JP2006194992A - Focus detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detecting device for making enlargement of an arrangement region of a focus detecting area and lowering of the degree of manufacturing difficulty compatible. <P>SOLUTION: The focus detecting device includes a main mirror for introducing to a finder optical system by reflecting a field light flux through a photographing lens and transmitting a partial light flux, a sub-mirror for reflecting a transmission light flux of the main mirror on a rear face side of the main mirror, and a focus detecting part for detecting a focus of the photographing lens on the basis of the reflection light flux of the sub-mirror. The sub-mirror is provided with a volume reflection hologram reflecting a paraxial light beam of the photographing lens at a larger reflection angle than an incident angle out of the light flux transmitting the main mirror. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a focus detection device that reflects an object light beam by a mirror and guides it to a focus detection unit, and more particularly to a focus detection device that can achieve both expansion of a focus detection area and reduction in manufacturing difficulty.

2. Description of the Related Art Conventionally, a single-lens reflex camera that includes a main mirror that guides a subject light beam incident on a camera to a finder optical system and moves the main mirror to a shooting position during shooting is known. In such a focus detection optical system of a single-lens reflex camera, generally, a transmission region is formed in a part of a main mirror, and the transmitted light beam is refracted downward by a sub mirror and guided to a focus detection unit. For example, Patent Document 1 discloses a focus detection device in which a sub-mirror is an ellipsoidal mirror. According to Patent Document 1, since a wider range of light flux is guided to the focus detection optical system, focus detection over a relatively wide range is possible.
Japanese Patent No. 3363683

  Also in the technique of Patent Document 1, it is necessary to enlarge the area of the sub-mirror in order to perform focus detection for a wider range in the vertical direction of the screen. However, since the sub mirror is arranged in a narrow space between the main mirror and the shutter, if the sub mirror is enlarged, it interferes with the shutter or the like. Therefore, even with the technique of Patent Document 1, there is still a limit to the expansion of the arrangement area of the focus detection area.

Further, the ellipsoidal mirror of Patent Document 1 has a very high manufacturing difficulty, and there is room for improvement in that it is difficult to ensure the focusing accuracy of the focus detection device and to reduce the cost.
The present invention is intended to solve the above-described problems of the prior art, and its purpose is to expand the arrangement area of the focus detection area, particularly for a focus detection apparatus that reflects a field light beam by a mirror and guides it to a focus detection unit. It is to provide a focus detection device that can achieve both a reduction in manufacturing difficulty.

  A first invention reflects a field light beam through a photographing lens and guides it to a finder optical system, and transmits a part of the light beam, and a transmitted light beam of the main mirror on the back side of the main mirror And a focus detection unit that detects a focus of the photographing lens based on a reflected light beam of the sub mirror, wherein the sub mirror includes a light beam transmitted through the main mirror, A volume reflection hologram for reflecting a paraxial ray of the photographing lens with a reflection angle larger than an incident angle is provided.

  In the first aspect of the invention, the paraxial light beam of the photographing lens is reflected at a reflection angle larger than the incident angle among the light fluxes transmitted through the main mirror by the volume reflection hologram, so that the angle of the sub mirror with respect to the optical axis can be set large. . In other words, the vertical size of the sub mirror can be increased without interfering with the shutter or the like in the same space as the conventional one, and the focus detection area can be expanded vertically. In addition, since volumetric holograms can be easily manufactured if the exposure conditions of the exposure apparatus are the same, processing errors in press processing, mold processing, and the like do not pose a problem unlike an elliptical mirror.

According to a second aspect of the present invention, in the first aspect of the invention, an interference fringe of a refractive reflection effect for converging a reflected light beam of the sub mirror toward the focus detection unit is recorded in the volume reflection hologram, The refractive power distribution is set to be rotationally asymmetric.
In the second invention, the reflected light beam of the sub-mirror is converged toward the focus detection unit by the volume reflection hologram, so that the focus detection unit can be downsized at the same time.

According to a third invention, in the first or second invention, the volume reflection hologram is formed by stacking a plurality of hologram elements corresponding to light beams having different wavelengths.
In the third invention, since the volume reflection type hologram is configured by laminating a plurality of hologram elements corresponding to light beams of different wavelengths, it is possible to suppress a decrease in focusing accuracy due to the color of the subject.

According to a fourth invention, in any one of the first to third inventions, the volume reflection hologram is formed by stacking a plurality of hologram elements corresponding to light beams having different incident angles. .
In the fourth aspect of the invention, a volume reflection type hologram is formed by laminating a plurality of hologram elements corresponding to light beams having different incident angles. Therefore, even if the angle selectivity of each hologram element is narrow, a matching lens corresponding to a large aperture lens is used. Focusing operation is possible.

In a fifth aspect based on any one of the first to fourth aspects, the sub-mirror further includes a mirror receiving portion for holding the volume reflection hologram from the outside, and an antireflection is provided on an inner surface of the mirror receiving portion. It is characterized by being treated.
In the fifth aspect of the invention, irregular reflection of the light beam that has passed through the volume reflection hologram on the inner surface of the mirror receiving portion is suppressed, so that a reduction in focusing accuracy due to stray light is suppressed.

  According to a sixth aspect of the present invention, there is provided a main mirror that reflects a field light beam through the photographing lens and guides it to the finder optical system, and transmits a part of the light beam, and a transmitted light beam of the main mirror on the back side of the main mirror. And a focus detection unit that detects a focus of the photographing lens based on a reflected light flux of the submirror, wherein the submirror holds a liquid crystal in a gap between two transparent electrodes. The liquid crystal optical element is formed by changing the refractive index according to the alignment direction of the liquid crystal, the light beam reflecting portion disposed on the back surface of the liquid crystal optical element, and the liquid crystal alignment direction is changed by controlling the electric field of the transparent electrode. A sub-mirror that reflects a paraxial light beam of the photographing lens at a reflection angle larger than an incident angle out of the light flux transmitted through the main mirror. The features.

  In the sixth aspect of the invention, the sub-mirror provided with the liquid crystal optical element reflects the paraxial light beam of the photographing lens with a reflection angle larger than the incident angle out of the light beam transmitted through the main mirror. Can be set larger. In other words, the vertical size of the sub mirror can be increased without interfering with the shutter or the like in the same space as the conventional one, and the focus detection area can be expanded vertically. In addition, the transparent electrode of the liquid crystal optical element is manufactured by photolithography, and even with electrode patterns that generate a complex refractive index distribution, the shape error is negligible, and it can be processed by pressing, molding, etc. like an ellipsoidal mirror. Errors do not matter.

In a sixth aspect based on the sixth aspect, a polarization separation layer that transmits a light beam having a predetermined polarization direction is formed in a region that transmits the light beam of the main mirror, and the polarization direction of the transmitted light beam of the polarization separation layer is It coincides with the polarization direction in which the liquid crystal optical element acts.
In the seventh invention, since the polarization direction of the polarization separation layer of the main mirror matches the deflection direction in which the liquid crystal optical element acts, the transmitted light flux of the main mirror is not significantly blocked by the liquid crystal optical element.

An eighth invention is the liquid crystal optical element according to the sixth or seventh invention, wherein the liquid crystal optical element is formed with a rotationally asymmetric gradient electric field when a voltage is applied by the structure of the transparent electrode or the electric field control of the control unit. Is characterized in that the reflected light beam of the sub-mirror is converged toward the focus detector as a lens having a rotationally asymmetric refractive power distribution.
In the eighth invention, since the reflected light beam of the sub-mirror converges toward the focus detection unit when a voltage is applied to the liquid crystal optical element, the focus detection unit can be downsized at the same time.

According to a ninth invention, in any one of the sixth to eighth inventions, the camera further includes a pupil position information acquisition unit configured to acquire pupil position information of the photographing lens, and the control unit is configured based on the pupil position information. The refractive power of the liquid crystal optical element is controlled, and the reflected light beam of the sub mirror is converged toward the focus detection unit.
In the ninth aspect of the invention, since the refractive power of the liquid crystal optical element is controlled according to the pupil position of the taking lens, it is possible to prevent vignetting of the peripheral light flux due to the fluctuation of the pupil position.

  A tenth aspect of the invention is to reflect a field light beam through the taking lens and guide it to the finder optical system, and to transmit a part of the light beam, and a transmitted light beam of the main mirror on the back side of the main mirror And a focus detection unit that detects a focus of the photographing lens based on a reflected light flux of the submirror, wherein the submirror holds a liquid crystal in a gap between two transparent electrodes. A liquid crystal optical element that has a refractive index that changes depending on the alignment direction of the liquid crystal, and a paraxial ray of the photographing lens that is disposed on the back surface of the liquid crystal optical element and that has passed through the main mirror. A volume reflection hologram that reflects with a reflection angle larger than the angle, and a reflected light flux of the sub-mirror by changing the orientation direction of the liquid crystal by controlling the electric field of the transparent electrode Characterized in that it comprises a control unit for converging toward the focus detection unit.

  In the tenth invention, the paraxial light beam of the photographing lens is reflected at a reflection angle larger than the incident angle among the light fluxes transmitted through the main mirror by the volume reflection hologram, so that the angle of the sub mirror with respect to the optical axis can be set large. . In other words, the vertical size of the sub mirror can be increased without interfering with the shutter or the like in the same space as the conventional one, and the focus detection area can be expanded vertically. Further, since the reflected light beam of the sub-mirror is converged toward the focus detection unit by the liquid crystal optical element, the focus detection unit can be downsized at the same time. Furthermore, the refracting power of the liquid crystal optical element can be controlled according to the pupil position of the photographic lens to prevent vignetting of the peripheral light flux due to the fluctuation of the pupil position.

  According to the present invention, a focus detection device with a wider field of view can be obtained by enlarging the arrangement area of the focus detection area without causing the sub mirror to interfere with the shutter or the like by the sub mirror including at least one of the volume reflection hologram and the liquid crystal optical element. realizable.

(Description of the first embodiment)
FIG. 1 is a schematic diagram showing a configuration of an electronic camera in which the focus detection device of the first embodiment is incorporated (corresponding to the focus detection device of claims 1 to 5).
The electronic camera according to the first embodiment includes a lens unit 10 in which a photographing optical system is accommodated, and a camera body 20. The lens unit 10 is coupled to the camera body 20 by a bayonet mechanism or the like, and the lens unit 10 is attached to the camera body 20 in an exchangeable manner. The lens unit 10 and the mount of the camera body 20 are each provided with an electrical contact so that the electrical connection between the lens unit 10 and the camera body 20 is established when the lens unit 10 is mounted on the camera.

  The lens unit 10 includes a photographic lens 11, a drive mechanism 12, a lens data unit 13, and a lens microcomputer 14. The taking lens 11 is composed of a plurality of lens groups including a focusing lens for adjusting the in-focus position. The lens driving mechanism 12 drives and adjusts the photographing lens 11. The lens driving mechanism 12 has an encoder, and outputs the lens position to the lens microcomputer 14. The lens data unit 13 stores a correspondence table between the defocus amount and the lens driving amount, a table of pupil position information that changes depending on the focal length and the in-focus state, and the like. The lens microcomputer 14 controls the lens driving mechanism 12 based on the data recorded in the lens data unit 13 and outputs pupil position information and the like to the camera body 20.

  At the center of the camera body 20, a main mirror 21, a shutter 22, and a solid-state image sensor 23 are arranged along the lens optical axis. A finder optical system including a diffusion screen 24, a condenser lens 25, a pentaprism 26 and an eyepiece lens 27 is disposed in the upper region of the camera body 20. Furthermore, a focus detection unit 28 and a CPU 29 (control unit) that executes AF calculation processing, operation control of each part of the camera, and the like are arranged inside the camera body 20.

  The main mirror 21 can switch between an observation position that is inclined in front of the shutter 22 and the solid-state imaging device 23 and a retracted position that is flipped upward. The main mirror 21 at the observation position reflects the light beam that has passed through the lens unit 10 upward and guides it to the finder optical system. The light beam incident on the finder optical system forms an image once on the diffusing screen 24, passes through the condenser lens 25 and the pentaprism 26, and reaches the eyes of the photographer through the eyepiece lens 27.

  On the other hand, when the main mirror 21 is in the retracted position, the light beam that has passed through the lens unit 10 is guided to the shutter 22 and the solid-state image sensor 23. At the time of shooting, the main mirror 21 moves to the retracted position, and shooting of the subject image is executed by the solid-state imaging device 23. The output of the solid-state imaging device 23 is subjected to predetermined image processing after A / D conversion, and the resulting captured image data is recorded on a recording medium or the like (A / D conversion unit, image processing unit, recording The illustration of the medium and the like is omitted).

The central region of the main mirror 21 is a half mirror that transmits part of light. A sub mirror 30 is disposed on the back surface of the central region of the main mirror 21. The sub-mirror 30 serves to refract the light beam transmitted through the main mirror 21 at the observation position and guide it to the focus detection unit 28.
The focus detection unit 28 detects the in-focus state of a plurality of focus detection areas set in the shooting screen by a phase difference detection method. The focus detection unit 28 includes a folding mirror 31, a field mask 32, secondary imaging lenses 33 arranged in pairs in each focus detection area, and a line sensor 34.

  The reflected light beam of the sub mirror 30 is refracted by the bending mirror 31, passes through the field mask 32, and then passes through the secondary imaging lens 33. Two images formed by the secondary imaging lens 33 are formed on the line sensor 34. The output of the line sensor 34 is connected to the CPU 29, and light intensity distributions (two-image interval data) of two images are output from the line sensor 34 to the CPU 29. The CPU 29 calculates a defocus amount (a shift direction and a shift amount from the in-focus position of the photographing lens 11) based on the two-image interval data, and outputs the defocus amount to the lens microcomputer 14 to perform a focusing operation. Is executed.

  Here, the configuration of the sub-mirror 30 of the first embodiment will be described in detail with reference to FIG. The sub-mirror 30 includes a volume reflection hologram 40, a light absorption layer 41, and a mirror receiving portion 42. The shape of the mirror receiving portion 42 is formed in a box shape having an opening on the side facing the main mirror 21. A volume reflection hologram 40 is disposed in front of the opening inside the mirror receiver 42, and a light absorption layer 41 is disposed behind the volume reflection hologram 40.

  In the volume reflection hologram 40, interference fringes for reflecting the paraxial light beam of the photographing lens 11 at a reflection angle larger than the incident angle are recorded. As shown in FIG. 3A, in the submirror 30a of the plane mirror, the incident angle θ1 and the reflection angle θ2 are equal according to Snell's law. However, in the present invention, the volume reflection hologram 40 functions as a reflecting mirror having a reflection angle characteristic in which the reflection angle θ2 ′ is larger than the incident angle θ1 (see FIG. 3B).

  The volume hologram 40 may be recorded with interference fringes having the same tilt angle, or has a refractive reflection effect for converging the reflected light beam in a concave mirror shape, and records interference fringes whose refractive power distribution is set to be rotationally asymmetric. It may be a thing. Note that the volume reflection hologram 40 can be easily manufactured if the exposure conditions of the exposure apparatus are the same, so that processing errors in press processing, mold processing, etc. do not become a problem as in the case of an ellipsoidal mirror. .

Here, the volume reflection hologram 40 is used in the present embodiment because the arrangement area of the focus detection area is enlarged vertically by the enlargement of the sub mirror 30 and the sub mirror 30 interferes with the main mirror 21 and the shutter 22. This is to prevent it.
Since the sub mirror 30 is disposed in a narrow space between the main mirror 21 and the shutter 22 and must be vertically symmetric with respect to the optical axis, the space in the vertical direction is severely restricted. For example, as shown in FIG. 4A, when the size of the sub-mirror 30a of the conventional ellipsoidal mirror is increased, the sub-mirror 30a interferes with the main mirror 21 and the like as indicated by arrows in the figure.

  On the other hand, FIG. 4B shows an example in which a volume reflection hologram 40 in which interference fringes having the same tilt angle are recorded is applied to the sub mirror 30. In the case of FIG. 4B, since the tilt angle with respect to the optical axis of the sub mirror 30 can be set larger, the sub mirror 30 can be arranged in the up and down direction than in FIG. Therefore, even if the size of the sub mirror 30 is increased in the vertical direction and the arrangement area of the focus detection area is enlarged, the sub mirror 30 can be accommodated in the same space as before, and the sub mirror 30 does not interfere with the main mirror 21 and the like.

  FIG. 4C shows an example in which a volume reflection hologram 40 in which interference fringes having a concave mirror-like refractive reflection effect are recorded is applied to the sub-mirror 30. When the sub-mirror 30 is increased in size, the reflected light beam becomes thicker, and the field lens 37 that receives the reflected light beam and the focus detection unit 28 itself are also increased in size. However, in the case of FIG. 4C, the volume reflection hologram 40 acts as a field lens, and the reflected light beam of the sub mirror 30 converges toward the focus detection unit, so that the arrangement area of the focus detection area is expanded. The focus detection unit 28 can be downsized. Further, in this case, since the entrance of the incident light in the focus detection unit 28 can be reduced, the incidence of stray light on the focus detection unit 28 can also be reduced.

  Further, since the volume reflection hologram 40 has a narrow reflection wavelength width and high angle selectivity of the light beam, it is preferable to stack a plurality of hologram elements 43 having different characteristics according to the purpose. FIG. 5A is a diagram showing an example in which a volume reflection hologram 40 is configured by laminating a plurality of hologram elements 43 corresponding to light beams having different wavelengths. In the example of FIG. 5A, the volume reflection hologram 40 is configured by laminating a blue light compatible hologram element, a green light compatible hologram element, and a red light compatible hologram element in order from the main mirror 21 side.

  In general, the reflection wavelength width of a hologram is about several tens of nm, and the light use efficiency is low in one hologram. For example, when the wavelength of the subject color is out of the reflection wavelength width of the hologram, the focusing accuracy may be lowered. On the other hand, since each hologram has a narrow reflection wavelength width, the effect of each hologram is hardly affected even if holograms that act on other wavelengths are stacked. Therefore, if a plurality of hologram elements 43 corresponding to different wavelengths are stacked, the light use efficiency can be increased, and a reduction in focusing accuracy due to the color of the subject can be suppressed. It should be noted that since light having a shorter wavelength is more likely to be scattered when transmitted through the hologram element 43, the hologram element 43 having the shortest wavelength is arranged on the surface side close to the main mirror 21 so that the wavelength becomes longer toward the back. It is preferable to laminate the hologram element 43 on the substrate.

  On the other hand, FIG. 5B is a diagram showing an example in which a volume reflection type hologram is configured by laminating a plurality of hologram elements 43 corresponding to light beams having different incident angles. In general, focus detection by the phase difference detection method uses a light beam in the vicinity of F5.6, but when using a large aperture lens, a light beam in the vicinity of F2.8 may be used in order to improve focusing accuracy. However, since the hologram element 43 has high angle selectivity of the light beam, there is a possibility that the necessary light beam cannot be reflected when the angle of the incident light beam is expanded to about F2.8. In this case, if a plurality of hologram elements 43 having different reflection angle ranges are stacked, a thicker light beam can be guided to the focus detection unit.

  In the example of FIG. 5B, a state in which two hologram elements 43 corresponding to a light beam having a spread of about F5.6 are stacked by changing the corresponding angles to correspond to the light beam of F2.8. Show. In this case, if the secondary imaging lens 33 of the focus detection unit 28 is arranged in a state that can handle the F2.8 light beam, a more accurate focusing operation is possible using the light beam near F2.8. It becomes.

  In addition, in the light absorption layer 41 arranged in the mirror receiving portion 42, black fine hairs are electrostatically implanted on the surface facing the volume reflection hologram 40. The light absorption layer 41 has a function of absorbing a light beam transmitted through the volume reflection hologram 40 and suppressing generation of stray light due to irregular reflection of the transmitted light beam. Therefore, since the contrast between the reflected light beam of the hologram and the background is also improved by the light absorption layer 41, the focusing operation can be stabilized. Note that the same effect as described above can be obtained even if a known antireflection treatment is applied to the inner surface of the mirror receiving portion 42 instead of the light absorbing layer 41, for example, the inner surface of the mirror receiving portion 42 is painted black. it can.

6 and 7 are diagrams showing the effect of enlarging the arrangement area of the focus detection area in the electronic camera of the first embodiment.
As shown in FIG. 6, it is known from experience that, in a composition such as a photograph, a balanced composition is obtained when a subject is placed on the 1/3 dividing line in the vertical direction of the screen or the horizontal direction of the screen or at the intersection of such dividing lines. .

  Here, the arrangement area of the focus detection area in the conventional sub-mirror 30a in the vertical direction of the screen is only about 1/3 of the vertical direction of the screen with respect to the center of the screen. For example, in the 135-format (24 × 36 mm) shooting screen 35, about 8 × 18 mm (about 1/3 in the vertical direction of the screen and about 1/2 in the horizontal direction of the screen) is the focus detection area arrangement area. A focus detection apparatus in which 45 rectangular focus detection areas 36 are arranged in this arrangement area has been put into practical use (see FIG. 7A). In this conventional focus detection apparatus, it has been pointed out that if the subject is arranged on a 1/3 dividing line in the vertical direction of the screen, the subject and the focus detection area 36 have little overlap, so that it is practically difficult to use.

  On the other hand, in the sub mirror 30 using the volume reflection hologram 40 of the first embodiment, the arrangement area of the focus detection area can be enlarged in the vertical direction of the screen. For example, in the shooting screen 35 in the case of the 135 format, the focus detection area is about 12 × 20 mm (about 1/2 in the vertical direction of the screen and about 1/2 or more in the horizontal direction of the screen) (see FIG. 6). ). In this arrangement area, 91 focus detection areas 36 having the same shape as in FIG. 7A can be arranged, and the arrangement area of the focus detection area 36 is approximately doubled in area ratio (FIG. 7B). )reference). As shown in FIG. 6, in the first embodiment, since the focus detection area covers the range surrounded by the 1/3 dividing line in the vertical direction of the screen or the horizontal direction of the screen, the degree of freedom in drawing during AF shooting. Is significantly increased. Note that when the shooting screen 35 is further reduced or when the shooting screen 35 is cropped and partially cut out, the arrangement area of the focus detection area is relatively expanded.

(Description of Second Embodiment)
FIG. 8 is a schematic diagram showing the configuration of the sub-mirror 30 in the focus detection apparatus of the second embodiment (corresponding to the focus detection apparatus of claims 6 to 9). The second embodiment is a modification of the first embodiment, and the liquid crystal optical element 50 is used for the sub mirror 30 to reflect the paraxial light beam of the photographing lens 11 at a reflection angle larger than the incident angle. In the following embodiments, the same reference numerals are given to the same components as those of the above-described embodiments, and the duplicated description is omitted.

  The sub mirror 30 includes a liquid crystal optical element 50, a reflecting mirror 51, and a mirror receiving portion 42. Inside the mirror receiving portion 42, a liquid crystal optical element 50 is disposed in front of the opening side, and a reflecting mirror 51 is disposed behind the liquid crystal optical element 50. The liquid crystal optical element 50 can change the refractive index of the internal liquid crystal by electric field control, and the liquid crystal optical element 50 can refract the light beam transmitted through the main mirror 21. The electric field control of the liquid crystal optical element 50 is performed by the CPU 29.

  Then, the light beam that has passed through the liquid crystal optical element 50 is reflected by the reflecting mirror 51 and then passes again through the liquid crystal optical element 50 and is guided to the focus detection unit 28. In the example of FIG. 8, the liquid crystal optical element 50 and the reflecting mirror 51 are configured as separate parts. However, a metal film is formed on the back side of the liquid crystal optical element 50 by vapor deposition or the like, and the reflecting mirror is integrated with the liquid crystal optical element 50. You may shape | mold (illustration is abbreviate | omitted). In the case where the liquid crystal optical element 50 and the reflecting mirror 51 are configured as separate parts, the optical path length after transmission through the liquid crystal optical element 50 becomes longer, so that the deflection angle can be further increased.

  Further, when a polarization reflecting mirror is used for the main mirror 21 to divide the optical path into the finder optical system and the focus detection optical system, the central portion (half mirror portion) of the main mirror 21 functions as a polarization separation layer. In this case, if the polarization direction of the transmitted light beam of the polarization separation layer is different from the polarization direction of the liquid crystal optical element 50, the transmitted light beam of the main mirror 21 may be significantly blocked by the liquid crystal optical element 50, making it difficult to detect the focus. There is sex. Therefore, it is preferable that the polarization direction of the transmitted light beam of the polarization separation layer coincides with the polarization direction in which the liquid crystal optical element 50 acts.

Here, the configuration of the liquid crystal optical element 50 of the second embodiment will be described in detail. FIG. 9 is a schematic diagram showing the configuration of the liquid crystal optical element 50. The liquid crystal optical element 50 includes a pair of translucent plates 52, a transparent conductive film 53 (transparent electrode) such as ITO, an alignment film 54, a liquid crystal layer 56 including liquid crystal molecules 55, and a spacer 57. ing.
The pair of translucent plate-like bodies 52 are arranged in a facing state with a predetermined gap therebetween. An electrode pattern made of a transparent conductive film 53 and an alignment film 54 for aligning liquid crystal molecules 55 in a predetermined direction are formed on the surfaces of the translucent plates 52 facing each other. A liquid crystal layer 56 in which liquid crystal molecules 55 are sandwiched between the alignment films 54 is formed. The interval between the alignment films 54 is kept almost constant by the spacer 57.

  In a state where the CPU 29 does not apply a voltage to the transparent conductive film 53, the liquid crystal molecules 55 are aligned in a predetermined alignment direction, and the liquid crystal optical element 50 does not produce a refraction effect (see FIG. 9A). On the other hand, when the CPU 29 applies a voltage to the transparent conductive film 53, the alignment direction of the liquid crystal molecules 55 with respect to the translucent plate-like body 52 changes according to the strength of the electric field. Since the liquid crystal molecules 55 have different refractive indexes depending on the direction of the molecules, when polarized light corresponding to the alignment direction of the liquid crystal molecules 55 enters the liquid crystal optical element 50, a refractive power distribution is generated, and the liquid crystal optical element 50 functions as a prism or a lens. .

  For example, if the gradient electric field applied to the transparent conductive film 53 is set so as to monotonically increase from one end of the liquid crystal optical element 50 to the other end, the refractive index change of the liquid crystal optical element 50 also monotonously increases according to the gradient electric field (as shown in the figure). (Omitted). In this case, the liquid crystal optical element 50 acts as a prism, and the sub mirror 30 can reflect the paraxial light beam of the photographing lens 11 at a reflection angle larger than the incident angle.

FIG. 9B is a diagram showing a state where the gradient electric field applied to the transparent conductive film 53 is set symmetrically with respect to the center of the liquid crystal optical element 50. In this case, the liquid crystal optical element 50 acts as a lens and can converge the light beam emitted from the sub mirror 30 toward the focus detection unit 28.
FIG. 10 shows an example of an electrode pattern of the transparent conductive film 53 when the liquid crystal optical element 50 acts as a lens. In FIG. 10, electrode patterns are formed concentrically with different intervals, and the same voltage is applied to each electrode to form a gradient electric field according to the electrode density per unit area.

  It is also possible to form the gradient electric field by forming electrode patterns in concentric circles at equal intervals and applying different voltages to the electrodes. Furthermore, if the electrode pattern is made more complicated, it is possible to produce a rotationally asymmetric and complex refractive power distribution like a free-form surface lens (both are not shown). Note that the electrode pattern of the transparent conductive film 53 is manufactured by photolithography, and even with an electrode pattern that generates a complicated refractive index distribution, the shape error is negligible. Therefore, even in the configuration of the second embodiment, processing errors in press processing, mold processing, and the like do not become a problem as in the case of an elliptical mirror.

Even in the second embodiment described above, substantially the same effect as in the first embodiment can be obtained. That is, by increasing the size of the sub mirror 30, it is possible to enlarge the arrangement area of the focus detection area vertically and to prevent the sub mirror 30 from interfering with the main mirror 21 and the like. Further, when the liquid crystal optical element 50 acts as a lens, the focus detection unit 28 can be downsized at the same time.
Furthermore, in the second embodiment, the CPU 29 controls the gradient electric field based on the pupil position information from the lens unit 10, and the refractive power of the liquid crystal optical element 50 so that the reflected light beam of the sub mirror 30 always converges to the focus detection unit 28. Can also be adjusted. FIG. 11 is a diagram showing a state in which the refractive power of the liquid crystal optical element 50 is adjusted based on the pupil position. FIG. 11A shows a case where the pupil position of the photographing lens 11 is close, and FIG. 11B shows a case where the pupil position of the photographing lens 11 is far. In this way, if the CPU 29 controls the refractive power of the liquid crystal optical element 50 in accordance with the pupil position of the photographic lens 11, vignetting of the peripheral light flux due to variations in the pupil position is prevented. As a result, the focus detection unit 28 can ensure the stability of the focus detection operation.

(Description of the third embodiment)
FIG. 12 is a schematic diagram showing the configuration of the sub-mirror 30 in the focus detection apparatus of the third embodiment (corresponding to the focus detection apparatus of claim 10). The sub mirror 30 according to the third embodiment includes a liquid crystal optical element 50, a volume reflection hologram 40 and a light absorption layer 41, and a mirror receiver 42. A liquid crystal optical element 50 is disposed in front of the opening side inside the mirror receiving portion 42, and a volume reflection hologram 40 and a light absorption layer 41 are disposed behind the liquid crystal optical element 50. In the third embodiment, the liquid crystal optical element 50 bears the function of adjusting the refractive power, and the volume reflection hologram 40 bears the function of reflecting the transmitted light beam.

  While the volume reflection hologram 40 can set the reflection angle with a high degree of freedom, the angle selectivity of the light beam is high. Therefore, if the pupil position of the photographic lens 11 varies greatly, there is a possibility that the volume reflection hologram 40 may not be able to fully reflect the transmitted light beam. On the other hand, the liquid crystal optical element 50 can cope with the fluctuation of the pupil position as described above, but it is relatively difficult to obtain a large deflection angle due to the restriction of the refractive index change of the liquid crystal molecules. Therefore, by combining the volume reflection type hologram 40 and the liquid crystal optical element 50, it is possible to realize the sub-mirror 30 that can cope with the change of the pupil position and obtain a large deviation angle.

(Supplementary items of the embodiment)
As mentioned above, although this invention has been demonstrated by said embodiment, the technical scope of this invention is not limited to the said embodiment. For example, in the above-described embodiment, an example in which the focus detection apparatus is applied to a single-lens reflex electronic camera has been described.

1 is a schematic diagram illustrating a configuration of an electronic camera in which a focus detection device according to a first embodiment is incorporated. The figure which shows the structure of the submirror of 1st Embodiment. The figure which shows the difference in the reflection angle characteristic of the conventional submirror and the submirror of 1st Embodiment. Diagram showing the arrangement of submirrors and the optical path of the focus detection optical system The figure which shows the example which laminated | stacked the hologram element and comprised the volume reflection type hologram The figure which shows the expansion effect of the arrangement | positioning area | region of the focus detection area in 1st Embodiment. The figure which shows the arrangement state of a focus detection area The figure which shows the structure of the submirror of 2nd Embodiment. Schematic diagram showing the configuration of the liquid crystal optical element The figure which shows the electrode pattern example of a transparent conductive film in the case of making a liquid crystal optical element act as a lens The figure which shows the state which adjusted the refractive power of the liquid crystal optical element based on the pupil position The figure which shows the structure of the submirror of 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Lens part 11 Shooting lens 20 Camera main body 21 Main mirror 22 Shutter 28 Focus detection part 29 CPU
30 Sub-mirror 40 Volume reflection hologram 41 Light absorption layer 42 Mirror receiving part 50 Liquid crystal optical element 51 Reflective mirror

Claims (10)

A main mirror that reflects the field light flux through the taking lens and guides it to the finder optical system, and transmits a part of the light flux; and a sub mirror that reflects the transmitted light flux of the main mirror on the back side of the main mirror; A focus detection unit having a focus detection unit that performs focus detection of the photographing lens based on a reflected light beam of the sub mirror,
The focus detection apparatus, wherein the sub-mirror includes a volume reflection hologram that reflects a paraxial light beam of the photographing lens at a reflection angle larger than an incident angle among light beams transmitted through the main mirror.   The volume reflection hologram is recorded with an interference fringe of a refractive reflection effect for converging the reflected light beam of the sub mirror toward the focus detection unit, and the refractive power distribution of the volume reflection hologram is set to be rotationally asymmetric. The focus detection apparatus according to claim 1.   The focus detection apparatus according to claim 1, wherein the volume reflection hologram is configured by stacking a plurality of hologram elements corresponding to light beams having different wavelengths.   The focus detection apparatus according to claim 1, wherein the volume reflection hologram is configured by stacking a plurality of hologram elements corresponding to light beams having different incident angles.   5. The sub-mirror further includes a mirror receiving portion for holding the volume reflection hologram from the outside, and an inner surface of the mirror receiving portion is subjected to an antireflection treatment. The focus detection apparatus according to any one of the above. A main mirror that reflects the field light flux through the taking lens and guides it to the finder optical system, and transmits a part of the light flux; and a sub mirror that reflects the transmitted light flux of the main mirror on the back side of the main mirror; A focus detection unit having a focus detection unit that performs focus detection of the photographing lens based on a reflected light beam of the sub mirror,
The sub mirror is formed by sandwiching a liquid crystal in a gap between two transparent electrodes, a liquid crystal optical element whose refractive index changes depending on the alignment direction of the liquid crystal, a light beam reflecting portion disposed on the back surface of the liquid crystal optical element, A control unit that changes the alignment direction of the liquid crystal by controlling the electric field of the transparent electrode, and the sub mirror reflects a paraxial light beam of the photographing lens that is larger than an incident angle among light beams transmitted through the main mirror. A focus detection device that reflects the light on the screen.   A polarization separation layer that transmits a light beam having a predetermined polarization direction is formed in a region that transmits the light beam of the main mirror, and the polarization direction of the transmitted light beam of the polarization separation layer matches the polarization direction that the liquid crystal optical element acts on. The focus detection apparatus according to claim 6.   A rotationally asymmetric gradient electric field is formed when a voltage is applied to the liquid crystal optical element due to the structure of the transparent electrode or electric field control of the control unit, and the liquid crystal optical element functions as a lens having a rotationally asymmetric refractive power distribution as a reflected light beam of the submirror. The focus detection apparatus according to claim 6, wherein the focus detection unit converges toward the focus detection unit. A pupil position information acquisition unit for acquiring pupil position information of the photographing lens;
9. The control unit according to claim 6, wherein the control unit controls a refractive power of the liquid crystal optical element based on the pupil position information, and converges a reflected light beam of the sub mirror toward the focus detection unit. The focus detection apparatus according to any one of the above. A main mirror that reflects the field light flux through the taking lens and guides it to the finder optical system, and transmits a part of the light flux; and a sub mirror that reflects the transmitted light flux of the main mirror on the back side of the main mirror; A focus detection unit having a focus detection unit that performs focus detection of the photographing lens based on a reflected light beam of the sub mirror,
The sub mirror is formed by holding a liquid crystal in a gap between two transparent electrodes. The sub mirror is disposed on the back surface of the liquid crystal optical element whose refractive index changes depending on the alignment direction of the liquid crystal, and is transmitted through the main mirror. Volume reflection holograms that reflect paraxial rays of the taking lens at a reflection angle larger than an incident angle, and reflected light beams of the sub-mirror by changing the orientation direction of the liquid crystal by electric field control of the transparent electrode. And a control unit that converges the light toward the focus detection unit.

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