JP2006080986A - Light receiving unit and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive light receiving unit with a high sensibility characteristic that a brightness shortage rarely occurs even if a high-speed shutter is used, and an imaging device suppressing increase in cost by deploying the inexpensive light receiving unit. <P>SOLUTION: A first prism 11a and a second prism 12a are laminated so that both surfaces are bonded. A dichroic mirror 13a is sandwiched between the bonded surfaces 11, and only G light is reflected by the dichroic mirror 13a. The reflection light (G light) is received by a first image pickup device 111a with a good sensibility. Thus, an inexpensive light receiving unit with a visibility characteristic similar to human eyes is composed, and an inexpensive light receiving unit 10a is deployed in the imaging device. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a two-plate type light receiving unit and a photographing apparatus including the light receiving unit.

  When receiving a subject light and displaying a color image based on the subject light, the subject light is separated into R, G, and B colors, which are the three primary colors of light, and image signals corresponding to the respective colors are created. Then, the color image is displayed on the display screen by driving each of the elements corresponding to R, G, and B, which are two-dimensionally arranged on the display screen, with their image signals.

  When separating the subject light into the three primary colors of R, G, and B, a single-plate type light receiving unit arranges R, G, and B filters for color spectroscopy in order on the light receiving surface of one image sensor. In a three-plate type light receiving unit, a spectral color separation mirror (a dichroic mirror, which is one of the color separation mirrors is often used) will be placed in front of each of the three image sensors. (For example, refer to Patent Documents 1 and 2).

  The single-plate type light receiving unit uses the R, G, and B color filters to separate colors, and thus has the disadvantage that the sensitivity of the image sensor is reduced due to transmission loss in the color filters. Since the structure is simple, it is often used for digital cameras, etc. The latter multi-plate type has the disadvantage that the number of parts increases and the structure becomes complicated, resulting in a slight increase in cost. A high-sensitivity image signal can be obtained by forming an image of a subject on an image sensor using a dichroic mirror without using it, so that it is used in a broadcast camera or the like.

  Further, the spectral components (R light, G light, and B light) that pass through the dichroic mirror and reach the light receiving surfaces of the three image sensors are received by the light receiving surfaces of the image sensors with high sensitivity. In some cases, the light receiving sensitivity is increased by forming an antireflection film for preventing reflection of R light, G light, and B light on each light receiving surface (see, for example, Patent Document 3).

By the way, in an imaging apparatus equipped with a single-plate type light receiving unit, when shooting is performed using a high-speed shutter, there is a case where insufficient brightness occurs due to insufficient exposure time due to a decrease in sensitivity of the imaging device. Therefore, it is considered to use a three-plate type with higher sensitivity than a single-plate type in place of the single-plate type light-receiving unit so that a sufficient amount of light is given to the light-receiving surface of the image sensor even if a high-speed shutter is used. It is done. However, the use of a three-plate type light receiving unit increases the cost.
Japanese Patent Laid-Open No. 6-281881 JP 2000-201290 A JP 2003-309858 A

  In view of the above circumstances, the present invention provides a low-cost light receiving unit having high sensitivity characteristics that is unlikely to cause insufficient brightness even when a high-speed shutter is used, and photographing with reduced cost by providing the low-cost light receiving unit. An object is to provide an apparatus.

The light receiving unit of the present invention that achieves the above object includes a dichroic mirror that separates incident light into reflected light in the green wavelength band and transmitted light in the red wavelength band and blue wavelength band;
A first imaging element that receives reflected light from the dichroic mirror and generates a green image signal;
And a second imaging device that receives light transmitted through the dichroic mirror in a red wavelength band and a blue wavelength band.

  As is well known, the subject light is composed of visible light having a wavelength between about 4000 mm and about 7500 mm, and light in the green wavelength band of about 5500 mm of the visible light has the highest visual sensitivity. It is said that it becomes.

  Therefore, in the light receiving unit of the present invention, only the light in the green wavelength band, which is said to be the light with the highest visibility of the human eye, is separated by the dichroic mirror, so that the visibility characteristics of the human eye I am trying to construct a light receiving unit with characteristics close to.

  In the above configuration, since only the light in the green wavelength band is separated, if the light is received by the first image sensor as it is, there is no need to transmit the color filter, so the light in the green wavelength band is highly sensitive. It can receive light. Since the light in the green wavelength band has the highest visibility, the light in the red wavelength band and the light in the blue wavelength band received by the second image sensor are added based on the light in the green wavelength band. If mixed, a light receiving unit close to the characteristics of visibility seen by human eyes can be configured.

  Therefore, according to the above light receiving unit, a highly sensitive light receiving unit that compensates for the decrease in sensitivity that is a defect of the single plate type and suppresses the high cost that is a defect of the three plate type is realized. As a result, it is possible to realize a light receiving unit that is unlikely to have insufficient luminance even when a high-speed shutter is used as in the conventional single-plate type, and that is much cheaper than using a three-plate type.

  It is also well known that a luminance signal can be obtained by integrating the light from the blue wavelength band having a short wavelength to the light in the red wavelength band having a long wavelength over all wavelengths. If the sensitivity of light in the wavelength band is high, the contribution ratio of light in the red wavelength band and light in the blue wavelength band may be reduced in integration, and integration may be performed only in the wavelength range of the light in the green wavelength band. It can be treated as if the same integrated value was obtained as when almost the whole was integrated. That is, the image signal generated by the first image sensor can be handled as a luminance signal. Then, even if only the image signal generated by the first image sensor is used as the luminance signal, accurate distance measurement can be performed.

  Here, it is preferable that the first image sensor is a CMOS image sensor.

  Thus, when the first image sensor is a CMOS image sensor, pixels in various regions can be read independently. Then, multipoint ranging can be performed based on the image signal generated by the first image sensor, and it is maximally possible that the image signal generated by the first image sensor can be handled as a luminance signal. To be used.

  By disposing such a light receiving unit in the photographing apparatus, it is possible to realize a photographing apparatus having a high-precision ranging function as well as high sensitivity and high resolution characteristics similar to those of a three-plate type. In addition, since the light receiving unit is inexpensive as described above, an increase in the cost of the photographing apparatus is suppressed by providing the inexpensive light receiving unit in the photographing apparatus.

In this way, in the case where the light receiving unit of the present invention is arranged in the photographing apparatus so as to suppress the cost increase,
An imaging device that includes an imaging optical system and that captures subject light incident via the imaging optical system and generates an image signal,
A dichroic mirror that separates the subject light incident via the above-mentioned photographing optical system into a reflected subject light in the green wavelength band and a transmitted subject light in the red wavelength band and the blue wavelength band, and receives the reflected subject light for green And a light receiving unit having a second image sensor that receives the transmitted subject light and generates a red image signal and a blue image signal. And

  Here, it is preferable that the first imaging device is a CMOS imaging device, preferably including a distance measuring device that adjusts the focus of the photographing optical system based on an image signal obtained by the first imaging device. It is desirable to be.

  Further, the distance measuring device reads out only the partial image signal corresponding to one or a plurality of partial areas of the light receiving area of the subject light of the CMOS image sensor from the CMOS image sensor, and performs the photographing based on the partial image signal. It is preferable to adjust the focus of the optical system.

  In addition, the photographing apparatus includes a camera head having the photographing optical system and the light receiving unit, and a camera body on which the camera head is detachably attached to receive an image signal from the camera head and perform signal processing. It may be a photographing device, and the camera head may include a distance measuring device that adjusts the focus of the photographing optical system based on an image signal obtained by the first image sensor.

   As described above, there is provided an inexpensive light receiving unit having a high sensitivity characteristic that is unlikely to cause insufficient luminance even when a high-speed shutter is used, and an imaging device that suppresses cost increase by providing the inexpensive light receiving unit. Realized.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a view showing a light receiving unit according to an embodiment of the present invention.

  The light receiving unit 10a shown in FIG. 1 is provided with two prisms 11a and 12a that are polyhedrons, and one surface 1101a of the polyhedral surfaces of one prism 11a and one surface 122a of the polyhedral surfaces of the other prism 12a. Are bonded together. In this embodiment, when separating incident light into light in the green wavelength band (hereinafter referred to as G light), light in the red wavelength band (hereinafter referred to as R light), and light in the blue wavelength band (hereinafter referred to as B light), G A dichroic mirror 13a that reflects light and transmits R light and B light is sandwiched between the two prisms 11a and 12a so that the surfaces of the two prisms 11a and 12a are bonded to each other.

  Here, the operation of the dichroic mirror 13a and the two prisms 11a and 12a will be described.

The dichroic mirror 13a is coated with a reflective film that reflects G light. When incident light incident on the incident surface 110a of the first prism 11a travels through the prism and reaches the dichroic mirror 13a, Only the G light in the incident light is reflected on the surface of the dichroic mirror 13a. The G light reflected by the dichroic mirror 13a starts to reverse and approaches the incident surface from a direction opposite to the incident light. In the present embodiment, when the light traveling backward from the joint surface 1101a side where the prisms 11a and 12a are joined to the incident surface side reaches the incident surface 110a, the air layer is such that total reflection occurs at the incident surface 110a. The angle of the joint surface 1101a and the angle of the incident surface 110a are set based on the refractive index (n _air ) and the refractive index (n _p1 ) of the first prism. For this reason, the G light traveling backward to the incident surface 110a is totally reflected by the incident surface 110a. The first image sensor 111a is provided in the traveling direction of the G light totally reflected on the incident surface, and the G light is received by the first image sensor 111a.

Further, the transmitted light (R light, B light) other than the G light transmitted through the dichroic mirror 13a is reflected by the mirror 123a formed at the end of the other prism 12a and travels backward toward the bonding surface. Get started. In the same manner as before, the angle of the mirror 123a and the joint surface 122a are based on the refractive index (n _p2 ) of the second prism 12a and the refractive index (n _d1 ) of the dichroic mirror 13a so that total reflection occurs at the joint surface 122a. Therefore, the R light and B light incident on the joint surface 122a are totally reflected and received by the second image sensor 121a. Since R filters and B filters are alternately arranged on the surface of the second image sensor 121a, R light and G light are separately received by these filters.

  As described above, the G light that is the reflected light of the dichroic mirror 13a is received by the first image sensor 111a, and the transmitted light of the dichroic mirror 13a is red by the filter disposed on the surface of the second image sensor 121a. R light that is light in the wavelength band and B light that is light in the blue wavelength band are received separately.

  With such a configuration, when the G light is received with high sensitivity by the first image sensor, the G light has a high sensitivity characteristic as in the conventional three-plate type, and the amount of one plate is small. A cheaper light receiving unit is realized.

  By providing such an inexpensive light receiving unit, it is possible to suppress an increase in the cost of the photographing apparatus.

  FIG. 2 is a diagram showing a camera system in which a camera head is detachably attached to a camera body as an example of a photographing apparatus.

  FIG. 2 shows a camera head 1a having a photographic optical system and an image sensor, and a camera body 1b to which the camera head 1a is detachably attached and receives an image signal from the camera head 1a and performs signal processing. Yes. In this example, the light receiving unit 10a of FIG. 1 is provided in the camera head 1a, and a distance measuring device using the first image sensor 111a of the light receiving unit 10a is provided. The configuration of this distance measuring device will be described later.

  Here, the external structure of the camera head and the camera body constituting this camera system will be briefly described.

  In the center of the camera body 1b, a head mount 10b having a large number of mount contacts is provided. A similar mount portion is also formed on the camera head 1a side, and when the camera head 1a is mounted on the camera body 1b along the alternate long and short dash line in the drawing so that the positions of both mount contacts match, The mount contacts are connected to each other, and the camera head 1a and the camera body 1b are electrically connected.

  Each of the mount contacts is assigned for communication and power supply, and communication from the camera body 1b to the camera head 1a is performed, or from the camera head 1a to the camera body 1b. In addition, power is supplied from the camera body 1b side to the camera head 1a side.

  An AWB sensor 11b is provided above the head mount 10b, and a light source type at the time of photographing is detected by the AWB sensor 11b. The light source type is, for example, whether it is sunlight or a fluorescent lamp. When this light source type is detected by the AWB sensor 11b, an appropriate color temperature is set in a digital signal processing unit described later. Optimal white balance adjustment. A flash light emission window 12b is provided beside the AWB sensor 11b, and a flash light emission device that emits flash light through the flash light emission window 12b is provided in the camera body 1b. Further, a release button 13b and a mode dial 14b are provided on the upper surface of the camera body 1b. The mode dial 14b selects a shooting mode and a playback mode. In the shooting mode, a still image shooting mode or a moving image shooting mode is further selected. In FIG. 1, one of a plurality of camera heads is shown as an example, and one of a plurality of main bodies is shown as an example.

  Here, an internal configuration of the camera head 1a will be described with reference to FIG.

  FIG. 3 is a block diagram showing the internal configuration of the camera head 1a.

  FIG. 3 shows the light receiving unit 10a described in FIG. 1 and the distance measuring device 100 using the first image sensor 111a provided in the light receiving unit 10a and the focus lens 118a in the photographing optical system. The photographing optical system is provided with a photographing lens including the focus lens, and further provided with a diaphragm. Although not shown, an interface for supplying image signals output from the CCD imaging processing circuit 119a and the COMS imaging circuit 112a to the camera body 1b is also provided. The interface is also provided on the camera body 1b side, and an image signal is received by the camera body 1b through the interface, and signal processing is performed by a signal processing unit in the camera body 1b. An image based on the image signal subjected to signal processing on the camera body side is displayed on a display screen or recorded on a recording medium.

  Here, the configuration of the distance measuring device 100 in the camera head 1a will be described.

  The distance measuring apparatus 100 shown in FIG. 3 has an arithmetic processing circuit 115a and a first imaging element 111a that supplies the arithmetic processing circuit 115a with an image signal for calculating contrast using the arithmetic processing circuit 115a as a control means. , A CMOS imaging circuit 112a, a BPF (abbreviation of Band Pass Filter) circuit 113a, an A / D conversion circuit 114a, and a motor drive circuit 116a for driving the focusing motor 117a in accordance with an instruction from the arithmetic circuit 115a. ing.

  In operating the distance measuring apparatus 100, first, the arithmetic processing circuit 115a issues an instruction to the motor drive circuit 116a, and the focusing lens 117a in the photographing optical system is associated with the focusing motor 117a corresponding to the closest point of the subject distance. Driving along the optical axis from the position to the position corresponding to the farthest point. The arithmetic processing circuit 115a supplies a timing signal at every predetermined time from the CMOS image pickup circuit 112a to the CMOS image pickup device 11a as the first image pickup device while driving the focus lens 108a. An instruction is issued, and an image signal for green is output from the CMOS image sensor 111a to the CMOS image sensor circuit 112a at a predetermined time according to the timing signal. The CMOS image pickup circuit 112a receives the green image signal and further supplies the green image signal to the BPF circuit 113a in order to remove noise on the green image signal. The BPF 113a receives the green image signal and removes an image signal based on light in a wavelength band other than the green wavelength band included in the green image signal as an unnecessary signal, and for high purity green use. An image signal is generated, supplied to the A / D conversion circuit 114a, and further supplied to the arithmetic processing circuit 115a. The arithmetic processing circuit 115a calculates the luminance ratio between the subject and the background, that is, the scene, as the contrast based on the green image signal, and the contrast is assumed that the subject is located where the contrast appears most greatly. AF (Auto Focus) calculation is performed. In this way, the position where the focus lens 108a should be driven is calculated by the arithmetic processing circuit 115a. FIG. 3 shows that the contrast AF calculation is performed by the arithmetic processing circuit 115a in a block manner in order to show that the arithmetic processing circuit 115a performs the contrast AF calculation.

  When the position of the subject (subject distance) captured by the photographic lens including the focus lens is obtained from the image signal obtained at every predetermined time by this contrast AF calculation, the focus position corresponding to the obtained subject distance is focused. The lens drive position is determined and an instruction is given to the motor drive circuit 116a to drive to the focus position, and the focus lens 107a is placed at the drive position by the focusing motor 107a.

  In the present embodiment, a COMS image pickup device is used as the first image pickup device 111a. However, in this CMOS image pickup device 111a, the CCD image pickup device has to read out for each line, but separately for each partial region. Can be read out. For this reason, not only ranging at the center of the subject but also multipoint ranging using a plurality of partial areas within the light receiving area can be performed.

  FIG. 4 is a diagram illustrating a light receiving region of the CMOS image sensor 111a which is the first image sensor.

  As shown in FIG. 4, a plurality of partial areas 1111a to 1117a are set in the light receiving area 1110a of the subject light of the CMOS image sensor 111a. From these partial areas 1111a to 1117a, only partial image signals (G light) corresponding to those partial areas can be read, and the focus adjustment of the photographing optical system can be performed based on the partial image signals.

  When a partial image signal for green is read from each of these partial areas and multipoint distance measurement is performed on the basis of these partial image signals by an arithmetic processing circuit, for example, an object in which two people are separated from each other is displayed. It is possible to prevent the distance measuring device 100 from focusing on the center of two persons who are lined up apart, that is, at infinity when shooting with the imaging device of FIG.

  As described above, since the first image sensor is very sensitive, a light receiving unit that is unlikely to cause insufficient luminance even when a high-speed shutter is used is realized. In addition, an imaging device with a reduced cost can be realized by providing the imaging device with a light receiving unit that is less expensive than the three-plate type light receiving unit.

  Further, in order to make the thickness in the optical axis direction as thin as possible, the two prisms are bonded together as shown in FIG. 3. However, as shown in FIG. 5, the configuration is further simplified, and the cost of the light receiving unit can be further reduced.

  FIG. 5 is a diagram showing another embodiment of the light receiving unit shown in FIG.

  As shown in FIG. 5, when the two prisms 21a and 22a are bonded together, the thickness in the optical axis direction is slightly thicker than that in FIG. 3, but the structure is simplified and the cost is further reduced. Can be achieved. If the thickness in the direction of the optical axis may be slightly increased, such a configuration can further reduce the cost of the light receiving unit, and thus the photographing apparatus.

It is a figure which shows the light reception unit which is one Embodiment of this invention. It is a figure which shows the external appearance of the imaging device provided with the camera head by which the light reception unit of this invention was arrange | positioned, and the camera main body. It is a block diagram which shows the structure of the ranging apparatus arrange | positioned in the camera head. It is a figure explaining operation | movement in the case of performing multipoint ranging in many partial area | regions. It is a figure which shows another embodiment of a light-receiving unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Camera system 1a Camera head 10a Light receiving unit 11a 1st prism 110a Incident surface 111a 1st image sensor (CMOS type image sensor)
1110a Light receiving area 1111a to 1117a Partial area 12a Second prism 120a Second image sensor (CCD type image sensor)
13a Dichroic mirror 1b Camera body 10b Head mount 11b AWB sensor 12b Flash emission window 13b Shutter button 14b Mode dial 100 Ranging device 112a CMOS imaging circuit 113a BPF circuit 114a A / D conversion circuit 115a Arithmetic processing circuit 116a Motor drive circuit 117a Focusing motor 118a Focus lens

Claims (8)

A color separation mirror that separates incident light into reflected light in the green wavelength band and transmitted light in the red and blue wavelength bands;
A first image sensor that receives reflected light of the color separation mirror and generates a green image signal;
And a second imaging device that receives the transmitted light of the color separation mirror in a red wavelength band and a blue wavelength band and generates a red image signal and a blue image signal. Light receiving unit.   The light receiving unit according to claim 1, wherein the first image sensor is a CMOS image sensor. In an imaging device that includes an imaging optical system and generates an image signal by capturing subject light incident via the imaging optical system,
A color separation mirror that separates subject light incident through the photographing optical system into reflected subject light in the green wavelength band and transmitted subject light in the red wavelength band and the blue wavelength band, and receives the reflected subject light in green A first image sensor for generating an image signal for use, and a second image sensor for receiving the transmitted subject light separately in a red wavelength band and a blue wavelength band to generate an image signal for red and an image signal for blue An imaging apparatus comprising a light receiving unit having an imaging element.   The photographing apparatus according to claim 3, further comprising a distance measuring device that performs focus adjustment of the photographing optical system based on an image signal obtained by the first image pickup device.   The imaging apparatus according to claim 3, wherein the first image sensor is a CMOS image sensor.   The distance measuring device reads out only the partial image signal corresponding to one or a plurality of partial areas of the light receiving area of the subject light of the CMOS image sensor from the CMOS image sensor, and the photographing optical based on the partial image signal 4. The photographing apparatus according to claim 3, wherein the focus adjustment of the system is performed.   This photographing apparatus includes a camera head having the photographing optical system and the light receiving unit, and a camera body on which the camera head is detachably mounted and receives an image signal from the camera head and performs signal processing. The photographing apparatus according to claim 3, wherein   8. The photographing apparatus according to claim 7, wherein the camera head includes a distance measuring device that performs focus adjustment of the photographing optical system based on an image signal obtained by the first image sensor. .

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