and arranged such that the light-receiving surface is parallel to the optical axis of the photographic lens. An extremely thin photo sensor array suitable for arranging two photo sensor arrays in this way is an amorphous photo sensor array on a glass substrate with the light receiving surface facing the glass substrate surface.
A device formed of a silicon photodiode can be used. The two glass substrates on which the photosensor arrays have been formed in this way are pasted together so that the photosensor arrays are sandwiched between them. Amorphous silicon photodiodes can be formed on a glass substrate with a thickness of about 1 μm, so when two photosensor arrays are bonded together with their backs facing each other, the distance between their respective light-receiving surfaces is about 2 μm. can be ignored in practice, and two photosensor arrays bonded together with their backs behave as if their respective light-receiving surfaces are on the same plane. The thickness of the photosensor array arranged as described above is only visible from the viewing direction, and since the thickness is extremely thin, it is hardly visible and does not interfere with observation of the image on the reticle.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail based on drawings showing embodiments.

FIG. 1 is a diagram showing an example of the arrangement of the focus detection device of the present invention in a single-lens reflex camera. In FIG. 1 (-), a photographing lens 2, a reflecting mirror 4, and a pentaprism 6 are components of a well-known single-lens reflex camera.

The focus plate 8 is made up of components as shown in the exploded view of FIG. be. Note that the dotted line 14 indicates a focal plane that is conjugate with the film exposure plane 16. The focusing plate 8 may be of a transparent type or may have a matte surface formed on the focal plane 14.

FIG. 1 is a diagram showing another example of the arrangement of the focus detection device.

The reflecting mirror 18 on the right side of the first diagram corresponds to the reflecting mirror of FIG. Make sure to pass towards 20. A focus detection device 22 according to the present invention is arranged below the sub-reflection mirror 20 and at the bottom of a mirror box (not shown).

This focus detection device 22 has a photo sensor array formed on each of glass substrates 24 and 26, and then bonded together so that both photo sensor arrays are placed back to back.

Next, the focus detection operation of the focus detection device of the present invention is shown in Fig. 2a.
, b, and c. Figure 2 a shows the imaging lens 2.
8 is a diagram showing the imaging state for five different points (not shown) in the vicinity of the optical axis 30 located at a certain distance in front of the imaging lens 28, and shows a specific light ray near the outer periphery of the imaging lens 28. Line 82 corresponds to the imaging plane of the five points. Now, assuming that five points in front of the imaging lens 28 exist extremely close to the optical axis 8o, the five points that have passed through a specific point 82, 84 near the outer periphery of the imaging lens 28 The rays to a point are nearly parallel to each other.

FIG. 2 is an enlarged view of the vicinity of the imaging plane in FIG. 2a, which is intended for such a case. In FIG. 2, points P1 to P5 on the imaging plane 32 are images of the five points in front of the imaging lens described above. Rays 11 and Ll from the same light source form an image PI, and similarly rays j2 and L2
is the image P2, rays 18 and L8 are the image P8, rays 14 and L
4 forms an image P4, and rays 15 and L5 form an image P5, respectively. Now, the ray L1 e L2 w”
If the points where 8 e L4 aL5 intersects with the optical axis 30 are Q1vQ2-QB1Q41Q5, then these points have rays 16914, lB,! 2+11 have passed respectively. Now, the light rays /, -15 group and Ll-L5 group pass through two points 82 and 84 on the imaging lens 28, which are symmetrical with respect to the optical axis 30, as shown in FIG. 2a. Also, images P1 * P2 other than image P8 on the optical axis
If e P4 m ” 5 is also located very close to the optical axis 80, then the point Ql.

Q2 is symmetrical with respect to the line 32 with points Q5 and Q4.

Therefore, if a photoelectric element receiving the light beam 16 is placed at point Q, and a photoelectric element receiving light beam Lr is placed at point q5, the outputs of these two photoelectric elements will be equal to each other. Similarly, ray 74. at point Q, g*Q4. X
If photoelectric elements are arranged to receive each r-sparrow, their respective outputs will be equal to each other.

Below, other light rays can be considered in the same way. In other words, if two photosensor arrays 86 and 38 in which a plurality of n photoelectric elements are arranged in a row along the optical axis are placed between points Q and Q5 as shown in FIG. When the image is located on the imaging plane 82, each element al, a2, . . . aH of the photosensor array 86 and each element b1 . b2. ...The outputs of bn are equal. In addition, the photo sensor array 86.8
8 are sensitive to light from the directions of arrows 40 and 42, respectively. The discussion so far has concerned rays passing through a particular point on the imaging lens. However, in reality, the subject light passes through the entire surface of the imaging lens. Therefore, let's also consider light rays that have passed through points other than the above-mentioned specific points.

In Fig. 2 C, create an image P2 of Fig. 2 and point Q1.
The rays that cross between and 95 are shown. In FIG. 2C, rays L2 and 12 are the same as in FIG. Ray L
2' is a ray passing through points Q1 and P2, and ray j2 is a ray passing through point P
2 and Q5. In the drawing, a light ray directed from above the optical axis 8o toward point P2 and passing between points Q1 and 95 is a light ray sandwiched between light rays L2 and L2/, and point Q
Cross between 1 and 92. On the other hand, a point P from below the optical axis 30
The ray that passes through 2 and intersects between point Ql and 95 is ray 1
2 and 12'. Under the condition that the image P2 is located very close to the optical axis 80, the triangle ΔQIQ2
P2 and Δq416P2 are congruent, and for the light forming image P2, the interval between points Q1 and Q2 and points Q4 and Q5
The amount of light that crosses the section between can be considered to be equal to each other. The same applies to images near the optical axis 80 other than image P2. In other words, even when including light passing through any point of the imaging lens in FIG.
Element a 1t a2°...Each output of van and element b of the photosensor array 38! , t12. . . , each output of b3 is equal to each other. Next, if the imaging is located in front of the plane 82, element a1 of the photosensor array 36
e a2 m..., an element of the photosensor array 38 for each output of m..., an, b2. . . .+bn are in a phase-lag relationship, and on the other hand, when the image formation is located behind the surface 82, the phases are in a lead-in relationship. Therefore, if the outputs from the photosensor arrays 88, 88 are processed by an appropriate signal processing circuit to obtain mutual correlation, the in-focus state can be rectified. This is the operating principle of the focus detection device of the present invention.

Examples of the present invention will be described below. Figure 4a is
4 is an exploded perspective view of the focus plate 14 shown in FIG. 1 having a photoelectric element therein, and FIG. 4 is a sectional view thereof. Fourth
In the figure, the reticle includes two reticle elements 44, 46 made of plastic material and a glass substrate 52, 54 on which a photosensor array 48, 50 having a photodiode D having the circuit configuration shown in FIG. 6 is formed by vapor deposition. It is broken down into two parts and shown below. Each of these elements is pasted together to form 1jl
It becomes the focusing plate of i. Glass substrates 52 and 54 are focus plates 14
The output terminal of each photodiode of the photosensor array 48.52 is provided at the end 52a #54a, and a transparent electrode material ITO is used between each photodiode and the output terminal.
It is tied with When the focusing plate 14 is installed in the finder of a camera, the photo sensor arrays 48 and 50 direct the optical axis of the photographic lens to the two photo sensor arrays 8 and 50.
It is placed in a position where it is sandwiched between the two. The light-receiving surfaces of these photosensor arrays 48 and 50 are on the glass substrate side on which they are deposited. FIG. 5 shows the cross-sectional structure of one photodiode deposited on a glass substrate. As shown in FIG. 5, a transparent electrode layer 58 is first formed on a glass substrate 56, and an amorphous silicon photodiode 60 is formed thereon. Furthermore, an aluminum electrode 62 is deposited on top of it. The photodiode 60 is a transparent electrode [58 side is a P-type semiconductor and serves as a light-receiving surface;
The aluminum electric 8i62 side is an N-type semiconductor. This photodiode is further covered with an insulating layer. by the way,
This amorphous silicon photodiode can be made with a thickness of about 1 μm. Therefore, when the glass substrates 52 and 54 shown in FIG. 4 are bonded together, the light receiving surfaces of the photosensor arrays 48 and 50 can be considered to exist on substantially the same plane. In other words, an operation based on the focus detection principle explained in FIG. 2 can be realized.

As described in detail above, the present invention has a plurality of photodiodes constituting a photosensor array for focus detection, each of which has a light-receiving surface parallel to the optical axis in the vicinity of the conjugate plane of the film exposure surface, and substantially This is a focus detection device characterized in that it is arranged in a row on the optical axis of the photographic lens, and since the light receiving elements are arranged parallel to the optical axis, when arranged on the focus plate,
There is no problem with the image focused on the focus plate, and thus it is possible to configure an exchangeable pentaprism unit equipped with a focus detection device.
An eye reflex camera system can be provided.
that's all

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the arrangement of the focus detection device of the present invention in a single-lens reflex camera, and FIGS. 2 and 8 are diagrams for explaining the principle of focus detection operation of the focus detection device of the present invention.
FIG. 4 is an exploded view of the focus plate in which the focus detection device of the present invention is arranged on the focus plate, and FIG. A diagram showing the configuration, FIG. 6 shows the glass substrate 5
It is a circuit diagram of a photosensor array formed on 2゜54. 2--Taking lens, 4--Reflecting mirror, 6--Penta prism, 8-- Focusing plate, 12-- Photo sensor array , 18... Transflective mirror, 20... Sub mirror, 22... Focus detection device, 44.46... Focus plate made of plastic material, 48.50... Photo sensor array, 52. 54...Glass substrate. Agent: Patent Attorney Division Kosuke (jL) Figure 1 Figure 5 Figure Z

Claims (1)

[Claims] +11 Two photo sensor arrays each having a plurality of thin photodiodes arranged in a row are placed in close contact back to back with their light-receiving surfaces facing outward, and the array direction of the photodiodes is set as an imaging lens. A focus detection device, characterized in that it is disposed parallel to the optical axis of the lens and perpendicularly penetrates the image plane of the lens at an intersection with the optical axis of the image plane. (2) The focus detection device according to claim 1, wherein the photosensor array using thin photodiodes is formed of amorphous silicon photodiodes on a glass surface with the light-receiving surface facing the glass side. . (3) In photosensor arrays placed back to back, each photodiode in one photosensor array is ranked from one end, and each photodiode in the other photosensor array is ranked from the opposite end. The non-inspection method according to claim 1 or 2, wherein photodiodes of the same rank in a photosensor array are made to correspond to each other, and focusing is evaluated based on the difference in the output of each corresponding photodiode.