Abstract:
The present invention provides an imaging device including a photographic optical system having a zoom function, an auxiliary light irradiation device which includes an auxiliary light source emitting auxiliary light and which irradiates the auxiliary light towards a subject, a range finding device which makes the auxiliary light reflected by the subject incident on the photographic optical system to perform a focusing operation, and an auxiliary light control device which controls at least one of emitted light quantity of the auxiliary light and irradiation range of the auxiliary light in accordance with a zoom position of the photographic optical system.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an imaging device, and more particularly to an imaging device which performs a focusing operation (AF) by irradiating a subject with auxiliary light. 
     2. Description of the Related Art 
     Conventionally, cameras provided with the autofocus (AF) function include those which perform the AF function by irradiating a subject with auxiliary light (AF auxiliary light) to photograph a dark object. As an example capable of changing an irradiation angle when irradiating the AF auxiliary light, there has been proposed an electronic flash light device described in the Japanese Patent Application Laid-Open No. 2003-156783. 
     In the camera having a zoom function, the photographing range (visual field) and the F value of a lens are changed in accordance with a zoom position of the taking lens. For this reason, depending on the zoom position of the taking lens, light quantity of the AF auxiliary light and the like becomes insufficient to cause a problem that the precision of AF is deteriorated. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above described circumstance. An object of the invention is to provide an imaging device capable of improving the precision of AF by appropriately controlling the AF auxiliary light. 
     In order to achieve the above described object, according to the present invention, there is provided an imaging device comprising: a photographic optical system having a zoom function, an auxiliary light irradiation device which includes an auxiliary light source emitting an auxiliary light and which irradiates the auxiliary light to a subject; a range finding device which makes the auxiliary light reflected by the subject incident on the photographic optical system to perform focusing operation; and an auxiliary light control device which controls at least one of emitted light quantity of the auxiliary light and irradiation range of the auxiliary light in accordance with a zoom position of the photographic optical system. 
     The imaging device according to the present invention is arranged to control the emitted light quantity and irradiation range of the auxiliary light (AF auxiliary light) at the time of automatic focusing (AF) depending on a zoom position of the photographic optical system, so that the precision of AF can be improved. 
     The above described imaging device according to the present invention may comprise an applied voltage change device which changes a power supply voltage applied to the auxiliary light source in accordance with the zoom position of the photographic optical system. In this example, the control of emitted light quantity of the auxiliary light is performed by changing the applied voltage applied to the auxiliary light source. 
     The above described imaging device according to the present invention may comprise a current quantity control device which controls the quantity of current flowing through the auxiliary light irradiation device in accordance with the zoom position of the photographic optical system. In this example, the control of emitted light quantity of the auxiliary light is performed by changing the quantity of current flowing through the auxiliary light source. 
     In the above described imaging device according to the present invention, the auxiliary light irradiation device includes a plurality of auxiliary light sources, and the auxiliary light control device may comprise a lighting light source number change device which changes the number of the auxiliary light sources that are turned on in accordance with the zoom position of the photographic optical system. In this example, the control of emitted light quantity of the auxiliary light is performed by changing the number of lighted auxiliary light sources. 
     In the above described imaging device according to the present invention, the auxiliary light irradiation device may comprise a plurality of irradiation lenses irradiating the auxiliary light irradiated from the auxiliary light source to the subject, and the auxiliary light control device may be arranged to control the irradiation range of the auxiliary light by exchanging or combining the plurality of irradiation lenses. In this example, the control of irradiation range of the auxiliary light is performed by changing the combination of the irradiation lenses for irradiating the auxiliary light. 
     According to the present invention, the emitted light quantity and the irradiation range of the auxiliary light (AF auxiliary light) at the time of automatic focusing (AF) are arranged to be controlled in accordance with the zoom position of the photographic optical system, so that the precision of AF can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of an imaging device according to an embodiment of the present invention; 
         FIG. 2  is a block diagram showing an internal structure of a digital camera  10 ; 
         FIG. 3  is a circuit diagram showing an exemplary configuration of an AF auxiliary light emission circuit; 
         FIG. 4  is a plan view showing an AF auxiliary light irradiation lens; 
         FIG. 5  is a figure schematically showing a method for controlling an irradiation range of AF auxiliary light; 
         FIG. 6  is a figure schematically showing another example of the method for controlling the irradiation range of AF auxiliary light; 
         FIG. 7  is a flow chart showing a process flow of AF auxiliary light control at the time of photographing; 
         FIG. 8  is a flow chart showing a method for controlling emitted light quantity of AF auxiliary light; 
         FIG. 9  is a flow chart showing a method for controlling the irradiation range of AF auxiliary light; 
         FIG. 10  is a circuit diagram showing a second exemplary configuration of the AF auxiliary light emission circuit; 
         FIG. 11  is a flow chart showing a method for controlling emitted light quantity of AF auxiliary light, in which method the AF auxiliary light emission circuit according to the second exemplary configuration is used; 
         FIG. 12  is a circuit diagram showing a third exemplary configuration of the AF auxiliary light emission circuit; and 
         FIG. 13  is a flow chart showing a method for controlling emitted light quantity of AF auxiliary light, in which method the AF auxiliary light emission circuit according to the third exemplary configuration is used. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, preferred embodiments according to the present invention will be described with reference to accompanying drawings.  FIG. 1  is a front view of an imaging device according to an embodiment of the present invention. An imaging device  10  shown in  FIG. 1  is a digital camera, on the front surface of which a taking lens  12 , an optical finder  14 , an electronic flash light  16  and an AF auxiliary light lamp  18  are exposed. Noted that reference numeral  20  in  FIG. 1  designates a release switch. 
       FIG. 2  is a block diagram showing an internal structure of the digital camera  10 . As shown in  FIG. 2 , a CPU  30  is connected with each block of the digital camera  10  via a bus  32 , and integrally controls each of the blocks on the basis of an operational input from an operation switch  34 . 
     The operation switch  34  comprises the above described release switch  20 . The release switch  20  is constituted in two steps, in which a S 1 =ON signal is generated by “half-depressing”, and a S 2 =ON signal is generated by “full-depressing”. The S 1 =ON signal and the S 2 =ON signal which are generated are inputted to the CPU  30  which detects the depressed state of the release switch  20  on the basis of the SI=ON signal and the S 2 =ON signal. 
     A control program of the camera, various kinds of setting data necessary for the control and the like are stored in an EEPROM  36 . A power supply circuit  37  supplies power to each block of the digital camera  10 . 
     The electronic flash light  16  is subjected to light emission control by an electronic flash light emission circuit  38  on the basis of an electronic flash light emission instruction from the CPU  30 . 
     The AF auxiliary light lamp  18  is constituted by, for example, an LED lamp. An AF auxiliary light emission control circuit  40  is controlled by the light emission instruction from the CPU  30  based on a zoom position of the taking lens  12 , so as to perform light emission control on the emitted light quantity of the AF auxiliary light lamp  18 . The region (irradiation range) irradiated by the AF auxiliary light is controlled by an AF auxiliary light irradiation lens  42  in accordance with the light emission instruction from the CPU  30  based on the zoom position of the taking lens  12 . The AF auxiliary light irradiation lens  42  is controlled by an AF auxiliary light irradiation lens control circuit  44  on the basis of an instruction from the CPU  30 . Noted that the method for controlling the emitted light quantity and irradiation range of the AF auxiliary light will be described below. 
     The digital camera  10  comprises, as an image pickup device, the taking lens  12 , an iris (diaphragm)  48  and an image sensor (CCD)  50 . 
     Focusing of the taking lens  12  is performed by moving a focus lens constituting the taking lens  12  by a focus motor  52 , while zooming is performed by moving a zoom lens constituting the taking lens  12  by a zoom motor  54 . The focus motor  52  and the zoom motor  54  are driven and controlled by a focus motor driver  56  and a zoom motor driver  58 , respectively. The CPU  30  outputs control signals to the focus motor driver  56  and the zoom motor driver  58  to control the drivers. 
     The diaphragm  48  is constituted by a so-called turret type diaphragm, which changes the diaphragm value (F value) by rotating a turret plate perforated with holes of F 2.8 and F8. The diaphragm  48  is driven by an iris motor  60 . The iris motor  60  is driven and controlled by an iris motor driver  62 . The CPU  30  outputs a control signal to the iris motor driver  62  to control the driver. 
     The image light from the subject is formed into an image on a light receiving surface of the CCD  50  via the taking lens  12  and the diaphragm  48 . A number of photosensors are arranged on the light receiving surface of the CCD  50 , and the optical image of the subject formed on the light receiving surface is converted by each of the photosensors into signal charges corresponding to the incident light. The signal charges stored in each of the photosensors are successively read in accordance with timing pulses fed by a timing generator (TG)  51 , and are outputted to an analog signal processing circuit  64  as voltage signals corresponding to the signal charges. 
     Noted that the CCD  50  is provided with the charge sweeping drain, and the storage time (shutter speed) of the signal charges stored in each of the photosensors is controlled by making the signal charges stored in each of the photosensors swept out to the charge sweeping drain. 
     The analog signal processing circuit  64  includes a correlated double sampling processing circuit (CDS) and an amplifier (AMP). The voltage signals successively read out from the CCD  50 , which are R, G, B signals corresponding to each pixel, are sampled, held and amplified by the analog signal processing circuit  64  so as to be inputted to an A/D converter  66 . 
     The A/D converter  66  converts the successively inputted analog R, G, B signals into digital R, G, B signals and outputs the digital R, G, B signals, which are then temporarily stored in a memory (SDRAM)  70  via an image input controller  68 . The R, G, B signals are then outputted to an image signal processing circuit  72  from the SDRAM  70 . 
     The image signal processing circuit  72  applies predetermined signal processing such as gain control processing including offset processing, white balance correction, sensitivity correction, gamma correction processing and the like, to the inputted image signal, and outputs image data after the signal processing to a VRAM  74 . 
     The VRAM  74  includes an area A and an area B in which the image data for one frame portion can be stored respectively, and the image data for one frame portion are rewritten alternately in the area A and the area B. Then, the rewritten image data are alternately read out. 
     The image data read out from the VRAM  74  are encoded by a video encoder  76 , and outputted to a monitor  78  of the digital camera  10 . A photographer determines the composition on the basis of the image (through image) displayed in the monitor  78 , to confirm the focusing state. 
     Then, under the above described photographing mode, when the release switch  20  is depressed half (S 1 =ON), automatic exposure adjustment (AE) and automatic focusing (AF) are operated. That is, the image data outputted from the A/D converter  66  are inputted into an AE/AWB detection circuit  80  and an AF detection circuit  82  via the image input controller  68 . 
     The AE/AWB detection circuit  80  integrates the R, G, B image data for each of R, G, B for every divided area obtained by dividing the imaging area into 64 (horizontally 8, perpendicularly 8), and outputs the integrated data for each of R, G, B for every divided area to the CPU  30 . 
     The AF detection circuit  82  calculates a contrast evaluation value representing the contrast of an image in a specific focus area set in advance (for example, the center of the imaging area), and outputs the contrast evaluation value to the CPU  30 . 
     The CPU  30  outputs a control signal to the focus motor driver  56  on the basis of the contrast information inputted from the AF detection circuit  82 , and performs AF control of the taking lens  12  to bring the main subjects into focus. 
     Further, the CPU  30  calculates lightness (EV value) of the subject on the basis of the integrated data inputted from the AE/AWB detection circuit  80 , and determines the diaphragm value (F value) of the diaphragm  48  and the shutter speed (charge storage time) of the CCD  50  on the basis of the EV value. 
     When the AE and the AF are completed and the release switch  20  is fully depressed (S 2 =ON), the CPU  30  outputs a drive signal to the iris motor driver  62  on the basis of the determined diaphragm value (F value), and performs drive control of the diaphragm  48  so as to make the diaphragm diameter become the determined diaphragm value (F value), while performing control of the charge storage time of the CCD  50  to effect the determined shutter speed. 
     The image data for one frame portion, which are taken in this way, are inputted to the SDRAM  70  from the image input controller  68  via the analog signal processing circuit  64 , the A/D converter  66 , and temporarily stored in the SDRAM  70 . Then, the image data are read out from the SDRAM  70  to the image signal processing circuit  72 , in which predetermined signal processing including processing for generating luminance data and color difference data (YC processing) is performed. 
     The image data after the signal processing are once stored in the SDRAM  70 , and thereafter outputted to a compression/expansion processing circuit  84 , in which predetermined compression processing such as JPEG (Joint Photographic Experts Group) processing is performed. Then, the image data are temporarily stored in the SDRAM  70  once more, and thereafter read out by a memory controller  86  so as to be recorded in a recording medium  88 . 
     The image data photographed and recorded in this way are reproduced and displayed in the monitor  78  by setting the mode of the camera to a reproduction mode. At the time of the reproduction mode, the image data recorded in the recording medium  88  are read to the SDRAM  70 , and are outputted from the SDRAM  70  to the compression/expansion processing circuit  84 . Further, the image data is subjected to expansion processing in the compression/expansion processing circuit  84 . Then, the expanded image data are temporarily stored in the SDRAM  70 , and thereafter outputted to the monitor  78  via the video encoder  76 . Thereby, the image data recorded in the recording medium  88  are reproduced and displayed in the monitor  78 . 
     Next, a method for controlling emitted light quantity of the AF auxiliary light is described with reference to  FIG. 3 .  FIG. 3  is a circuit diagram showing an exemplary configuration of an AF auxiliary light emission circuit. The AF auxiliary light emission circuit  40  shown in  FIG. 3  comprises a voltage regulation circuit  100  and a voltage amplifier  102 . The EEPROM  36  stores a table (voltage value-emitted light quantity table) in which the correspondence relation between the voltage value applied to the AF auxiliary light lamp  18  and the emitted light quantity of the AF auxiliary light lamp  18  is recorded. In making the AF auxiliary light emitted, the CPU 30  refers to the voltage value-emitted light quantity table in accordance with a zoom position, so as to control an electronic volume (EVR) of the voltage regulation circuit  100 . The voltage regulation circuit  100  regulates a power supply voltage supplied from the power supply circuit  37  on the basis of an input from the EVR. Then, the power supply voltage is amplified by the power supply amplifier  102  at a predetermined ratio (ratio of resistance values R 1  and R 2 ), and applied to the AF auxiliary light lamp (LED)  18 . Thereby, the emitted light quantity of the AF auxiliary light lamp  18  is controlled. 
     Next, a method for controlling the irradiation range of the AF auxiliary light is described with reference to  FIG. 4  and  FIG. 5 .  FIG. 4  is a plan view showing the AF auxiliary light irradiation lens, and  FIG. 5  is a figure schematically showing the method for controlling the irradiation range of the AF auxiliary light. As shown in  FIG. 4 , the AF auxiliary light irradiation lens  42  is constituted by fitting lenses  106  in a plate-like member  104 . In making the AF auxiliary light emitted, the CPU  30  controls the AF auxiliary light irradiation lens control circuit  44  in accordance with a zoom position. Then, as shown in  FIG. 5 , the lenses  106  on the optical axis L 1  of the AF auxiliary light lamp  18  is exchanged or added. Thereby, the irradiation range of the AF auxiliary light lamp  18  is controlled. 
     Noted that as shown in  FIG. 6 , the irradiation range of the AF auxiliary light lamp  18  may be arranged to be controlled by providing a guide  108  for moving the AF auxiliary light irradiation lens  42  in parallel with the optical axis L 1  of the AF auxiliary light lamp  18  so as to move the AF auxiliary light irradiation lens  42  in the optical axis L 1  direction. 
       FIG. 7  is a flow chart showing a process flow of AF auxiliary light control at the time of photographing. First, when the release switch  20  is half depressed (S 1 =ON) (step S 10 ), a zoom position is detected by the CPU  30  (step S 12 ), and emitted light quantity (step S 14 ) and an irradiation range (step S 16 ) of the AF auxiliary light are controlled. 
     Here, a method for controlling the emitted light quantity of the AF auxiliary light in step S  14  is described.  FIG. 8  is a flow chart showing the method for controlling the emitted light quantity of the AF auxiliary light. First, on the basis of the zoom position detected in step S 12  described above, the voltage value-emitted light quantity table stored in the EEPROM  36  is referred to (step S 140 ). Then, the electronic volume (EVR) of the voltage regulation circuit  100  is controlled (step S 142 ), so that the emitted light quantity of the AF auxiliary light is controlled. 
     Subsequently, a method for controlling the irradiation range of the AF auxiliary light in step S 16  is described.  FIG. 9  is a flow chart showing the method for controlling the irradiation range of the AF auxiliary light. First, on the basis of the zoom position detected in step S 12  described above, a combination of the lenses  106  used for irradiating the AF auxiliary light is determined (step S 160 ). Then, the AF auxiliary light irradiation lens control circuit  44  is controlled by the CPU  30 , so that the lenses  106  on the optical axis L 1  of the AF auxiliary light lamp  18  is exchanged or added (step S 162 ). 
     Reverting to the flow chart in  FIG. 7 , the process continues to step S 18 , and whether the AF auxiliary light is necessary or not at the time of AF is judged on the basis of the luminance of a screen display and the like. When the AF auxiliary light is judged to be necessary in step S 18 , the AF auxiliary light lamp  18  is turned on (step S 20 ), and AF photometry is performed (step S 22 ). On the other hand, when the AF auxiliary light is judged to be unnecessary in step S 18 , AF photometry is performed without making the AF auxiliary light lamp  18  turned on (step S 22 ). 
     Next, when the release switch  20  is fully depressed (S 2 =ON) (step S 24 ), photographing is performed, and an image is recorded in the recording medium  88 . Further, the image is read out from the recording medium  88  and displayed in the monitor  78  (step S 26 ). 
     According to the present embodiment, the emitted light quantity and the irradiation range of the AF auxiliary light are controlled in accordance with the zoom position of the taking lens  12 , so that the precision of AF can be improved. 
     Next, another exemplary configuration of the AF auxiliary light emission circuit is described.  FIG. 10  is a circuit diagram showing a second exemplary configuration of the AF auxiliary light emission circuit. The AF auxiliary light emission circuit  40  shown in  FIG. 10  comprises a current control circuit  110  for controlling current flowing through the AF auxiliary light lamp  18 . The current control circuit  110  controls the resistance value by controlling resistance changeover switches SW 1 . Noted that in  FIG. 10 , three sets of a resistance and a resistance changeover switches SW 1  are connected in parallel, but the number of resistors and the circuit configuration is not limited to this configuration. For example, a variable resistance may be used. 
       FIG. 11  is a flow chart showing a method for controlling the emitted light quantity of the AF auxiliary light in which the AF auxiliary light emission circuit according to the second exemplary configuration is used. First, on the basis of the zoom position detected in step S 12  described above, the emitted light quantity of the AF auxiliary light for performing AF is calculated, and a current value necessary for emitting the AF auxiliary light is judged (step S 30 ). Then, the resistance changeover switches SW 1  of the current control circuit  110  is controlled (step S 32 ), so that the emitted light quantity of the AF auxiliary light is controlled. 
       FIG. 12  is a circuit diagram showing a third exemplary configuration of the AF auxiliary light emission circuit. In the example shown in  FIG. 12 , a plurality of (three in the example in  FIG. 12 ) AF auxiliary light lamps  18  are provided, and the AF auxiliary light emission circuit  40  comprises lighting number changeover switches SW 2  for controlling the number of the AF auxiliary light lamps  18  which are made to turn on. Noted that in  FIG. 12 , three sets of a resistance and an AF auxiliary light lamp  18  are connected in parallel, but the number of the auxiliary light lamp  18  is not limited to this configuration. 
       FIG. 13  is a flow chart showing a method for controlling the emitted light quantity of the AF auxiliary light in which the AF auxiliary light emission circuit according to the third exemplary configuration is used. First, on the basis of the zoom position detected in step S 12  described above, the emitted light quantity of the AF auxiliary light for performing AF is calculated, and the lighting number of the AF auxiliary light lamp  18  necessary for emitting the AF auxiliary light is determined (step S 40 ). Then, the lighting number changeover switches SW 2  is controlled (step S 42 ), so that the emitted light quantity of the AF auxiliary light is controlled.