JP2007187806A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a focal surface corresponding to the change of optical path length caused by inserting/retreating an optical member in/from an optical path with simple constitution. <P>SOLUTION: The imaging apparatus has an imaging device 106 photoelectrically converting a subject image formed by a photographic optical system 102, and a focus detection means 112 performing focus detection by using luminous flux from the photographic optical system. It has the optical member 103 which is a member for splitting the luminous flux from the photographic optical system to luminous flux going toward the imaging device and luminous flux guided to the focus detection means, and which can move to a first position where it is arranged in the optical path of the luminous flux from the photographic optical system and a second position where it is arranged out of the optical path. It has a first mechanism for making a distance from the photographic optical system to the imaging device longer when the optical member moves to the first position than when it moves to the second position. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is capable of moving an optical member such as a beam splitter with respect to an optical path of a light beam from a photographing optical system, and imaging an image such as a digital camera that performs focus detection using the light beam guided by the optical member. Relates to the device.

  Conventionally proposed is an imaging device that splits a part of the light beam from the photographic lens using an optical member such as a half mirror or a beam splitter, and guides the divided light beam to the focus detection unit to detect the focus of the photographic lens. Has been.

Patent Documents 1 and 2 disclose a camera in which a prism-shaped optical member that divides a part of a light beam is provided on an optical path from a photographing lens, and focus detection is performed using the light beam divided by the optical member. ing. In the cameras disclosed in Patent Documents 1 and 2, one of the two light beams divided by the optical member is guided to a focus detection sensor, and the other is guided to an imaging device for acquiring a subject image.
JP-A-63-195630 (page 3, upper right column, line 20 to same page, lower left column, line 7, line 1, etc.) JP 2003-140246 A (paragraphs 0033 to 0034, FIG. 1, etc.)

  In the cameras disclosed in Patent Documents 1 and 2, a part of the light beam from the photographing lens is divided and guided to the focus detection sensor even during imaging using the imaging element, so that the amount of light reaching the imaging element is reduced. .

  For this reason, at the time of imaging, it is conceivable to retract the optical member out of the optical path to avoid a decrease in the amount of light incident on the imaging device.

  However, when the optical member is retracted out of the optical path, the optical optical path length between the photographing lens and the image sensor changes as compared with the state in which the optical member is inserted into the optical path. Therefore, it is necessary to correct the focus surface by the change in the optical optical path length.

  In this case, it is common to correct the focal plane by moving the focus lens in the photographic lens. However, the correction amount of the focus surface and the movement amount of the focus lens are not the same, and if the zoom ratio of the photographing lens is different, the movement amount of the focus lens for correcting the focus surface also changes.

  For this reason, it is necessary to previously store in the memory data on the amount of movement of the focus lens necessary for correcting the focus surface for each photographing lens and each zoom ratio. This data becomes a considerable amount, and the memory also requires a large capacity. Even if the focus lens is driven based on the stored information, the correction result may vary due to individual differences of the photographing lens, which is disadvantageous for high-precision focus correction.

  The present invention enables correction of the focus surface in accordance with the change in the optical path length due to insertion and withdrawal of the optical member with respect to the optical path without requiring a large data storage amount and without being affected by the change in the zoom ratio. An object of the present invention is to provide an image pickup apparatus and a control method.

  An imaging apparatus according to an aspect of the present invention includes an imaging element that photoelectrically converts a subject image formed by a photographing optical system, focus detection means that performs focus detection using a light beam from the photographing optical system, and the photographing optical A member that separates a light beam from the system into a light beam directed to the image sensor and a light beam guided to the focus detection means, the first position disposed in the optical path of the light beam from the photographing optical system, and disposed outside the optical path And an optical member movable to the second position. And when the optical member is arranged at the first position, the optical member has a first mechanism for increasing the distance from the photographing optical system to the image pickup device as compared with the case where the optical member is arranged at the second position. To do.

  According to another aspect of the present invention, there is provided a method for controlling an imaging apparatus, comprising: an imaging element that photoelectrically converts a subject image formed by a photographing optical system; and focus detection that performs focus detection using a light beam from the photographing optical system. And a member for separating the light beam from the photographing optical system into a light beam directed to the image sensor and a light beam guided to the focus detection unit, and a first position disposed in the optical path to the image sensor and the optical path It is a control method of an imaging device which has an optical member which can move to the 2nd position arranged outside. Then, the method includes a step of moving the optical member between the first position and the second position, and a step of changing the distance from the imaging optical system to the image sensor in accordance with the movement of the optical member. In the step of changing the distance, when the optical member is disposed at the first position, the distance from the photographing optical system to the image sensor is made longer than when the optical member is disposed at the second position. Features.

  According to the present invention, the correction of the focus surface according to the change of the optical optical path length due to the insertion and retraction of the optical member with respect to the optical path can be performed by directly changing the distance between the imaging optical system and the imaging element that is not affected by the zoom ratio. Do. For this reason, it is not necessary to store the movement amount of the focus lens for each photographing lens or each zoom ratio, and the focus surface correction can be performed with high accuracy.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows the configuration of a digital still camera (imaging device) that is Embodiment 1 of the present invention. FIG. 1A illustrates a case where a subject image acquired by an image sensor described later before photographing is observed through the display 107, or a photographing preparation operation including focus adjustment and photometry using a focus detection sensor described later is performed immediately before photographing. Shows the state. A display 107 provided on the back surface of the camera can display an image having an angle of view substantially the same as the shooting angle of view, and has a role of a so-called electronic viewfinder (EVF). FIG. 1B shows a state at the time of photographing. After shooting, the display 107 has a function of displaying the shot image for a predetermined time and confirming the shot image. This state is also obtained when performing focus adjustment by so-called TV-AF alone.

  The display 107 is composed of an organic EL spatial modulation element, a liquid crystal spatial modulation element, a spatial modulation element using electrophoresis of fine particles, and the like. These are low in power consumption and thin, and are effective for miniaturization of the camera.

  In FIG. 1, reference numeral 101 denotes a digital camera body, and reference numeral 102 denotes an imaging optical system (shooting optical system) for forming an object image. Reference numeral 104 denotes an optical axis of the imaging optical system 102, and reference numerals 105 a to 105 c denote constituent members of a lens barrel that houses the imaging optical system 102.

  The imaging optical system 102 can adjust the imaging position in the direction of the optical axis 104 by an actuator (not shown) and a driving mechanism. The imaging optical system 102 can be configured by a single focus lens, a zoom lens, a shift lens, or the like.

  In this embodiment, a digital camera in which a lens barrel is integrally provided will be described. However, the present invention relates to an interchangeable lens having an imaging optical system having various characteristics (F number, focal length, etc.). It can also be applied to a detachable camera.

  Reference numeral 103 denotes a beam splitter as an optical member having a light dividing function surface 103a. Reference numeral 110 denotes an optical axis in the beam splitter 103. Reference numeral 111 denotes a shutter release button (hereinafter simply referred to as a release button), and 108 denotes a recording medium for storing image data, and a semiconductor memory, an optical disk, or the like is used.

  Reference numeral 109 denotes an eyepiece of an optical finder, and reference numeral 106 denotes an imaging device constituted by a two-dimensional CCD sensor or a CMOS sensor. Reference numeral 112 denotes a focus detection sensor having a light receiving element, and reference numeral 113 denotes an optical low-pass filter.

  The state shown in FIG. 1A is hereinafter referred to as a first mode, and the position of the beam splitter 103 at this time is hereinafter referred to as a first mode position. In the first mode, the beam splitter 103 is disposed in an optical path (hereinafter referred to as a photographing optical path) from the imaging optical system 102 toward the image sensor 106. Therefore, a part of the light beam in the photographing optical path is separated into an AF light beam directed toward the focus detection sensor 112 and an image display light beam directed toward the image sensor 106 by the light dividing function surface 103a in the beam splitter 103. . Further, the light beam that does not pass through the light splitting function surface 103 a passes through the beam splitter 103 and travels toward the image sensor 106. Details of the beam splitter 103 and the light splitting functional surface 103a will be described later.

  On the other hand, the state shown in FIG. 1B is hereinafter referred to as a second mode, and the position of the beam splitter 103 at this time is hereinafter referred to as a second mode position. In the second mode position, the beam splitter 103 is disposed outside the imaging optical path. For this reason, of the light beams from the imaging optical system 102, a light beam effective for photographing toward the image sensor 106 reaches the image sensor 106 without passing through the beam splitter 103.

  The charge accumulated by photoelectric conversion in the image sensor 106 is thinned out and read at a certain rate when a display image on the display 107 is generated. At the time of shooting, the accumulated charges from all the pixels are read out and used to generate a high-definition image.

  FIG. 2 shows an electrical configuration of the digital camera of this embodiment. First, a description will be given of the part relating to the photographing and recording of object images.

  The camera has an imaging system, an image processing system, a recording / reproducing system, and a control system. The imaging system includes an imaging optical system 102 and an imaging element 106. The image processing system includes an A / D converter 130, an RGB image processing circuit 131, and a YC processing circuit 132.

  The recording / reproducing system includes a recording processing circuit 133 and a reproduction processing circuit 134. The control system includes a camera system control circuit 135, an operation detection circuit 136, and an image sensor driving circuit 137.

  A standardized connection terminal 138 is connected to an external device such as a personal computer to transmit and receive data. These electric circuits are driven by electric power from a power source such as a secondary battery or a fuel cell (not shown).

  The imaging system is an optical processing system that forms an image of a light beam from an object on the light receiving surface of the imaging element 106 via the imaging optical system 102. This imaging system adjusts a diaphragm and a mechanical shutter (not shown) of the imaging optical system 102 to expose the imaging element 106 with an object light beam having an appropriate amount of light.

  The image sensor 106 has, for example, a total of about 8 million pixels in which 3264 square pixels are arranged in the long side direction and 2448 in the short side direction. Each pixel is provided with a color filter of any one of R (red), G (green), and B (blue) to form a so-called Bayer array in which four pixels are combined.

  In the Bayer array, the overall image performance is improved by arranging more G pixels that are easily felt when an observer views the image than the R and B pixels.

  In general, in image processing using this type of image sensor, a large portion of a luminance signal is generated from G, and a color signal is generated from R, G, and B.

  The image signal read from the image sensor 106 is supplied to the image processing system via the A / D converter 130.

  The A / D converter 130 converts the signal (accumulated charge) read from each pixel into, for example, a 12-bit digital signal corresponding to the amplitude and outputs the digital signal. The subsequent signal processing is executed by digital processing.

  The image processing system obtains an image signal of a desired format from R, G, B digital signals. This image processing system converts R, G, and B color signals into a luminance signal Y and YC signals represented by color difference signals (RY) and (BY).

  The RGB image processing circuit 131 processes a signal for 3264 × 2448 pixels received from the image sensor 106 via the A / D converter 130. The RGB image processing circuit 131 includes a white balance circuit and a gamma correction circuit, and further includes an interpolation calculation circuit that performs high resolution by interpolation calculation.

  The YC processing circuit 132 generates a luminance signal Y and color difference signals (R−Y) and (B−Y). The YC processing circuit 132 includes a low-frequency luminance signal generation circuit that generates a low-frequency luminance signal YL, a high-frequency luminance signal generation circuit that generates a high-frequency luminance signal YH, and color difference signals (RY) and (BY). It consists of a color difference signal generation circuit to be generated. The luminance signal Y is formed by combining the low-frequency luminance signal YL and the high-frequency luminance signal YH.

  The recording / reproducing system outputs the image signal to the above-described recording medium and outputs the image signal to the display 107. The recording processing circuit 133 performs image signal writing processing and reading processing on the recording medium. The reproduction processing circuit 134 reproduces the image signal read from the recording medium and outputs it to the display 107.

  The recording processing circuit 133 includes a compression / expansion circuit that compresses YC signals representing still images and moving images in a predetermined compression format, and expands the compressed data when reading the compressed data. The compression / decompression circuit includes a frame memory for signal processing and the like, and accumulates YC signals from the image processing system for each image in the frame memory. Then, the YC signal is read and compressed and encoded for each of a plurality of blocks. The compression coding is performed by, for example, performing two-dimensional orthogonal transformation, normalization, and Huffman coding on the image signal for each block.

  The reproduction processing circuit 134 is a circuit that performs matrix conversion of the luminance signal Y and the color difference signals (R−Y) and (B−Y), for example, into RGB signals. The signal converted by the reproduction processing circuit 134 is output to the display 107. Thereby, the visible image is displayed and reproduced.

  The control system includes an operation detection circuit 136 that detects operations of various operation members such as the release button 111. In addition, a camera system control circuit 135 that controls each unit in accordance with the detection signal and generates and outputs a timing signal at the time of shooting is included. Furthermore, an image sensor drive circuit 137 that generates a drive signal for driving the image sensor 106 under the control of the camera system control circuit 135, an information display device in the optical viewfinder, and an information display device provided on the outer surface of the camera Includes an information display circuit 142 for controlling.

  The control system controls the imaging system, the image processing system, and the recording / reproducing system according to the operation of the operation member. For example, the operation of the release button 111 is detected to control the driving of the image sensor 106, the operation of the RGB image processing circuit 131, the compression processing of the recording processing circuit 133, and the like. Further, the control system controls the state of each segment provided in the information display device in the optical viewfinder by the information display circuit 142.

  An AF control circuit 140 and a lens system control circuit 141 are further connected to the camera system control circuit 135. These communicate with each other data necessary for each processing, centering on the camera system control circuit 135.

  In the first mode, the AF control circuit 140 obtains a signal output from the focus detection sensor 112 provided corresponding to a predetermined position on the shooting screen and generates a focus detection signal. The focus detection signal is a signal indicating a phase difference between a plurality of images formed by a light beam from the imaging optical system 102, and the phase difference indicates an imaging state of the imaging optical system 102. When the phase difference is a predetermined value, the imaging optical system 102 is in a focused state, and when the phase difference is other than the predetermined value, the imaging optical system 102 is in a defocused state.

  When the defocus is detected, the AF control circuit 140 converts this into a driving amount of a focusing lens (see FIGS. 3 and 4) included in the imaging optical system 102. Then, the drive amount information is transmitted to the lens system control circuit 141 via the camera system control circuit 135. This AF is hereinafter referred to as phase difference AF.

  In the present embodiment, a TV-AF that evaluates the contrast on the image sensor 106 and detects the imaging state of the imaging optical system 102 can be used following or independently of the phase difference AF. When performing the TV-AF following the phase difference AF, a display image signal obtained by thinning out reading from the image sensor 106 is used while the beam splitter 103 is disposed at the first mode position. Specifically, the contrast evaluation value of the image on the image sensor 106 is generated while driving the focusing lens, and the position with the highest contrast is determined as the in-focus position. In this embodiment, after the focusing lens is driven to a predetermined focusing range by phase difference AF, high-precision focusing is performed by TV-AF.

  In this way, by using phase difference AF and TV-AF together, the direction in which the focusing lens in TV-AF should be driven can be determined in advance from the result of phase difference AF, so that the speed of AF operation as a whole is increased. And high accuracy.

  Note that the detection accuracy by phase difference AF is lowered for a subject with low contrast, but even in such a case, there is a case where reliable focus adjustment can be performed by using TV-AF. In such a case, the photographer can select the TV-AF mode from the beginning. In this case, the beam splitter 103 is moved to the second mode position to perform TV-AF.

  For a moving object, the driving amount of the focusing lens is instructed by predicting an appropriate lens position in consideration of a time lag from when the release button 111 is pressed down until the actual imaging control is started. When it is determined that the brightness of the object is low and sufficient focus detection accuracy cannot be obtained, the object is illuminated by a flash unit, a white LED or a fluorescent tube (not shown) to compensate for the brightness.

  When the lens system control circuit 141 receives the information on the driving amount of the focusing lens from the AF control circuit 140, the lens system control circuit 141 moves the focusing lens in the imaging optical system 102 in the direction of the optical axis 104 by an unillustrated driving mechanism, Adjust the focus.

  As a result of a series of focus adjustment operations, when the AF control circuit 140 detects that the object is in focus, this information is transmitted to the camera system control circuit 135.

  At this time, when the release button 111 is operated up to the second stage, the beam splitter 103 is driven by a driving mechanism described later, and the first mode is switched to the second mode in which the beam splitter 103 is retracted from the imaging optical path. . Thereby, the subject image is formed by a light beam that does not pass through the beam splitter 103. Then, photographing control is performed by the above-described imaging system, image processing system, and recording / reproducing system.

  By simply moving the beam splitter 103 between the first mode in which the beam splitter 103 is disposed on the imaging optical path and the second mode in which the beam splitter 103 is not disposed on the imaging optical path, the spatial optical path length (air (Also referred to as the converted optical path length) changes, and the position of the focus surface changes. However, in this embodiment, the spatial optical path length is not changed even when the mode is switched by a method described later.

  Since the spatial optical path length does not vary, it is possible to check the image variation state on the display 107. For this reason, the photographer can confirm the photographed image without dropping frames until immediately before the photographing is started. Therefore, a short release time lag can be realized without impairing the high-speed focus detection operation.

  FIG. 3 shows the configuration of the lens barrel 105 in the first mode in the digital camera 101 of this embodiment. FIG. 4 shows the configuration of the lens barrel 105 in the second mode. Further, FIG. 5 shows a detailed configuration of the beam splitter 103. Hereinafter, the beam splitter 103 and its peripheral part will be described in detail with reference to these drawings.

  The beam splitter 103 is disposed between the rear end of the lens 102 a constituting the imaging optical system 102 and the image sensor 106. The lens 102 a is a focusing lens, and performs focus adjustment by moving in the direction of the optical axis 104.

  The lens barrel 105 includes barrel constituent members 105a, 105b, and 105c. The lens barrel 105 is expanded and contracted in a direction along the optical axis 104 by a driving mechanism (not shown). Thereby, the interval between the lenses constituting the imaging optical system 102 varies, and the zoom ratio can be changed. A lens barrel constituent member (hereinafter referred to as a reference lens barrel) 105c is a reference member for determining the position of the imaging optical system 102 with respect to the camera body 101.

  The image sensor 106 is positioned with respect to a fixed ground plate (not shown). Reference numeral 120 denotes a rotating lens barrel that constitutes a part of a driving mechanism for inserting and retracting the beam splitter 103 into the imaging optical path with respect to the fixed base plate. By rotating the rotating barrel 120 in conjunction with the movement of the beam splitter 103, the reference barrel 105c, which is the reference member of the imaging optical system 102, can be moved in the optical axis direction.

  Next, the beam splitter 103 will be described with reference to FIGS. FIG. 5A shows the beam splitter 103 in an exploded state, and FIG. 5B shows the completed beam splitter 103.

  The beam splitter 103 is made by bonding two prisms 103-1 and 103-2 made of a transparent body with a light splitting functional surface 103a. The light incident surface of the beam splitter 103 includes a surface 103-1b of the prism 103-1 and a surface 103-2b of the prism 103-2. In addition, the exit surface for the straight traveling light that passes through the beam splitter 103 and travels toward the image sensor 106 is composed of a surface 103-1d of the prism 103-1 and a surface 103-2d of the prism 103-2.

  Each of the prisms 103-1 and 103-2 is made of a ring-opening metathesis polymer polymer (HROP; refractive index 1.53) made of a plastic material having a small birefringence. Further, the surfaces 103-1b and 103-1d of the first prism 103-1, and the surfaces 103-2b and 103-2d of the second prism 103-2 are parallel to each other and spaced apart from each other.

  Further, two angles formed by the surface 103-1a of the first prism 103-1 with respect to the surface 103-1b and the surface 103-1d are such that the surface 103-2a of the second prism 103-2 is the surface 103-1d. And two angles formed with respect to the surface 103-1b. Therefore, when the first prism 103-1 and the second prism 103-2 are joined by the surfaces 103-1 a and 103-2 a (the surface after joining is denoted by 103 a), the joined beam splitter 103 is Except for the light splitting functional surface 103a, it exhibits the same characteristics as the optically parallel plate. Therefore, no matter which region of the incident surface 103b the light beam enters, it passes through the same wavefront, so that no change in aberration occurs regardless of the incident position.

  A dielectric multilayer film is formed on the surface 103-2a of the second prism 103-2 so that the surface 103a of the beam splitter 103 has a light beam separating function. And the 2nd prism 103-2 is bonded together with the 1st prism 103-1, using the optical adhesive agent which took the index matching.

  Since the dielectric multilayer film can reduce light absorption so that it can be almost ignored, the incident light is divided in either direction of the image sensor 106 and the focus detection sensor 112 on the light splitting functional surface 103a. That is, the light splitting functional surface 103a reflects a part of incident light in a predetermined wavelength region and transmits the other part.

  The optical characteristics of the light splitting functional surface 103-a thus formed are shown in FIG. The spectral transmittance characteristics from a wavelength of 400 nm to 1000 nm are valley-shaped having a minimum value near 500 nm. On the other hand, the spectral reflectance characteristic is a mountain shape having a maximum value in the vicinity of 500 nm. Here, in the visible region from 450 nm to 650 nm, the spectral transmittance characteristic is constant at approximately 45%. In a camera that captures a color image, the sensitivity region of the image sensor 106 is matched with the visibility region, so that the light splitting functional surface 103-a has a flat spectral reflectance characteristic in the sensitivity wavelength region of the image sensor 106. .

Further, an antireflection coating AR is formed on the entrance surface 103b of the beam splitter 103 and the AF exit surface 103c formed on the upper end of the second prism 103-2. The antireflection coating is formed by laminating a thin film having a different refractive index on the lens base material with SiO ₂ , TiO ₂ , ZnO ₂ or the like at a quarter wavelength thickness (for example, 0.1 to 0.3 μm), thereby reflecting the surface. The rate can be kept low. The characteristics of the antireflection coating are shown in FIG.

  Further, an infrared (IR) cut filter film IRC is formed on the exit surface 103 d of the beam splitter 103. With this filter film IRC, only the visible region wavelength can be guided to the image sensor 106, and a camera with good color reproducibility can be constructed.

  On the other hand, the light beam reflected by the light splitting function surface 103a among the light beams incident inside from the incident surface 103b of the beam splitter 103 is internally reflected (total internal reflection) by the incident surface 103b of the beam splitter 103, and is reflected from the AF exit surface 103c. The light is emitted and guided to the focus detection sensor 112.

  Since the light beam reaching the focus detection sensor 112 does not pass through the IR cut filter film IRC, it includes infrared light. For this reason, the luminous flux has higher luminance than the light transmitted through the IR cut filter film, and the AF performance in a dark scene can be improved.

  Since the spectral reflectance characteristic of the visible region wavelength on the light splitting function surface 103a is about 55% and about 30% in the infrared region wavelength, high-precision focus detection is possible with a sufficient amount of light.

  Next, the focus detection sensor 112 will be described. FIG. 8 shows a focus detection field of the focus detection sensor 112.

  In FIG. 8, reference numeral 120 denotes a finder field as an imaging range (observation range), and 121-1 to 121-9 denote focus detection fields.

  If the focus detection field is basically set near the center of the finder field 120, it is easy to use.

  Since the focus detection visual field formed by the pixel columns extending in the vertical direction is sensitive to the luminance distribution in the vertical direction, for example, focus detection can be performed on horizontal lines. On the other hand, since the focus detection visual field formed by the pixel rows extending in the horizontal direction is sensitive to the luminance distribution in the horizontal direction, for example, focus detection for vertical lines is possible.

  The actual focus detection sensor 112 is configured as shown in FIG. FIG. 9 is a view of the focus detection sensor 112 when viewed from the optical axis direction of the sensor. Reference numerals 112-1 to 112-9 denote pixel columns constituting the focus detection visual fields 121-1 to 121-9.

  FIG. 10 is a cross-sectional view of the pixel portion of the focus detection field of view (for example, 112-1) of the focus detection sensor 112. 11A is a plan view showing a photoelectric conversion unit of one pixel of the focus detection sensor 112, and FIG. 11B is a plan view of one pixel of the focus detection sensor 112.

  In FIG. 10, light enters the focus detection sensor 112 from above, and in FIGS. 11A and 11B, the light enters the focus detection sensor 112 from above perpendicular to the paper surface. The focus detection sensor 112 is a CMOS type sensor having an on-chip type microlens, and the F number of the focus detection light beam can be defined by the action of the microlens.

  In FIG. 10, reference numeral 151 denotes a silicon substrate, and 152A and 152B denote photoelectric conversion portions of embedded photodiodes. Reference numeral 154 denotes a light-shielding first wiring layer made of aluminum or copper. Reference numeral 155 denotes a second wiring layer using aluminum or copper. Reference numeral 156 denotes an interlayer insulating film and a passivation film made of silicon oxide film, hydrophobic porous silica, silicon oxynitride film, or silicon nitride film. Reference numeral 158 denotes a microlens, and 157 denotes a flattening layer for setting the distance from the second wiring layer 155 to the microlens 158 with high accuracy. The first wiring layer 154 and the second wiring layer 155 are metal films having openings provided discretely and do not transmit visible light except for the openings.

  The first wiring layer 154 and the second wiring layer 155 have both an electrical function for operating the focus detection sensor 112 and an optical function for controlling the angle characteristics of the received light flux.

  The flattening layer 157 is formed by a method of curing a thermosetting resin or an ultraviolet curable resin after spin coating or adhering a resin film.

  As shown in FIG. 11A, the photoelectric conversion units 152A and 152B are formed in a zigzag shape, and circuit portions 159A and 159B are connected to both ends thereof. In the circuit portions 159A and 159B, a transfer MOS transistor serving as a transfer switch and a reset MOS transistor for supplying a reset potential are provided. A source follower amplifier MOS transistor, a selection MOS transistor for selectively outputting a signal from the source follower amplifier MOS transistor, and the like are also provided.

  On the photoelectric conversion unit 152, as shown in FIG. 11B, five microlenses 158 are provided in a zigzag manner for one pixel.

Here, the microlens 158 is formed of resin, SiO ₂ , TiO ₂ , Si ₃ N ₄ or the like. Since the microlens 158 is used not only for condensing but also for imaging, the microlens 158 is configured by an axially symmetric spherical lens or an axially symmetric aspherical lens.

  Since the microlens 158 has a shape having the symmetry axis 160, the microlens 158 is circular when viewed in a plan view. However, by providing a plurality of microlenses 158 in one pixel, the pixel pitch can be reduced while reducing the pixel pitch. The light receiving area can be increased. Therefore, a sufficient focus detection output can be obtained even for a low-luminance object. Further, a shape that does not have an axis of symmetry, such as a semi-cylindrical type, is not suitable for the focus detection sensor 112 because there is no image forming action as a lens.

  In addition, in order to suppress the surface reflection of light at the microlens 158, a thin film having a low refractive index or a fine structure (so-called sub-wavelength structure) below the wavelength of visible light is formed on the surface of the microlens 158. Also good.

  The light beam emitted from the beam splitter 103 enters the microlens 158 of the focus detection sensor 112. Among these components, the component passing through the opening 155A provided in the second wiring layer 155 and the opening 154A provided in the first wiring layer 154 enters the photoelectric conversion unit 152A. In addition, a component passing through the opening 155A provided in the second wiring layer 155 and the opening 154B provided in the first wiring layer 154 enters the photoelectric conversion unit 152B. The light beams incident on the photoelectric conversion units 152A and 152B are converted into electric signals.

  Since the light shielding layer for forming the opening is also used as the first wiring layer 154 and the second wiring layer 155, there is no need to provide a light shielding layer for the opening, and the configuration of the focus detection sensor 112 is simplified. Can do.

  FIGS. 12 and 13 are a plan view and a perspective view, respectively, showing a state in which the pixels shown in FIG. 11 are connected to form a pixel row for use in focus detection.

  In FIG. 12, illustration of the microlenses 158 at both ends is omitted so that the photoelectric conversion units 152A and 152B can be seen so that the positional relationship between the photoelectric conversion units 152A and 152B and the microlens 158 can be understood.

  In FIG. 13, the photoelectric conversion units 152A and 152B, the first wiring layer 154, the second wiring layer 155, and the microlens 158 are extracted from the constituent elements and are shown in the vertical direction. Further, in order to make the boundary of one pixel easy to understand, the zigzag shape of the photoelectric conversion unit is projected on the first wiring layer 154 and the second wiring layer 155 and indicated by a broken line.

  In FIG. 12, five microlenses 158a with hatching constitute one pixel. A large number of such pixels are arranged in the horizontal direction to form the pixel columns 112-1 to 112-9 shown in FIG.

  Since the microlenses 158 arranged in a zigzag form a space between the adjacent microlenses 158, the microlenses 158 are densely arranged on the pixel array. Therefore, the amount of light that is not used without entering the microlens 158 is small enough to be ignored.

  In addition, since the microlenses 158 are arranged in a zigzag manner, the frequency response of pixels near the Nyquist frequency can be lowered. As a result, even if an object image including a spatial frequency component higher than the Nyquist frequency is projected, aliasing distortion hardly occurs, and phase difference detection between output signal waveforms of the focus detection sensor 112 described later can be performed with high accuracy.

  Further, a micro lens 158b that is not disposed on the photoelectric conversion units 152A and 152B and does not contribute to photoelectric conversion is formed around the pixel column. This is because the microlens 158 can be manufactured with high accuracy by arranging the microlenses 158 as uniformly as possible.

  The first wiring layer 154 shown in FIG. 13 has a large number of rhombus-like openings 154A and 154B. As shown in FIG. 14 which is a plan view, the openings 154A and 154B are provided in pairs corresponding to each of the microlenses 158, and are formed in the vicinity of the focal position of the microlens 158.

  With such a configuration, the openings 154A and 154B are back-projected onto the exit pupil of the imaging optical system 102 by the microlens 158. For this reason, it is possible to determine the light receiving angle characteristic of the light beam taken in by the pixel depending on the shapes of the openings 154A and 154B.

  The opening 155A provided in the second wiring layer 155 is a stop for preventing light from entering the openings other than the openings 154A and 154B of the first wiring layer. As a result, only the light beams incident on the openings 154A and 154B enter the photoelectric conversion units 152A and 152B, respectively.

  Here, in order not to cause nonuniformity in the output signal output from each pixel row of the focus detection sensor 112, the shapes of the openings 154A and 154B are constant for the pixel row forming one focus detection field.

  15 and 16 are partial cross-sectional views of the focus detection visual field 112-1 shown in FIG. Each microlens 158 back-projects the openings 154A and 154B of the first wiring layer 154 onto the exit pupil of the imaging optical system 102. Accordingly, as shown in FIG. 15, the passage of the light beam 132A through the opening 154A is equivalent to the emission of the light beam 132A from the back-projected image of the opening 154A of the first wiring layer 154.

  Similarly, as shown in FIG. 16, the fact that the light beam 132B can pass through the opening 154B is equivalent to the light beam 132B being emitted from the back projection image of the opening 154B of the first wiring layer 154.

  Therefore, light rays incident on the focus detection sensor 112 from other than the back-projected images of the openings 154A and 154B are always blocked by the first wiring layer 154 or the second wiring layer 155 and cannot reach the photoelectric conversion units 152A and 152B. There is no conversion.

  An output signal waveform obtained by arranging the output signals from the photoelectric conversion unit 152A and an output signal waveform obtained by arranging the output signals from the photoelectric conversion unit 152B for a pixel row constituting one focus detection field of view. There is the following relationship between them. That is, a relatively laterally shifted state is observed between them depending on the imaging state of the object image formed by the imaging optical system 102 on the focus detection field.

  This is because the region through which the light beam passes on the exit pupil of the imaging optical system 102 arranges the output signal waveform obtained by arranging the output signals from the photoelectric conversion unit 152A and the output signal from the photoelectric conversion unit 152B. This is because the output signal waveform obtained in this way is different.

  The shift direction of the output signal waveform is reversed between the front pin and the rear pin, and the principle of focus detection is to detect this phase difference (shift amount) including the direction using a technique such as correlation calculation.

  17 and 18 show output signal waveforms of the focus detection sensor 112 input to the AF control circuit 140. FIG. The horizontal axis represents the pixel arrangement, and the vertical axis represents the output value. FIG. 17 shows an output signal waveform when the object image is not in focus, and FIG. 18 shows an output signal waveform when the object image is in focus.

  In this way, focus detection can be performed by first determining the identity of a set of signals. Furthermore, the defocus amount can be obtained by detecting the phase difference using a known method using correlation calculation, for example, a method disclosed in Japanese Patent Publication No. 5-88445.

  If the obtained defocus amount is converted into an amount to drive the focusing lens 102a of the imaging optical system 102, automatic focus adjustment is possible. Since the amount by which the focusing lens 102a is to be driven is known in advance, the lens is normally driven only once up to the in-focus position, and extremely fast focus adjustment can be performed.

  Here, the focus detection light beam will be described. In the focus detection sensor 112, the F-number (Fno) of the focus detection light beam is different for each focus detection field by controlling the light receiving angle characteristic for each focus detection field. The size of the region through which the light beam passes on the exit pupil of the imaging optical system 102 is large in the central focus detection field 112-1 and small in the peripheral focus detection field (for example, 112-4).

  FIG. 19 shows the luminance of an object imaged by the image sensor 106. FIG. 19A shows an image at Fno 2.8, FIG. 19B shows an image at Fno 4, and FIG. 19C shows an image at Fno 8. The shaded portion in the image is an image portion formed by the light beam that has passed through the light splitting functional surface 103a.

  As shown in FIG. 19, the spread of luminance unevenness at the edge portion of the light splitting functional surface 103a differs depending on Fno. However, the spectral characteristics are substantially the same regardless of the image height and Fno. Therefore, at the time of playback processing on the display 107, appropriate brightness correction parameters corresponding to Fno are stored in advance, and the playback processing is controlled by the camera system control circuit 135 shown in FIG. 2 based on the Fno information. To do. As a result, it is possible to display a reproduced image without a sense of incongruity. The luminance correction parameter is information corresponding to the light amount difference (luminance difference) between the light beam that has passed through the light splitting function surface and the light beam that has not passed.

  The state of uneven brightness as shown in FIG. 19 shows different characteristics depending on the manufacturing method of the beam splitter 103 and the film characteristics of each optical surface. However, by measuring and storing the luminance unevenness information for each Fno as initial data in advance during the manufacturing process or the like, individual differences in the luminance unevenness correction parameters can be absorbed.

  FIG. 20 shows a drive mechanism (second mechanism) for the beam splitter 103 and a drive mechanism (first mechanism) for the reference barrel 105c. The drive mechanism of the reference barrel 105 c is driven by the drive mechanism of the beam splitter 103 and interlocks with the movement of the beam splitter 103.

  (A) is the front view seen from the imaging optical system 102 side in imaging | photography preparation state (1st mode), (b) is a side view at that time. Further, (c) is a front view in a photographing state (second mode), and (d) is a side view at that time.

  The beam splitter 103 and the focus detection sensor 112 are joined by an adhesive, and these are held by the splitter holding frame 201. The reference barrel 105c is disposed inside the rotary barrel 200, and a cam pin 204 is formed on the outer peripheral surface of the reference barrel 105c. A cam groove portion 206 that engages with the cam pin 204 is formed on the peripheral wall surface of the fixed barrel 200.

  Reference numeral 202 denotes a guide bar for guiding the splitter holding frame 201 in the vertical direction (the vertical direction of the camera) in the drawing. Reference numeral 203 denotes a holding frame drive pin formed at the rear end of the rotary lens barrel 200. The holding frame driving pin 203 is engaged with an arm portion extending in the horizontal direction from the splitter holding frame 201.

  Therefore, when the rotary lens barrel 200 is rotated by an actuator (for example, the microstepping motor 250 shown in FIG. 2), the splitter holding frame 201 is driven in the vertical direction, and the beam splitter 103 is moved to the first mode position and the second mode position. Move between. Here, the rotary lens barrel 200 is provided as a member of the drive mechanism of the beam splitter 103. In this embodiment, the reference lens barrel 105c is also driven by the rotary lens barrel 200. That is, when the rotating lens barrel 200 rotates, the cam groove 206 formed in the rotating lens barrel 200 moves with respect to the cam pin 204 provided in the reference lens barrel 105c, and the reference lens barrel 105c moves in the direction of the optical axis 104. Driven.

  Reference numeral 205 denotes a stopper for determining the vertical position of the beam splitter 103 on the photographing optical path by contacting the arm portion of the splitter holding frame 201 in the first mode position. The stopper 205 is formed on a fixed ground plate (not shown).

  The shooting preparation state shown in FIGS. 20A and 20B is set by rotating the rotating barrel 200 in the clockwise direction from the shooting state shown in FIGS. 20C and 20D. . When the rotary lens barrel 200 rotates in the clockwise direction, the holding frame driving pin 203 moves the splitter holding frame 201 downward. Thereby, the beam splitter 103 is inserted into a position on the photographing optical path which is the first mode position. At this time, since the lower end surface of the arm portion of the splitter holding frame 201 abuts against the stopper 205, the beam splitter 103 is accurately positioned in the vertical direction, so that the focus detection by the focus detection sensor 112 can be accurately performed. .

  At this time, due to the engagement of the cam pin 204 and the cam groove portion 206, the reference barrel 105c moves to a position farther from the image sensor 106 by a distance d than the position in the optical axis direction in the photographing state. As a result, the position of the imaging optical system 102 moves in the direction of the subject as a whole compared to the shooting state, and the distance from the imaging optical system 102 (the image side lens surface of the focusing lens 102a) to the image sensor 106, that is, The spatial optical path length is increased by d.

  On the other hand, the imaging state shown in FIGS. 20C and 20D is obtained by rotating the rotating barrel 200 counterclockwise in the drawing from the imaging preparation state shown in FIGS. 20A and 20B. Is set. When the rotary lens barrel 200 rotates counterclockwise, the holding frame driving pin 203 moves the splitter holding frame 201 upward. As a result, the beam splitter 103 retracts to a position outside the imaging optical path that is the second mode position.

  At this time, due to the engagement between the cam pin 204 and the cam groove 206, the reference barrel 105c moves to a position closer to the image sensor 106 by a distance d than the position in the optical axis direction in the photographing preparation state. As a result, the position of the imaging optical system 102 moves in the direction of the imaging element as a whole compared to the imaging preparation state, and the distance from the imaging optical system 102 (the image side lens surface of the focusing lens 102a) to the imaging element 106. That is, the spatial optical path length is shortened by d.

  Here, the distance d corresponds to the difference in the spatial optical path length between when the beam splitter 103 is inserted into the imaging optical path and when it is retracted outside the imaging optical path.

  By adopting the above configuration, it is possible to reliably correct the variation (d) in the spatial optical path length between the insertion state and the retracted state of the beam splitter 103, that is, the variation in the focus surface position. For this reason, the focus state on the image sensor 106 of the imaging optical system 102 can be made equal between the insertion state and the retracted state of the beam splitter 103. Therefore, a change in focus state due to the movement of the beam splitter 103 can be avoided.

  Further, in this embodiment, since the entire imaging optical system 102 is moved to correct the focus surface position, even if the zoom ratio of the imaging optical system 102 fluctuates, the imaging optical system 102 moves. There is no need to change the amount. Therefore, it is not necessary to control the movement amount of the imaging optical system 102 according to the zoom ratio. Further, in this embodiment, the drive mechanism that drives the entire imaging optical system is operated by the drive mechanism of the beam splitter 103. Accordingly, it is possible to correct the focus surface position with a very simple configuration.

  FIG. 21 is a flowchart showing the operation sequence of the camera of this embodiment. The operation shown in this flowchart starts when the camera is turned on, and is performed under the control of the camera system control circuit 135 according to the computer program. Then, the process ends when the power is turned off.

  In step (denoted as S in the figure) 1001, it is determined whether the photographer has selected the AF mode. If the shooting mode is the normal AF mode, the process proceeds to step 1002.

  In step 1002, first, in order to perform focus detection by the focus detection sensor 112 for phase difference AF, the rotating lens barrel 200 is rotated, and the beam splitter 103 and the imaging optical system 120 (reference lens barrel 105c) are moved to FIG. Move to the position shown in (a), (b). Then, the process proceeds to Step 1003. If the AF mode is the TV-AF mode in step 1001, the process proceeds to step 1011.

  In the normal AF mode, in step 1003, the image sensor 106 is driven to photoelectrically convert the subject image. Then, the RGB processing circuit 131 and the YC processing circuit 132 perform various processes and output image data to the display 107. Thereby, the photographer can check the subject image through the display 107.

  In addition, in the series of processes, the aperture in the lens barrel 105 is adjusted according to the brightness of the subject, or the gain of the signal of the image sensor 106 is adjusted to obtain an appropriate brightness for the display 107. The subject image is displayed.

  In step 1004, it is determined whether or not the half-press (first stage) operation SW1 of the release button 111 has been performed. If not, the process returns to step 1003. If the first stage operation SW1 has been performed, the process proceeds to step 1005.

  In step 1005, the focus detection sensor 112 performs photoelectric conversion on the subject image formed by the light beam incident through the beam splitter 103. Based on the output from the focus detection sensor 112, the defocus amount and the drive amount and drive direction of the focusing lens 102a corresponding to the defocus amount are calculated by the method described above. That is, the phase difference AF is performed in this step and the next step 1006.

  In step 1006, the focusing lens 102a is driven by the calculated driving amount in the calculated driving direction to perform focusing. Thereby, the imaging optical system 102 is substantially focused on the subject.

  In step 1007, the focus detection sensor 112 again photoelectrically converts the subject image formed by the light beam incident through the beam splitter 103. Then, based on the output from the focus detection sensor 112, it is confirmed whether or not focus is achieved. If the subject is in focus, a sound or light is emitted to notify the photographer of the in-focus state, and the process proceeds to step 1008.

  Although not shown in this flow, if it is determined that the subject is out of focus, the focusing lens 102a is driven again based on the defocus detection result. Then, focus confirmation is performed again. If in-focus confirmation cannot be performed even after repeating this operation a plurality of times, it is displayed that the in-focus state is impossible, and the mode is switched to TV-AF.

  In step 1008, it is determined whether or not the fully-pressed (second stage) operation SW2 of the release button 111 has been performed. If not, the process returns to step 1004. If the second-stage operation SW2 has been performed, the process proceeds to step 1009.

  In step 1009, the beam splitter 103 and the imaging optical system 120 (reference barrel 105c) are moved to the positions shown in FIGS. 20 (c) and 20 (d). Then, the process proceeds to Step 1010.

  In step 1010, the image sensor 106 is exposed (photographed). Here, in the exposure in this step, the charge accumulated in the image sensor 106 is reset, and after the accumulation time corresponding to the brightness of the subject elapses, the light receiving surface of the image sensor 106 is shielded by the shutter and accumulated. This is an operation of reading out the charged charges. In step 1010, the captured image data is recorded on the recording medium 108.

  After the exposure is completed, although not shown in the present flow, if the first and second step operations SW1 and SW2 of the release button 111 are continued, the process stays at step 1010 and is taken during that time. Continue to play the image on the display 107. When the operation of the release button 111 is released, the shutter is opened again and the process returns to step 1001.

  In this flowchart, the flow does not advance to step 1008 unless it is confirmed that the subject is in focus. However, the present invention is not limited to this. Also good. That is, it is possible to perform exposure according to the second-stage operation SW2 of the release button 111 even when the focus is not achieved.

  Next, a case where the photographer selects the TV-AF mode in step 1001 will be described.

  In Step 1011, the beam splitter 103 and the imaging optical system 120 (reference barrel 105c) are moved to the positions shown in FIGS. 20 (c) and 20 (d).

  In step 1012, as in step 1003, the image sensor 106 is driven to photoelectrically convert the subject image. Then, the RGB processing circuit 131 and the YC processing circuit 132 perform various processes and output image data to the display 107.

  In step 1013, it is determined whether or not the first-stage operation SW1 of the release button 111 has been performed. If not, the process returns to step 1012. If the first stage operation SW1 has been performed, the process proceeds to step 1014.

  In step 1014, the focusing lens 102a is step-driven by a predetermined driving amount to calculate a contrast evaluation value, and based on the result, the focusing lens 102a reaches the in-focus position.

  In this flow, TV-AF is not performed unless the first-stage operation SW1 of the release button 111 is performed. However, even if the first-stage operation SW1 is not performed, TV-AF is performed at any time. The occurrence of a so-called blurred state may be avoided. As a result, the subsequent TV-AF can be speeded up.

  In step 1015, it is confirmed that the contrast evaluation value is at a peak (in-focus position), and the photographer is notified of the focus by sound or light.

  In step 1016, it is determined whether or not the second-stage operation SW2 of the release button 111 has been performed. If not, the process returns to step 1013. When the second-stage operation SW2 is performed, the process proceeds to step 1010, where the image sensor 106 is exposed and a captured image is recorded.

  As described above, in the present embodiment, the phase difference AF using the focus detection sensor 112 is usually performed in order to speed up the focus adjustment. However, in the case where the state of the subject or high-precision focus adjustment is required, TV-AF can also be selected.

  Further, according to the present embodiment, the focus surface position correction drive (drive in the entire optical axis direction of the entire imaging optical system 102) is performed in conjunction with the insertion drive and the retraction drive of the beam splitter 103 with respect to the imaging optical path. . For this reason, it is possible to perform imaging immediately after retracting the beam splitter 103 and focus detection operation immediately after insertion, and smooth imaging can be performed.

  22A and 22B show a cross section of a lens barrel portion of a digital camera that is Embodiment 2 of the present invention. In the present embodiment, the same constituent elements as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description is omitted. 22A shows a shooting preparation state, and FIG. 22B shows a shooting state.

  In the imaging preparation state (first mode), the beam splitter 103 is positioned between the focusing lens 102a constituting the imaging optical system 102 and the image sensor 106.

  The image sensor 106 is supported so as to be movable in the direction of the optical axis 104 with respect to a fixed ground plate (not shown). The image sensor 106 also moves in the optical axis direction in conjunction with a drive mechanism (which will be described later) for inserting and retracting the beam splitter 103 with respect to the imaging optical path.

  At this time, the amount of movement of the image sensor 106 matches the amount of variation (d) in the spatial optical path length between the insertion state and the retracted state of the beam splitter 103, so that the variation in focus surface position can be reliably corrected. . For this reason, the focusing state on the image sensor 106 of the imaging optical system 102 can be made equal between the insertion state and the retracted state of the beam splitter 103, and the change of the focusing state due to the movement of the beam splitter 103 is avoided. be able to.

  FIG. 23 shows a drive mechanism (second mechanism) for the beam splitter 103 and a drive mechanism (first mechanism) for the image sensor 106. The drive mechanism of the image sensor 106 is driven by the drive mechanism of the beam splitter 103 and interlocks with the movement of the beam splitter 103. (A) is the front view seen from the imaging optical system 102 side in imaging | photography preparation state (1st mode), (b) is a side view at that time. Further, (c) is a front view in a photographing state (second mode), and (d) is a side view at that time.

  The beam splitter 103 and the focus detection sensor 112 are joined by an adhesive, and these are held by a splitter holding frame 301.

  Reference numeral 302 denotes a guide rod that guides the splitter holding frame 301 in the vertical direction, and 303 denotes a microstepping motor as an actuator that drives the splitter holding frame 301 in the vertical direction. A lead screw 304 is integrated with the output shaft of the microstepping motor 303. A rack formed on the splitter holding frame 301 is engaged with the lead screw.

  When a pulse signal is input to the microstepping motor 303, the lead screw 304 rotates and the splitter holding frame 301 moves up and down along the guide bar 302. For this reason, it is possible to move the beam splitter 103 up and down while suppressing the shake of the beam splitter 103. Also, by setting the number of input pulses to a predetermined number, the vertical position of the splitter holding frame 301 can be controlled, and the beam splitter 103 can be accurately moved to the first mode position and the second mode position.

  Note that the position of the beam splitter 103 can be held by energizing the microstepping motor 303 at the first mode position and the second mode position. In addition, by appropriately setting the cogging torque of the microstepping motor 303 and the friction with the lead screw 304, the position of the beam splitter 103 can be held in a state where energization is stopped.

  Reference numeral 308 denotes an image sensor holding frame that holds the image sensor 106, and is guided in the optical axis direction by guide rods 305a and 305b. 306a and 306b are stoppers that determine the position of the image sensor 106 in the optical axis direction during AF.

  In the imaging preparation state shown in FIGS. 23A and 23B, a predetermined number of pulse signals are input to the microstepping motor 303 from the imaging state shown in FIGS. It is set by moving it down to the first mode position.

  Here, a cam 301 a is formed on the surface of the splitter holding frame 301 on the image sensor side. On the other hand, a follower 308a capable of contacting the cam 301a is formed on the surface of the image sensor holding frame 308 on the beam splitter side. Note that the image sensor 106 is biased toward the beam splitter by springs 307a and 307b disposed around the guide rods 305a and 305b.

  For this reason, when the splitter holding frame 301 moves downward, the cam 301a abuts on the follower 308a and pushes the image sensor holding frame 308 backward (rightward in the figure) against the urging force of the springs 307a and 307b. The image sensor 106 moves backward by the amount of movement for correcting the focus surface position described above. As a result, the distance from the imaging optical system 102 (the image side lens surface of the focusing lens 102a) to the image sensor 106, that is, the spatial optical path length, is longer than the shooting state by the distance d. Note that the back surface of the image sensor holding frame 308 abuts against the stopper 308a, so that the image sensor 106 is prevented from being tilted and accurate rearward movement of the distance d is guaranteed.

  On the other hand, in the imaging preparation state shown in FIGS. 23C and 23D, a predetermined number of pulse signals are reversely input to the microstepping motor 303 from the imaging preparation state shown in FIGS. 23A and 23B. This is set by moving the beam splitter 103 up to the second mode position.

  When the splitter holding frame 301 moves up, the cam 301a is detached from the follower 308a, and the image sensor holding frame 308 is pushed forward (leftward in the figure) by the urging force of the springs 307a and 307b. The image sensor 106 moves forward by an amount of movement for correcting the focus surface position described above. As a result, the distance from the imaging optical system 102 (the image side lens surface of the focusing lens 102a) to the image sensor 106, that is, the spatial optical path length, is shortened by a distance d as compared with the imaging preparation state. The front surface of the image sensor holding frame 308 is in contact with the ends of the guide rods 305a and 305b, so that the tilt of the image sensor 106 is prevented and accurate forward movement of the distance d is guaranteed.

  By adopting the above configuration, it is possible to reliably correct the variation (d) in the spatial optical path length between the insertion state and the retracted state of the beam splitter 103, that is, the variation in the focus surface position. For this reason, the focus state on the image sensor 106 of the imaging optical system 102 can be made equal between the insertion state and the retracted state of the beam splitter 103. Therefore, a change in focus state due to the movement of the beam splitter 103 can be avoided.

  In this embodiment, the image pickup device 106 is moved to correct the focus surface position. Therefore, even if the zoom ratio of the imaging optical system 102 fluctuates, it is necessary to change the moving amount of the image pickup device 106. Absent. Therefore, it is not necessary to control the movement amount of the image sensor 106 according to the zoom ratio. Further, in this embodiment, the driving mechanism for driving the image sensor 106 is operated by the driving mechanism for the beam splitter 103. Accordingly, it is possible to correct the focus surface position with a very simple configuration.

  In each of the above embodiments, the description has been continued by taking a digital still camera as an example. However, the present invention is also applicable to other imaging devices such as a video camera, a surveillance camera, a web camera, and a mobile phone camera. can do.

1 is a cross-sectional view of a digital camera (beam splitter inserted state) that is Embodiment 1 of the present invention. 1 is a cross-sectional view of a digital camera (beam splitter retracted state) that is Embodiment 1 of the present invention. 1 is a block diagram illustrating an electrical configuration of a digital camera according to Embodiment 1. FIG. FIG. 3 is a cross-sectional view of a lens barrel portion (beam splitter inserted state) in the digital camera of Embodiment 1. FIG. 3 is a cross-sectional view of a lens barrel portion (beam splitter retracted state) in the digital camera of Embodiment 1. FIG. 3 is a cross-sectional view of a beam splitter used in the digital camera of Embodiment 1. FIG. 4 is a diagram illustrating optical characteristics of a light splitting function surface in the beam splitter according to the first embodiment. FIG. 3 is a diagram illustrating optical characteristics of an antireflection coating in the beam splitter according to the first embodiment. FIG. 3 is a diagram illustrating a focus detection field of the focus detection sensor in the digital camera according to the first embodiment. 2 is a plan view of a focus detection surface of a focus detection sensor in the digital camera of Embodiment 1. FIG. 2 is a cross-sectional view of a pixel portion of a focus detection sensor in the digital camera of Embodiment 1. FIG. The top view showing the photoelectric conversion part of 1 pixel of the focus detection sensor of FIG. 10, and the top view of this 1 pixel. The top view showing the pixel row | line | column which connected each pixel of the focus detection sensor of FIG. FIG. 11 is a perspective view illustrating a pixel row in which pixels of the focus detection sensor in FIG. 10 are connected. FIG. 11 is a plan view showing an opening of a first wiring layer of the focus detection sensor of FIG. 10. FIG. 11 is a partial cross-sectional view of a focus detection visual field of the focus detection sensor of FIG. 10. FIG. 11 is a partial cross-sectional view of a focus detection visual field of the focus detection sensor of FIG. 10. The figure showing the output signal waveform of the focus detection sensor of FIG. The figure showing the output signal waveform of the focus detection sensor of FIG. FIG. 4 is a diagram for explaining a state of luminance unevenness in the first embodiment. The front view and side view explaining the interlocking drive mechanism in Example 1. FIG. 3 is a flowchart showing an operation sequence in the digital camera of Embodiment 1. Sectional drawing of the lens-barrel part of the digital camera which is Example 2 of this invention. Sectional drawing of the lens-barrel part of the digital camera which is Example 2 of this invention. FIG. 6 is a diagram for explaining an interlocking drive mechanism in Embodiment 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 102 Imaging optical system 103 Beam splitter 105 Lens barrel 106 Image pick-up element 112 Focus detection sensor 113 Optical low-pass filter 200 Rotating barrel 201, 301 Splitter holding frame 204 Cam pin 206 Cam 301a Cam 303 Micro stepping motor 304 Lead screw 308 Imaging element Holding frame 308a Follower

Claims (5)

An image sensor that photoelectrically converts a subject image formed by the photographing optical system;
Focus detection means for performing focus detection using a light beam from the photographing optical system;
A member that separates a light beam from the photographing optical system into a light beam directed to the imaging element and a light beam guided to the focus detection unit, and is a first position disposed in an optical path of the light beam from the photographing optical system And an optical member movable to a second position disposed outside the optical path;
A first mechanism that increases the distance from the imaging optical system to the imaging element when the optical member is disposed at the first position, compared to when the optical member is disposed at the second position; An imaging apparatus characterized by that. The imaging apparatus includes a photographing optical system,
The imaging apparatus according to claim 1, wherein the first mechanism changes the distance by changing a position of the photographing optical system.   The imaging apparatus according to claim 1, wherein the first mechanism changes the distance by changing a position of the imaging element. A second mechanism for moving the optical member between the first position and the second position;
The imaging apparatus according to claim 1, wherein the first mechanism is driven by the second mechanism. An image sensor that photoelectrically converts a subject image formed by the photographing optical system, a focus detection unit that performs focus detection using a light beam from the photographing optical system, and a light beam that directs the light beam from the photographing optical system to the image sensor. And a light beam guided to the focus detection means, and is movable to a first position arranged in the optical path to the image sensor and a second position arranged outside the optical path A method for controlling an imaging apparatus having an optical member,
Moving the optical member between the first position and the second position;
Changing the distance from the imaging optical system to the image sensor in accordance with the movement of the optical member,
In the step of changing the distance, when the optical member is arranged at the first position, the distance from the imaging optical system to the imaging element is made longer than when the optical member is arranged at the second position. An image pickup apparatus control method comprising: