JPH07117644B2 - Focus detection device - Google Patents

Description

The present invention relates to a focus detection device, and more particularly to a device for detecting the focus adjustment state of an objective lens.

[Conventional technology]

It is quite common for photographic or video cameras to incorporate a detection device for autofocusing. However, the range-finding range is determined in the center of the finder, and a camera that focuses on a subject at a desired position within the finder screen has not yet been realized.

That is, if the distance measuring field of view is set in the center of the screen, there will be no problem if the main part of the subject is located in the center of the screen, but if it is out of the center of the screen, false distance measurement will occur, and focus will occur. There is an inconvenience that it becomes a blurred picture of. In order to eliminate this difficulty, shake the camera once to put the main part of the subject in the center of the screen to measure the distance, and then return the camera direction while keeping the focus adjustment state at that time, then shoot Although the release operation can be performed, the operation is troublesome and may not be performed when the user is in a hurry. For example, it was difficult to respond to a request that a subject moving laterally should take a photograph located outside the center of the screen.

On the other hand, the imaging light flux from the objective lens is guided to a set of re-imaging lenses, and the light amount distribution formed by these lenses is received by the pixel row of the photoelectric conversion element, and the focus adjustment state of the objective lens is adjusted from the interval of both light amount distributions. Devices for detecting are well known.

As a method for satisfying the requirement to measure the distance without shaking the camera for objects located outside the center of the screen, another pixel row is arranged outside the pixel row arranged on the optical axis. However, it is conceivable that the newly provided pixel row receives a subject image that is off the center of the screen.

[Problems to be Solved by the Present Invention]

However, aberrations generally remain in the optical lens, and the image formation state of the light beam differs between a position near the optical axis of the objective lens and a position far from the optical axis. Therefore, it is difficult to perform accurate focus detection at a position far from the optical axis. Is.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and provide a realistic structure capable of actually performing distance measurement at many positions. And
In order to achieve the object, a mask provided with a plurality of openings arranged in the vicinity of the planned image forming surface of the objective lens and having different distances from the optical axis position of the objective lens arranged in parallel, and arranged adjacent to the mask. And a re-imaging means for forming a light quantity distribution based on an object image, the relative position of which changes according to the focus adjustment state of the objective lens, and a field lens having a plurality of lens parts having different optical functions, and the light quantity distribution. A plurality of sets of pixel columns for receiving, and photoelectric conversion means for converting a light amount distribution into an electric signal is provided, and the arrangement direction of the openings is optically orthogonal to the arrangement direction of the pixel rows, and the field lens is The difference between the converged states appearing in the light flux passing through the opening near the optical axis of the objective lens and the light flux distant from the optical axis is corrected. However, optically orthogonal, for example, even if the optical axis is not physically orthogonal because it is bent at the reflecting surface,
When the optical axis is expanded on the reflecting surface, it means a case where they are orthogonal to each other.
Further, light is not limited to visible light.

〔Example〕

The focus detection device of the present invention can be used not only in a single-lens reflex camera using a silver salt film, a single-lens reflex electronic camera or a video camera, but also in a recording device, a position detecting device of a processing machine, a robot eye, or the like.

FIG. 6 shows an example of a usage mode, which illustrates an optical system of a single-lens reflex camera, 10 is a camera body, and 20 is a detachable and replaceable or fixed lens barrel. Reference numeral 21 is an objective lens, and 1 is its optical axis. The optical axis 1 reaches a quick return mirror 22 having a semi-transmissive region and is split into two. A focusing screen 23, a pentaprism 24, and an eyepiece lens 25 are arranged in order along the inverted optical axis to form a finder system for visual recognition. A movable sub-mirror 26 along the transmitted optical axis, and then a focus detection device 27 according to the present invention.
Is arranged, the driver (not shown) is activated by the output of the focus detection device 27, and the position of the objective lens 21 is adjusted. It is well known that the movable sub mirror 26 is held by the quick return mirror 22. 28 is an example of a subject illumination device
The projection chart 29 on which the projection pattern is formed is illuminated by a light source such as an LED, and the transmitted light is projected by the projection lens 30.

The configuration of the focus detection device shown at 27 is shown in FIGS.
This will be explained using the figure. FIG. 1 is a perspective view, FIG. 2 is a vertical sectional view, and FIG. 3 is a positional relationship between a pixel row and a light amount distribution of a photoelectric conversion device composed of a single chip. Reference numeral 42 denotes a porous field mask, which has long sides in the horizontal direction in the drawing and has parallel rectangular openings, and is arranged, for example, in the vicinity of the planned image plane of the objective lens 21 in FIG. 43 is a filter that blocks longer wavelength light than near infrared light. Reference numeral 50 is a split field lens, which is arranged slightly offset from the planned image forming plane of the objective lens. The split field lens 50 is composed of lens parts 50a, 50b, 50c, 50d, 50e, 50f and 50g having different optical functions as described later, and these components are either the lens thickness or the radius of curvature of the lens surface or It is formed by changing both. Further, instead of the split field lens 50, it is possible to use a combination of a Fresnel lens-like optical system in which different prisms are arranged for each aperture of the perforated field mask and a biconvex lens.

51 and 53 form a re-imaging lens unit with a two-hole diaphragm 52 sandwiched therebetween, and a convex lens 51 converts incident light into a state close to parallel light (optical action is described in Japanese Patent Publication No. 62-33564). ,
Further, the two-image forming lens 53 in which the two convex lenses 53a and 53b are arranged side by side and cemented together forms a secondary image of the object image formed by the objective lens.
Form one. The above-mentioned two-hole aperture 52 is provided with vertically elongated elliptical openings 52a and 52b arranged in the horizontal direction in the drawing.

54 is a concave lens for correcting field curvature, which is a photoelectric conversion device 55
It is arranged on a transparent plastic package 56 for containing (FIGS. 2 and 3). In addition, split field lens 50,
The convex lens 51 and the concave lens 54 of the re-imaging lens unit are shaped to be vertically long, but both are rotationally symmetric spherical lens systems.

The light flux that has passed through the openings 42 ... 42g of the multi-view field lens 42 is
Lens section 50a of split field lens 50 as shown
-Transmitting 50b, 50c, 50d, 50e, 50f and 50g to form a secondary image of the object on the photoelectric conversion device, respectively. Fig. 3 shows this situation. It is 60a and 60b, ... 60m and 60n and 62a.
62b is a set of pixel rows composed of a large number of pixels, and a filter having a bandpass characteristic substantially equal to the emission wavelength of an object illuminating device described later is formed on 62a and 62b. An image 61 of the openings 42a ... 42g of the perforated field mask corresponding to these pixel columns
61n is projected, and a secondary image of the object is formed inside this. At that time, the mask 42 and the device are formed in accordance with the width of each opening of the porous field-of-view mask 42, the width of the light-shielding bands 42h ... 42m between each opening, the width of the pixel row on the photoelectric conversion device 55 and the pitch of the pixel row.
Since the refracting powers of the optical system relaying 55, especially the respective lens parts of the split field lens and the re-imaging lens unit are adjusted, the light-shielding bands 42h ... 42m of the perforated field mask are the light beams emitted from the respective predetermined apertures. A part of the incident light is prevented from entering a pixel column other than the pixel column corresponding to this opening in a one-to-one correspondence.
In addition, the field mask image shows the aperture openings 52a and 52b and the lens unit 5
By the action of 3a and 53b, two perforations are formed side by side in one opening of the perforated field mask 42, and the secondary image of the object inside the arrow is accompanied by the arrow in relation to the position of the object image with respect to the planned image forming plane. Move in directions A and B. Therefore, since the set of each pixel row detects the relative interval of the light amount distribution regarding the secondary image forming a pair based on the photoelectric conversion output, it is possible to know the focus state of the objective lens at a plurality of distance measuring positions. .

The pixel row has a shape that matches the distortion of the field-of-view mask image,
It is desirable that the moving direction of the secondary image and the pixel column direction are completely aligned with each other. Further, although each pixel column is formed in a separated form, a set may be formed by allocating two ranges of one pixel line.

The operation of the split field lens will be described below. For comparison, a configuration in which a conventional field lens 101 and a single-hole field mask 100 are provided in place of the split field lens and the multi-hole field stop according to the embodiment of the present invention (first First, the operation will be described with reference to FIG.

Point P on the optical axis in the distance measuring field and point Q in the distance measuring field outside the optical axis
Both are on the planned image plane, but the state of the light flux when these are projected onto the photoelectric conversion device 55 through the field mask opening 100a is as shown in FIG. 112 and 1 in the figure
Reference numerals 13 are light rays emitted from the points P and Q, respectively, and their imaging points are the point R on the photoelectric conversion means and the point S in the concave lens 54.
Is. When this focus detection device is applied to a single-lens reflex camera, the distance between point P and point Q is 6 to 15 [mm], and the distance from point P to the photoelectric conversion element is 20 to 35 [mm]. Because of the limitation, even if the concave lens 54 for correcting the field curvature is used, such deviation of the secondary image surface due to the distance measuring field cannot be eliminated. As a result, the focus / detection accuracy greatly changes depending on the distance measuring field of view, which is not preferable.

On the other hand, it is extremely difficult with a field lens configuration in which it is easy to prevent the light flux passing through the distance measuring field near the optical axis 1 and the light flux passing through the distance measuring field away from the optical axis 1 from vignetting by the objective lens 21.

Vignetting of the luminous flux will be described with reference to FIG. In the figure
114 and 115 are images obtained by back-projecting the two apertures of the two-hole aperture for each pixel row position onto the exit pupil of the objective lens 21 through the field mask aperture 100a, and conversely, through the regions 114 and 115, the field mask aperture. The light flux passing through 100a reaches the photoelectric conversion device through the diaphragm. Therefore, as shown in the figure, when the back projection areas 114 and 115 are displaced from the exit pupil of the objective lens, the AF light flux that should reach the photoelectric conversion element is eclipsed by the objective lens, and the focus detection accuracy is significantly deteriorated. However, focus detection becomes impossible.

Since the ordinary field lens cannot correct the above difficulties in optical operation, the light flux emitted from the aperture outside the perforated field stop and the light flux emitted from the aperture close to the optical axis can be corrected by different field lenses. Can be corrected.

Next, the effect of the split field lens according to the present invention will be described with reference to FIGS. In FIG. 4, a point T (FIG. 2) in the distance measuring field on the optical axis on the planned image forming plane and a point U in the distance measuring field outside the optical axis are photoelectrically converted through the field mask openings 42d and 42g. It represents a state of being projected on an element, and in the figure, 70 is a ray emitted from a point T and 71 is a ray emitted from a point U. As shown in FIG. 2, the light ray 70 passes through the central lens portion 50d of the field lens, while the light ray 71 passes through the peripheral lens portion 50f.
-Transmits 50g. At this time, these two lens portions are configured to align the image formation state on the photoelectric conversion device, and qualitatively, by increasing the lens thickness of 50f · 50g, the connection between points T and U is formed. Both image points are points V and W located on the photoelectric conversion device. As a result, it is possible to keep the focus detection accuracy of each distance measuring visual field uniformly high.

FIG. 5 shows images obtained by back-projecting the two openings 52a and 52b of the diaphragm 52 onto the exit pupil of the objective lens through the endmost opening 42a of the perforated field mask and the field mask opening 42d on the optical axis. , 80a, 81a and 80b, 81b are aperture openings 52a, 52b, respectively.
It is a back projection image of (FIG. 1), 80a and 80b have passed through the field mask opening 42d, and 81a and 81b have passed through the field mask opening 42a. As can be seen from the figure, by optimizing the field lens for each distance measuring visual field, it is possible to realize a configuration in which the focus detection light beam is not eclipsed at any distance measuring visual field position. As a result, the distance measuring visual field position is not limited to the vicinity of the optical axis 1 and can be set in a wide range.

It should be noted that the light directed to the junctions 50h to 50g of the field lens is blocked by the light-shielding bands 42h, 42i, 42l, 42m of the visual field mask to prevent the generation of ghost light due to the light incident on this portion.

Further, although the divided field lens shown in the figure is made by integral molding of plastics, it is also possible to form each lens part and then combine them.

FIG. 10 shows the arrangement of the distance measuring fields. In the case of the single lens reflex camera shown in FIG. 6, the distance measuring fields are on the central axis of the focusing screen 23 in the long side direction. 91a
… 91g and 92 are laid out in parallel.

Then, the set of pixel columns 60a, 60b, ... 60m, 60n of FIG. 3 is back-projected onto the planned image forming surface by both imaging lens units, while the distance measuring field of the focusing screen 23 is projected on the planned image forming surface. If they are replaced, the set of pixel rows and the distance measuring visual field will overlap each other. Speaking in relation to the arrangement direction of the set of pixel columns with the members in the camera body, the direction of intersection of the surface including the semi-transparent surface (light splitting surface) of the quick return mirror 22 and the surface including the movable sub-mirror 26 (see the drawing). Vertical direction).

By adopting this arrangement, there is an advantage that the range from the distance measuring visual field at one end to the distance measuring visual field at the other end can be maximized without increasing the vertical width of the movable sub-mirror.

The horizontal stripe pattern in FIG. 11 shows an example of a projection pattern projected on an object of low contrast or low brightness,
It is depicted on chart 29 in FIG. Assuming that this figure is a projection pattern image projected on the object, 93 indicates the range-finding range when back-projecting the set of pixel rows 62a and 62b of FIG. 3 onto the object. As described above, a bandpass filter having a wavelength substantially equal to the emission wavelength of the illumination light source 28 (Fig. 6) is formed on the pixel rows 62a and 62b, and the pixel rows select the projection pattern reflected by the object. Sense. As a result, the contrast is forcibly added even to an object that is normally difficult to detect, and focus detection by the pixel rows 62a and 62b becomes possible. Incidentally, 94 is the range-finding range on the object by the pixel rows 60g and 60h.

With the above configuration, the electric signal from the photoelectric conversion device 56 (FIG. 1 etc.) is read out for each pixel column, and for example, the focus state calculation is performed for each distance measuring field of view. Select a close object and adjust the focus of the objective lens,
The continuity of the degree of focusing between adjacent distance measuring fields is verified, and a close object within a range with strong continuity is selected, or a predetermined distance measuring field is selected in advance, and the object that enters there is focused. Various signal processing algorithms such as performing matching can be selected.

〔The invention's effect〕

According to the present invention described above, there is an effect that it is possible to realize the distance measurement at a large number of positions including the distance measuring visual field which is off the center.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention. FIG. 2 is an optical sectional view thereof. FIG. 3 is a front view of the photoelectric conversion device. FIG. 4 is an optical partial sectional view. FIG. 5 is a perspective view. FIG. 6 is a sectional view of a configuration showing an application example to a camera. FIG. 7 is an optical cross-sectional view for explaining the comparative operation. FIG. 8 is an optical partial sectional view. FIG. 9 is a perspective view for comparative explanation of the operation. Figure 10 is a plan view of the field of view. FIG. 11 is a diagram showing the relationship between the projection pattern and the pixel row. In the figure, 42 is a multi-field mask, 50 is a split field lens,
50a ... 50g are lens parts, 51 is a convex lens of a re-imaging lens unit, 53 is a two-image forming lens, 52 is a two-hole diaphragm, 55 is a hole-electric conversion device, and 60a ... 60n, 62a, 62b are pixel columns.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akira Ishizaki Akira Ishizaki, Kanagawa Prefecture 770 Shimonoge, Takatsu-ku, Kanagawa Prefecture Tamagawa Plant (72) Inventor Keisuke Aoyama 770 Shimonoge, Takatsu-ku, Kawasaki, Kanagawa Prefecture Canon Inc. Tamagawa Plant (56) Reference JP 59-65814 (JP, A) JP 58-156909 (JP, A) JP 58-78101 (JP, A) JP 63-278012 (JP, A) A)

Claims (1)

[Claims] 1. An apparatus for detecting a focus adjustment state of an objective lens, comprising a plurality of apertures arranged in the vicinity of a planned image forming surface of the objective lens and having different distances from an optical axis position of the objective lens. A mask arranged in parallel, a field lens provided adjacent to the mask and having a plurality of lens portions having different optical functions, and a light amount based on an object image whose relative position changes depending on a focus adjustment state of an objective lens. The image forming device includes a re-imaging unit that forms a distribution and a plurality of sets of pixel columns that receive the light amount distribution, and a photoelectric conversion unit that converts the light amount distribution into an electric signal. And a field lens that corrects a difference in convergence state that appears between a light beam passing through an opening near the optical axis of the objective lens and a light beam away from the optical axis. Detection device.