JPH01243009A - Focus detecting device - Google Patents

Abstract

PURPOSE:To accomplish accurate focus detection by providing a cylindrical lens having a prescribed form on the surface of a light receiving means and imparting the refracting power of secondary image forming lenses. CONSTITUTION:The cylindrical lens 15 is arranged to turn its curvature toward a second direction orthogonal to a first direction in which sensor trains 14A and 14B line up. Thus, an image is formed in an area wherein the curvature of the cylindrical lens 15 exists; it is arranged in front of the light receiving means 14 ahead of the secondary image forming lenses 12A and 12B. In this case, each element of openings 16A and 16B of a diaphragm 16 is set such that the secondary image forming lens 12 and the cylindrical lens 15 cam form an image in an area in the width direction of the sensor trains 14A and 14B. Therefore, accurate focus detection is accomplished by reducing adverse effects of several types of aberration occurred in the width direction of the sensor trains: they are color aberration, distortion aberration, etc., and are generated by the secondary image forming system.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a focus detection device suitable for photographic cameras, video cameras, etc., and in particular, a focus detection device that divides the pupil of a photographic lens into a plurality of regions, for example, two regions, Relates to a focus detection device that detects the in-focus state of a photographic lens by forming a light intensity distribution for two subject images using the light flux passing through each area and determining the relative positional relationship between these two light intensity distributions. It is.

(Prior art) As one type of focus adjustment device conventionally used in photographic cameras, the exit pupil of the photographic lens is divided into two by an optical system for focus detection, and a device passes through each exit pupil region. The two subject images formed by the light flux are received by a photoelectric conversion element array (for example, a sensor array such as a CCD), the focal state of the photographing lens is detected from the output, and the photographing lens is driven based on the detection result. A so-called image shift detection method is well known.

FIG. 5 is a schematic diagram of an optical system of a conventional focus detection device of this type. In the figure, the photographing lens L whose focus should be detected
A field lens FLD is arranged in the same direction as the NS and the optical axis. Behind it, two 2
Next, imaging lenses FCLA and FCLB are arranged. Furthermore, sensor arrays SAA and SAB are arranged behind it. An aperture DIA is located near the secondary imaging lenses FCLA and FCLB.

A DIB is provided. The field lens FLD focuses the exit pupil of the photographing lens LNS into two secondary imaging lenses FCLA,
The image is almost formed on the pupil plane of FCLB. As a result, the ray bundles incident on the secondary imaging lenses FCLA and FCLB are each incident on the exit pupil plane of the photographing lens LNS.

They are emitted from areas of equal area that do not overlap with each other and correspond to FCLB. Field lens F
Aerial image formed near LD is secondary image lens FCL
A. When re-imaged on the surfaces of sensor arrays SAA and SAB by FCLB, the two images on sensor arrays SAA and SAB change their positions based on the displacement of the aerial image position in the optical axis direction. Become. Therefore, by detecting the amount of displacement (shift) in the relative positions of the two images on the sensor array, it is possible to know the focal state of the photographic lens LNS.

FIG. 6 shows the sensor array SAA in FIG. 5.

An example of charging conversion output of two images formed on the SAB is shown.

The output image signal of the sensor array SAA is A(i).

Let B(i) be the output signal of the sensor array SAB.

Note that the number of pixels of the sensor used is about 5 to 10 or more.

In FIG. 6, as a signal processing method for detecting the image shift amount PR from the image signals A(i) and B(i), for example, Japanese Patent Laid-Open No. 58
The present applicant has disclosed such methods as JP-A-142306, JP-A-59-107313, JP-A-60-101513, and Japanese Patent Application No. 61-160824. The methods disclosed in these documents focus the photographic lens by adjusting the focus of the photographic lens based on the amount of image shift between the two images.

This type of focus detection device generally has the advantage of being able to detect even a relatively large defocus and being able to quantitatively calculate the amount of defocus, so it is often used in reflex cameras. However, in the - direction, the adjustment of the secondary imaging system tends to be complicated, and it is difficult to properly correct the aberrations of the secondary imaging system, and there are many focusing points with a large angle of view. There were problems such as difficulty in optimizing the system.

In particular, when adjusting the assembly of each element, adjust so that the two photoelectric sensor arrays SAA and SAB view the same position on the subject plane on the intended imaging plane (a thin surface such as a film) where the field lens FLD is placed. This has become important.

7 is a perspective view of each element after the field lens FLD in FIG. 5. FIG. In the figure, when each element is correctly assembled, the optical image ZA when projected in the opposite direction by the photoelectric sensor array SAA is formed into a secondary image by the lens FCLA, and the photoelectric sensor array SAB is formed into a secondary image by the lens FCLB. It completely overlaps with the optical image ZB projected in the opposite direction.

However, for example, an integrally molded secondary imaging lens F
For example, if the CLA or FCLB as a whole has a component that rotates around the central axis 31 as shown by an arrow 32, or if the photoelectric sensor chips SSA and SSB have a rotating component 33, as shown in the figure. field lens FL
The positions of the optical images ZA and ZB on D will shift. In general, the allowable value for the deviation at this time needs to be kept to a very small value, for example, about 17,100 times the width of the photoelectric sensor array.

Generally, the width of the photoelectric sensor arrays SAA and SAB is set on the order of 100 μm, so accuracy on the order of 1 μm in terms of sensor surface is required. Accuracy of real injection molding,
The accuracy of installing sensor chips and molded optical components is much worse than this, so adjustments are practically required.

FIG. 8 is a perspective view of a conventional focus detection device having a field mask consisting of field apertures 21 and 22 showing two distance measurement fields on a predetermined imaging plane existing at least in the vicinity of a conventional field lens FLD. be.

In the figure, which of the field apertures 21, 22 is to be used is selected manually or automatically. The optical image of the field aperture Zl is separately formed onto the sensor array 5AAI by the secondary imaging lens FCLA, and onto the sensor array SAB 1 by the secondary imaging lens FCLB. Similarly, the optical image of the field aperture Z2 is secondary imaged onto the sensor array 5AA2 by a secondary imaging lens FCLA, and is secondary imaged onto the sensor array 5AA2 by a lens FCLB.
They are each separately imaged onto AB2.

Two viewing apertures 21. Z2 and 4 sensor rows 5AAI
, 5ABI, 5AA2, and 5AB2 are not necessarily essential requirements, or are arranged approximately symmetrically with respect to the central axis 41 of the entire system.

In such a focus detection device, the optical axis 4 of the secondary imaging lens
Since the field mask and the sensor array are not arranged on the plane including 2 to 43 and the central axis 41 of the optical system, chromatic aberration of magnification occurs in the direction perpendicular to the longitudinal direction of the field mask (i.e., the arrangement direction of the sensor array). will occur. For this reason, the position of the distance measurement field of view changes in the width direction due to the color analysis of the object.

Furthermore, due to the distortion of the secondary imaging lens, the field of view on the intended imaging plane seen by each sensor array is distorted. If this distortion is not equal at the corresponding positions of the sensor arrays 5AAI and 5ABI, the two separated images will look at different locations.

For example, FIG. 9 is an explanatory diagram showing the situation at this time.

In the same figure, ZAI is the back-projected image of the sensor array SAA 1 onto the intended imaging plane by the secondary imaging lens FCLA, that is, the position on the subject plane actually viewed by the sensor array 5AAI, and similarly, ZBI is the This is the position where the sensor array 5ABI is viewing on the planned imaging plane.

This also applies to the sensor arrays 5AA2 and 5AB2.

For this reason, conventionally, the width of the field mask 7 placed near the planned image formation plane near the field lens is narrowed, and the width of the sensor row is further widened to accommodate the field mask image within the wide sensor row with plenty of room. The method is used.

Generally, if the width of the sensor array is wide, it can be handled even if the optical image formed by the secondary imaging system of the field mask is distorted, or if the position changes in the width direction due to assembly errors or optical aberrations. However, in addition to the photoelectric conversion element, the charging sensor chip has many other components such as a capacitor for accumulating each pixel output, a gate for selectively reading out a specific pixel output, a shift register for driving this gate, and a control circuit for controlling the accumulation time. Since circuit elements are integrated, it is difficult to freely set the charging conversion element to be large and wide. Furthermore, as the area of the charging conversion element increases, dark current increases and random noise increases. The increase in area in this case is a margin for positional fluctuation of the optical image, and the amount of incident light does not increase, so the S/N ratio deteriorates and the low-luminance operating limit of the focus detection system deteriorates.

For this reason, the combination of a narrower field of view mask and a wider sensor array than before has been difficult to achieve, and is not often used. It is projecting an image. In this case, the field mask only has the function of preventing a double optical image from being formed on one sensor row, and the distance measurement field of view is determined by the light receiving area of the sensor row.

As described above, in order to eliminate the need for adjustment and improve the functionality of a focus detection system using a secondary imaging optical system, there has been a strong desire for a new technique that solves the above problems.

(Problems to be Solved by the Invention) The present invention provides an image shift type focus detection device, in which a cylindrical lens of a predetermined shape is arranged on the light receiving means surface, and the refractive power of the secondary imaging lens is appropriately set. This makes it easy to adjust the position between the field mask and the sensor array, and also reduces the negative effects of various aberrations that occur in the width direction of the sensor array, such as chromatic aberration and distortion in the secondary imaging system. The purpose of this invention is to provide a focus detection device that is capable of

(Means for solving the problem) The exit pupil of the photographic lens is divided into a plurality of different regions along the first direction by an optical means arranged on the image plane side of the photographic lens, and the exit pupil of the photographic lens is divided into a plurality of different regions. , forming a plurality of light intensity distributions regarding a subject image on a light receiving means surface consisting of a plurality of photoelectric conversion element arrays using a light beam that has passed through a shared field mask disposed near the planned image forming plane of the photographic lens; In the focus detection device, the relative positional relationship of the light quantity distribution of the photoelectric conversion element array is determined by the light receiving means, and the in-focus state of the photographing lens is determined by the calculation means using the output signal from the light receiving means. A cylindrical lens having a curvature in a second direction perpendicular to the first direction is disposed in front, and the optical means focuses the field mask image in the second direction within a region formed by the curvature of the cylindrical lens. This is what we do.

(Embodiment) FIG. 1 is a schematic diagram of a main part of an optical system according to a first embodiment of the present invention. In the figure, reference numeral 11 denotes a field lens, which is placed on the same optical axis 13 as a photographic lens (not shown). A secondary imaging system 12 has two secondary imaging lenses 12A and 12B located symmetrically with respect to the optical axis 13. 14 is a light receiving means, and two sensor rows 14A, 1
It has 4B. A cylindrical lens 15 is arranged with its curvature directed in a second direction orthogonal to the first direction, which is the direction in which the sensor rows 14A and 14B are arranged. 16
A and 16B are apertures, and secondary imaging lenses 12A and 12
It is located in front of B. Reference numeral 17 denotes a field mask having a field aperture Z, in contact with the field lens 11,
or located nearby.

In this embodiment, the field lens 11 and the secondary imaging system 12 constitute part of the optical means. field lens 11
are back-projected onto the pupil planes of the two secondary imaging lenses 12A and 12B near the exit pupil of a photographing lens (not shown).

As a result, the light beams incident on the secondary imaging lenses 12A and 12B are emitted from areas of equal area that do not overlap each other on the exit pupil plane of the photographic lens. Then, the field lens 11 is formed by the secondary imaging system 12.
The aerial image formed in the vicinity of is re-imaged onto the sensor rows 14A and 14B.

The focal state of the photographic lens is determined by detecting the relative light amount distribution regarding the two images on the sensor arrays 14A and 14B at this time.

At this time, in this embodiment, the width of the field aperture 2 of the field mask 17 forms an image within a region having the curvature of the cylindrical lens 15 disposed in front of the light receiving means 12 from the secondary imaging lenses 12A and 12B, and , each element is set so that the apertures 16A and 16B of the diaphragm 16 form images within the widthwise regions of the sensor rows 14A and 14B, respectively, by the secondary imaging lens and the cylindrical lens 15. This imaging relationship ensures that the light that passes through the field mask opening Z and passes through the apertures 16A and 16B reaches the sensor light receiving area.

An enlarged schematic diagram of the imaging relationship at this time is shown in FIG. Second
The figure shows the secondary imaging lens 12A and sensor array 1 in FIG.
FIG. 4A is a cross-sectional view of the 4A side.

As shown in the figure, in this embodiment, the field aperture is set such that the width WM of the field aperture Z of the field mask 17 is smaller than the width WL of the portion forming the curvature of the cylindrical lens 15 by the secondary imaging lens 12A. The width of the portion Z, the refractive power of the secondary imaging lens 12A, the distance between each element, etc. are set.

In general, considering optical aberrations, assembly errors, parts manufacturing, and dimensional errors, the surface conversion of the cylindrical lens 15 is Δ1.
Looking at the margin, the magnification of the secondary imaging lens 12A is β2A
Then (β 2A) xWM +Δ 1 < WL
It is better to set it like this.

For example, Δ1 is 100 μm in normal process accuracy.
If the precision of the inside and outside, assembling, and parts is high, it is sufficient to consider it to be around 30 μm.

Further, when the light receiving area WS in the width direction of the sensor row 14A is back-projected onto the pupil plane of the secondary imaging lens 12A by the cylindrical lens 15, the refraction of the cylindrical lens is adjusted so that the back-projected image is larger than the pupil aperture size W2. Various optical elements such as power and refractive power of the secondary imaging lens 14A are set.

In general, taking into account the alignment error Δ2 between the surface vertex of the cylindrical lens 15 and the center of the sensor array 14A, the back projection magnification of the cylindrical system is set as βC: (βC)X (WS-Δ2) > W2. It's good to do that.

For example, Δ2 is 100 μm in normal process accuracy.
If the precision of the inside and outside, assembling, and parts is improved, it is sufficient to consider 30 μm or less. If the alignment between the cylindrical lens surface apex and the center of the sensor row width is controlled, the margin can be reduced a little more.

In this embodiment, by satisfying the above two conditions, all the light beams passing through the field aperture Z of the field mask 17 and the effective apertures of the secondary imaging lenses 12A and 12B are free from manufacturing errors and optical The sensor array 14A, regardless of aberrations etc.
14B.

Therefore, according to this embodiment, the two sensor arrays can see exactly the same distance measurement field of view of the subject.

In this embodiment, the distance measurement field is defined by the shape of the field aperture Z of the field mask 17, so the edges of the field aperture Z of the field mask 17 are precisely formed.

In particular, in this embodiment, one side of the field lens 11 is made flat, and a light-shielding material layer is etched on that surface, thereby patterning and forming the field opening Z of the rectangular field mask 17.

FIG. 3 is a perspective view of an optical system according to a second embodiment of the present invention.

In this embodiment, a field mask 30 has two field apertures 21 and 22 showing distance measurement fields, and is arranged near the field lens 11. Viewing aperture Zl, 2
Which of the two viewing apertures to use is selected manually or automatically. The optical image of the field opening Z1 is separately formed onto the surface of the sensor row 14A by the secondary imaging lens 12A, and onto the surface of the sensor row 14B by the secondary imaging lens 12B. Similarly, the optical image of the field opening Z2 is separately formed onto the surface of the sensor row 14C by the secondary imaging lens 12A, and onto the surface of the sensor row 140 by the secondary imaging lens 12B.

Two viewing apertures 21. Z2 and four sensor rows 14A,
14B, 14C, and 14D are arranged approximately symmetrically with respect to the central axis 31 of the entire system, although this is not necessarily an essential requirement.

15A and 15B are cylindrical lenses, each of which is arranged in front of the sensor row.

The two cylindrical lenses 15A and 15B are each connected to the sensor array 14A, similar to the embodiment shown in FIG.

14B, or a second direction perpendicular to the first direction, which is the direction in which the sensor rows 14C and 14D are arranged.

In this embodiment, the secondary imaging lens 12A.

Since each principal ray of the lens 12B is not within the plane that includes the central axis 31 of the optical system and the axes 32 and 33 of the secondary imaging lens, the cylindrical lens 15A has an angle corresponding to the inclination angle of the imaging principal ray.
, 15B are shifted in the width direction of the sensor row based on the positional relationship between the apex of the surface and the center of the sensor row.

Further, this embodiment is particularly effective when increasing the number of distance measurement points. For example, if a large number of distance measurement points distributed over a wide angle of view are attempted to be implemented using the combination of conventional optical systems shown in Figure 8, even if the optical system parts can be integrally molded, the position of the apex of the lens surface cannot be controlled on the order of 1 μm. Because injection molding technology is difficult, adjustment work is required for each distance measurement point. In this case, adjustment is extremely difficult and the shape of the focus detection optical system becomes large; however, according to this embodiment, a focus detection device that solves these problems can be achieved.

FIG. 4 is a schematic diagram of an optical system according to a third embodiment of the present invention.

In this figure, the same elements as those shown in FIG. 3 are given the same reference numerals.

This embodiment is an embodiment of a two-point ranging system having sensor array directions in two orthogonal directions, that is, sensor rows 14A, 14B and 14C, 14D.

According to this embodiment, problems caused by optical aberrations, component errors, and assembly errors can all be absorbed by the cylindrical lenses 15A and 15B placed in front of the sensor row, so it is highly effective when applied to such a focus detection optical system. That is, in order to widen the tolerance for error, the field lens 11, the secondary imaging lenses 12A and 12B, the cylindrical plate 41, and the charging element chip that integrates the sensor array bears of the 2 series, etc., are common to the two distance measurement fields of view. It is integrally molded and requires no adjustment. or,
Regardless of aberrations in the secondary imaging system, the two separated optical images seen at one distance measurement point see exactly the same field of view in the width direction of the sensor row, so the reliability of the correlation calculation between the two images is basically excellent. It becomes something.

(Effects of the Invention) According to the present invention, in the image shift type focus detection device, each of It makes it easy to adjust the position and assemble the optical elements, and it also makes it easy to obtain separated optical images with high optical performance with less occurrence of various aberrations, and it also makes it easy to take a large number of distance measurement points at a large angle of view, resulting in high-performance focusing. A focus detection device capable of detection can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the main parts of the optical system according to the first embodiment of the present invention, FIG. 2 is an enlarged schematic diagram of a portion of FIG. 1, and FIGS. 3 and 4 are respectively the second embodiment of the present invention. A schematic diagram of the main parts of the optical system of the third embodiment,
5, 7, and 8 are schematic diagrams of the optical system of a conventional image shift type focus detection device, FIG. 6 is an explanatory diagram of an image shift signal obtained from the light receiving means in FIG. 5, and FIG. This figure is an explanatory diagram of the distance measurement field of view 3 in FIG. 8. In the figure, 11 is a field lens, 12 is a secondary imaging system, f
2A, 12B are secondary imaging lenses, 13 is an optical axis of a photographing lens, 14 is a light receiving means, 15° 15A, 15B are cylindrical lenses, 14A, 14B, 14C, 14D are sensor rows, 16A, 16B are an aperture, 17 is the visual field mask, Z. Zl and Z2 are field apertures. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] (1) The exit pupil of the photographic lens is divided into a plurality of different regions along the first direction by an optical means arranged on the image plane side of the photographic lens, and the projected result of the photographic lens is passed through the plurality of regions. A plurality of light intensity distributions related to the subject image are formed on a light receiving means surface consisting of a plurality of photoelectric conversion element arrays using the light flux that has passed through a shared field mask placed near the image plane, and the relative light intensity distributions of the plurality of light intensity distributions are calculated. Determining the positional relationship by the light receiving means,
A focus detection device that uses an output signal from the light receiving means to determine the in-focus state of the photographic lens by means of a calculation means,
A cylindrical lens having a curvature in a second direction perpendicular to the first direction is arranged in front of the photoelectric conversion element array, and the field mask image is formed in the second direction by the optical means in an area where the curvature of the cylindrical lens is formed. A focus detection device characterized in that an image is formed within the center of the image.