JPH0258012A - Focus detector - Google Patents

Abstract

PURPOSE:To perform accurate focus detection even not on an axis by providing a focus detecting means which detects the relative displacement of a couple of light images by using outputs of at least two of three image sensors. CONSTITUTION:In a step S1, an arithmetic control part 202 reads an open aperture F value and an exit pupil position P.O out of the memory part 104 of a photographic lens. In a step S2, the arithmetic control part 202 determines which of requirements A, B, and C the mounted photographic lens meets. Consequently, an image sensor which generates an eclipse is identified. In a step S3, the storage of the image sensor is started and when charges are accumulated by a specific quantity, image data are transferred and stored in the memory part 206 in a step S4. Then the outputs of a couple of image sensors which generate no eclipse are used in a step S5 to perform focus detection arithmetic and in a step S6, a movable lens 103 is driven according to the result, which is also displayed on a display device 207.

Description

[Detailed description of the invention] A. Industrial application field The present invention relates to a focus detection device for a camera or the like.

B. Prior Art As a conventional device of this type, the one shown in FIG. 9 is known. On the focus detection surface 1, an area of approximately ±2 to ±3 mm centered on the position (b) that intersects with the optical axis LX of the photographic lens (
A) to (C) are used as focus detection areas, and an image of this range is formed by a pair of re-imaging lenses 2a.

Image sensor section 3a on IC board 3 is indicated by 2b.

Focus detection is performed by detecting the amount of relative image shift from the image outputs of the two image sensor sections 3a and 3b.

By the way - in the focus detection device of an eye reflex camera.

It is necessary to prevent vignetting in the focus detection optical system even for interchangeable lenses with an open F value of around F5.6. The exit pupil position of an F5.6 photographic lens is often
It is often somewhere in the range of 50m+a to 200m+ shown by hatching, and in order to avoid vignetting with an F5.6 lens whose exit pupil position is in this range,
The spread α of the detection light beam needs to be around F7.

Furthermore, the re-imaging lenses 2a, 2 are formed by the field lens 6.
If the aperture b is projected at the exit position [approximately 100 mm (range L in the figure), the light flux (broken line) passing through points (a) and (c) at an image height of 2 to 3 mm from the optical axis will be Also, focus detection is possible without vignetting for an F5.6 lens with an exit pupil position of 50 mm to 200 mn+. By employing such a configuration, the conventional focus detection device was able to detect a focus within an image height range of approximately 3 mm without vignetting.

C1 Problem to be solved by the invention By the way, a position 3 to 4 mm or more away from the center of the optical axis (d)
, (e), and (f) as focus detection areas. Therefore, for example, a point (E) with an image height of 7 mm is set as the center (2).

The re-imaging lenses 4a and 4b and the IC board 5 are arranged as shown in FIG. 9 so that (e) and (f) are the focus detection areas. Here, this focus detection optical system is replaced by a re-imaging lens 4 a
, '4b is configured so that a conjugate image is created by the field lens 6 at approximately the exit pupil position of 100 mm. In this case, as is clear from the figure, the focus detection area (d).

Even if a photographic lens of F5.6 is used for (e) and (f), vignetting will not occur only when the exit pupil position of the photographic lens is within the range of Ll of around 100 mm. Therefore, there are restrictions on the interchangeable lenses that can be used.
There are many practical problems.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focus detection device that can accurately detect focus for photographic lenses having various exit pupil positions even when the focus detection area is centered at a position far from the optical axis of the photographic lens. There is a particular thing.

Means for Solving the D0 Problem The present invention is applied to a focus detection device that uses a position off the optical axis of a photographic lens as the center of a focus detection area and performs focus detection in the focus detection area.

The above-mentioned problem is solved by at least three re-imaging optical systems that re-image the optical image of the target object formed by the photographing lens on its predetermined focal plane as at least three identical optical images in the focus detection area. (For example, reference numeral 214 in FIG.
ia, 214xb.

214xc) and at least three image sensors (for example, Xa in FIG. 3(c)) that photoelectrically convert these at least three optical images, respectively.

(denoted as Xb, This is solved by arranging them in a straight line.

The image forming apparatus may further include determining means for determining which two of the three image sensors are not vignetted, based on information indicating whether vignetting has occurred in the three re-imaging optical systems.

In the focus detection region outside the E0 action axis, three optical images for focus detection are projected onto the three image sensors, respectively, by three reimaging lenses. If the conjugate image position of the pupil of the focus detection optical system and the exit pupil position of the photographing lens are appropriately determined, even if one of the outer three light images is vignetted, the other outer light image will not be vignetted. . Therefore, focus detection can be performed using the outputs of a pair of image sensors onto which a central optical image and an outer optical image without vignetting are projected.

F. Example Embodiments of the present invention will be described using FIGS. 1 to 6.

In FIG. 1(a), an exchangeable photographic lens barrel 10
0 is the lens driver 1 of the body 200. The drive force from the II device 201 is received by the coupler 101, and the gear train 102
This is a well-known configuration in which the movable lens 103 is moved through the lens.

A storage means 104 provided within the photographic lens barrel 100 stores the aperture F value and exit pupil position information of the photographic lens, and performs calculations and calculations within the body as necessary via a contact point 105 with the body 200. The control section 200 reads out these data.

A part of the light passing through the photographic lens is guided to the optical system 210 of the focus detection device via the central semi-transparent part of the quick return mirror 203 and the sub-mirror 204. Here, as shown in FIG. 1(b), the focus detection optical system 210 in this embodiment has an optical system Y disposed on the optical axis of the photographing lens as in the conventional case, and a focus detection optical system 210 separated from the optical axis by a predetermined distance. The optical systems X and 2 are arranged symmetrically, respectively. Each optical system Y, X, and Z includes a field diaphragm 211 that cuts extra light outside the focus detection area, a field lens 212, an aperture plate 213 that determines the pupil of the re-imaging lens, and a re-imaging lens 21.
4, and an IC board 215 equipped with a plurality of image sensors.

This figure 1 (b) shows the focus detection optical system 2 from the film surface side.
10 is a view of the figure.

Image outputs regarding the optical images formed on the respective image sensors of the optical systems X, Y, and Z are stored in the memory unit 206 via the interface unit 205 in FIG. 1(a). The calculation/control unit 202 calculates a relative image shift amount with respect to a pair of image outputs having different parallaxes using a well-known method, and based on this calculates the relative image shift amount by driving the lens driving device 201 by a predetermined amount to achieve focusing. At this time, the display device 207 is turned on.

2 and 3 show FIG. 1(b) in more detail, and FIG. 2 shows each focus detection optical system Y.

3A is a front view of the field stop 211, FIG. 3B is a front view of the aperture plate 213, and FIG. 3C is a front view of the IC board 215. The field stop 211 is an aperture 211Y for three optical systems y, x, and z.

It has 211X and 2112. Similarly, the aperture plate 213 is
Aperture (II!3) for the three optical systems y, x, z ya, y
b, xa, xb, xc, za, zb.

It has zc. As you can see from the diagram, there are three pupils xa, x
b, xc are arranged so that their pupil centers are in a straight line. Similarly, the IC board 215 also has three optical systems y,
Image sensor Ya for x and z.

It has Yb, Xa, Xb, Xc and Za, Zb, Zc. Note that the optical systems X and Z are arranged symmetrically with respect to the optical axis of the photographing lens, and since the optical system Z is the same as the optical system X except that it is symmetrical, a description thereof will be omitted.

Further, as shown in FIG. 2, the re-imaging lens of the optical system Y has a pair of lenses 214ya and 214yb as before, and the re-imaging lens of the optical system X has three lenses 214xa and 214yb.
It has 4xb and 214xc. The field lens 212 of this embodiment forms a military image of each aperture of the re-imaging lens at approximately the exit pupil position IW of 100 mm, and the spread α of the detection light flux is set to approximately F7.

Furthermore, the focus detection area (a) to (a) on the optical axis of the photographic lens is
The images of (b) to (c) are formed on the image sensors Ya and Yb, and the images of focus detection areas (d) to (e) to (f) are formed on the three re-imaging lenses 214xa, 214xb, 214xc and in front of them. The image is formed on the image sensors Xa, Xb, and Xc through three pupils xa, xb, and xc placed in the center. Reference numerals 215a and 215b in FIG. 2 are light shielding plates for preventing stray light from entering from next door.

Next, regarding the focus detection optical system X configured in this way,
The relationship between the exit pupil of the attached photographic lens and the vignetting of the detected light beam will be explained in detail with reference to FIGS. 4 and 5.

FIG. 4 is a diagram illustrating in which range of the exit pupil position the detected light flux of the optical system X is eclipsed for an F5.6 lens.
Figure 5 shows the exit pupil of the photographing lens with the field lens 21.
2 is a diagram projected onto the pupil position of the diaphragm 213 by No. 2.

The following can be seen from FIGS. 4 and 5.

■Reimaging lenses 21.4xa, 214
xb, 214xc detection light beams La, Lb, L
c also has no vignetting, so the image sensors Xa, Xb, and Xc
All three image outputs can be used for focus detection.

(2) For a photographic lens whose exit pupil position is in the L range of about 50 mm to 80 mm, the image output of the image sensor Xc cannot be used because the detection light flux Lc is vignetted. However, the detection light flux La.

Since Lb does not cause vignetting, image sensors Xa and
Focus detection is possible by detecting image shift from the image output of b.

■The exit pupil position is about 1420-200+++a.

For a photographic lens within the range of , the detection light beam La is vignetted and cannot be used. However, since no vignetting occurs in the detection light beams Lb and Lc, focus detection is possible by detecting image shift from the image outputs of the image sensors Xb and Xc.

Since vignetting does not always occur in the optical system Y, focus can be detected from the image outputs of the image sensors Ya and Yb. That is, in the focus detection optical system Y along the optical axis, focus detection is always performed by the pair of image sensors Ya and Yb.

Here, in the focus detection optical systems X and Z, the calculation/control unit 202 determines which image sensor's image output is to be used as a pair of image outputs having different parallaxes, as shown in Table 1 below. Ru.

In the focus detection optical systems X and z described above, depending on the exit pupil position and the aperture F value of the photographic lens to be attached, as shown in Table 1, a condition A is established in which no vignetting occurs in any of the detection light fluxes La, Lb, and Lc. , condition B under which the detection light beam LC is eclipsed, and condition C under which the detection light beam La is vignetted are known in advance. For example, if the exit pupil position is between 90 and 109.9 mm and the aperture F value is 5.6 or less, then condition A is met, and the exit pupil position is between 50 and 59.9 mm and the aperture F value is over 2.8 and is 5.6 or less. Then, condition B is determined, and condition C is determined if the exit pupil position is between 110 and 129.9 mm and the open F value is more than 5 and 5.6 or less.

In the case of condition A, image pairs are taken using image sensors Xa and Xb for optical system X.

Image sensors xb and Xc, image sensors Xa and Xc
As for the optical system 2, any of the pairs of image sensors Za and Zb, image sensors zb and Zc, and image sensors Za and Zc can be used. In the case of condition B, optical system X is used as the method of taking the image pair.

2 is a pair of image sensors Xa and xb and image sensors Za and zb. Furthermore, in the case of condition C, image pairs are taken for optical systems X and Z, such as image sensors xb and Xc and image sensors zb and Zc.

In the case of condition A, three choices are possible;
It is advantageous in terms of detection accuracy to use the pair c.

Next, the focus detection operation will be explained with reference to the flowchart shown in FIG.

In step S1, the calculation/control unit 202 reads the aperture F value and the exit pupil position PO from the memory unit 104 of the photographing lens.

In step S2, the calculation/control unit 202 determines, based on Table 1, which of conditions A, B, and C the attached photographic lens corresponds to. This allows the image sensor in which vignetting occurs to be identified. Next, in step S3, the image sensor starts accumulating the charge, and when a predetermined amount of charge is accumulated, the image data is transferred to the memory section 20 in step S4.
6. Here, the accumulation time is calculated by the calculation/control unit 202.
and is controlled by the interface unit 205 in a well-known manner. In this case, since the transfer takes time, it is more efficient to omit the transfer of the output of the image sensor that is determined to cause vignetting. For example, CCD as an image sensor
When using this method, only the CCD determined to cause vignetting among the three CCDs is prevented from performing transfer.

Next, in step S5, a focus detection calculation is performed using the pair of image sensor outputs without vignetting,
Based on this result, the movable lens 103 is driven in step S6, and a display is performed on the display device 207.

Note that it may be determined which image sensor pair to use the image output using only the exit pupil position information of the photographing lens. For example, if the exit pupil position is 100 mm or less (P○<1
00mm), always use a pair of image sensors Xa and xb and image sensors Za and zb, and PO≧100+
+n+, control may be performed to use a pair of image sensors xb and Xc and image sensors zb and Zc.

Next, a modification of the above-described embodiment will be described.

In the above embodiment, there are three focus detection areas (a) to (b).
-(c),(d)-(e)-(e).

(g) - (ch) - (su) are arranged in a straight line as shown in Fig. 3, but the present invention is not necessarily limited to this arrangement; for example, as shown in Fig. 7, outer focus detection Area (d) - (e) - (e) is the focal voltage detection area (a) in the center
- Each aperture 311X of the field stop 311 is tilted with respect to (b)=(c).

311z, and the pupil xa of the aperture plate 313,
xb and xc are also arranged tilted in the same way. However, pupil xa,
It is preferable that the centers of xb and xc be on a straight line.

In the layout of each optical element shown in FIG. 7, the extension lines of focus detection areas (d)-(e)-(f) extend approximately toward the optical axis of the photographing lens, and the closed pupils xa, xb, xc The pupil centers of both are on the same straight line, and this straight line also extends toward the optical axis.

This kind of layout is similar to the one in Figure 3, and 1.
It is possible to increase ixa', xb, and xc, resulting in a bright optical system, which is favorable for detection performance.

Furthermore, as long as a desired amount of light can be guided to the image sensor, a field stop 411 as shown in FIG. It is also possible to use an aperture plate 413. That is, the aperture 411X that defines the focus detection areas (d)-(e)-(f)
are arranged parallel to (a) - (b) and (c), and correspondingly, the alignment direction of the centers of pupils xa, xb, and xc is the direction of focus detection areas (d) - (e) - (f). Match.

That is, center lines 81 and 82 are made parallel. The optical system Z is similarly configured.

Now, in accordance with the position of the exit pupil of the photographing lens, the area where vignetting does not occur changes along a straight line 83 passing through the optical axis, as shown by circles 84, 85° 86 indicated by broken lines. Therefore, if we try to form a pupil without vignetting in this state, the pupils xa and xb in FIG.

The diameter of xc must be made smaller than the pupil diameter in FIGS. 3 and 7. For this reason, the amount of light received by the image sensor decreases and the detection performance deteriorates, resulting in the following restrictions. In other words, it is preferable that the angle C between the direction 81 in which the focus detection areas are lined up and the straight line 83 connecting the center of the focus detection areas and the optical axis of the photographic lens be 10 degrees or less, and at most
The limit is about <30 degrees from the top of the figure.

In the above embodiment, the memory section 10 in the photographic lens
4 (exit pupil position, aperture F value, etc.) to identify an image sensor in which vignetting has occurred, it is also possible to identify it without using data from the photographing lens.

For example, when the arithmetic/control unit 202 determines that there is no lens data, the presence or absence of vignetting is determined from the data obtained in conjunction with the focus detection calculation.

The applicant previously reported in Japanese Patent Application Laid-open No. 60-37513 that the output of each pixel constituting an image sensor is a□...
The maximum correlation position and maximum correlation amount Cext are determined from the image data pair represented by an, bl...bn.

We proposed a method for detecting focus from these data.

That is, the correlation amount C(L) of both images is defined as follows, with the mutual shift amount of both images being L, and C(L) = Σ1a
i-bi+t.

Find C(L) for the number of consecutive shifts.

The minimum value of this C('L) is set as C0, and C(L) on both sides of it is set as C0.
) are respectively C□ and C-0, the extreme value Cext of the interpolated correlation amount is Cext=Co-0, 5X C-0-C.

is given by If both images have no distortion due to vignetting and can be superimposed by mutual shift including fractions, the value of Cext above is E=Max(C□-Co, C-1
-C, ) is a sufficiently small value close to zero. On the other hand, when vignetting occurs and the two images cannot be completely superimposed due to mutual shift, the value of Cext does not become a small value.

Therefore, Cext is calculated for the image data pair regarding the image sensor pair Xa, Xb, and the remaining image sensor pair X
If Cext is also calculated for the image data pair related to b and Xc and the values of both Cext are compared, the smaller value Ce
The image data pair giving xt can be identified as corresponding to one without vignetting.

Although it is possible to increase the number of divided pupils to four or more, in that case, the area of the pupils becomes smaller, resulting in disadvantages such as an increase in the low luminance limit and an increase in the scale of the device. Therefore, when the focus detection area is set to an image height range of about 5 to 10 mm, the optimal number of split pupils is three.

G1 Effects of the Invention According to the present invention, at least three optical images are projected onto the respective image sensors in the off-axis focus detection area, so vignetting is always avoided regardless of the exit pupil position of the imaging lens. It is possible to obtain an image output related to a one-inch optical image without any distortion, and to perform focus detection with high precision even off-axis.

[Brief explanation of the drawing]

Figures 1 to 6 explain one embodiment, and Figure 1 (
a) is a block diagram showing the overall configuration, FIG. 1(b) is a front view of the focus detection optical system seen from the film side, FIG. 2 is an enlarged view thereof, and FIGS. 3(a) to (c) are A front view showing the field diaphragm, diaphragm plate, and IC board, respectively; FIG. 4 is an optical path diagram illustrating vignetting of the detected light beam for the focus detection optical system X;
FIG. 5 is a diagram illustrating the case where the exit pupil of the photographic lens in various positions is projected onto the pupil via the field lens,
FIG. 6 is a flowchart showing a sequence of processing steps for focus detection calculation. FIG. 7 and FIG. 8 are diagrams showing modified examples. FIG. 9 is an optical path diagram explaining the conventional problems. 100: Interchangeable lens 2oO: Camera body 202:
Calculation/control unit 210: Focus detection optical system 211: Field diaphragm 212: Field lens 213: Aperture plate 214: Re-imaging lens 214
xa~214xc: Re-imaging lens 215: Ic substrate xa+'+xc: Pupils Xa~XC: Image sensor La-Lc: Detection light flux

Claims (1)

[Scope of Claims] 1) In a focus detection device in which a position off the optical axis of a photographic lens is set as the center of a focus detection area and focus detection is performed in the focus detection area, a focal point formed by the photographic lens on its expected focal plane; at least three re-imaging optical systems that re-image an optical image of a target object as at least three identical optical images in the focus detection area; and at least three image sensors that photoelectrically convert each of these at least three optical images. and a focus detection means for detecting a relative displacement of a pair of optical images using the outputs of at least two of these three image sensors, the pupil centers of each of the reimaging optical systems being aligned in a straight line. A focus detection device characterized by: 2) The image sensor further comprises a determining means for determining whether vignetting has not occurred in two of the three image sensors based on information indicating whether vignetting has occurred in the three re-imaging optical systems. The focus detection device according to claim 1.