JP2009210874A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus that improves efficiency in the auxiliary illumination of a subject and is capable of selective auxiliary illumination of the vicinity of the center of a screen on a subject regardless of the distance of the subject. <P>SOLUTION: The imaging apparatus includes: a first prism 301 that bends a photographing luminous flux 7 by a first rear reflecting face 307; a photographic-lens front group 2; a photographic-lens rear group 306; a second prism 1 having a second rear reflecting face 5 opposite the first rear reflecting face 307; and an auxiliary illuminating light source 3. The auxiliary illuminating light source 3 is disposed behind the second prism 1. Part of an auxiliary illuminating luminous flux 6 emitted, with the second prism 1 in close contact with the first prism 301, transmits through the second prism 1 and first prism 301 and consequently illuminates a subject. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging apparatus typified by a digital camera, and more particularly to an imaging apparatus characterized by an auxiliary illumination light source of an imaging optical system.

  In general, an imaging apparatus such as a digital camera may be forced to perform automatic focus adjustment in an environment where a sufficient amount of light from a subject cannot be obtained. In preparation for this, it is common to provide an auxiliary illumination light source for assisting automatic focusing (AF). The subject is illuminated with the illumination light beam from the auxiliary illumination light source, and the contrast information obtained from the subject is increased.

  The auxiliary illumination light source is used when it is completely dark and no contrast information can be obtained from the subject. In addition, the auxiliary illumination light source is slightly bright in the surroundings to obtain the contrast of the subject, but is also used when it is not sufficient.

  As an automatic focus adjustment mechanism that performs focus adjustment of an imaging optical system of a digital camera, a mechanism that performs focus adjustment using an image signal from an image sensor is known.

A known automatic focusing method called so-called hill-climbing (TV) AF or the like uses contrast information extracted from a subject image formed on an image sensor. The automatic focusing method is known as disclosed in Patent Documents 1 and 2 and the like, and thus detailed description thereof is omitted.
Japanese Patent Laid-Open No. 62-038083 JP-A-62-038406

  The auxiliary illumination light source for illuminating the subject is usually installed in the vicinity of the periphery of the photographing lens of the camera housing so as to project the auxiliary illumination light toward the subject. In rare cases, a strobe light source may be used as an auxiliary illumination light source, but in many cases, a dedicated auxiliary illumination light source is installed.

  If the direction in which the intensity peak of the photographing lens illumination light beam propagates is the optical axis of the auxiliary illumination light source, the auxiliary illumination light beam and the optical axis of the photographing lens are different. This is because the photographic lens and the auxiliary illumination light source are installed at different positions. For this reason, the following problems exist.

  First, AF operates within a predetermined area in the screen, but is basically effective in a range near the center of the screen.

  Therefore, due to the parallax between the auxiliary illumination light and the photographing lens, if the directivity of the auxiliary illumination light source is high, the center of the screen and the light intensity center of the auxiliary illumination light are shifted depending on the photographing distance, so that the illumination effect changes depending on the distance. In order to solve this, it is necessary to increase the diffusibility of the auxiliary illumination light source.

  As a result, the efficiency of illuminating the subject decreases with the same amount of light, the subject cannot be illuminated with a sufficient amount of light, and the AF assist effect itself decreases.

  Moreover, the effective distance that auxiliary illumination light reaches for the same reason is shortened. In order to solve this, the amount of light of the light source itself must be increased. However, since the problem of parallax remains, the shooting distance for effectively illuminating the range of the screen used for AF is limited.

  An object of the present invention is to provide an imaging apparatus capable of increasing the efficiency of auxiliary illumination of a subject and selectively selectively illuminating the vicinity of the center of the screen on the subject regardless of the subject distance.

  In order to achieve the above object, an imaging apparatus according to claim 1 is disposed in an optical path of a photographic light beam from a subject to an image sensor, and has a first prism that bends the photographic light beam by a first back surface reflecting surface. A photographing lens front group disposed on the subject side of the first prism and a photographing lens disposed at a position where the photographing light beam incident on the photographing lens front group and totally reflected by the first prism is incident. A rear lens group; a second prism having a second back surface reflecting surface facing the first back surface reflecting surface; and a second prism disposed behind the second prism, wherein the second prism is connected to the first prism. In the state of being close to the prism, a part of the emitted auxiliary illumination light beam passes through the second prism and the first prism and passes on the optical axis of the front lens group to illuminate the subject. Auxiliary illumination light source It is characterized in.

  According to the imaging apparatus of the present invention, it is possible to increase the efficiency of auxiliary illumination of a subject and selectively and selectively illuminate the vicinity of the center of the screen on the subject regardless of the subject distance.

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

  FIG. 1 is a block diagram of an imaging apparatus according to an embodiment of the present invention.

  In FIG. 1, an image pickup apparatus (digital camera) 100 includes an optical system 101 including a lens and a diaphragm, a mechanical shutter (shown as a mechanical shutter) 102, and an image pickup element 103 that is an image sensor such as a CCD or a CMOS.

  In addition, the imaging apparatus 100 includes a CDS circuit 104 that performs analog signal processing, an A / D converter 105 that converts an analog signal into a digital signal, and a signal that operates the imaging element 103, the CDS circuit 104, and the A / D converter 105. A timing signal generation circuit 106 is provided.

  In addition, the imaging apparatus 100 stores an optical system 101, a mechanical shutter 102, a drive circuit 107 for the imaging element 103, a signal processing circuit 108 that performs signal processing necessary for captured (captured) image data, and stores the signal-processed image data. An image memory 109 is provided.

  In addition, the imaging apparatus 100 includes an image recording medium 110 that is removable from the imaging apparatus 100, a recording circuit 111 that records signal-processed image data on the image recording medium 110, and an image display apparatus 112 that displays the signal-processed image data. Is provided.

  In addition, the imaging apparatus 100 includes a display circuit 113 that displays an image on the image display apparatus 112 and a system control unit 114 that controls the entire imaging apparatus.

  The system control unit 114 includes a non-volatile memory (ROM) 115 that stores a program describing a control method executed by the system control unit 114 and control data such as parameters and tables used when executing the program. Prepare. The nonvolatile memory (ROM) 115 also stores correction data such as a scratch address.

  Further, the system control unit 114 transfers and stores the program, control data, and correction data stored in the nonvolatile memory, and the volatile memory (when used by the system control unit 114 to control the imaging device 100). RAM) 116.

  Hereinafter, a photographing (imaging) operation using the mechanical shutter 102 using the imaging device 100 configured as described above will be described.

  Prior to the shooting operation, necessary programs, control data and correction data are transferred from the non-volatile memory 115 to the volatile memory 116 and stored at the start of the operation of the system control unit 114 such as when the imaging apparatus 100 is turned on. I shall keep it.

  These programs and data are used when the system control unit 114 controls the imaging apparatus 100, and additional programs and data are transferred from the nonvolatile memory 115 to the volatile memory 116 as necessary. Shall be used. Further, it is assumed that the system control unit 114 directly reads and uses data in the nonvolatile memory 115.

  First, the optical system 101 drives a diaphragm and a lens according to a control signal from the system control unit 114 to form a subject image set to an appropriate brightness on the image sensor 103.

  Next, the mechanical shutter 102 is driven by a control signal from the system control unit 114 so as to shield the image sensor 103 in accordance with the operation of the image sensor 103 so that a necessary exposure time is obtained.

  At this time, when the image sensor 103 has an electronic shutter function, it may be used together with the mechanical shutter 102 to ensure a necessary exposure time. The image sensor 103 is driven by a drive pulse based on an operation pulse generated by the timing signal generation circuit 106 controlled by the system control unit 114, converts the subject image into an electrical signal by photoelectric conversion, and outputs it as an analog image signal. To do.

  The analog image signal output from the image pickup device 3 is subjected to an operation pulse generated by the timing signal generation circuit 6 controlled by the system control unit 114, and the clock synchronization noise is removed by the CDS circuit 104, and an A / D converter is obtained. 5 is converted into a digital image signal.

  Next, the signal processing circuit 108 controlled by the system control unit 114 performs image processing such as color conversion, white balance, and gamma correction, resolution conversion processing, and image compression processing on the digital image signal.

  The image memory 109 is used for temporarily storing a digital image signal during signal processing and for storing image data that is a digital image signal subjected to signal processing.

  The image data signal-processed by the signal processing circuit 108 and the image data stored in the image memory 109 are converted into data suitable for the image recording medium 110 (for example, file system data having a hierarchical structure) by the recording circuit 111. Recording on the image recording medium 110.

  Alternatively, the image data is subjected to resolution conversion processing by the signal processing circuit 108, and then converted into a signal suitable for the image display device 112 (for example, an NTSC analog signal) by the display circuit 113, and the image display device 112. Is displayed.

  Here, the signal processing circuit 108 may output the digital image signal as it is as image data to the image memory 109 or the recording circuit 111 without performing signal processing by the control signal from the system control unit 114.

  Further, when requested by the system control unit 114, the signal processing circuit 108 outputs information on digital image signals and image data generated in the signal processing process to the system control unit 114. The information is, for example, information such as the spatial frequency of the image, the average value of the designated area, the data amount of the compressed image, or information extracted from them.

  Further, the recording circuit 111 outputs information such as the type and free capacity of the image recording medium 110 to the system control unit 114 when requested by the system control unit 114.

  Next, the reproduction operation when image data is recorded on the image recording medium 110 will be described.

  The recording circuit 111 reads image data from the image recording medium 110 by a control signal from the system control unit 114. Similarly, when the image data is a compressed image, the signal processing circuit 108 performs an image expansion process according to a control signal from the system control unit 114 and stores it in the image memory 9.

  The image data stored in the image memory 9 is subjected to resolution conversion processing by the signal processing circuit 108, converted to a signal suitable for the image display device 112 by the display circuit 113, and displayed on the image display device 112. .

  FIG. 2 is a flowchart showing a procedure of photographing processing executed by the imaging apparatus of FIG.

  This process is executed under the control of the system control unit 114 in FIG.

  In FIG. 2, first, in step S201, the system control unit 114 detects the state of a main switch (power switch) (not shown) included in the operation unit (not shown), and if it is on, the process proceeds to step S202.

  In step S202, the system control unit 114 checks the remaining capacity of the image recording medium 110 loaded in the recording circuit 111. If the remaining capacity is larger than the captured image data size determined from, for example, the image quality setting, the process proceeds to step S204. Otherwise, the process proceeds to step S203.

  In step S203, the system control unit 114 warns that the remaining capacity of the image recording medium 110 is insufficient, and returns to step S201. The warning can be performed by displaying a message on the image display device 112, outputting a sound from a sound output unit (not shown), or both.

  In step S <b> 204, the system control unit 114 displays a distance measurement area on the image display device 112. That is, in the display process in which the captured image is stored in the image memory 109 which is a temporary storage unit, and the display circuit 113 generates a display image and displays it on the image display device 112, it is set during normal shooting. The distance measurement area is also displayed.

  In step S205, the system control unit 114 checks the release state. If the release state is half-pressed, the system control unit 114 proceeds to step S207, otherwise proceeds to step S206. Here, the imaging apparatus 100 according to the present embodiment starts processing prior to the main photographing, such as an automatic focusing operation (AF) and an automatic exposure control operation (AE), by pressing the release halfway.

  In step S206, the state of the main switch is checked. If it is on, the process returns to step S204, and if not, the process returns to step S201.

  In step S <b> 207, the system control unit 114 detects subject brightness from the output of the A / D converter 105.

  Thereafter, in step S208, automatic focusing processing (AF processing) is performed. If the subject brightness is lower than the predetermined value from the detection result in step S207, the auxiliary illumination light source projects the auxiliary illumination light toward the subject for a predetermined time to perform the AF process.

  After focusing, in step S209, it is checked whether or not a release (not shown) is fully pressed. If it is fully pressed, the process proceeds to step S211. Otherwise, the process proceeds to step S210. In step S211, the photographing process is started by fully pressing the release.

  In step S210, it is checked whether the release is half-pressed. If the release is half-pressed, the process returns to step S209. Otherwise, the process returns to step S204.

  In step S212, as in step S202, the remaining capacity of the image recording medium 110 is checked. If there is a remaining capacity necessary for the next shooting, the process proceeds to step S213, and if not, the process proceeds to step S203.

  In step S213, it is checked whether the release is in the fully pressed state. If not, the process proceeds to step S210.

  FIG. 3 is a diagram showing a detailed configuration of the first embodiment of the optical system in FIG.

  The optical system 101 is an arrangement of two or more zoom mechanisms having a so-called front group concave and rear group convex power and having a retrofocus configuration, and has the following configuration.

  First, the basic configuration will be described.

  The first prism 301 is disposed in the optical path of the photographic light beam 7 from the subject to the image sensor 103, and bends the photographic light beam 7 by the back surface reflecting surface (first back surface reflecting surface) 307.

  The photographing lens front group 2 (photographing lenses 302 and 303) has a negative refractive power and is closer to the object side than the first prism 301 (bending mirror, back surface reflecting prism).

  The taking lens rear group 306 is located on the image side of the first prism 301, has a positive refractive power, and performs zooming and focusing from the wide-angle end to the telephoto end by movement.

  The photographing light beam 7 from the subject incident from the photographing lenses 302 and 303 enters the first prism 301 through the photographing lens front group 2. The photographing light beam 7 is bent by the first prism 301, enters the photographing lens rear group 306, and forms an image on the image sensor 103 through the filters 304 and 305.

  In this embodiment, the second prism 1, the auxiliary illumination light source 3, the urging mechanism (not shown), and the auxiliary illumination light source 3 are turned on on the back side (back surface 307 side) of the first prism 301. Means and their control means are newly added / arranged.

  Here, in the auxiliary illumination light source 3, a part of the emitted auxiliary illumination light beam 6 exits the second prism 1 and the first prism 301 in a state where the second prism 1 is brought close to the first prism 301. The light passes through and passes through the optical axis of the front lens group 2 to illuminate the subject. Illumination of the subject with the auxiliary illumination light beam 6 is performed when automatic focus adjustment is performed.

  In the first prism 301, in the prism and / or its cross section, the incident surface of the light beam and the surface from which the light beam reflected by the back surface reflecting surface 307 exits are isosceles, and the isosceles triangle having the back surface reflecting surface 307 as the base. This is a triangular prism shape.

  The second prism 1 arranged so that the back surface reflecting surface 307 of the first prism 301 faces the back surface reflecting surface (second back surface reflecting surface) 5 is smaller than the first prism 301. .

  The auxiliary illumination light source 6 causes the auxiliary illumination light beam 6 to enter the second prism 1 from behind the second prism 1. The auxiliary illumination light beam 6 undergoes total reflection at the back surface reflecting surface 5 of the second prism 1, and the traveling direction is bent at a substantially right angle.

  At this time, a slight oozing of the reflected light flux occurs on the back surface 5 of the second prism 1. That is, a reflected light beam (evanescent wave) slightly oozes out from the medium side (glass side) through the back surface reflecting surface 5 into the air on the back surface side (evanescent effect).

  In general, when a refraction boundary surface due to another transparent medium is close to the back side of the back surface reflecting surface 5 and approaches a range where the evanescent wave oozes from the back surface reflecting surface 5, one of the light flux components of the auxiliary illumination light beam 6 is obtained. The part does not reflect and goes straight into the medium behind. This is called FTIR (Frustrated Total Internal Reflection).

  At the boundary surface from the medium 1 to the medium 2, the evanescent wave seepage distance is calculated as follows.

  The respective refractive indexes are Np and Nair. When the refractive index of glass is Np = 1.5, the oozing distance ξ into the air (Nair = 1.0) is given by the following equation, where θ is the incident angle on the boundary surface and λ is the wavelength. This relationship is shown in FIG.

  FIG. 4 is a characteristic diagram showing the bleeding length of the evanescent wave at the boundary surface between the prism (glass) and air in FIG. 3 (1).

  When the incident angle θ is 45 ° ± 2 °, the auxiliary illumination light source 3 is a monochromatic LED, and the wavelength λ is 580 nm, ξ is in the range of about 260 nm. Accordingly, it is necessary to approach a distance of about λ / 2 or less in the visible range.

  In order to perform auxiliary illumination using this effect, the following configuration is adopted.

  The back reflecting surface 307 of the first prism 301 is a highly accurate polished surface, and the illumination light beam 7 is reflected back by this surface during photographing.

  When it is desired to project auxiliary illumination light, the second prism 1 is urged in the direction of a double-headed arrow 4 in the figure by a driving device (not shown). As a result, the second prism 1 is in close contact with the first prism 301 at the back surface reflecting surface 307 and the back surface reflecting surface 5 and satisfies the condition of FTIR.

  The auxiliary illumination light source 3 is turned on, and the auxiliary illumination light beam 6 that should be totally reflected by the back surface reflecting surface 5 of the second prism 1 is extracted into the first prism 301.

  The auxiliary illumination light beam 6 is given a converging power by an auxiliary lens included in the auxiliary illumination light source 3, but is combined with only the photographing lens front group 2 placed in front of the first prism 301 (subject side). Due to the power, the light beams become substantially parallel. The auxiliary illumination light beam 6 passes through the optical axis of the front lens group 2 and is projected onto the subject to illuminate the subject.

  Since the auxiliary illumination light beam 6 is always irradiated on the optical axis of the photographing lenses 302 and 303, only the portion corresponding to the vicinity of the center on the screen is illuminated regardless of the photographing distance. Further, the photographing light beam 7 reflected / scattered from the subject reaches the rear surface 307 of the first prism 301 via the photographing lenses 302 and 303.

  Since the back surface reflecting surface 307 is close to the pupils of the photographing lenses 302 and 303, the photographing light beam 7 passes through the effective portion of the back surface reflecting surface 307 here. At this time, since the back surface reflecting surface 5 of the second prism 1 is smaller than the effective diameter of the back surface reflecting surface 307, the photographic light beam 7 other than that transmitted through the auxiliary illumination light source 3 in the region outside the back surface reflecting surface 5 is Then, an image is formed on the image sensor 103 through the rear lens group 306 and the filters 304 and 305. TVAF and EVF can be displayed using the information of the photographing light beam 7.

  The second prism 1 is brought into an FTIR state by being brought into close contact with the first prism 301, and the light flux between the second prism 1 and the first prism 301 is separated by separating them to a predetermined distance. The passage of is blocked.

  However, in order to prevent inadvertent stray light, the auxiliary illumination light source 3 is turned off simultaneously with the release of the bias. At the time of image capture, if the energization of the second prism 1 to the second prism 1 by the driving device (not shown) is released, the photographing light beam 7 is immediately totally reflected in the first prism 301. The image is formed on the image sensor 103.

  In order to realize FTIR, it is only necessary to urge the second prism 1 in close contact with the first prism 301. If the urging is released, the optical path of the auxiliary illumination light source 3 becomes invalid. However, the second prism 1 may be attracted to the first prism 301.

  In order to prevent this, the second prism 1 on the movable side may be held by a flexible member, an elastic body, or the like. Alternatively, there is a technique in which a thin film is formed in a frame shape on the surface to which the first prism 301 and the second prism 1 are in close contact.

  Although it is a driving means (not shown), the required driving amount (moving amount) is on the order of μm or less, and since it is a very small amount, a large-scale device is not necessary. Further, since it is sufficient to simply press and hold, the accuracy of the driving distance is not required at all.

  Furthermore, it is only necessary to apply an urging force when making contact, and simply releasing the urging force as described above will leave the contact state without permission by elasticity etc. as described above. It is not necessary and may be controlled by one on / off system.

  In the present embodiment, when the wavelength of the auxiliary illumination light beam 6 is λ, the distance between the back surface 307 and the back surface 5 is the wavelength of the second prism 1 with respect to the first prism 301. It is close to λ until it becomes λ / 2 or less, and is separated until it exceeds λ / 2.

  Further, the auxiliary illumination light beam 6 is incident on the second prism 1 and then is incident on the back reflecting surface 5 under conditions that satisfy the total reflection condition.

  FIG. 5 is a characteristic diagram showing the bleeding length of the evanescent wave at the boundary surface between the prism (glass) and air in FIG. 3 (2).

  FIG. 5 shows bleeding into air (Nair = 1.0) when the wavelength is limited to 3 types and the refractive index of glass is Np = 1.5 in the range of 45 ° ± 2 °. This shows the extraction distance ξ. In this way, the oozing distance varies almost twice in the range of 45 ° ± 2 °.

  When a strong convergence / diffusion power is given to the auxiliary illumination light beam 6, the oozing at the boundary surface is different in the light beam, so that it is considered that intensity unevenness occurs in the auxiliary illumination light beam 6.

  In the second embodiment of the present invention, a thin film or the like is attached to the back surface reflecting surface 5 of the second prism 1 with a predetermined thickness, and a difference corresponding to the incident angle of light is given to the gap when closely attached. Thereby, even when the amount of oozing varies depending on the incident angle, it is possible to make the passage of the auxiliary illumination light beam 6 evenly close.

  FIG. 6 is a diagram showing a main configuration of the second embodiment of the optical system in FIG.

  In FIG. 6, a large step 20 is provided on the upper side of the thin film and a small step 21 is provided on the lower side, thereby causing an arbitrary difference in the distance between the two back reflecting surfaces 5 and 308 on the upper side and the lower side of the figure. It is.

It is a block diagram of the imaging device concerning an embodiment of the invention. 3 is a flowchart illustrating a procedure of imaging processing executed by the imaging apparatus of FIG. 1. It is a figure which shows the detailed structure of 1st Embodiment of the optical system in FIG. FIG. 4 is a characteristic diagram showing a bleeding length of an evanescent wave at a boundary surface between the prism (glass) and air in FIG. 3 (1). FIG. 4 is a characteristic diagram showing the bleeding length of the evanescent wave at the interface between the prism (glass) and air in FIG. 3 (2). It is a figure which shows the principal part structure of 2nd Embodiment of the optical system in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 2nd prism 2 Shooting lens front group 3 Auxiliary illumination light source 5 Back surface reflecting surface 6 Auxiliary illumination light beam 7 Photographing light beam 301 First prism 306 Shooting lens rear group 307 Back surface reflecting surface

Claims (7)

A first prism disposed in an optical path of a photographic light flux from a subject to an image sensor and bending the photographic light flux by a first back surface reflecting surface;
A taking lens front group disposed on the subject side of the first prism;
A photographic lens rear group disposed at a position where the photographic light beam incident on the photographic lens front group and totally reflected by the first prism is incident;
A second prism having a second back surface reflecting surface facing the first back surface reflecting surface;
A part of the auxiliary illumination light beam which is disposed behind the second prism and is made close to the first prism is partly emitted from the second prism and the first prism. An auxiliary illumination light source that passes through the optical axis of the front lens group and illuminates the subject.
An imaging apparatus comprising:   The imaging apparatus according to claim 1, wherein illumination of the auxiliary illumination light beam to the subject is performed when automatic focus adjustment is performed.   When the wavelength of the auxiliary illumination light beam is λ, the distance between the first back surface reflecting surface and the second back surface reflecting surface is the wavelength λ with respect to the first prism. The imaging apparatus according to claim 1, wherein the imaging device is close to λ / 2 or less and spaced apart to exceed λ / 2.   The imaging apparatus according to claim 1, wherein the auxiliary illumination light beam is incident on the second prism and then is incident on the second back reflecting surface under a condition that satisfies a total reflection condition.   When the second prism is brought close to the first prism, a part of the auxiliary illumination light beam is transmitted through the second back surface reflecting surface without being totally reflected. The imaging apparatus according to claim 2, wherein the imaging apparatus is incident on the first prism through a back surface reflecting surface.   When the second prism is brought close to the first prism, a part of the auxiliary illumination light beam transmitted through the second prism to the first prism again causes the second prism to pass through the second prism. The imaging apparatus according to claim 2, wherein when separated from the first prism, the second back surface reflecting surface causes total reflection again.   When the second back surface reflecting surface is brought close to the first back surface reflecting surface, a step for arbitrarily setting a distance between the second back surface reflecting surface and the first back surface reflecting surface is provided. The imaging apparatus according to claim 1, wherein the imaging apparatus is provided on the back surface of the second back surface.

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