JPH1068863A - Focus detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detection result with a proper temperature correction. SOLUTION: A lens holding member 60 of a thin plate form is fixed in a curved state to a holding member 50 holding an image sensor 90, and a multiple lens body 40 is fixed on the curvature part. And, plural lens pieces of the multiple lens body 40 guide plural luminous fluxes passing through different areas of a photographic lens to an image sensor 90, and a focus adjustment state of the photographic lens is detected based on an output signal of the image sensor 90. Since the multiple lens body 40 is an integral molding of plural plastic lenses and a length between optical axes of lens pieces of the plural lens pieces varies due to temperature changes, a focus detection error is generated. On the other hand, a change in a warp of the curvature part of the lens holding member 60 due to temperature change causes a change in a length between the multiple lens body 40 and the image sensor 90, and this also causes a focus detection error. Here, it is preferable that the former focus detection error offsets the latter focus detection error with respect to the curvature of the lens holding member 60. Thus, it is possible to accurately correct the focus detection error caused by the change in the length between the optical axes of the lens pieces of the multiple lens body 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase difference detection type focus detection apparatus for detecting a focus adjustment state of a photographic lens such as a camera.

[0002]

2. Description of the Related Art A focus detection device of a phase difference detection type is widely used in single-lens reflex cameras and the like. In this device, a light beam from a pair of subjects passing through different regions of the photographing lens is guided onto an image sensor by a pair of re-imaging lenses arranged at a predetermined interval, and a pair of subject images formed on the image sensor is formed. The focus state of the photographing lens is detected from the interval.

Usually, a pair of re-imaging lenses are often integrally formed of plastic in order to reduce the size and cost of a focus detection device. However, in such a focus detection device having an integrally molded structure, the distance between the optical axes of the pair of re-imaging lenses changes with temperature fluctuation, and as a result, the distance between the pair of subject images on the image sensor changes. An error occurs in the focus detection result. In addition, since plastic generally has a large coefficient of thermal expansion, a detection error becomes a size that cannot be ignored in practical use.

Therefore, in order to prevent such a problem, there has been proposed a focus detection device in which a temperature sensor is installed in a camera and the focus detection result is corrected based on the detected temperature (for example, Japanese Patent Application Laid-Open No. 60-1985). -235110).

[0005]

By the way, usually, as described above, the focus detection device is made compact by integrally forming the focus detection optical system with plastic as described above. Therefore, it is difficult to secure a space for the temperature sensor and its wiring near the re-imaging lens. As a result, the temperature sensor and the re-imaging lens are installed at a certain distance, and the temperature of the detection unit of the temperature sensor and the temperature of the re-imaging lens may not match. In such a case, the focus detection result cannot be correctly corrected at the temperature detected by the temperature sensor. In particular, since the distance between the re-imaging lens and the image sensor is only about 2 to 4 mm, it is possible that the temperature near the re-imaging lens greatly changes locally due to radiant heat of the image sensor itself.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a focus detecting device which corrects the temperature of a focus detection result correctly.

[0007]

[Means for Solving the Problems]

(1) The invention according to claim 1 is an image sensor that outputs a signal corresponding to a light amount distribution of a light beam, and a plastic multi-lens body formed by integrally molding a plurality of lens pieces.
A multi-lens body that guides a plurality of light beams transmitted through different areas of the photographing lens by the plurality of lens pieces to the image sensor; and a holding member that holds the image sensor. The focus of the photographing lens is determined based on an output signal of the image sensor. The present invention is applied to a focus detection device that detects an adjustment state. A thin plate-shaped member having a coefficient of thermal expansion different from that of the holding member, which is fixed to the holding member in a curved state, and includes a lens supporting member having a curved portion to which the multi-lens body is fixed. (2) A focus detection device according to claim 2, wherein a focus detection error caused by a temperature change of an optical axis interval of a pair of lens pieces out of a plurality of lens pieces, and a multi-eye lens caused by a temperature change of a bending portion bending. The curvature of the lens support member is set so that a focus detection error caused by a change in the distance between the body and the image sensor is offset. A thin plate-shaped lens support member was fixed to a holding member for holding the image sensor in a curved state, and a multi-lens body was fixed to the curved portion. Then, a plurality of luminous fluxes that have passed through different regions of the photographing lens by the plurality of lens pieces of the multi-lens body are guided to the image sensor, and a focus adjustment state of the photographing lens is detected based on an output signal of the image sensor. The multi-lens body is made of plastic in which a plurality of lenses are integrally molded,
The optical axis interval of a pair of lens pieces among the plurality of lens pieces changes in temperature, and a focus detection error occurs. On the other hand, the change in the temperature of the bending of the curved portion of the lens supporting member changes the distance between the multi-lens body and the image sensor, causing a focus detection error. Here, it is desirable to set the degree of curvature of the lens support member such that the former focus detection error is offset by the latter focus detection error. As a result, it is possible to accurately correct a focus detection error caused by a temperature change in the optical axis interval of the lens pieces of the multi-lens body. (3) In the focus detecting device according to the third aspect, the lens supporting member is provided with a plurality of aperture openings for restricting a light beam from a subject incident on each lens piece of the multi-lens body. Since the aperture opening is provided in the lens supporting member that supports the multi-lens body, there is no need to separately install an aperture mask, the number of parts of the apparatus is reduced, and the number of assembling steps can be reduced. (4) The focus detecting device according to claim 4, wherein the holding member has an opening having a gap in which the multi-lens body can slide, and the posture of the multi-lens body when the multi-lens body moves due to the bending of the curved portion. It is intended to keep it constant. When the multi-lens body moves due to the bending of the curved part of the lens support member,
Since the posture of the multi-lens body is kept constant without tilting, an accurate focus detection result can be obtained. (5) In the focus detection device according to claim 5, the holding member is made of plastic, and the lens support member is made of metal.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment for detecting a focus adjustment state of a photographing lens of a single-lens reflex camera will be described. FIG. 1 shows a configuration of a single-lens reflex camera equipped with a focus detection device according to one embodiment. The taking lens 10 is interchangeably mounted on the camera body 20. The luminous flux from the subject passes through the taking lens 10 and is partially reflected by the main mirror 21 of the camera body 20 and guided to a finder.
Another part is transmitted through the main mirror 21 and reflected by the sub-mirror 22, and is converted into a light beam for focus detection by the focus detection device 23.
Led to.

FIG. 2 shows the configuration of the optical system of the focus detection device shown in FIG. Note that the photographing lens 10 is also shown for easy understanding. The focus detection optical system includes a field mask 70, a condenser lens (also referred to as a field lens) 30, an infrared cut filter 100, a re-imaging lens 40, an aperture mask 60, and an image sensor 9.
0 is provided. Note that the condenser lens 30 is actually
A mirror for bending the optical path is inserted between the infrared cut filter 100 and the infrared cut filter 100, but is not shown in the drawing.

The re-imaging lens 40 has two lens pieces 41
a and 41b are arranged in the horizontal direction and are integrally formed on a plastic substrate. The aperture mask 60 installed on the subject side of the re-imaging lens 40 is made of a steel plate, and has a matte black coating for anticorrosion and preventing light reflection, and has a pair of openings 61a and 61b at the center thereof. The aperture mask 60 also serves as a support member for the re-imaging lens 40, as will be described in detail later. The image sensor 90 outputs an electric signal corresponding to the light amount distribution of the subject image formed on the light receiving surface by the focus detection optical system.

The focus detecting device 23 is disposed behind a plane optically equivalent to a film plane, which is a predetermined focal plane of the taking lens 10. The condenser lens 30 includes an aperture mask 60
The images of the pair of openings 61a and 61b are projected near the exit pupil plane of the photographing lens 10. The light flux transmitted through the regions 11a and 11b surrounded by the pair of aperture images once forms a subject image near the predetermined focal plane. Next, the light sequentially passes through the aperture of the field mask 70, the condenser lens 30, and the infrared cut filter 100, and further passes through the apertures 61a and 61b of the aperture mask 60 and the lens piece 41 of the re-imaging lens 40, respectively.
a, a pair of subject images or a pair of blurred light quantity distributions are formed on the sensor rows 91a, 91b of the image sensor 90. In this specification, this blurred light amount distribution is also called an "image" unless otherwise specified.

The displacement between the image forming position of the light beam from the subject transmitted through the photographing lens 10 and the predetermined focal plane is called a defocus amount, and the sign thereof indicates that the image forming position is shifted from the predetermined focal plane toward the subject ( (In the case of the front pin) is positive. And
When the defocus amount is 0, that is, in a focused state, the distance between a pair of subject images on the image sensor 90 is set to d. When the defocus amount is positive (front focus), the subject image interval is smaller than d, and when the defocus amount is negative (back focus), the subject image interval is larger than d. The difference between the distance between the pair of subject images and d is a value that is substantially proportional to the defocus amount. Therefore, the subject image interval is calculated based on the outputs of the sensor rows 91a and 91b, and the focus adjustment state of the photographing lens 10 based on the lateral contrast of the subject is detected.

The focus detection principle of such a phase difference method is as follows.
For example, Japan Society of Applied Physics, Optical Society, “Optics”, No.18
Vol. 11 (November 1989), which is described in detail in a document such as "Autofocus Technology for Single-Lens Reflex Cameras" by Suzuki, and a detailed description thereof will be omitted.

FIG. 3 is a longitudinal sectional view of the focus detecting device 23. The same members as those shown in FIG. 2 are denoted by the same reference numerals, and the description will be focused on the differences. Also, in order to make the description easy to understand, an aperture mask / lens support member 60 is used.
The exaggeration of the curvature of is drawn larger. Aperture mask 60
Is a thin plate-shaped metal, and fixes the re-imaging lens 40 to the curved portion. As described above, since the aperture mask 60 also serves as a support member for the re-imaging lens 40, the number of components is reduced, and the number of assembly steps is reduced. The surface mirror 120 is a surface mirror that bends the optical path of the light beam for focus detection, and is installed between the condenser lens 30 and the infrared cut filter 100. The holding member 50 is a member that holds each member of the focus detection optical system, and is an injection-molded product made of polycarbonate resin reinforced with glass fiber chips. The image sensor 90 is bonded to the holding member 50.

FIG. 4 is a perspective view showing a mounting portion of the re-imaging lens 40. The two bosses 42a and 42b provided on the re-imaging lens 40 are arranged so that the flat surface at the base of each boss abuts on the aperture mask 60.
And the round hole 62b. Then boss 42
The heads of a and 42b are crushed with a heated iron or the like, and the re-imaging lens 40 is fixed to the aperture mask 60 by thermal caulking.

The height L1 of the aperture mask 60 is different from that of the holding member 5.
0 is slightly longer than the distance L2 between the two support member fixing portions 5la and 51b. Therefore, FIG.
When the aperture mask 60 is incorporated in the holding member 50 as shown in FIG. To assemble in this state, the diaphragm mask 60 is inserted into the holding member 50 in a curved state, and its ends 63a and 63b are respectively attached to the supporting member fixing portions 5la of the two cylindrical portions of the holding member 50.
And 51b. And the end portions 63a, 63
The aperture mask 60 is fixed to the holding member 50 by applying an adhesive between the b and the holding member 50.

In practice, the difference between L1 and L2 is very small. For example, in this example, L2 is about 10 mm and L1 is only 0.01 mm longer. The lift due to the curvature in the assembled state is about 0.2 mm.

The holding member 50 is made of polycarbonate resin reinforced with glass fiber chips, while the aperture mask 60 is made of steel plate. The thermal expansion coefficients of the former are about 2.2 × 10 ⁻⁵ (1 / ° C.), and the latter are about 1.2 × 10 ^−5.
(1 / ° C.), the former is larger by about 1 × 10 ⁻⁵ (1 / ° C.). Then, when these temperatures rise by 1 ° C., L1
And L2 is reduced, and the lift amount is reduced by about 1 μm. That is, the re-imaging lens 40 is connected to the image sensor 9.
It approaches 0 by about 1 μm. The change in the difference between L1 and L2 and the change in the lift amount are substantially proportional to the range in which the lift amount is small and the change in the difference between L1 and L2 is small.

In this focus detecting device, if there is no change in the floating amount of the re-imaging lens 40, the lens pieces 41a and 41a of the re-imaging lens 40 are mainly changed by the temperature change.
The change of the interval of 1b causes an error of -4 μm in the detected defocus amount per 1 ° C. increase. More specifically, the distance between the lens pieces 41a and 41b of about 1.6 mm increases by about 0.1 μm per 1 ° C. increase in temperature. As a result, the object image interval on the image sensor 90 increases by about 0.12 μm, and the detected defocus amount becomes about −4 μm.
Error occurs.

On the other hand, when the distance between the re-imaging lens 40 and the image sensor 90 changes, the detected defocus amount changes by about 4 μm per 1 μm. That is, when the distance of 1 μm decreases, the defocus amount of 4 μm changes. Therefore, the error of the detected defocus amount due to the temperature change is almost offset by the change of the floating amount of the re-imaging lens 40 described above.

In the above-described structure, if the length L1 of the aperture mask / lens support member 60 is increased, the degree of curvature in the mounted state is also increased. Then, the ratio of the floating change amount of the re-imaging lens 40 to the temperature change amount decreases. Conversely, if L1 is reduced, this ratio increases. Therefore, even for a focus detection device in which the ratio between the detected defocus amount error and the temperature change is different from that of the present embodiment, the structure of this embodiment can be designed to have an appropriate floating amount, so that the error can be offset. it can. However,
As the ratio of the lift amount to the fixed portion interval L2 increases, the linearity of the change in the lift amount with respect to the change in the overall length L1 of the aperture mask 60 tends to deteriorate. It is desirable.

Also, the focus detection error is not completely canceled by the above structure, but a predetermined ratio (for example, half) thereof.
And the rest can be temperature corrected by software using a temperature sensor built into the camera as in the conventional method. Even in this case, the focus detection error due to the temperature difference between the temperature sensor and the vicinity of the re-imaging lens is sufficiently reduced as compared with the conventional device which completely relies on the temperature sensor.

Further, after substantially eliminating the error due to the temperature change of the focus detection result according to the above-described embodiment, based on the temperature detected by the temperature sensor, the temperature change of the interval between the film surface and the photographing lens surface is calculated. The correction may be made by software. In this case, the temperature sensor is deliberately kept away from the focus detection device and other electronic components that are a source of heat so that the temperature sensor is not affected by local temperature rise due to the heat generated by the image sensor itself. Install at the position where temperature is detected. This method enables focus detection with less error.

In the above embodiment, the example in which the aperture mask 60 also serves as the re-imaging lens support member has been described, but the aperture member and the support member may be separate members.

Also, contrary to the above embodiment, the holding member may be made of metal and the lens support member may be made of a resin film, and the warp direction of the lens support member may be reversed. That is, the central portion is warped in a direction approaching the image sensor. In this case, when the temperature rises, the difference between L1 and L2 increases, and the floating amount of the re-imaging lens 40 increases, that is, it changes in a direction approaching the image sensor. In this manner, a change in the detected defocus amount due to a temperature change is canceled by the same principle as in the above embodiment.

Further, in the above embodiment, the change in the inclination due to the ups and downs of the re-imaging lens depends on the symmetry of the deformation of the lens supporting member. For example, a guide mechanism that regulates the posture may be provided by making the hole for moving the re-imaging lens provided in the holding member a gap such that the re-imaging lens can slide. In this case, it is desirable that the joining between the re-imaging lens and the lens supporting member be made relatively inclining like a universal joint.

In the above embodiment, the re-imaging lens having a pair of lens pieces has been described as an example. However, the present invention is also applied to an apparatus that performs focus detection based on the contrast of a subject in both vertical and horizontal directions. can do. FIG.
Are two pairs of lens pieces 141a,
Re-imaging lens 1 having 141b, 141c, 141d
40 and openings 161a, 161a,
14 shows an aperture mask / lens support member 160 having 161b, 161c, and 161d. For an apparatus that performs focus detection based on the contrast of the subject in both the vertical and horizontal directions, the refocusing lens 140 and the aperture mask / lens support section 160 shown in FIG. can do. Furthermore, with a re-imaging lens in which three or more pairs of lens pieces are integrally formed,
The present invention can also be applied to a phase difference detection type focus detection device having a multiple number of focus detection areas.

In the configuration of the above embodiment of the present invention,
The image sensor 90 is an image sensor, the re-imaging lens 40 is a multi-lens body, the lens pieces 41a and 41b are lens pieces, the holding member 50 is a holding member, the aperture mask and lens supporting member 60 is a lens supporting member. Configure each.

[0029]

As described above, according to the present invention, the thin plate-shaped lens supporting member is fixed to the holding member for holding the image sensor in a curved state, and the multi-lens body is fixed to the curved portion. Then, a plurality of luminous fluxes that have passed through different regions of the photographing lens by the plurality of lens pieces of the multi-lens body are guided to the image sensor, and a focus adjustment state of the photographing lens is detected based on an output signal of the image sensor. The multi-lens body is made of plastic in which a plurality of lenses are integrally formed, and the optical axis interval of a pair of lens pieces among the plurality of lens pieces changes in temperature, causing a focus detection error. On the other hand, the change in the temperature of the bending of the curved portion of the lens supporting member changes the distance between the multi-lens body and the image sensor, causing a focus detection error. Here, it is desirable to set the degree of curvature of the lens support member such that the former focus detection error is offset by the latter focus detection error. As a result, it is possible to accurately correct a focus detection error caused by a temperature change in the optical axis interval of the lens pieces of the multi-lens body. In addition, since the aperture opening is provided in the lens supporting member that supports the multi-lens body, there is no need to separately install an aperture mask, the number of parts of the apparatus is reduced, and the number of assembly steps can be reduced. Further, an opening having a gap in which the multi-lens body can slide is provided in the holding member, so that the posture of the multi-lens body is kept constant when the multi-lens body moves due to the bending of the curved portion. Thus, when the multi-lens body moves due to the bending of the curved portion of the lens supporting member, the posture of the multi-lens body is kept constant without tilting, so that an accurate focus detection result can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a single-lens reflex camera equipped with a focus detection device according to an embodiment.

FIG. 2 is a diagram showing a configuration of an optical system of the focus detection device shown in FIG.

FIG. 3 is a longitudinal sectional view of the focus detection device.

FIG. 4 is a perspective view showing a mounting portion of a re-imaging lens.

FIG. 5 is a diagram showing a modification of the embodiment applied to a phase difference detection type focus detection device having a multiple number of focus detection areas.

[Explanation of symbols]

 23 Focus detecting device 30 Condenser lens 40 Re-imaging lens 41a, 41b Lens piece 42a, 42b Boss 50 Holding member 60 Aperture mask / lens support member 61a, 61b Opening 62a Elongated hole 62b Round hole 63a, 63b End 70 Field mask 90 Image sensor 91a, 91b Sensor row 100 Infrared cut filter 120 Surface mirror

Claims (5)

[Claims] 1. An image sensor for outputting a signal corresponding to a light quantity distribution of a light beam, and a plastic multi-lens body formed by integrally molding a plurality of lens pieces, wherein a photographing lens differs depending on the plurality of lens pieces. A multi-lens body that guides a plurality of light beams transmitted through an area to the image sensor; and a holding member that holds the image sensor, and detects a focus adjustment state of the photographing lens based on an output signal of the image sensor. In the focus detection device, a thin plate-shaped member having a coefficient of thermal expansion different from that of the holding member is fixed to the holding member in a curved state, and a lens supporting member having the multi-lens body fixed to the curved portion. A focus detection device, comprising: 2. The focus detection device according to claim 1, wherein a focus detection error caused by a temperature change of an optical axis interval of a pair of lens pieces of the plurality of lens pieces and a deflection of the bending portion. A focus detection device, wherein a degree of curvature of the lens support member is set such that a focus detection error caused by a change in a distance between the multi-lens body and the image sensor due to a temperature change is offset. 3. The focus detection device according to claim 1, wherein the lens support member has a plurality of aperture openings for restricting a light beam from a subject incident on each lens piece of the multi-lens body. A focus detection device comprising: 4. The focus detection device according to claim 1, wherein an opening having a gap in which the multi-lens body is slidable is provided in the holding member, and the opening is formed by bending of the curved portion. A focus detection device, wherein the posture of the multi-lens body is kept constant when the multi-lens body moves. 5. The focus detection device according to claim 1, wherein the holding member is made of plastic, and the lens support member is made of metal.