JP2009015186A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device carrying a TTL type OVF while having a thin and lightweight structure. <P>SOLUTION: The imaging device has a first optical member 201 provided with a first face 201a, and a second optical member 1 provided with a second face 1a and movable between a first position, wherein the second face is separated apart from the first face, and a second position wherein the second face is brought close to the first face beyond the first position. While the second optical member is in the first position, light from an object is totally reflected by the first face to be led to an imaging element 103. While the second optical member is in the second position, a part of light from the object is reflected by the first face to be led to the imaging element, and another part of the light is transmitted through the first and second faces to be led to an ocular optical system 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging apparatus such as a digital camera, and more particularly to a configuration for guiding light from an object to an eyepiece of an imaging element and a finder optical system.

  The imaging apparatus is required to be small and light and thin (reduction in thickness in the optical axis direction of the imaging optical system). Among these factors, a factor that hinders the reduction in thickness is that the dimension of the optical system (particularly, the imaging optical system) tends to be large in the optical axis direction. One method for reducing the dimension of the optical system in the optical axis direction is to bend the optical system by disposing a reflecting surface in the optical system. An imaging apparatus having such a configuration of a bending optical system is disclosed in Patent Documents 1 to 4.

  FIG. 5 shows an example of a bent imaging optical system in which a prism is disposed in the optical system and the optical system is bent. Reference numerals 302 and 303 denote first and second lenses constituting the object side portion of the imaging optical system. Reference numeral 301 denotes a right-angle prism. Reference numeral 306 denotes a rear lens unit constituting an image plane side optical system portion of the image pickup optical system. Reference numerals 304 and 305 denote optical filters such as an infrared cut filter and a low-pass filter. Reference numeral 307 denotes an image sensor such as a CCD sensor.

  Light from an object incident on the bending imaging optical system passes through the first and second lenses 302 and 303 and enters the right-angle prism 301. The light incident on the right-angle prism 301 is internally reflected by the surface 301 a of the right-angle prism 301, passes through the rear lens unit 306 and the optical filters 304 and 305, and reaches the image sensor 307.

The image sensor 307 photoelectrically converts an object image formed by the bending imaging optical system. An image generated based on an output signal from the image sensor 307 is recorded on a recording medium (not shown) or displayed on a display (not shown). A display for displaying an image is used as an electronic viewfinder (hereinafter referred to as EVF) for observing an electronic image of an object.
JP 2000-187160 A JP 2003-228003 A JP 2006-053275 A JP 2006-005587 A

  However, in terms of ease of use and the like, an imaging device may preferably be equipped with not only EVF but also an optical viewfinder (hereinafter referred to as OVF). In addition, a TTL (Through The Lens) OVF that can observe an optical image of an object formed by light passing through the imaging optical system, in which parallax between the imaging optical system and the optical viewfinder hardly occurs is more preferable.

  For this reason, even when using the bending imaging optical system as described above, it is necessary to study a method of mounting a TTL OVF and suppressing an increase in the size and weight of the imaging device.

  The present invention provides an imaging apparatus having a thin and lightweight configuration and mounted with a TTL OVF.

  An imaging apparatus according to one aspect of the present invention includes a first optical member having a first surface, a second surface, the first position where the second surface is separated from the first surface, and the second surface. The second optical member is movable between the second position closer to the first surface than the first position. Then, with the second optical member in the first position, the light from the object is totally reflected by the first surface and guided to the image sensor. In addition, with the second optical member in the second position, a part of the light from the object is reflected by the first surface and guided to the image sensor, and the other part is the first and second surfaces. And is guided to the eyepiece optical system.

  According to the present invention, by moving the second optical member between the first and second positions with respect to the first optical member that bends the imaging optical system, light from the object is only applied to the imaging device. It is possible to switch between guiding or guiding the light to the image sensor and the eyepiece optical system. Accordingly, it is possible to realize an imaging device equipped with a TTL OVF while having a thin and lightweight configuration.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 2 shows a configuration of a digital still camera as an image pickup apparatus that is an embodiment of the present invention. In the following description, the digital still camera is referred to as an imaging device.

  An imaging optical system 101 includes a plurality of lenses and a diaphragm. Reference numeral 102 denotes a mechanical shutter. Reference numeral 103 denotes an image sensor, which is composed of a CCD sensor or a CMOS sensor. Light from an object (subject) (not shown) forms an object image by the imaging optical system 101 and reaches the image sensor 103. The image sensor 103 photoelectrically converts an object image and accumulates electric charges according to the amount of light. The mechanical shutter 102 operates to control the exposure amount and exposure timing of the image sensor 103.

  A CDS circuit 104 performs predetermined analog signal processing on an output signal from the image sensor 103. Reference numeral 105 denotes an A / D converter that converts an analog signal output from the CDS circuit 104 into a digital signal.

  A timing signal generation circuit 106 outputs operation timing signals of the image sensor 103, the CDS circuit 104, and the A / D converter 105. Reference numeral 107 denotes a drive circuit that drives the imaging optical system 101, the mechanical shutter 102, and the imaging element 103. A signal processing circuit 108 performs various image processing on the output signal from the A / D converter 105 to generate an image (image data). An image memory 109 stores the generated image data.

  Reference numeral 110 denotes a recording medium that can be attached to and detached from the imaging apparatus, and includes a semiconductor memory, an optical disk, and the like. Reference numeral 111 denotes a recording circuit that records data of a recording image on the recording medium 110. Reference numeral 112 denotes a display for displaying image data, which includes an LCD, a self-luminous element, and the like. A display circuit 113 displays an image on the display 112.

  The signal processing circuit 108 sequentially generates frame images constituting the moving image, and the display circuit 113 causes the display 112 to sequentially display the frame images. Thereby, an electronic moving image of the object is displayed on the display 112. Thus, the display 112 that displays an electronic moving image is used as an EVF. Further, the signal processing circuit 108 generates a recording image (still image) at the time of actual imaging. The recording image is recorded on the recording medium 110 and displayed on the display 112 for a predetermined time.

  Reference numeral 114 denotes a system control unit as control means for controlling the entire imaging apparatus.

  Next, the configuration of the imaging optical system 101 will be described with reference to FIGS. 1A and 1B. In these drawings, the mechanical shutter 102 shown in FIG. 2 is omitted.

  Reference numerals 202 and 203 denote first and second lenses constituting the object-side optical system part (first optical system part) 2 of the imaging optical system 101. Reference numeral 201 denotes a first right-angle prism as a first optical member, which is formed in a triangular prism shape having an entrance surface 201b, an exit surface 201c, and a reflection / transmission surface (first surface) 201a.

  Reference numeral 1 denotes a second right-angle prism as a second optical member, which has a triangular prism shape having an entrance surface 1a (second surface) and an exit surface 1b. The first and second right-angle prisms 201 and 1 are made of an optical material such as glass or resin, and the refractive index thereof is higher than that of air. The second right-angle prism 1 can be moved in a direction in which the incident surface 1a approaches and separates from the reflection / transmission surface 201a of the first right-angle prism 201 by a driving mechanism 10 described later.

  Reference numeral 206 denotes a rear lens unit that constitutes an image plane side optical system portion (second optical system portion) of the imaging optical system 101. Reference numerals 204 and 205 denote optical filters such as an infrared cut filter and a low-pass filter. Reference numeral 103 denotes the image sensor described above.

  Light from an object that has entered the imaging optical system 101 passes through the first and second lenses 202 and 203 and enters the first right-angle prism 201. In FIG. 1A, the incident surface 1a of the second right-angle prism 1 is separated from the reflection / transmission surface 201a of the first right-angle prism 201 (that is, the first and second surfaces are separated by a predetermined distance L). . In this state, the light incident on the first right-angle prism 201 is totally reflected by the reflection / transmission surface 201a and bent in a traveling direction at a right angle, and the first right-angle prism 201 passes through the emission surface 201c. Eject. The light passes through the rear lens unit 206 and the optical filters 204 and 205 and reaches the image sensor 103.

  As described above, the object image formed by the imaging optical system 101 is photoelectrically converted by the imaging element 103 and recorded on the recording medium 110 or displayed on the display 112 as an EVF (electronic viewfinder) image. The reflection at the reflection / transmission surface 201a is total reflection. As a result, the light incident on the imaging optical system 101 can efficiently reach the imaging element 103, and a bright image can be generated.

  The imaging optical system 101 is a bending optical system in which the optical axis AXL is bent by the first right-angle prism 201. Therefore, it is possible to reduce the thickness of the imaging apparatus on which the imaging optical system 101 is mounted.

  On the other hand, in FIG. 1B, the incident surface 1a of the second right-angle prism 1 is closer to the reflection / transmission surface 201a of the first right-angle prism 201 than the position of the predetermined distance L. The term “approaching” here includes both the case where it is not in contact and the case where it is in contact (contact).

  In the state shown in FIG. 1B, part of the light incident on the first right-angle prism 201 is reflected by the reflection / transmission surface 201 a, exits from the first right-angle prism 201, and travels toward the image sensor 103. Further, another part of the light incident on the first right-angle prism 201 is transmitted through the reflection / transmission surface 201 a and exits from the first right-angle prism 201, and the incident surface 1 a is incident on the second right-angle prism 1. Incident from. The light emitted from the second right-angle prism 1 passes through the eyepiece optical system 3 and reaches the eyes of the user (not shown). In this way, the object-side optical system portion 2 of the imaging optical system 101, the first and second right-angle prisms 201, 1 and the eyepiece optical system 3 are formed by light passing through (a part of) the imaging optical system 101. A TTL OVF (finder optical system) that enables observation of an optical image of an object is configured.

  Reference numeral 10 denotes a drive mechanism for moving the second right-angle prism 1 between the first position shown in FIG. 1A and the second position shown in FIG. 1B. The drive mechanism 10 is controlled by the system control unit 114. Specifically, the system control unit 114 moves the second right-angle prism 1 to the first position when using the EVF using the image sensor 103 (EVF mode) and when acquiring a recording image (main imaging). The drive mechanism 10 is controlled to be (or set). Further, during optical image observation using OVF (OVF mode), the drive mechanism 10 is controlled so as to move (or set) the second right-angle prism 1 to the second position.

  Even in the OVF mode, part of the light from the object travels to the image sensor 103, so that it is possible to use the EVF or perform main imaging.

  The second right-angle prism 1 is disposed in a region that is originally a dead space between the first right-angle prism 201 and the eyepiece optical system 3, and the first and second of the second right-angle prism 1 by the driving mechanism 10 are arranged. The amount of movement between positions is also small as will be described later. Therefore, a TTL OVF can be configured without impairing the thin characteristics of an imaging apparatus that employs a bending optical system as the imaging optical system 101 (while suppressing an increase in size).

  Next, the movement of the second right-angle prism 1 between the first and second positions causes the light from the object to be totally reflected by the first right-angle prism 201 (reflection / transmission surface 201a), and the reflection and transmission. The principle of switching between states will be described.

  When the second right-angle prism 1 is disposed at the first position and the incident surface 1a is separated from the reflection / transmission surface 201a of the first right-angle prism 201 by a predetermined distance L, the object incident on the reflection / transmission surface 201a The light from here causes total internal reflection. The EVF state is realized by guiding the totally reflected light to the image sensor 103.

  However, at this time, a slight oozing of light occurs on the reflection / transmission surface 201a. That is, an evanescent wave is slightly exuded from the medium (glass or resin) side of the first right-angle prism 201 to the back surface (air) side of the reflection / transmission surface 201a.

  For this reason, the second right-angle prism 1 is moved to the second position, and the reflection boundary surface (incident surface) of the second right-angle prism 1 which is another medium (glass or resin) from the back side to the reflection / transmission surface 201a. Close 1a). When the incident surface 1a comes closer to the reflection / transmission surface 201a than the range where the evanescent wave oozes, a part of the light incident on the reflection / transmission surface 201a is transmitted through the reflection / transmission surface 201a without being totally reflected. And proceed into the second right angle prism 1. This is a phenomenon called total reflection attenuation (FTIR). In the present embodiment, this FTIR is used to realize OVF.

  The range (distance) at which the evanescent wave exudes at the boundary surface from the medium (glass) I to the medium (air) II is calculated. When the refractive indexes of the medium I and the medium II are Np and Nair, the distance ξ at which the evanescent wave oozes into the medium II is

It can be expressed as. θ is the incident angle of light on the boundary surface, and λ is the wavelength of the light. This relationship is shown in FIG.

  Here, the refractive index of the medium I is Np = 1.5, the refractive index of the medium II is Nair = 1.0, the incident angle θ is 45 ° ± 2 °, and the wavelength λ is 380 to 780 nm which is the wavelength region of visible light. Then, ξ is in the range of about 150 nm to 580 nm. Accordingly, in the wavelength region of visible light, the incident surface 1a may be brought closer to a position where the distance is λ / 2 or less (more preferably λ / 4 or less) with respect to the reflection / transmission surface 201a.

  In order to enable efficient light guide into the second right-angle prism 1 by FTIR, the reflection / transmission surface 201a of the first right-angle prism 201 and the incident surface 1a of the second right-angle prism 1 are polished surfaces with high accuracy. It is good to do.

  In the state of FIG. 1B which is the OVF state, the light transmitted through the reflection / transmission surface 201a of the first right-angle prism 201 is in an incomplete image formation state only by the object side optical system portion of the imaging optical system 101. . Therefore, a combination with the eyepiece optical system 3 disposed behind the second right-angle prism 1 constitutes a finder optical system that can present an optical image in a good image formation state.

  For the imaging optical system 101 and the finder optical system, for example, the following optical configuration can be employed.

  (1) Of the imaging optical system 101, the object side optical system portion 2 has a negative refractive power, and the image plane side optical system portion (206) has a positive refractive power. A zoom optical system of a retrofocus type that performs zooming by moving a part of lenses constituting the image plane side optical system portion in the optical axis direction.

  (2) Other part of the lens constituting the image plane side optical system portion, and the lens arranged on the image pickup element side (image plane side) with respect to the zoom lens moves in the optical axis direction. A rear focus type that performs focusing.

  (3) The eyepiece optical system 3 has a positive refractive power, and constitutes an inverse Galileo type finder optical system in combination with the negative refractive power of the object side optical system portion 2 of the imaging optical system 101.

  Next, an example of the drive mechanism 10 will be described.

  The drive mechanism 10 has a biasing member such as a spring that biases the second right-angle prism 1 in the direction indicated by the arrow 4 in FIG. 1A, and a second right angle against the biasing force of the biasing member. And an actuator for returning the prism 1 from the position shown in FIG. 1B to the position shown in FIG. 1A. By releasing the holding of the second right-angle prism 1 by the actuator at the position shown in FIG. 1A, the second right-angle prism 1 is moved to the position shown in FIG. 1B by the urging force of the urging member.

  At this time, when the incident surface 1a of the second right-angle prism 1 is brought into close contact with the reflection / transmission surface 201a of the first right-angle prism 201, the light transmitted through the reflection / transmission surface 201a is reflected by the incident surface 1a. Without being incident on the second right-angle prism 1.

  However, by bringing the incident surface 1a into close contact with the reflection / transmission surface 201a, the incidence surface 1a and the reflection / transmission surface 201a are attracted to each other, and the drive mechanism 10 smoothly moves the second right-angle prism 1 to the position of FIG. 1B. It may hinder driving. In order to prevent this, a flexible member (elastic member) is interposed between the incident surface 1a and the reflective / transmissive surface 201a, and the incident surface 1a approaches the reflective / transmissive surface 201a while deforming the member. You may make it make it. Further, a frame-shaped thin film may be formed on at least one of the incident surface 1a and the reflective / transmissive surface 201a so that the incident surface 1a and the reflective / transmissive surface 201a are not in close contact with each other.

  The drive mechanism 10 only needs to realize a very small drive amount on the order of μm or less as the required drive amount (movement amount) between the first and second positions of the second right-angle prism 1. Further, the second right-angle prism 1 is simply pressed in the direction of the first right-angle prism 201 by the urging force and moved to the second position, or returned to the original position (first position) by the actuator. You just have to move. For this reason, there is no need for a complicated mechanism for obtaining a large driving amount, and high accuracy is not required for the driving amount.

  Next, the operation of the system control unit 114 of the imaging apparatus will be described using the flowchart shown in FIG. This operation is executed according to a computer program stored in a ROM (not shown) in the system control unit 114.

  First, in step S301, the system control unit 114 detects the state of a main switch (power switch) included in an operation unit (not shown). If the main switch is on, the process proceeds to step S302. If the main switch is off, the detection in step S301 is repeated.

  In step S302, the system control unit 114 checks the remaining capacity of the recording medium 110 through the recording circuit 111, and proceeds to step S304a if the remaining capacity is larger than the image data size determined by the image quality setting through the operation unit. If not, the process proceeds to step S303.

  In step S303, the system control unit 114 warns that the remaining capacity of the recording medium 110 is insufficient, and returns to step S301. The warning is performed by displaying a message on the display 112 or outputting sound from a sound output unit (not shown).

  In step S304a, the system control unit 114 determines whether the finder mode selected by the user on the operation unit is the EVF mode or the OVF mode. If it is the EVF mode, the process proceeds to step S304b, and if it is the OVF mode, the process proceeds to step S304c.

  In step S304b, the system control unit 114 sets the second right-angle prism 1 to the first position shown in FIG. 1A via the driving mechanism 10, and starts image display by EVF. The system control unit 114 temporarily stores images (frame images) sequentially generated using the image sensor 103 in the image memory 109, and displays the images sequentially read out from the image memory 109 on the display 112 through the display circuit 113. Thereby, the EVF moving image is displayed. Then, the process proceeds to step S305.

  In step S304c, the system control unit 114 sets the second right-angle prism 1 to the second position shown in FIG. 1B via the drive mechanism 10, and enables observation of an optical image by OVF. Then, the process jumps to step S306.

  In step S <b> 305, the system control unit 114 displays a plurality of predetermined focus detection areas so as to be superimposed on the EVF moving image displayed on the display 112.

  In step S306, the system control unit 114 checks the state of the release switch provided in the operation unit. If the release switch is half pressed, the system control unit 114 proceeds to step S308. Otherwise, the process proceeds to step S307. In step S307, the system control unit 114 checks the state of the main switch. If the main switch is on, the system control unit 114 returns to step S305, and otherwise returns to step S301.

  By half-pressing the release switch in step S306, the system control unit 114 detects (photometric) the subject brightness from the output of the A / D converter 105 in step S308, and performs an automatic exposure control operation (based on the photometric result). AE).

  Further, in step S310, the system control unit 114 performs an automatic focusing operation (AF) in the focus detection region selected by the system control unit 114 automatically or by the user through the operation unit among the plurality of focus detection regions. Do. This AF generates an AF evaluation value signal indicating the contrast state of an image from the output of the A / D converter 105, and moves the focus lens so as to search for a position where the AF evaluation value is maximized. Done in However, AF may be performed by other methods (phase difference detection method, external distance measurement method, etc.). When the subject brightness is lower than a predetermined value, the AF operation is performed in a state where an auxiliary light source (not shown) emits light and the AF auxiliary light is emitted toward the object.

  When the in-focus state is obtained, in step S311, the system control unit 114 checks whether or not the release switch is fully pressed. If fully depressed, the process proceeds to step S312a; otherwise, the process proceeds to step S316.

  In step S312a, the system control unit 114 determines whether or not the current finder mode is the OVF mode. If it is the OVF mode, the process proceeds to step S312b, and if not (the EVF mode), the process proceeds to step S313.

  In step S312b, the system control unit 114 moves the second right-angle prism 1 to the first position shown in FIG. 1A via the drive mechanism 10. Thereby, the light from the object is totally reflected by the reflection / transmission surface 201a of the first right-angle prism 201 and guided to the image sensor side, and a bright recording image can be obtained.

  In step S313, the system control unit 114 starts recording image acquisition processing (main imaging).

  In step S316, the system control unit 114 checks whether or not the release switch is half pressed. If it is half pressed, the process returns to step S311; otherwise, the process returns to step S305.

  In step S314, as in step S302, the system control unit 114 checks the remaining capacity of the recording medium 110, and if there is a remaining capacity necessary for recording the recording image acquired by the next main imaging, the process proceeds to step S315. . If the remaining capacity is insufficient, the process proceeds to step S303, and the above-described warning is given.

  In step S315, the system control unit 114 checks whether or not the release switch is fully pressed. If not fully depressed, the process proceeds to step S316. If it is fully pressed, the process proceeds to step S313, and the next main imaging is performed.

  In the above embodiment, the digital still camera that acquires a still image as a recording image has been described. However, another embodiment of the present invention includes a video camera that acquires a moving image as a recording image.

  Moreover, although the case where the right-angle prism is used as the first and second optical members has been described in the above embodiment, the shape of each optical member is not limited to this, and may have other shapes.

FIG. 3 is a cross-sectional view illustrating a configuration of an imaging optical system in a state where a second right-angle prism is in a first position in the imaging apparatus that is an embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating a configuration of an imaging optical system in a state where a second right-angle prism is in a second position in the imaging apparatus according to the embodiment. 1 is a block diagram illustrating a configuration of an imaging apparatus according to an embodiment. 6 is a flowchart illustrating the operation of the imaging apparatus according to the embodiment. The figure which shows the distance which the evanescent wave by a total reflection attenuation oozes out. Sectional drawing which shows the structure of the imaging optical system in the conventional imaging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 2nd right-angle prism 2 Object side optical system part 3 Eyepiece optical system 101 Imaging optical system 103 Image pick-up element 206 Image surface side optical system part

Claims (4)

A first optical member having a first surface;
A first position having a second surface, wherein the second surface is separated from the first surface, and a second position in which the second surface is closer to the first surface than the first position. A second optical member movable between and
With the second optical member in the first position, the light from the object is totally reflected by the first surface and guided to the image sensor,
While the second optical member is in the second position, a part of the light from the object is reflected by the first surface and guided to the imaging device, and the other part is the first and An imaging apparatus characterized by passing through a second surface and guiding it to an eyepiece optical system. When the wavelength of light from the object is λ,
The distance between the first and second surfaces is λ / 2 or less in a state where the second optical member is in the second position. Imaging device. A drive mechanism for moving the second optical member between the first and second positions;
The imaging apparatus according to claim 1, further comprising a control unit that controls the driving mechanism. A first optical system portion that constitutes an imaging optical system is disposed closer to the object side than the first optical member, and a second optical device that constitutes the imaging optical system closer to the imaging element than the first optical member. The system part is arranged,
2. A finder optical system is constituted by the first optical system portion, the first optical member, the second optical member at the second position, and the eyepiece optical system. 4. The imaging device according to any one of items 1 to 3.