JPS59102205A - Automatic focus detecting device - Google Patents

Abstract

PURPOSE:To detect exactly a focus of a lens even in case it has any of F- numbers by providing a luminous flux control member for cutting gradually a light quantity of a peripheral light of a luminous flux passing through an optical path, in accordance with F-number, on the optical path for detecting a focus. CONSTITUTION:When a driving lever 34 moves downward by a prescribed quantity by an F-number signal of a lens from a full-aperture signal pin or a diaphragm lever, masks 32, 33 rotate in the opposite directions, respectively, centering around a pin 34, and an opening degree of an opening part 28a is opened by a prescribed quantity so as to extend the base of an inverse triangle in accordance with brightness of a lens. As a result, only a peripheral light of a luminous flux is cut with respect to not only a luminous flux of wide width passing through a bright lens but also a lens of narrow width passing through a dark lens, therefore, influence due to a lens aberration can be prevented, a focus can be detected exactly, also no light quantity loss is generated, and the photometry can be executed sufficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus detection device, and in particular detects a focus position by comparing the sharpness of an object image at two positions approximately equidistant in front and behind a predetermined focal plane of an imaging optical system. This relates to improvements in equipment for

Generally, the sharpness of the image is equal at positions equidistant in front and behind the point where the light from the lens forms an image. Utilizing this principle, in the camera, line sensors 2.3 are arranged at positions equidistant in front and behind the planned focal plane 1, as shown in Fig. 1, and the objective lens 4
(For example, take the difference in the detection signals between the respective elements in the line sensors 2 and 3, square them, and then add them together and compare them.) , there is a force to detect the focal position of the objective lens 40.

In other words, as shown in Fig. 2, the lens 4 force is extended (
(The focus moves to the front) The sharpness value 3' of the line sensor 3 increases, followed by the sharpness value 2' of the line sensor 2. The ability to detect the peak sharpness value at the 0 point of line sensor 3; this means that the focus position is line sensor 3.
It shows that you have come to the top. After that, line sensor 3
The sharpness value 3' begins to decrease and becomes equal to the sharpness value 2' of the line sensor 2 at the 0 point, and this point becomes the in-focus position. Thereafter, the visibility value 3' of the line sensor 3 continues to decline, while the visibility value 2' of the line sensor 2 reaches its peak at the zero point. That is, the focus position has come to the position of the line sensor 2. As you can see from the above, the clarity value of the line sensor 2.3 is 2'.

By comparing 3', the in-focus position or direction of out-of-focus can be detected, and an automatic focus detection operation can be performed.

However, this detection method has the following problems.

1. Objective lens In particular, near the open F-number, the object light 5 has aberrations in the lens 4, so even if the lens 4 is in the in-focus position, the sharpness values at equal distances in front and behind the planned focal plane l are not actually the same. Therefore, accurate focus detection cannot be performed.

2. If the focus is far from the intended focal plane,
As can be seen from the fact that the OTF curve in FIG. 3 takes a negative value at a certain frequency, a false r phenomenon occurs. For this reason, at iA, which is greatly out of focus in Figure 2, the sharpness value that changed by 1 increases again due to the false resolution, and becomes 0.
At the point and the zero point, the visibility values of the line sensors 2 and 3 become equal again. Therefore, in the above-mentioned in-focus position detection method, the 0 point and 0 point, which are largely out of focus, are detected as the in-focus position. In this case, if the detection status is only displayed in the viewfinder, it is possible to determine that the display is incorrect by looking at the viewfinder image and move the lens to the focus position. In the so-called autofocusing system, in which the lens is automatically moved to the in-focus position based on the signals from the sensors 2 and 3, if the sharpness values of the sensors 2 and 3 are equal, it means that it is not the in-focus position. Either way, the lens will be locked in that position, which is very problematic. Therefore, as a means to solve these problems, it is proposed to provide a light flux regulating means such as a mask or a filter in the optical path for focus detection to cut the peripheral light rays with respect to the center of the optical path.
It has been proposed in the public domain. That is, the problem (1) above is caused by lens aberration, and lens aberration is more likely to occur around the lens where the refractive index is large.
By providing such a regulating means as described above, the light rays that pass through the periphery of the lens and are significantly affected by aberrations are cut, and problem (1) can be solved.

Also, the problem (2) is caused by false resolution, but
False resolution occurs when an image becomes largely blurred, and parts of the image with high contrast values are overlapped, causing parts with originally low contrast values to become high. In this case, the peripheral light is shaped into the shape of the liner member so that there is no overlap between parts with high contrast values. That is, as shown in FIG. 4(1), if no regulating member is provided for the focus detection optical path 6, the object light 5 passes through the optical path 6 as it is, and the OTF curve is as shown in FIG. As shown in (1) of Figure 4 (2L (
3) The regulating members 7 and 8 shown in Fig. 5 (2L (3)
), there are almost no negative values, and false resolution does not occur. That is, it is possible to prevent the influence of false resolution at a position that is significantly out of focus.

By the way, the lpg of the luminous flux of the subject light changes variously depending on the F number of the lens. For this reason, for example, Figure 6 (1
) As shown in FIG. Since it is a large object, the surrounding light can be effectively canted, but in the case of a dark lens with an F number of F4,
Since the luminous flux 12 becomes small as shown in the figure, the shape of the regulating member 9 cannot cut out any peripheral light.

On the other hand, if a regulating member 13 having a shape that reduces the aperture of the optical path 9 as shown in FIG. ,
Ambient light is cut well, but Fl. For the light beam 11 of a bright lens like No. 4, there is a problem that the loss in the amount of light becomes very large, making it impossible to measure the distance to a dark subject.

The present EJA was developed in view of the above circumstances, and includes a light flux regulating member that changes its shape in response to a signal from the lens open signal pin (G) or aperture lever in the optical path for focus detection. For any F number lens,
The objective is to cut out the peripheral light of the distance measuring light in an optimal state.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 shows the overall configuration of an eye reflex camera. In the figure, 21 is an objective lens, 22 is a main mirror having a half mirror part 22a, and when the subject light passes through the objective lens 21, it is reflected by the main mirror. While being guided to the finder optical system 23, a part of the light passes through the half mirror part 22a.

24 is a long mirror placed behind the main mirror, which reflects the light passing through the half mirror part 23 downward;
The transmitted light is guided to the optical path splitting prism 25 and made to enter line sensors 26 and 27 at positions corresponding to the front and rear of the planned focal plane.

The passing light that has entered the line sensors 26 and 27 is compared in sharpness by a processing circuit (not shown), and the lens 22
The in-focus position is detected.

FIG. 8 shows an enlarged view of the area around the main mirror 22 in FIG. 7, FIG. 8 (1) shows its side view, and FIG.
2) shows the back side. In the figure, the mirror holder that holds the 28t/i main mirror 22 is a plate, and the half mirror part 22
In order to allow the passage of the luminous flux from a, the line sensor 26
, 27 (7) Corresponding to the line direction, the left and right sides have extending longitudinal openings 28a. Also, in this mirror holder, the plate 28 is rotatably supported around the shaft 28, and 91 is normally urged by a spring 282 and abuts against a stopper 283, or when photographing, the plate 28 is supported by the urging force of the spring 282. Against the axis 28
1\i- Rotate around the center to raise and retract the mirror 22.

29, on the sliding plate, the planting pins 29a and 29b are inserted into the elongated hole 30a of the holding plate 30.31 provided on the plate 22, and the mirror holder is
31a and can be slid up and down. Moreover, the sliding plate 29 has a spring 29 attached to the planting pin 29c. The spring 29. The other end is the pin 2 of the mirror holder.
8b, the sliding plate 29 is urged upward. 3
2.33 is a triangular mask as a light flux regulating member for adjusting the aperture degree of the opening 28a of the plate 28, and pins 32a and 33a provided at one end of the mirror holder are attached to the sliding plate 29. The mirror holder is fitted into the long 29d extending left and right, and the other end is pivotally supported under the opening 28a in the plate 28 by a common pin 34. Therefore, the portion of the light beam that is allowed to pass through the opening 2.8a of the sliding plate 29 has an inverted triangular shape with the base facing upward, and by moving the sliding plate up and down, the length of the base can be adjusted. changes, and the opening state of the opening 28a changes. In addition, in this drive lever, the opening 28a has a retaining portion 34a that can engage with the protruding pieces 29e and 29f provided on the inverted three-slide plate 29, and is biased upward by the spring 341 to generate an opening signal. The sliding plate 29 is moved downward in response to a signal from the pin or aperture lever. Also 1. Drive Renoku 3
The retaining portion 34a of No. 4 has a spring-up shape, and during exposure, the plate 28 of the mirror holder rotates around the shaft 28.
When returning from the mirror-up state to the original state, the engaging portion 34a can engage with the protruding pieces j9e, 29f of the sliding plate 29 no matter where the drive lever 34 is located.

The drive lever 34 moves the mirror holder upward while the plate 28 is raised and retracted, and the mirror holder moves downward when the plate 28 comes down to its original position, causing the sliding plate 29 to move upward. It may be structured so that it can be pushed down into a predetermined position.

Next, the operation of the above configuration will be explained. A signal from the opening signal pin or the aperture lever causes the drive lever 34 to move downward a predetermined distance of 11 degrees. Then, the protruding piece 29 of the sliding plate 29
e and 29f are pressed and moved by the engaging portion 34a of the drive lever 34, the mask 32 rotates counterclockwise around the pin 34 and the mask 33 rotates clockwise around the pin 34. move. As a result, the mirror holder is attached to the opening 2 of the plate 28.
The aperture 8a is opened by a predetermined amount in accordance with the brightness of the lens so as to extend the base of the inverted triangle. That is, for example, FIG. 9 (
As shown in 1), for a wide beam 35 that passes through a bright lens with an F number of Fl, 4, the amount of downward movement of the drive lever 34 is large, and the mask 32.33
Since the aperture 28a formed by the aperture 28a is also large with a long base, the light flux has a large amount of light, but for the light flux 36 with a small width that has passed through a lens with a dark F number such as F4, it is difficult to use the drive lever. The amount of downward movement of 34 becomes smaller and the opening 28a formed by the mask 32.33
On the other hand, since the aperture form is small with a short base,
When the shutter is released and the plate 28 rises, the mirror holder moves to the protruding piece of the sliding plate 29, so that the movable mask 32, 33 completely covers the opening 28a of the plate 28, and the finder optical system 23 It acts as a light shielding member that prevents reverse light from entering.

In this embodiment, the light flux regulating member is mechanically constructed with two sets of triangular masks, but the shape of the mask may be made variable using photochromy provided in a pattern or a liquid crystal plate. Alternatively, different masks may be evacuated and the masks may be selectively brought out onto the optical path for focus detection.

That is, the light flux regulating member may adjust the peripheral light of the subject light flux according to the F number of the lens. Further, the regulating member may be provided anywhere in the optical path between the objective lens and the sensor, but it is preferably provided as close to the objective lens as possible.

As described above, according to the present invention, the open signal pin or Since we have provided a light flux regulating member that changes the aperture of the optical path according to the F-number signal of the lens from the aperture lever, even for a wide light flux that has passed through the bright lens, the width of the light that has passed through the dark lens is limited. Even with a narrow lens, only the peripheral light of the light beam is cut, which prevents the effects of lens aberrations, allows accurate focus detection, and eliminates light loss, making it suitable even for dark subjects. It is possible to measure distances.

Therefore, false resolution does not occur even at a position that is significantly out of focus, and malfunction of the automatic focus detection device can be prevented.

Furthermore, in the present invention, the mirror is raised and retracted when photographing.
Since the light flux regulating member completely covers the light flux passing portion of the mirror during the period of time, reverse light from the finder can be completely prevented.

[Brief explanation of the drawing]

The zi diagram is a diagram showing the principle of the automatic focus detection method applied to the present invention. Figure 2 is a graph showing the relationship between the amount of lens extension and the image clarity value. Figure 3 is a graph showing the relationship between the lens extension amount and the image clarity value. Figure 5 is a schematic diagram showing the mask shape of the conventional device that provides the 0TFIltI line in Figure 4. Figure 6 is an explanatory diagram showing the drawbacks of the mask shape of the conventional device. , FIG. 7 is a configuration diagram showing an embodiment of the camera to which the present invention is applied, FIG. 8 is an enlarged view showing the vicinity of the mirror of the camera in FIG. 7,
(1) is its side view, and (2) is its rear view. FIG. 9 is a schematic diagram showing an embodiment of the mask obtained by the present invention, 1. Planned focal plane, 2, 3. Line sensor, 4.
...Objective lens, 5...Subject light, 6...Optical path, 7
゜8...Light flux regulating member, L...Subject light, 21...
・Objective rhythm, 26.27...Line sensor, 28
...Mirror holder is a plate, 29...Sliding plate, 32.33.
... Mask, 34..., Drive lever, 35... Luminous flux of bright lens, 36... Luminous flux of dark lens.

Claims (3)

[Claims] (1) By detecting the imaging state of the image of the object formed by the imaging optical system at least at two positions optically different distances from the object, In an automatic focus detection device configured to detect a focus adjustment state, the automatic focus detection device is arranged in an optical path from the imaging optical system to a focus detection sensor, and is arranged in an optical path leading from the imaging optical system to a focus detection sensor, and adjusts the optical path according to the F number of the imaging optical system. An automatic focus detection device characterized by changing the aperture of the light beam passing through the optical path. (2) The light flux regulating member is configured integrally with the main mirror so as to change the aperture of a light flux passing section provided on the main mirror. Automatic focus detection device. (3) The light flux regulating member is configured to block and close a light flux passage section provided on the main mirror in conjunction with the movement of the main mirror during photographing. The automatic focus detection device according to item 1.