JPS58123511A - Detector of focus - Google Patents

Abstract

PURPOSE:To obtain a detector of focus at a low cost which eliminates a lowering of the accuracy in focus detection owing to temp. variation, by using a concave mirror which is formed on a plastic substrate having the almost fixed wall thickness in an image foramtion optical system. CONSTITUTION:A reflected surface 3 of a concave mirror 2 is faced to the side of an object 5 to be photographed and is fitted to the inner part of a case 4 and the front surface part 6 of case 4 is opened in a detector of focus 1. The focus of the miror 2 is positioned in the vicinity of the center of the apperture part 6, and a projected part 9 provided to a lever 8 which is turned by making a shaft 7 as a fulcrum is positioned. A photodiode to detect a contrast is stuck on the projected part 9. The concave mirror 2 is made by plastic molding and the thicknes of a substrate is made constant so that the shape resembles at the time of expansion and contraction owing to the temp. variation. The variation of focus position owing to expansion and contraction is very small as compared with the case in change of the refractive index in plastic lenses.

Description

Detailed Description of the Invention Technique '5) Field The present invention is suitable for an automatic focusing device for a camera that detects the point of maximum contrast of an image on an imaging plane to detect the focal position of an imaging optical system. The present invention relates to a focus detection device.

Prior Art Conventionally, as a means for detecting the contrast of an image on the imaging surface of an imaging optical system, for example, a large number of pairs of two minute photodiodes arranged next to each other are provided on a plane, and these are optically A system has been proposed in which the absolute values of the differences in signal levels output by two photodiodes in each pair are added together, and the point where the sum is maximum is found. There is.

The present invention utilizes such a contrast detection means to construct a focus detection module suitable for being incorporated into a compact camera. On the other hand, a focus detection module that applies the principle of triangulation to focus detection is known. A plastic lens is used in the optical system of this known Nomosur. Therefore, when converting a contrado detection type focus detection device into a module, it is conceivable to use a plastic lens in its optical system. However, the refractive index of plastic changes significantly with changes in humidity compared to glass, so if a plastic lens is used, the focal position will change in response to temperature changes, and therefore, it will not be possible to compensate for this temperature change without compensating for it. , the focusing accuracy of the camera lens in which this module is installed cannot be guaranteed. However, if a means for temperature compensation were to be provided, the purpose of reducing costs by using a plastic lens instead of a glass lens would be defeated.

OBJECTS OF THE INVENTION The present invention has been made in view of the following two circumstances, and provides a focus detection module using a contrast detection method that does not require consideration of compensation for temperature changes and can be constructed at low cost. The purpose is to obtain.

Summary The present invention uses a concave mirror in the imaging optical system in the focus detection module, arranges a contrast detection element in the imaging area of the concave mirror, and adjusts the distance between the concave mirror and the contrast detection element by adjusting the focus of the photographic lens. The main feature is that it is configured so that it can be changed relatively in conjunction with each other. With such a configuration, even if the refractive index of the plastic changes due to temperature changes, this change will not be directly related to the optical characteristics of the concave mirror, so a plastic molded product can be used as the concave mirror.

EXAMPLES Hereinafter, the present invention will be described in detail based on drawings showing examples. In FIG. 1, a focus detection device (1) according to the present invention
is placed at the back of a case (4) with its sides shielded from light, with the reflective surface (3) of the concave mirror (2) facing the subject (5), and the front part (6) of the case (4) is It is open. The focus of the concave mirror (2) is located near the center of this opening (6),
A lever (8) that rotates around the shaft (7) in this area
The protrusion (9) provided at A photodiode (10) for contrast detection is attached to the protrusion (9) with its light receiving surface facing the concave mirror (2). The protrusion (9) is made of a glass plate, for example, and is attached to amorphous silicon so that the light-receiving surface of the diode comes into contact with the glass surface. Since an amorphous silicon photodiode can be attached using a glass plate as a substrate, the protrusion O) can be made of a transparent glass plate, and light can be introduced into the photodiode through the protrusion (9). Therefore, the moisture-resistant film that protects the photodiode can be covered from the back of the light-receiving surface, eliminating the need for packaging and preventing deterioration of the imaging state due to optical non-uniformity.

The concave mirror Q) is molded from plastic, and is formed on the front or back surface of the substrate with a constant thickness so that the shape before and after L1 is similar when it expands and contracts due to temperature changes. Fluctuations in focal position due to expansion and contraction are extremely small compared to changes in refractive index in plastic lenses.

The concave mirror is also aspheric to provide the desired imaging performance across the front surface of the photodiode array.

The opposite part (11) of the lever (8) to the fulcrum (7) is cut with a groove (14) that engages with a pin (13) provided on the photographic lens barrel (12), so that the photographic lens (15) When you move back and forth along the optical axis direction, the lever (8
) rotates around the fulcrum (7), albeit at a slight angle. Due to the rotation, the light receiving surface of the photoelectric element (10) moves back and forth along the optical axis of the concave mirror (2). Strictly speaking, the photoelectric element (10) moves in a circular motion, but this does not cause any practical problems. Thus, in conjunction with the movement of the photographing lens, the photoelectric element (lO) scans the image formed by the concave mirror Q) in the optical axis direction. It goes without saying that the subject light passing through the opening O) which is not shaded by the protrusion (9) of the lever (8) enters the concave mirror (O).

The photographing lens barrel (12) is set at a close distance point in conjunction with a film charging mechanism (not shown), and is driven toward a far distance point by a spring (16) during focus adjustment. On the other hand, as a means for stopping the driving of the photographic lens barrel (12), a movable piece coupling bar (18) having a sawtooth section (07) is provided on the lens barrel side. The movable piece (20) of the electromagnet (19) faces towards it. When the excitation of the electromagnet (19) is interrupted, the movable piece (20) is rotated by the spring (21) and falls into the sawtooth portion (17), stopping the movement of the movable piece coupling bar (18).

In this way, the photographing lens (15) is adjusted to a position corresponding to the timing of activation of the electromagnet (19).

Next, referring to the block circuit in Fig. 2, the photoelectric element (10)
The output processing circuit will be explained. In Fig. 2, photodiodes (PRl), (PLI), -(PR
n) and (PLn) constitute the photoelectric element (10) arranged on the convex part (9) in Fig. 1, and the paired element (PR
i, ) and (PL i) are led to an absolute value circuit (Dl) that outputs a signal corresponding to the absolute value of the difference between their respective outputs. Just 1=1=1°2, ・n. Each output of the absolute value circuit (Dl) is input to an adder circuit, and the sum of each output is determined. The output of the adder circuit (22) is then input to the maximum value detection circuit (24). Maximum value detection circuit (2
4) outputs a signal at the point in time when the output of addition circuit 23) reaches the maximum value and then begins to fall. In response to this output signal, the electromagnet drive circuit (25) cuts off the excitation of the electromagnet (19).

When photographing, aim the optical axis of the focus detection device (1) at the subject you want to focus on through a viewfinder (not shown),
Press the release button down one step.

This pushing down causes the photographic lens (15) to move onto the film surface (
22) and tightens, and in conjunction with this, the convex part (9
) The photoelectric element (10) also moves towards the concave mirror (2).

During this movement process, when the image formed on the light-receiving surface of the photoelectric element (10) becomes the sharpest, that is, when the contrast of the image becomes the greatest, the output of the adder circuit (23) becomes maximum. This is detected by the maximum value detection circuit (24), and as a result, the excitation of the electromagnet (19) is cut off. In this movement of the photographic lens, the amount of movement of the light receiving element (10) is proportional to the amount of movement of the photographic lens, and is reduced. Depending on this reduction ratio, the relative position change between the film surface (2 tumor photographing lens (15)) and the concave mirror 0
) and the contrast detection element (10) are not in a proportional relationship from a geometric optics point of view;
The relative positions of both optical systems regulated by do not correspond exactly. However, it is fully practical as an X-type camera.

Furthermore, by introducing a cam mechanism into the interlocking system between the focus adjustment mechanism of the photographic lens 15 and the contrast detection element moving mechanism, it is easy to improve the accuracy of the optical correspondence between the focal positions of both optical systems. Furthermore, in the example, the photoelectric element (10) was moved relative to the concave mirror (2), but
Conversely, the concave mirror may be moved.

As explained above, a concave mirror formed on a plastic substrate with a constant wall thickness is used in the imaging optical system of the focus detection device that detects the contrast of the image and detects the focus. By doing so, it is possible to obtain a low-cost focus detection device that does not cause a decrease in focus detection accuracy due to temperature changes.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing the configuration of an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a focus detection circuit used in the focus detection device of the present invention. = 9- 1. Non-inspection detection device, 2. Concave mirror, 1o. Photoelectric element, 15. Photographing lens. Applicant: Minolta Camera Co., Ltd. 10-

Claims (1)

[Claims] 1. A concave mirror formed on a base material whose front and back sides are approximately equal in shape so that the thickness is approximately constant, is arranged so as to face the same direction as the photographing lens, and the concave mirror is A focus detection device includes a contrast detection element in an imaging region and an interlocking mechanism that changes the relative distance between the concave mirror and the contrast detection element in accordance with focus adjustment of a photographic lens. 11. The focus detection device according to claim 10, wherein the contrast detection element comprises a plurality of amorphous silicon photodiodes attached on a glass substrate with their light-receiving surfaces in contact with each other. 3. The concave mirror is placed on the light receiving surface of the contrast detection element.