JPS62138808A - Focus detecting device - Google Patents

Abstract

PURPOSE:To put, for example, a sweater of lateral stripe pattern and a window blind which can not be detected by a conventional passive type focus detecting device in focus by performing focus detection based on object brightness distributions in plural directions. CONSTITUTION:A visual field mask 103 is arranged nearby the primary image forming surface of a photographic lens 106 and a field lens 102 is so arranged as to project an image of a multi-aperture stop 103 on the exit pupil of the photographic lens, so visual field mask images 109a-109d are formed with pieces of luminous flux passed through four mutually separated areas 108a-108d of the exit pupil 107. Namely, phase difference detection type focus detection optical systems are constituted for the respective pieces of luminous flux passed through the areas 108a and 108c, and 108b and 108d on the exit pupil. Therefore, the image illuminance distribution in a visual field mask image 109 shifts inward from the position in an in-focus state as shown by an arrow in an out-of-focus state.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a focus detection device that detects the focus adjustment state of an objective lens based on the brightness distribution of a subject, and particularly relates to a focus detection device that detects the focus adjustment state of an objective lens based on the brightness distribution of a subject. The present invention relates to a device for detecting.

<Conventional technology> Traditionally, passive automatic focus detection devices.

For example, as shown in Japanese Patent Application Laid-Open No. 58-150918,
It was configured to detect the amount of defocus of the photographic lens from the luminance distribution in only one specific direction of the subject. Therefore, the focus cannot be detected at all for an object that does not have a brightness distribution in a direction that can be detected by the focus detection device.

For example, a camera's passive focus detection device generally has the ability to detect only horizontal luminance distribution, so a sweater with horizontal stripes at even horizontal intervals or a repeating striped pattern like a window blind can be used. The drawback was that it was difficult to focus on the subject.

<Problems to be Solved by the Invention> The present invention eliminates the above-mentioned drawbacks, makes it possible to detect the focus adjustment state of the photographing lens regardless of the appearance or pattern of the subject, and makes it possible to detect the focus adjustment state of the photographic lens regardless of the appearance or pattern of the subject. The purpose is to provide a device that facilitates processing.

In order to achieve this purpose, the optical system is equipped with an optical system that forms an image with parallax from the light flux passing through the same objective lens, and a photoelectric conversion means that receives these images. A device for detecting an accommodation state, in which a plurality of images with the parallax are formed in different directions, and the amount of change in the distance between each image due to defocusing of the objective lens is constant. There is.

<Embodiment> An embodiment of the present invention will be described below with reference to FIGS. 1 to 8. Figure 1 depicts the focus detection optical system, but if the focus detection optical system is incorporated into a single-lens reflex camera, it is assumed that the photographing lens is placed in front of this optical system. .

In the figure, 101 is a field mask equipped with linear apertures in the shape of a cross;
102 is a field lens, 103 is a porous aperture, 104
105 is a secondary imaging lens body, and 105 is a photoelectric conversion device having four pixel columns. Further, X is the optical axis of the photographing system.

The field of view mask lot is located near the planned imaging plane (including the case of the planned imaging plane) of the photographing lens (not shown), and the aerial image of the subject formed by the photographing lens is formed by the secondary imaging lens body 10.
4, each pixel column 105a of the photoelectric conversion device 105
-105d. Here, the porous aperture 103
Apertures 103a are arranged vertically across the optical axis of the imaging system.

103c, horizontally aligned apertures 103b and 103d (FIG. 2), and correspondingly a secondary imaging lens body 104.
has positive lens parts 104a and 104c arranged vertically and positive lens parts 104b and 104d arranged horizontally (FIG. 3). The aerial image is separated into four images with parallax and re-imaged. The secondary imaging lens body 104 in FIG. 3 includes a pair of positive lens parts 10 arranged vertically and horizontally.
4a and 104c.

104b and 104d are shaped as if the edges of the lenses were cut off and then joined together so that the distance between the optical axes of each positive lens part is smaller than the diameter, which helps increase the effective amount of light.

Field of view mask 101. transmitted through the field lens 102,
The light flux that has entered the aperture aperture 103a then enters the lens portion 104a of the secondary imaging lens body 104, and as shown in FIG. 4, a field mask image 10 is formed on the photoelectric conversion device 105.
Form 9'a. A pixel column 105a is located inside the visual field mask image 109a, and the illuminance distribution of the subject image is extracted here as an electrical signal. Similarly, the light flux transmitted through the diaphragm aperture 103b and the lens portion 104b forms a field mask image 109b, and 103c, 104c
The light flux that has passed through the field forms a field mask image 109c, and 10
3d.

The light beams transmitted through 104d each form a field mask image 109d, so the subject image is composed of pixel rows 105b and 10
Photoelectric conversion is performed at 5c and 105d.

FIGS. 5(a) and 5(b) are cross-sectional views showing this optical effect. In the figure, 106 is a photographing lens, and field mask 1
03 is placed near the primary imaging plane of the taking lens, and the field lens 102 is placed so as to project the multi-hole diaphragm 103 onto the exit pupil of the taking lens. 4 areas separated from each other on the top 1
08a, 108b, 108c.

A visual field mask image 109a is formed by the light beam passing through 108d.
, 109b, 109c, and 109d are formed. That is, the area 108a on the exit pupil.

For the light beams passing through 108c, 1osb, and 1oad, a phase difference detection type focus detection optical system is configured.

Therefore, in the front focus state where an object in front of the subject is imaged on the planned imaging plane, the illuminance distribution of the image within the field mask image 109 is smaller than the arrow in the focused state, as shown in FIG. 7(a). On the other hand, in the rear focus state where the object behind the subject is imaged on the expected imaging plane, the 7th
Move in the direction of the arrow shown in Figure (b).

FIG. 8 shows the photoelectric change detection power in the front focus and rear focus states, and shows pixel rows 105a, 105c and pixel row 105b when a point image is formed at the center of the visual field mask lot by the photographing lens.

The photoelectric conversion outputs of the 0 pixel rows 105a and 105b, which are the photoelectric conversion outputs of the pixel row 105d, correspond to the A series.
The photoelectric conversion outputs of 5c and 105d correspond to the B series. Figure 8 (a) shows the photoelectric change detection power when the photographic lens is in the focusing position, Figure 8 (b) shows the front focus state, and Figure (c
) is in the rear pin state. The distance between the two images is narrower at the front focus and wider at the rear focus. By detecting the relative interval between these two images, it becomes possible to calculate the amount of defocus of the photographic lens. An outline of the calculation method will be discussed later, but a detailed explanation will be omitted since it is outside the scope of the present invention.

9 to 12 show other embodiments according to the invention. In FIG. 9, 11B is a field mask having a square aperture whose diagonals coincide in the vertical and horizontal directions, 102 is a field lens, 117 is a multi-hole diaphragm, 118 is a secondary imaging lens body, and 119 is a vertical and horizontal direction. It is a photoelectric conversion device that has pixel rows arranged in rows. It is assumed that the photographing lens is placed in front of this row as well. The aperture 117 has four apertures 117a, 117b, and 117c each having a point-symmetrical shape.
, 117d (FIG. 1O), and the secondary imaging lens body 118 has four lens portions 118a at corresponding positions.

118b, 118c, and 118d, and further include aberration correction prism sections 118e, 118f, 118g, and 118h. That is, the light flux that has entered the aperture aperture 118a then enters the lens section 118a and exits from the prism section 118e, forming an image of the field mask 116 on the photoelectric conversion device 119. There is a pixel column 1 inside the visual field mask image 125a.
19a, a pixel column 119 is inside the visual field mask image 125b.
b. Inside the visual field mask image 125c, there is a pixel column 119C1.
Pixel rows 119d are located inside the visual field mask image 125d, and the illuminance distribution of the subject image is extracted as an electrical signal.

FIG. 10 depicts details of the secondary imaging lens body 118. A pair of convex lens portions 118a and 118C, 118b and 1
The pairs 18d are assembled so that the distance between optical axes is smaller than the diameter and diameter of each lens, and there is also a correction prism at the exit end of the columnar body that is symmetrical in the horizontal and vertical directions and tilted in the direction of the pixel row. A pair of 118e and 118gc7) and a pair of 118f and 118h are formed. The correction prism is intended to remove aberrations such as distortion that occur in separated images due to, for example, a difference between the position where the lens section 118a looks at the subject and the position where the lens section 118C looks at the subject. This objective is achieved by tilting the exit surface around the optical axis position. Therefore, the same in-focus position is maintained no matter where in the focus detection field of view the subject image is incident.

FIG. 11 is a detailed view of the aperture. The shape of the aperture opening is
It is set to maximize the symmetry of the blurred image and the baseline length of the focal system. That is, the blurred image caused by the aperture as shown in FIG. 2 becomes as shown in FIGS. 8(b) and 8(C), resulting in a blurred state in which the two images are non-congruent. The reason why the blurred images become non-congruent is that the aperture openings 103a and 103C are shaped so that even if one is moved in parallel, it does not overlap with the other, which is the case with 103b.

The same applies to 103d. In other words, in the case of the shape shown in Figure 2, the two sets of apertures are in a mirror image relationship, so their blurred images also become mirror images as shown in Figure 8, and are overlapped by parallel movement. The result is that it does not. On the other hand, the aperture shape shown in FIG.
If 7a is translated in parallel, it will overlap with 117c, and if 117b is translated in parallel, it will overlap with 117d.

Accordingly, the blurred images have congruent shapes as shown in FIG. 13, and by moving one in parallel, it is possible to superimpose it on the other, and the phase difference between the two images can be detected with high accuracy.

Furthermore, in order to maximize the baseline length of the focus detection system while satisfying such conditions, the maximum diameter of the four openings is made circular to match the exit pupil shape of the photographing lens.

Furthermore, in order to effectively utilize the amount of light, a square aperture as shown in FIG. 14 may be used.

Note that in the aperture shape shown here, the aperture centroid spacing of the aperture aperture pair is set to be the same in order to equalize the base line lengths of the respective focus detection optical systems. In other words, 103 in Figure 2
．． a-103c and 103b-103d, Ml 117a-117c and 117b-117d and the first
The aperture center spacings 136a-136c and 136b-136d in FIG. 1
09c and 109b-109cl are equal.

FIG. 12 shows a field mask image on the photoelectric conversion element in the focus detection optical system shown in FIG. 9. The field mask is separated into four images and projected by a secondary imaging lens body 118 having four lens parts. 9th
Points a, b, c, and d within the field mask aperture shown in the figure are a:, b', c', and d in Figure 12, respectively.
'corresponds to '.

In FIG. 9, the image of the subject is formed in the vicinity of the field mask 116 by a photographing lens (not shown), and the light flux that has passed through the aperture further passes through a multi-hole diaphragm 117 and is photoelectronized by a secondary imaging lens body 118. The images are formed on the conversion device 119 as two pairs of images with parallax. At this time, similarly to FIG. 5(a), the light beam that has passed through the aperture 117a of the multi-hole diaphragm 117 is subjected to an imaging action in the positive lens part 118a, and after being subjected to an aberration correction action in the prism part 118e, the light beam is An image is formed at 119a.

Further, the light beam passing through the aperture 117c is directed to the positive lens portion 118c.
After receiving an imaging action at , and an aberration correction action at the prism section 118g, an image is formed at the pixel row 119c. These pixel rows 1
The separated images on 19a and 119c move symmetrically in the vertical direction in response to focus adjustment of a photographing lens (not shown).A is the same as that described in FIG. 7. Also, the porous apertures 117b and 1
The light beams passing through 17d are pixel columns 119b and 11, respectively.
An image is formed on 9d, and the focal point 2g1 of a photographing lens (not shown) is
Move horizontally symmetrically depending on the node.

The defocus amount of the photographing lens can be calculated as follows from the phase difference of the image projected onto the pixel row of the photoelectric conversion device.

d is the defocus amount of the photographing lens, Z is the relative shift amount of the two images, M is the imaging magnification of the secondary imaging system, and FO is the ray passing through the center of the partial coverage area of the divided pupil. The angle made with the optical axis of the lens is expressed by the F number, and g is the distance between the film surface and the exit pupil plane of the photographing lens, a= (Fo/M) Z/ (1+FoZ/ (Mg)
The arithmetic expression 1-----1-(L) holds true. Thereby, the defocus amount of the photographing lens can be calculated from the relative shift amount Z of the two images. The relative shift amount 2 between the two images can be determined, for example, by the method disclosed in Japanese Patent Laid-Open No. 142306/1983.

Alternatively, the above deviation amount Z may be determined after adding up the outputs of two sets of vertical and horizontal pixel columns.

FIG. 15 is an explanatory diagram of this method of detecting the amount of image shift.
0 to 135 represent the outputs of the pixel columns, (a)-C is the pixel column 105a, and (a)-I is the pixel column 105c.

(b)-E corresponds to 105b, and (b)-F corresponds to 105d, respectively. Furthermore, FIG. 14(C) is (a).

The sum of the outputs shown in (b), (c) - G
(c)-H adds sensor outputs 131 and 133, respectively. The defocus amount of the photographic lens can be calculated by calculating the relative image shift amount using the method described above from the combined sensor outputs 134 and 135 obtained in this way. If such processing is performed, even if the contrast of the image on a pixel column is low and the amount of image shift cannot be detected with high accuracy using only the output of this pixel column, as shown in Figure 15(b), the image on the other pixel column will be If a high-contrast image is formed at It will only be done once. This effect is particularly effective when an image with no contrast is projected onto one set of pixel columns, for example, when the subject has vertical stripes.

FIG. 16 is a diagram showing the position of the distance measurement field within the viewfinder field of the camera. In FIG.

The distance measuring unit indicator mark is written on the focus plate of the camera (not shown). Further, the subject image incident on the distance measurement field of view 127 is the photoelectric conversion pixel row 105b.

The object image re-imaged on 105d or 119b, 119d and incident on the distance measurement field of view 128 is the photoelectric conversion pixel row 1
05a, 105c or 119a, 119c.

<Effects of the Invention> As explained above, by making it possible to detect focus based on the object brightness distribution in multiple directions, it is possible to detect objects that could not be detected with conventional passive focus detection devices, such as a sweater with horizontal stripes. It is now possible to focus on things like window blinds, making it possible to eliminate subjects that are difficult to photograph. In particular, there is an effect that the focus detection accuracy remains constant regardless of the direction of the coverage distribution of the subject.

Furthermore, in the above-mentioned calculation formula for the defocus amount of the photographic lens, Fo can be treated as a constant, which has the advantage of facilitating calculation processing.

On the other hand, after performing output addition between a pair of sensors, for example, the first
The defocus amount of the objective lens can be detected by adding the signals 130 and 132 and the signals 131 and 133 in FIG. 5 to create signals 134 and 135, and then calculating the amount of image shift. According to this, the image shift amount calculation only needs to be performed once.

In this case, even if a flat object image is incident in the direction of a certain pixel column, since there is contrast in the direction of other pixel columns, focus detection will not become impossible.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a focus detection device which is a first embodiment of the present invention, Fig. 2 is a plan view of an aperture, Fig. 3 is a detailed view of a secondary imaging lens body, and Fig. 4 is a photoelectric conversion device. Explanatory diagram showing the upper visual field mask image. Fig. 5 is a cross-sectional view of the focus detection device, Fig. 6 is an explanatory drawing showing the pupil division state of the objective lens, Fig. 7 is an explanatory drawing showing the moving direction of illuminance distribution in the field mask image, and Fig. 8 is an explanatory drawing showing the objective lens. FIG. 9 is a perspective view showing another embodiment of the focus detection device;
Figure 10 is a detailed view of the secondary imaging lens body, Figure 11 is a plan view of the aperture, Figure 12 is an explanatory diagram showing the field mask image on the photoelectric conversion device, and Figure 13 is the focused state of the objective lens. FIG. 14 is a plan view showing a modified example of the aperture, FIG. 15 is an explanatory diagram showing an example of addition of pixel row outputs, and FIG. 16 is an explanatory diagram showing an example of addition of pixel row outputs. FIG. 2 is an explanatory diagram showing a finder field of view and a distance measuring unit when applied to the device. In the figure, 101.116---Field mask, 102-1---Field lens, 1
03.117---Porous aperture. 103a-103d, 117a-117d-111 aperture, 104.118--Secondary imaging lens body, 104a-
104d, 118a-118d-111 Positive lens section, 105.119--1 Photoelectric conversion device, 105a-
105d, 119a-119d-111 pixel row (photoelectric conversion means).

Claims (3)

[Claims] (1) Equipped with an optical system that forms images with parallax from light beams passing through the same objective lens, and photoelectric conversion means that receives these images, and detects the focusing state of the objective lens based on a signal related to the image interval. The apparatus is characterized in that a plurality of sets of images with the parallax are formed in different directions, and the amount of change in the distance between each image due to defocusing of the objective lens is constant. Focus detection device. (2) The focus detection device according to claim 1, wherein the optical system includes a plurality of pairs of imaging lenses whose optical axes are parallel to each other, and each pair of imaging lenses has the same power. (3) Equipped with an optical system that forms images with parallax from light beams passing through the same objective lens and photoelectric conversion means that receives these images, and detects the focusing state of the objective lens based on a signal related to the image interval. In the apparatus, a plurality of sets of images with parallax are formed in different directions, and the amount of change in the distance between each image due to defocusing of the objective lens is constant, and each image is 1. A focus detection device characterized in that the distance between the aperture centers of a pair of apertures of an aperture that regulates the formed light flux is constant for each pair.