Patent Publication Number: US-2023142109-A1

Title: Light emitting device for assisting photographing, method of controlling same, and storage medium

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a light emitting device, a method of controlling the same, and a storage medium, and more particularly to a light emitting device used for a plurality of photographing assist uses, a method of controlling the same, and a storage medium. 
     Description of the Related Art 
     Conventionally, an AF sensor of a single-lens reflex camera has high compatibility with light of an infrared wavelength region, and infrared light has been used as an AF assist light. However, an AF sensor embedded in an image capturing sensor of a recent mirrorless camera has high compatibility with light of a visible wavelength region, and hence a white or bulb-color LED has been made available as the AF assist light. 
     The white or bulb-color LED can be used not only as the AF assist light, but also as a LED flashlight, a video light, and a modeling lamp. Further, there are a variety of uses, such as signals for indicating charge completion of a wireless communication strobe, by flickering the LED. 
     Here, the video light is used in a case where the screen is dark when photographing a moving image, and the modeling lamp is lit before photographing a still image in order to check how an object is irradiated with light emitted from the modeling lamp and how a shade is formed by the light in final photographing, in advance. Therefore, the video light and the modeling lamp are longer in lighting time, compared with the uses, such as the AF assist light and LED flashlight, and are often used for several tens of seconds to several tens of minutes. 
     On the other hand, in a case where the LED is used as the AF assist light, although time is required to find an in-focus point by driving a focus lens, most of focus lenses can be focused within several seconds. 
     When the LED is lit, the LED temperature increases, and hence it is necessary to perform heat limitation control, e.g. by dimming or lighting off the LED before the LED temperature reaches a use upper limit temperature, so as to avoid breakage or malfunction of the LED. 
     The LED package internal temperature cannot be directly measured, and hence this heat limitation control is performed by disposing a thermistor in the vicinity of the LED and predicting the LED package internal temperature from a temperature detected by the thermistor. More specifically, there is a difference and a time lag between the LED package internal temperature and the temperature detected by the thermistor, and hence the LED package internal temperature is required to be predicted with a margin of several degrees centigrade of temperature. 
     For example, Japanese Laid-Open Patent Publication (Kokai) No. 2003-5023 discloses a technique for acquiring a temperature around an LED used as the AF assist light by using a thermistor and changing the degree of brightness of light emitted from the LED according to a value of the acquired temperature around the LED. This makes it possible to reduce the brightness of light emitted from the LED by reducing electric current caused to flow through the LED when the value of the temperature around the LED is high and thereby suppress the rise of the LED package internal temperature. 
     However, in the conventional technique disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2003-5023, there is no description of uses of the LED other than the AF assist light, specifically, uses of the LED for continuously lighting for a relatively long time period, as in the case of a modeling lamp and a video light. 
     Since the lighting time is short in a case where the LED is used as the AF assist light, the rise of the LED temperature is small and the rise of the temperature around the LED is also small. On the other hand, when the LED is used for lighting continuously for a relatively long time period, as in the case of a modeling lamp and a video light, the rise of the LED temperature by one lighting operation is large, and the rise of the temperature around the LED is also large. 
     Therefore, it is not preferable to perform the heat limitation control of the LED using the same temperature threshold value between the case where the LED is used as the modeling lamp or the video light and the case where the LED is used as the AF assist light. This is because when the LED is used as the AF assist light, the lighting of the LED may be limited by the heat limitation control even if the LED temperature has not reached an upper limit temperature. 
     SUMMARY OF THE INVENTION 
     The present invention provides a light emitting device that is capable of performing optimum temperature control of an LED in accordance with each of a plurality of photographing assist uses and sufficiently exhibiting performance of each use while ensuring reliability of the LED, a method of controlling the same, and a storage medium. 
     In a first aspect of the present invention, there is provided a light emitting device including a light emission unit, a temperature detection unit, the light emitting device operating at least in one of a first light emission mode in which a light emission time in one lighting operation of the light emission unit is a first time period and a second light emission mode in which the light emission time is a second time period shorter than the first time period, at least one processor; and a memory coupled to the at least one processor, the memory having instructions that, when executed by the processor, perform the operations as a control unit configured to perform different light emission controls on the light emission unit between the first light emission mode and the second light emission mode, based on temperature information detected by the temperature detection unit. 
     In a second aspect of the present invention, there is provided a method of controlling a light emitting device including a light emission unit and a temperature detection unit, including operating the light emitting device at least in one of a first light emission mode in which a light emission time in one lighting operation of the light emission unit is a first time period and a second light emission mode in which the light emission time is a second time period shorter than the first time period, and performing different light emission controls on the light emission unit between the first light emission mode and the second light emission mode based on temperature information detected by the temperature detection unit. 
     According to the present invention, it is possible to perform optimum temperature control of the LED in accordance with each of a plurality of photographing assist uses and sufficiently exhibiting performance of each use while ensuring reliability of the LED. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram showing a hardware configuration of a camera system including a light emitting device according to a first embodiment. 
         FIG.  2    is a flowchart of a modeling lamp-lighting process performed by a strobe controller appearing in  FIG.  1   . 
         FIG.  3    is a flowchart of an AF control process performed by a camera controller appearing in  FIG.  1   . 
         FIG.  4 A  is a flowchart of an AF assist light control process performed by an image capturing apparatus in a step in  FIG.  3   . 
         FIG.  4 B  is a continuation of  FIG.  4 A . 
         FIG.  4 C  is a flowchart of an AF assist light control process performed by a light emitting device in a step in  FIG.  3   . 
         FIG.  4 D  is a continuation of  FIG.  4 C . 
         FIG.  5    is a graph showing a relationship between an open F-number (lens aperture value at the time of AF) of a lens device appearing in  FIG.  1    and a light emission amount Raf of the AF assist light. 
         FIG.  6    is a block diagram showing a hardware configuration of a camera system including a light emitting device according to a second embodiment. 
         FIG.  7    is a flowchart of a charge completion process performed by a strobe controller appearing in  FIG.  6   . 
         FIG.  8    is a block diagram showing a hardware configuration of a camera system including a light emitting device according to a third embodiment. 
         FIG.  9    is a flowchart of an LED flashlight emission process performed by a strobe controller appearing in  FIG.  8   . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The present invention will now be described in detail below with reference to the accompanying drawings showing embodiments thereof. 
     First, a description will be given of the configuration of a camera system  1  including a light emitting device  300  according to a first embodiment of the present invention, with reference to  FIG.  1   . 
       FIG.  1    is a block diagram showing a hardware configuration of the camera system  1  including the light emitting device  300  according to the present embodiment. 
     The camera system  1  includes an image capturing apparatus (camera body)  100 , a lens device (interchangeable lens)  200  which can be attached/removed to/from the image capturing apparatus  100 , and the light emitting device (external strobe)  300 . However, the camera system  1  is not limited to the configuration of the present embodiment insofar as the light emitting device  300  is connected to the image capturing apparatus, and for example, the image capturing apparatus  100  and the lens device  200  may be replaced by an image capturing apparatus including a camera body and a lens integrally provided therein. 
     The image capturing apparatus  100  includes an image sensor  101 , a camera controller  102 , a memory section  103 , a photometry section  104 , an AF detection section  105 , a signal input section  106 , an image processor  107 , a recording/outputting section  108 , an LED  109 , a camera mount section  120 , and a camera-side ACC connection section  140 . 
     The image sensor  101  is implemented e.g. by a CCD or a CMOS sensor, and photoelectrically converts an optical image formed on an imaging surface of the image sensor  101  by an optical system of the lens device  200  to output the resulting analog image signals to the camera controller  102 . 
     The camera controller  102  is a control unit provided in the image capturing apparatus  100 , which reads control programs for the respective blocks included in the image capturing apparatus  100  from a ROM of the memory section  103 , and loads the programs into a RAM of the memory section  103 , for execution. This enables the camera controller  102  to control the operations of the respective blocks included in the image capturing apparatus  100  and perform centralized control of the image capturing apparatus  100  and the lens device  200 . To the camera controller  102 , there are connected the image sensor  101 , the memory section  103 , the photometry section  104 , the AF detection section  105 , the signal input section  106 , the image processor  107 , the recording/outputting section  108 , the LED  109 , the camera mount section  120 , the camera-side ACC connection section  140 , and so forth. 
     The camera controller  102  has an analog-to-digital converter provided therein, and in a case where analog image signals output from the image sensor  101  are converted from analog to digital by the analog-to-digital converter, the camera controller  102  outputs the digital signals to the RAM provided in the memory section  103  as image data. Further, in a case where the image sensor  101  is caused to function as a photometry sensor, or in a case where pixels forming the image sensor  101  are partially used for phase difference detection, the camera controller  102  directly outputs analog image signals output from the image sensor  101  to the memory section  103 . 
     Further, the camera controller  102  transmits signals to and from a focus adjustment section  205  and a diaphragm driving section  204 , referred to hereinafter, of the lens device  200 , via a lens mount section  220  and a lens controller  206 , referred to hereinafter, of the lens device  200 . 
     In the present embodiment, the memory section  103  not only includes the above-mentioned ROM and RAM, but also has a function of storing analog image capturing signals output from the image sensor  101 . 
     The photometry section  104  acquires analog image signals output from the image sensor  101  which also plays the role of a photometry sensor, from the memory section  103 , as luminance signals corresponding to the brightness of a field, and calculates an object luminance by performing amplification, logarithmic compression, analog-to-digital conversion, and so forth, on the luminance signals. 
     The AF detection section  105  acquires signal voltages of analog image signals from the memory section  103 , which have been output from a plurality of detection elements (a plurality of pixels) used for phase difference detection, which are included in the pixels forming the image sensor  101 , and performs analog-to-digital conversion thereof to thereby generate image signals. Further, the camera controller  102  acquires the generated image signals from the AF detection section  105  and calculates a distance to each focusing point of an object. This is a technique (known art) referred to as the imaging surface phase difference AF. 
     The image processor  107  performs a variety of image processing operations on image data stored in the RAM provided in the memory section  103 . Specifically, there are performed a variety of image processing operations for developing, displaying, and recording digital image data, including processing for correcting defects of pixels caused by the optical system of the lens device  200  or the image sensor  101 , demosaicing, white balance correction processing, color interpolation, and gamma processing. 
     The signal input section  106  refers to a release button, to which are connected a switch SW 1  (not shown) which outputs an on-signal when a first stoke depression (half depression) is performed, and a switch SW 2  (not shown) which outputs an on-signal when a second stoke depression (full depression) is performed. The on-signals output from the switches SW 1  and SW 2  are input to the camera controller  102 . When the on-signal from the switch SW 1  is output, the camera controller  102  starts photometry and ranging of the image capturing apparatus  100 , and when the on-signal from the switch SW 2  is output, the camera controller  102  starts a photographing operation. 
     The recording/outputting section  108  performs recording of data including image data in a recording medium, such as a removable memory card, outputting of the data to an external apparatus via an external interface, and the like. 
     The LED  109  is built into the image capturing apparatus  100 , and performs lighting as an AF assist light, or performs flickering as a self-timer lamp for notifying a user of a photographing timing when self-timer photographing is performed. 
     The camera-side ACC connection section  140  is connected to a strobe-side ACC connection section  340 , referred to hereinafter, of the light emitting device  300  to transmit an instruction signal from the camera controller  102  to a strobe controller  311 . With this, the strobe controller  311  having received the instruction signal controls flashlight emission of a flashlight emitting tube  321 , referred to hereinafter, and light emission of an LED  322 , described hereinafter. 
     The lens device  200  includes an optical system comprised of a zoom lens  201 , a focus lens  202 , and a diaphragm  203 , in addition to the diaphragm driving section  204 , the focus adjustment section  205 , the lens controller  206 , and the lens mount section  220 . 
     The optical system of the lens device  200 , when in a state attached to the image capturing apparatus  100 , guides a light flux from an object to the image sensor  101  to form an object image on the imaging surface of the image sensor  101 . 
     The lens controller  206  receives instruction signals for the diaphragm driving section  204  and the focus adjustment section  205  from the camera controller  102  via a mount contact portion, not shown, provided across the camera mount section  120  and the lens mount section  220 , and the diaphragm driving section  204  and the focus adjustment section  205  are drive-controlled according to instructions from the lens controller  206 . 
     Next, the light emitting device  300  will be described. 
     The light emitting device  300  is broadly divided into three sections: a strobe body section  310 , a strobe head section  320 , and a bounce mechanism section  330 . 
     The strobe body section  310  accommodates the strobe controller  311  that controls the overall operation of the light emitting device  300 , a strobe operation section  312  including a power switch, a display section  313 , a power supply  314 , the strobe-side ACC connection section  340 , and so forth, which are mounted on a main substrate, not shown. 
     The strobe controller  311  receives an instruction from the camera controller  102  or an instruction from the strobe operation section  312  and controls light emission of the flashlight emitting tube  321  and the LED  322  included in the strobe head section  320 , as will be described hereinafter. This light emission control is performed based on temperature information acquired by a temperature sensor  323  provided in the strobe head section  320 , as will be described hereinafter. Note that in the present embodiment, the light emission mode of the LED  322  has a first light emission mode in which the LED  322  is used as a modeling lamp and a second light emission mode in which the LED  322  is used as the AF assist light. For the sake of LED light emission control in these modes, a temperature threshold value of each light emission mode is set by the strobe controller  311  (first setting unit). Specifically, as the temperature threshold value for the first light emission mode, there are set a first modeling lamp temperature threshold value Tlim_mod1 and a second modeling lamp temperature threshold value Tlim_mod2 lower than the first modeling lamp temperature threshold value Tlim_mod1. Further, as the threshold value for the second light emission mode, there are set a first AF assist light temperature threshold value Tlim_AF1 (first temperature threshold value) and a second AF assist light temperature threshold value Tlim_AF2 (second temperature threshold value) lower than the first AF assist light temperature threshold value Tlim_AF1. Details of these temperature threshold values will be described hereinafter. 
     The bounce mechanism section  330  accommodates an irradiation direction-changing mechanism, not shown, as a known system in an external strobe, such as the light emitting device  300 , a bounce mechanism, not shown, and so forth. 
     The irradiation direction-changing mechanism holds the strobe head section  320  in a state rotatable in a horizontal direction and a vertical direction with respect to the strobe body section  310 . This makes it possible to perform bounce photographing by changing the irradiation direction of light emitted from the flashlight emitting tube  321 . 
     A main capacitor  331  boosts the voltage of the power supply  314  to several hundred volts (V) using a boost circuit, not shown, to charge (accumulate) electrical energy in the main capacitor  331 . A resistor (voltage detection unit), not shown, for detecting a voltage of the main capacitor  331 , is integrated as a component in the boost circuit. 
     The strobe head section  320  accommodates the flashlight emitting tube  321 , the LED  322 , the temperature sensor  323 , and so forth, necessary for strobe light emission. 
     The flashlight emitting tube  321  (flashlight emission unit) is a xenon tube or a quartz tube, and emits flashlight by converting electrical energy charged in the main capacitor  331  to light energy according to a light emission signal received from the strobe controller  311 . Around the flashlight emitting tube  321 , there are arranged a reflection umbrella and a Fresnel lens, neither of which is shown, to adjust light distribution. 
     The LED  322  (light emission unit) is lit as the modeling lamp or the AF assist light, for the purpose of assisting photographing of the image capturing apparatus  100 , according to a light emission signal received from the strobe controller  311 . A lens, not shown, is disposed in front of the LED  322  so as to adjust light distribution of the LED  322 . As the color temperature of the LED  322  in the present embodiment, one of color temperatures within a range of 3000 to 6500 K is used. The amount of light emitted from the LED  322  is controlled by PWM control. A table of the light emission amount and the duty ratio in the PWM control is recorded in a nonvolatile memory, not shown, such as an EEPROM, disposed within the strobe controller  311 . 
     The temperature sensor  323  (temperature detection unit) is disposed in the vicinity of the LED  322  on a substrate, not shown, on which the LED  322  is mounted, and detects a temperature in the vicinity of the LED  322  so as to estimate the internal temperature of the LED  322 . The temperature sensor  323  outputs a measurement result to the strobe controller  311  as temperature information. The strobe controller  311  performs heat limitation based on the temperature information acquired from the temperature sensor  323  to prevent the temperature of the LED  322  from exceeding a rated temperature and the LED  322  from being overheated and broken. Details of this control will be described hereinafter. 
     Although in the present embodiment, the LED  322  is mounted in the strobe head section  320 , the location where the LED  322  is mounted is not limited to this insofar as the light emission direction of the LED  322  is within the light emitting device  300  and is substantially the same as the light emission direction of the flashlight emitting tube  321 . For example, the LED  322  may be mounted in a central portion of the strobe body section  310 . In this case, the use of the LED  322  is changed from the modeling lamp to a video light. Note that in this case, the LED  322  can also be used as the AF assist light. 
     This concludes the description of the basic configuration of the camera system  1  including the image capturing apparatus  100 , the lens device  200 , and the light emitting device  300 . 
     Next, the operation of the present embodiment will be described below with reference to  FIGS.  2 ,  3 ,  4 , and  5   . 
       FIG.  2    is a flowchart of a modeling lamp-lighting process. 
     The present process is executed by the strobe controller  311  that loads a program stored in a ROM, not shown, of the strobe body section  310  into a RAM, not shown, of the same. 
     First, in a step S 101 , when a user selects the first light emission mode by operating the strobe operation section  312  and inputs a light emission amount Rmod of the LED  322  in the first light emission mode, the strobe controller  311  acquires the light emission amount Rmod input by the user and proceeds to a step S 102 . 
     In the step S 102 , an LED lighting instruction is received by the user performing an operation for turning on a modeling lamp ON/OFF button of the strobe operation section  312 , the process proceeds to a step S 103 . 
     In the step S 103 , the strobe controller  311  acquires temperature information Tth from the temperature sensor  323  disposed in the vicinity of the LED  322 . 
     In a step S 104 , the strobe controller  311  determines whether or not the temperature information Tth acquired in the step S 103  is equal to or higher than the first modeling lamp temperature threshold value Tlim_mod1. If the acquired temperature information Tth is equal to or higher than the first modeling lamp temperature threshold value Tlim_mod1 (YES to the step S 104 ), the process proceeds to a step S 105 , wherein the LED  322  is controlled not to be lit, followed by terminating the present process. On the other hand, if the acquired temperature information Tth is lower than the first modeling lamp temperature threshold value Tlim_mod1 (NO to the step S 104 ), the process proceeds to a step S 106 . 
     In the step S 106 , the strobe controller  311  determines whether or not the acquired temperature information Tth is equal to or higher than the second modeling lamp temperature threshold value Tlim_mod2. If the acquired temperature information Tth is equal to or higher than the second modeling lamp temperature threshold value Tlim_mod2 (YES to the step S 106 ), the process proceeds to a step S 107 . On the other hand, if the acquired temperature information Tth is lower than the second modeling lamp temperature threshold value Tlim_mod2 (NO to the step S 106 ), the process proceeds to a step S 111 . 
     In the step S 107 , the strobe controller  311  determines whether or not the light emission amount Rmod specified by the user in the step S 101  is larger than ½ of a maximum light emission amount Rmax_initial of the LED  322 . If Rmod&gt;½ Rmax_initial holds (YES to the step S 107 ), the process proceeds to a step S 108 , whereas if Rmod≤½ Rmax_initial holds (NO to the step S 107 ), the process proceeds to the step S 111 . 
     In the step S 108 , since the acquired temperature information Tth is equal to or higher than the second modeling lamp temperature threshold value Tlim_mod2, it is necessary to protect the LED  322  from heat. For this reason, the LED  322  is lit with ½ Rmax_initial which is the light emission amount of half of the maximum light emission amount Rmax_initial. Then, the process proceeds to a step S 109 . 
     On the other hand, in the step S 111 , since the acquired temperature information Tth is lower than the second modeling lamp temperature threshold value Tlim_mod2, the LED  322  is lit by the user input value Rmod acquired in the step S 101 . Then, the process proceeds to the step S 109 . 
     In the step S 109 , the strobe controller  311  confirms whether or not an instruction for turning off the LED  322  has been received from the user. There are two methods of the user instructing turning off of the LED  322 : As the first method, the user presses the modeling lamp ON/OFF button (not shown) of the strobe operation section  312  to turn off this button. As the second method, the user provides performs the second stroke depression (full depression) of the signal input section  106  of the image capturing apparatus  100 . In this case, when an on-signal is output from the switch SW 2  to the strobe controller  311  via the camera controller  102  and the ACC connection section, the strobe controller  311  confirms that the instruction for turning off the LED  322  has been received from the user. If the instruction for turning off the LED  322  has been received from the user (YES to the step S 109 ), the process proceeds to a step S 110 , wherein the LED  322  is turned off, followed by terminating the present process. On the other hand, if the instruction for turning off the LED  322  has not been received from the user (NO to the step S 109 ), the process returns to the step S 103  in a state in which the LED  322  continues to be lit. 
     Thus, according to the present process, the temperature information Tth is repeatedly acquired to monitor the temperature of the LED  322  until the LED  322  is controlled not to be lit (step S 105 ) or turned off according to the turning off instruction from the user (step S 110 ). With this, even in a case where light emission from the LED  322  continues for a long time, it is possible to prevent a situation where the temperature within the LED  322  largely increases and exceeds the rated temperature of the LED  322 . 
     Next, an AF control process will be described with reference to  FIG.  3   . In this process, the lighting timing of the AF assist light of the image capturing apparatus  100  is set. 
       FIG.  3    is a flowchart of the AF control process. 
     The present process is executed by the camera controller  102  that loads an associated control program stored in the ROM of the memory section  103  into the RAM of the memory section  103 . 
     First, in a step S 201 , when the user performs the first stroke depression (half depression) of the signal input section  106  of the image capturing apparatus  100 , whereby an on-signal is output from the switch SW 1  to the camera controller  102 , the process proceeds to a step S 202  to start the AF control operation. On the other hand, in a case where the on-signal is not output from the switch SW 1 , the camera controller  102  waits to receive the on-signal in the step S 201 . 
     In the step S 202 , the camera controller  102  starts to output analog image signals from the image sensor  101  to the memory section  103 . 
     In a step S 203 , the camera controller  102  acquires an object luminance calculated based on the analog image signals stored in the memory section  103 , from the photometry section  104 . 
     In a step S 204 , the camera controller  102  determines whether or not the object luminance acquired in the step S 202  is equal to or higher than a threshold value. If it is determined that the object luminance is equal to or higher than the threshold value (YES to the step S 204 ), the process proceeds to a step S 205 , whereas if it is determined that the object luminance is lower than the threshold value (NO to the step S 204 ), the process proceeds to a step S 206 . 
     In the step S 205 , the camera controller  102  executes normal AF control. When execution of the normal AF control is completed, the process proceeds to a step S 207 . Note that the normal AF control is the AF control of the conventional technique in which the LED  322  is not used for the assist light, and hence detailed description of the control is omitted. 
     In the step S 206 , the camera controller  102  performs an AF assist light control process for performing AF control by lighting the LED  322  for the assist light. Note that although details will be described hereinafter, actually, the AF assist light control process is executed by not only the camera controller  102 , but also the strobe controller  311 , in cooperation. When the AF assist light control process is completed, the process proceeds to the step S 207 . 
     In the step S 207 , when the user performs the second stroke depression (full depression) of the signal input section  106  of the image capturing apparatus  100 , whereby an on-signal is output from the switch SW 2  to the camera controller  102 , the process proceeds to a step S 208 . On the other hand, in a case where the on-signal is not output from the switch SW 2 , the camera controller  102  waits to receive the on-signal in the step S 207 . 
     In the step S 208 , the camera controller  102  executes still image photographing, followed by terminating the present process. 
       FIGS.  4 A to  4 D  are flowcharts of details of the AF assist light control process in the step S 206  in  FIG.  3   . 
       FIGS.  4 A and  4 B  are a flowchart of the AF assist light control process performed by the image capturing apparatus  100 , and  FIGS.  4 C and  4 D  are a flowchart of the AF assist light control process performed by the light emitting device  300 . 
     First, the AF assist light control process performed by the image capturing apparatus  100  (the camera controller  102 ) will be described with reference to  FIGS.  4 A and  4 B . 
     The present process is executed by the camera controller  102  that loads an associated control program stored in the ROM of the memory section  103  into the RAM of the memory section  103 . 
     First, in a step S 301 , the camera controller  102  starts camera-strobe communication via the camera-side ACC connection section  140 . 
     In a step S 302 , the camera controller  102  determines whether or not the light emitting device  300  as an external strobe is connected to the image capturing apparatus  100 . If the light emitting device  300  is not connected (NO to the step S 302 ), the process proceeds to a step S 303 , whereas if the light emitting device  300  is connected (YES to the step S 302 ), the process proceeds to a step S 307 . 
     In the step S 303 , the camera controller  102  turns on the LED  109  of the image capturing apparatus  100  for the AF assist light with a fixed light amount. 
     In a step S 304 , the camera controller  102  performs focus adjustment processing while lighting the LED  109  for the AF assist light with the fixed light amount. More specifically, first, the camera controller  102  instructs the AF detection section  105  to acquire analog image signals output from the image sensor  101  after the LED  109  has started to be lit in the step S 303 , from the memory section  103 , and generate image signals to be used for phase difference detection. Next, the camera controller  102  calculates the AF information from the image signals generated by the AF detection section  105 . Specifically, the camera controller  102  calculates a defocus distance to the object (defocus amount), the contrast, the reliability, and so forth. After that, the camera controller  102  instructs the lens controller  206  to move the focus lens  202  to an in-focus position by driving the focus adjustment section  205  based on results of these calculations. Note that in a case where the defocus amount cannot be calculated, the focus lens  202  is search-driven, and is driven to a position where the defocus amount can be calculated. 
     In a step S 305 , when the focus lens  202  is moved to the in-focus position, the focusing operation is terminated. Note that in a case where the defocus amount cannot be calculated even when the focus lens  202  is moved over the whole focusing region by search driving, it is determined that the focus cannot be obtained, and the focusing operation is terminated. 
     In a step S 306 , the LED  109  is turned off, followed by terminating the present process. 
     In the step S 307 , the camera controller  102  determines whether or not a flash assist light emission instruction has been received in a step S 404 , referred to hereinafter. If the flash assist light emission instruction has been received (YES to the step S 307 ), the process proceeds to a step S 308 , whereas if the flash assist light emission instruction has not been received (NO to the step S 307 ), the process proceeds to a step S 312 . 
     In the step S 308 , the camera controller  102  transmits an instruction (flashlight emission instruction) for causing the flashlight emitting tube  321  to start intermittent light emission for the AF assist light (hereinafter referred to as light emission of the flash AF assist light) to the strobe controller  311 . The light emission of the flash AF assist light is a known technique, and hence detailed description thereof is omitted. 
     In a step S 309 , the camera controller  102  performs the same focus adjustment processing as in the step S 305  while causing the flashlight emitting tube  321  to perform the intermittent light emission for the AF assist light. 
     In a step S 310 , the focusing operation is terminated by the same processing as in the step S 305 . 
     In a step S 311 , the camera controller  102  transmits an instruction for stopping light emission of the flash AF assist light (flashlight stop instruction) to the strobe controller  311 , followed by terminating the present process. 
     Next, a description will be given of the step S 312  and steps S 313  to S 319  executed in a case where, in the light emitting device  300 , not the flashlight emitting tube  321 , but the LED  322  is caused to emit light for the AF assist light. 
     First, a light emission amount Raf of the AF assist light (AF assist light emission amount Raf) using the LED  322  will be described. The light emission amount Raf is determined according to condensing capability of the lens device  200 , i.e. the aperture of the diaphragm  203  at the time of AF processing. The setting of the aperture of the diaphragm  203  at the time of AF processing is set to an open F-number of the lens device  200  differently from the photographing time. This is because it is possible to maintain high AF performance, i.e. the in-focus reaching distance and the response by taking in more amount of light when the AF is performed. 
       FIG.  5    is a graph showing a relationship between the open F-number (the lens aperture value at the time of AF processing) of the lens device  200  and the light emission amount Raf of the AF assist light. 
     This graph shows a light emission amount required when focusing on a chart placed at a distance specified by the standard with the fixed exposure (ISO and Tv) of the image capturing apparatus  100  at the time of AF processing. As a value of the aperture of the diaphragm  203  is smaller, the aperture is closer to the open state, and the condensing capability is higher, and hence it is possible to take in an amount of light sufficient to perform AF processing even with a small amount of the assist light, and prevent a person as an object from feeling dazzled. Although the light emission amount is determined according to the value of the diaphragm  203  in the present embodiment, the light emission amount may be determined according to a focal length of the lens device  200 . Further, the light emission amount Raf of the AF assist light is basically determined with reference to the open F-number of the lens device  200  indicated in the graph shown in  FIG.  5    but is sometimes changed depending on a state of the light emitting device  300 . Details of the change will be described in the explanation of the following step S 312  et seq. 
     Referring again to  FIG.  4 A , in the step S 312 , the camera controller  102  communicates with the strobe controller  311  of the light emitting device  300  to receive initial settings of the AF assist light emission amount Raf, an upper limit light emission amount Rmax, and a lower limit light emission amount Rmin of the LED  322 . Here, the initial setting of the AF assist light emission amount Raf is an AF assist light emission amount Raf_F having the lens aperture value F as a variable, the initial setting of the upper limit light emission amount Rmax is Rmax_initial, and the initial setting of the lower limit light emission amount Rmin is Rmin_initial. 
     In the step S 313 , the camera controller  102  determines whether or not a temperature limitation notification has been received from the strobe controller  311  in a step S 411 , referred to hereinafter. If the temperature limitation notification has been received (YES to the step S 313 ), the process proceeds to the step S 314 , wherein the camera controller  102  updates the upper limit light emission amount Rmax by overwriting the initial setting Rmax_initial with a light emission amount Rmax_TH included in the temperature limitation notification, and then proceeds to a step S 315  in  FIG.  4 B . The light emission amount Rmax_TH is set to be smaller than the initial setting Rmax_initial, for example, smaller by one stop. If the temperature limitation notification has not been received (NO to the step S 313 ), the process directly proceeds to the step S 315  in  FIG.  4 B  without limiting the light emission amount. 
     In the step S 315 , the camera controller  102  determines whether or not a notification that the modeling lamp is being lit at present (modeling lamp notification) has been received from the strobe controller  311 . If the modeling lamp notification has been received (YES to the step S 315 ), the process proceeds to a step S 316 , whereas if the modeling lamp notification has not been received (NO to the step S 315 ), the process proceeds to a step S 320 . The modeling lamp notification includes information on the light emission amount Rmod with which the LED  322  is being lit as the modeling lamp at present, as will be described hereinafter. 
     In the step S 316 , the camera controller  102  updates the light emission amount Raf of the AF assist light by overwriting the AF assist light emission amount Raf_f with the light emission amount Rmod which is the current light emission amount of the modeling lamp. 
     In the step S 317 , the camera controller  102  notifies the strobe controller  311  of an AF assist light-lighting instruction for setting the light emission amount Raf of the AF assist light to the light emission amount Rmod. That is, this means that light emission from the LED  322  is continued without changing the current light emission amount Rmod. 
     In the step S 318 , the camera controller  102  performs the same focus adjustment processing as in the step S 305  under an environment in which the LED  322  is being lit with the light emission amount notified in the immediately preceding step (step S 317 ). 
     In the step S 319 , when the focusing operation is terminated by the same processing as in the step S 305 , the camera controller  102  maintains the light emitting state of the LED  322 , followed by terminating the present process. 
     This concludes the process performed by the image capturing apparatus  100  (the camera controller  102 ) in the case where the AF assist light-lighting instruction is provided when the modeling lamp is being lit. 
     Next, a description will be given of the step and steps S 320  to S 325  executed in a case where the AF assist light-lighting instruction is provided when the modeling lamp is not being lit. 
     In the step S 320 , the camera controller  102  determines whether or not a notification that the strobe head section  320  is in a bounce state (bounce notification) has been received from the strobe controller  311 . If the bounce notification has been received (YES to the step S 320 ), the process proceeds to a step S 321 , whereas if the bounce notification has not been received (NO to the step S 320 ), the process proceeds to a step S 322 . The bounce notification includes information on a light emission amount Rba specific to the bounce state, described hereinafter, in the step S 321 . 
     In the step S 321 , the camera controller  102  updates the light emission amount Raf of the AF assist light by overwriting the AF assist light emission amount Raf_f with the light emission amount Rba. In the bounce photographing, light reflected from a wall and/or a ceiling is used, and hence an amount of light not smaller than a predetermined amount is required. Further, on the other hand, assuming that a light emitting surface of the light emitting device  300  faces toward a photographer, consideration needs to be taken, for setting the light emission amount to such a value as will prevent light from dazzling the photographer&#39; eyes even if the light from the LED  322  enters the photographer&#39;s eyes from a close distance. Taking these points into consideration under the bounce state, the light emission amount Raf of the AF assist light is set to the light emission amount Rba which is a fixed light emission amount. 
     In the step S 322 , the camera controller  102  notifies the strobe controller  311  of an AF assist light-lighting instruction for setting the light emission amount Raf of the AF assist light to the light emission amount Rba. 
     With this, in a case where the strobe head section  320  is in the bounce state, the light emission amount Raf of the AF assist light is set to the light emission amount Rba specific to the bounce state, which is included in the bounce notification received from the strobe side in the step S 321 . On the other hand, in a case where the strobe head section  320  is in a non-bounce state, the light emission amount Raf of the AF assist light is set to the light emission amount Raf_F according to the condensing capability of the lens device  200 , i.e. the aperture of the diaphragm  203 . Further, as for the light emission amount Raf of the AF assist light, in a case where the temperature limitation notification is received in the step S 411 , referred to hereinafter, the upper limit light emission amount Rmax is set to the light emission amount Rmax_TH. 
     In the steps S 323  and S 324 , the same processing operations as in the steps S 318  and S 319  are executed. 
     In the step S 325 , the camera controller  102  provides a turn-off instruction to the strobe controller  311 , followed by terminating the present process. 
     Thus, when the AF assist light-lighting process performed by the image capturing apparatus  100  (the camera controller  102 ) is terminated, the process returns to the step S 207  in  FIG.  3   . 
     Next, the AF assist light-control process performed by the light emitting device  300  (the strobe controller  311 ) will be described with reference to  FIGS.  4 C and  4 D . 
     The present process is executed by the strobe controller  311  that loads an associated program stored in the ROM, not shown, of the strobe body section  310  into the RAM, not shown, of the same. 
     First, in a step S 401 , the strobe controller  311  starts camera-strobe communication via the strobe-side ACC connection section  340 . 
     In a step S 402 , the strobe controller  311  acquires the temperature information Tth from the temperature sensor  323  disposed in the vicinity of the LED  322 . 
     In a step S 403 , the strobe controller  311  determines whether or not the temperature information Tth acquired by the temperature sensor  323  is equal to or higher than the first AF assist light temperature threshold value Tlim_AF1 (first temperature threshold value). If Tth Tlim_AF1 holds (YES to the step S 403 ), the process proceeds to the step S 404 , whereas if Tth&lt;Tlim_AF1 holds (NO to the step S 403 ), the process proceeds to a step S 409 . 
     The first AF assist light temperature threshold value Tlim_AF1 set to be higher than the first modeling lamp temperature threshold value Tlim_mod1 (i.e. such that Tlim_AF1&gt;Tlim_mod1 holds). The modeling lamp is lit before photographing a still image in order to check in advance how strobe light is irradiated and how a shade appears, and when the modeling lamp is once lit, the modeling lamp continues to be lit for several tens seconds to several minutes (first time period), and hence the temperature rise is large. Compared with this, the light emission time of the AF assist light in one lighting operation is a time period required to search the whole region when the focus lens  202  is search-driven, and hence this light emission time is a short time period of several hundreds msec to several seconds (second time period). Therefore, the temperature rise is smaller than in the case where the LED  322  is used as the modeling lamp, and the temperature is lowered by natural heat dissipation after turning off the LED  322 . Further, the temperature sensor  323  disposed in the vicinity of the LED  322  is not configured to directly measure an internal temperature Tled_internal of the LED  322 . For this reason, there is a deviation between the actual internal temperature Tled_internal of the LED  322  and the temperature information Tth acquired from the temperature sensor  323 , and further, there is a time lag. Taking the above into consideration, the threshold value is set such that Tlim_AF1&gt;Tlim_mod1 holds. 
     In the step S 404 , the strobe controller  311  transmits an instruction for lighting not the AF assist light using the LED  322 , but the flash AF assist light using the flashlight emitting tube  321  formed e.g. by a xenon tube or a quartz tube (flash assist light emission instruction) to the camera controller  102 . This makes it possible to prevent the LED  322  from being broken or deteriorated by heat. 
     In a step S 405 , the strobe controller  311  receives an instruction for starting light emission of the flash AF assist light (flashlight emission instruction) from the camera controller  102 , and the process proceeds to a step S 406 . 
     In the step S 406 , the flashlight emitting tube  321  starts intermittent light emission as the flash AF assist light. The flash AF assist light is a known technique, and hence detailed description thereof is omitted. 
     In a step S 407 , the strobe controller  311  receives an instruction for stopping light emission of the flash AF assist light (flashlight emission stop instruction) from the camera controller  102 , and the process proceeds to a step S 408 . 
     In the step S 408 , the flashlight emitting tube  321  stops intermittent light emission as the flash AF assist light, followed by terminating the present process. 
     Next, a description will be given of the step S 409 , a step  410 , the step S 411 , and steps S 412  to S 415  executed in a case where the temperature information Tth acquired by the temperature sensor  323  is lower than the first AF assist light temperature threshold value Tlim_AF1 (lower than the first temperature threshold value). In this case, the control for causing not the flashlight emitting tube  321  but the LED  322  to emit light as the AF assist light is performed. 
     In the step S 409 , the strobe controller  311  transmits the initial settings of the AF assist light emission amount Raf, the upper limit light emission amount Rmax, and the lower limit light emission amount Rmin of the LED  322  of the light emitting device  300  to the camera controller  102 . The initial settings are as described in the step S 312  in  FIG.  4 A . Specifically, the initial setting of the AF assist light emission amount Raf1 is Raf_F, the initial setting of the upper limit light emission amount Rmax is Rmax_initial, and the initial setting of the lower limit light emission amount Rmin is Rmin_initial. 
     In the step S 410 , the strobe controller  311  determines whether or not the temperature information Tth acquired by the temperature sensor  323  is equal to or higher than the second AF assist light temperature threshold value Tlim_AF2. If Tth≥Tlim_AF2 holds (YES to the step S 410 ), the process proceeds to the step S 411 , whereas if Tth&lt;Tlim_AF2 holds (NO to the step S 410 ), the process skips the step S 411  and proceeds to a step S 412  in  FIG.  4 D . 
     The second AF assist light temperature threshold value Tlim_AF2 is set to be higher than the second modeling lamp temperature threshold value Tlim_mod2 (i.e. such that Tlim_AF2&gt;Tlim_mod2 holds). This is because the temperature rise is smaller when the LED  322  is lit as the AF assist light than when the LED  322  is lit as the modeling lamp. Note that details of this reason have been described above as the reason for setting the first AF assist light temperature threshold value Tlim_AF1 to be higher than the first modeling lamp temperature threshold value Tlim_mod1, and hence description thereof is omitted. 
     Further, the AF assist light temperature threshold value and the modeling lamp temperature threshold value each have two temperature threshold values as described above. These temperature threshold values are set such that a difference between the first AF assist light temperature threshold value Tlim_AF1 and the second AF assist light temperature threshold value Tlim_AF2 is smaller than a difference between the first modeling lamp temperature threshold value Tlim_mod1 and the second modeling lamp temperature threshold value Tlim_mod2. This is also because the temperature rise is smaller when the LED  322  is lit as the AF assist light than when the LED  322  is lit as the modeling lamp. 
     That is, in the present embodiment, the following expression holds: 
         T lim_AF1 −T lim_AF2 &lt;T lim_mod1 −T lim_mod2 
     In the step S 411 , the strobe controller  311  of the light emitting device  300  transmits a notification (temperature limitation notification) that the upper limit light emission amount Rmax of the LED  322  is limited (reduced) to the light emission amount Rmax_TH (e.g. Rmax_initial minus one stop) so as to protect the LED  322  from heat. With this, in the image capturing apparatus  100 , the upper limit light emission amount Rmax is overwritten with the light emission amount Rmax_TH notified in the step S 409  for update. 
     In the step S 412  in  FIG.  4 D , the strobe controller  311  determines whether or not the modeling lamp is being lit, i.e. the LED  322  is being lit as normal light emission lighting. If the modeling lamp is being lit (YES to the step S 412 ), the process proceeds to the step S 413 , whereas if the modeling lamp is not being lit (NO to the step S 412 ), the process proceeds to a step S 416 . 
     In the step S 413 , the strobe controller  311  transmits a notification that the modeling lamp is being lit at present (modeling lamp notification) to the camera controller  102 . The modeling lamp notification includes a request for setting the light emission amount Raf of the AF assist light to the light emission amount Rmod with which the LED  322  is being lit as the modeling lamp at present. 
     In the step S 414 , the strobe controller  311  receives an instruction for lighting the LED  322  by setting the light emission amount Raf of the AF assist light to the light emission amount Rmod (AF assist light-lighting instruction) from the camera controller  102 . 
     In the step S 415 , the strobe controller  311  continues to light the LED  322  without changing the current light emission amount Rmod according to the AF assist light-lighting instruction received in the step S 414 , followed by terminating the present process. 
     This concludes the description of the process performed by the light emitting device  300  (the strobe controller  311 ) in a case where an AF assist light-lighting instruction is provided when the modeling lamp is being lit. 
     Next, a description will be given of the step S 416  and steps S 417  to S 421  executed in a case where an AF assist light-lighting instruction is provided when the modeling lamp is not lit. 
     In the step S 416 , the strobe controller  311  determines whether or not the strobe head section  320  is in the bounce state, i.e. whether or not the light emission surface of the strobe head prat  320  faces toward the front, based on a detection signal output from a detection switch, not shown. If the strobe head section  320  is in the bounce state (YES to the step S 416 ), the process proceeds to the step S 417 , whereas if the strobe head section  320  is in the non-bounce state (NO to the step S 416 ), the process skips the step S 417  and proceeds to the step S 418 . 
     In the step S 417 , the strobe controller  311  transmits a notification that the strobe head section  320  is in the bounce state (bounce notification) to the camera controller  102 . The bounce notification includes a request for setting the light emission amount Raf of the AF assist light to the light emission amount Rba specific to the bounce state. Note that details of the light emission amount Rba have already been described in the step S 321 . 
     In the step S 418 , the strobe controller  311  receives an instruction for setting the light emission amount Raf of the AF assist light to the light emission amount Rba specific to the bounce state, which is the fixed light emission amount, (AF assist light-lighting instruction) from the camera controller  102 . 
     In the step S 419 , the strobe controller  311  turns on the LED  322  with the light emission amount Rba according to the AF assist light-lighting instruction received in the step S 418 . 
     In the step S 420 , the strobe controller  311  receives a turn-off instruction for stopping lighting of the AF assist light using the LED  322  from the camera controller  102 , and the process proceeds to the step S 421 . 
     In the step S 421 , the strobe controller  311  stops light emission from the LED  322  according to the turn-off instruction received in the step S 420 , followed by terminating the present process. 
     As described above, in the present embodiment, the different temperature threshold values are provided so as to be set for the respective cases where light emission of the LED  322  is used as the modeling lamp and where light emission of the LED  322  is used as the AF assist light. With this, the strobe controller  311  (control unit) can control light emission of the LED  322  according to a use. For example, if the temperature information Tth acquired by the temperature sensor  323  exceeds the modeling lamp temperature threshold value, the LED  322  used as the modeling lamp is sometimes not lit or is sometimes dimmed. Even in such a case, unless the temperature information Tth reaches the AF assist light temperature threshold value lower than the modeling lamp temperature threshold value, it is determined that the LED  322  can be used up to the maximum light emission amount as the AF assist light, whereby the light emission control is performed. Further, in a case where the temperature information Tth exceeds the first AF assist light temperature threshold value Tlim_AF1, the AF assist light is switched to the flash AF assist light using the flashlight emitting tube  321 , whereby the control for achieving the role of the AF assist light is performed. According to the present embodiment, it is possible to cause the LED  322  to exhibit sufficient performance for respective uses of the case where the LED  322  is used as the modeling lamp and the case where the LED  322  is used as the AF assist light, while ensuring the temperature reliability of the LED  322 . 
     Next, a method of calculating the temperature threshold value Tlim set by the strobe controller  311  in advance will be described. 
     The temperature threshold value Tlim in each light emission mode is determined from the maximum energy total sum EN applied to the LED  322  in each of the above-described first and second light emission modes. 
     The maximum energy total sum EN is expressed by a product of the number of times of light emission N which is the maximum number in an assumed continuous use time TIME, and the power consumption H and the light emission time LT of the LED  322  in one lighting operation: 
     
       
      
       EN=N×H×LT  
      
     
     Further, the temperature threshold value Tlim is expressed by the following equation: 
         T lim= Tj−k×EN−a    
     In the above equation, Tj represents a junction temperature of the LED  322 , k represents a heat loss correction coefficient based on the LED light emission efficiency, and a represents a temperature margin. It is preferable to cause a difference between the internal temperature of the LED  322  and the measured temperature Tth acquired by the temperature sensor  323  to be included in the temperature margin a. 
     An example of calculation of the temperature threshold value Tlim in a case where the assumed continuous use time TIME is 1800 sec, the junction temperature Tj of the LED  322  is 120° C., and the temperature margin a is 10° C. will be described below. 
     In the first light emission mode in which the LED  322  is used for the modeling light emission, since the LED  322  can be continuously lit, the number Nmod of times of light emission is 1. Further, the power consumption Hmod and the light emission time LTmod of the LED at the time of the maximum light emission are 0.6 W and 1800 sec, respectively. Further, assuming that the heat loss correction coefficient kl based on the LED light emission efficiency is 0.0185, the maximum energy total sum in the first light emission mode is calculated by the following equation: 
         EN  mod= N  mod× H  mod× LT  mod=1×0.6×1800=1080
 
     Therefore, the temperature threshold value of the modeling light emission is calculated by the following equation: 
     
       
         
           
             
               
                 
                   
                     Tlim_mod 
                     ⁢ 
                     1 
                   
                   = 
                     
                   
                     Tj 
                     - 
                     
                       k 
                       ⁢ 
                       1 
                       × 
                       EN 
                       ⁢ 
                       mod 
                     
                     - 
                     a 
                   
                 
               
             
             
               
                 
                   = 
                     
                   
                     
                       120 
                       - 
                       
                         0.0185 
                         × 
                         1080 
                       
                       - 
                       10 
                     
                     = 
                     
                       90 
                       ⁢ 
                       ° 
                       ⁢ 
                           
                       
                         C 
                         . 
                       
                     
                   
                 
               
             
           
         
       
     
     On the other hand, in the second light emission mode in which the LED  322  is used for the AF assist light, the light emission time LTaf, i.e. the search-driving time varies with the lens device  200  and the image capturing apparatus  100  in use. For example, the search-driving time is several hundreds msec in a case where it is short, but in a case where the focus lens  202  is a lens requiring time to move, such as a super-telephotographic lens or a macro lens, the search-driving time becomes several tens msec. The difference in search-driving time is caused by the size of a focusing area, the weight of the focus lens  202 , the type of the focus adjustment section  205  (a stepping motor or an ultrasonic motor), and further, the value of current supplied to the focus adjustment section  205  which varies with a place in the camera ranking of the image capturing apparatus  100 . Therefore, the temperature threshold value of the AF assist light may be changed according to the lens device  200  and the image capturing apparatus  100  in use. 
     Assuming that the light emission time (=search-driving time) LTaf is 5 sec, and a time period LTaf_pause to elapse after the AF assist light is turned off until it is turned on again is 3 sec, the number Naf of times of light emission of the AF assist light is calculated by the following equation: 
         Naf =1800/(5+3)=225 (times) 
     Further, assuming that the LED power consumption Haf of the AF assist light is 0.6 W, and the heat loss correction coefficient kl based on the LED light emission efficiency is 0.0185, the maximum energy total sum of the AF assist light emission is calculated by the following equation: 
         ENaf=Naf×Haf×LTaf =225×0.6×5=675
 
     Therefore, the temperature threshold value of the AF assist light is calculated by the following equation: 
     
       
         
           
             
               
                 
                   
                     Tlim_AF 
                     ⁢ 
                     1 
                   
                   = 
                     
                   
                     Tj 
                     - 
                     
                       k 
                       ⁢ 
                       1 
                       × 
                       ENaf 
                     
                     - 
                     a 
                   
                 
               
             
             
               
                 
                   = 
                     
                   
                     
                       120 
                       - 
                       
                         0.0185 
                         × 
                         675 
                       
                       - 
                       10 
                     
                     = 
                     
                       97.5 
                       
                         ( 
                         
                           ° 
                           ⁢ 
                               
                           
                             C 
                             . 
                           
                         
                         ) 
                       
                     
                   
                 
               
             
           
         
       
     
     As indicated by the above calculation example, in the present embodiment, the different temperature threshold values are set according to respective uses, for example, such that the first modeling lamp temperature threshold value Tlim_mod1 is set to 90° C., and the first AF assist light temperature threshold value Tlim_AF1 is set to 97.5° C. This is because, as mentioned above, the temperature threshold value is set based on the maximum energy total sum which is calculated from how the light emission is performed according to each use. Although in the above description, an influence of heat dissipation is omitted to simplify the explanation, it is possible to calculate a temperature threshold value with higher accuracy by performing calculation with a heat dissipation element included therein. 
     Next, a description will be given of a second embodiment of the present invention. In the first embodiment, the strobe head section  320  has the LED  322  and the temperature sensor  323  mounted therein. On the other hand, in the present embodiment, the LED  322  and the temperature sensor  323  are mounted in the central portion of the strobe body section  310 . Further, although in the first embodiment, the light emitting device  300  is attached to the image capturing apparatus  100 , in the present embodiment, the light emitting device  300  and the image capturing apparatus  100  are separately arranged at respective locations, and the light emitting device  300  is used as a slave strobe for wireless strobe photographing. The present embodiment has the same configuration as the first embodiment except these points, and hence the same components in the present embodiment as those in the first embodiment are denoted by the same reference numerals and redundant descriptions thereof are omitted. 
       FIG.  6    is a block diagram showing a hardware configuration of a camera system  1   a  including the light emitting device  300  according to the present embodiment. 
     A wireless module  315  is further disposed in the strobe body section  310 , and further, a transmitter  400  is connected to the camera-side ACC connection section  140  of the image capturing apparatus  100 . Note that a wireless communication device connected to the image capturing apparatus  100  is not limited to the transmitter  400  insofar as it is the master device of the light emitting device  300  and is communicably connected to the image capturing apparatus  100 , and for example, a master device strobe having a wireless module mounted therein may be employed. 
     The wireless module  315  includes a strobe antenna and performs wireless communication with the transmitter  400  via the strobe antenna. 
     The strobe controller  311  receives information (instruction) for controlling the light emission timing and the light emission amount from the transmitter  400  via the wireless module  315 . 
     Thus, in the present embodiment, the LED  322  is moved to the central portion of the strobe body section  310 , and its use is not the modeling lamp, but the video light. Here, a process for lighting the video light, which is started when the user operates the strobe, is the same as the process described with reference to  FIG.  2   , and hence the description thereof is omitted. Further, also in the present embodiment, the LED  322  and the light emitting tube  321  can continue to be used as the AF assist light as well, and the AF assist light control process in the step S 206  in  FIG.  3   , described with reference to  FIGS.  4 A to  4 D , can be used by omitting the steps associated with the bounce. Therefore, the description of this process is also omitted. 
     In the present embodiment, the light emission mode of the LED  322  has a third light emission mode in which light emission is used as a signal indicating charge completion of the main capacitor  331  of the light emitting device  300  which is used as a slave device, in strobe wireless photographing. The following description will be given of a charge completion process for controlling lighting of the LED  322  in the third light emission mode. 
       FIG.  7    is a flowchart of the charge completion process. 
     The present process is executed by the strobe controller  311  that loads an associated program stored in the ROM, not shown, disposed in the strobe body section  310  into the RAM, not shown, also disposed in the strobe body section  310 . 
     First, wireless multi-light photographing will be briefly described. The wireless multi-light photographing refers to strobe photographing in which a wireless communication device as a master device is connected to the image capturing apparatus  100 , and instructs the light emission amount and the light emission timing to one or more slave strobes placed at locations remote from the wireless communication device, using radio wave communication or optical communication. 
     In a step S 501 , the strobe controller  311  confirms settings of wireless photographing of the light emitting device  300 , and determines whether or not the light emitting device  300  is a slave strobe (slave to the transmitter  400  as the master device). If the light emitting device  300  is not a slave strobe (NO to the step S 501 ), the present process is immediately terminated. On the other hand, if the light emitting device  300  is a slave strobe (YES to the step S 501 ), the process proceeds to a step S 502 . 
     In the step S 502 , the strobe controller  311  determines whether or not the main capacitor  331  is in a charge completed state. Here, the charge completed state refers to a state in which electric power sufficient for full light emission has been charged in the main capacitor  331 . Note that in the present embodiment, the above-mentioned resistor, not shown, for detecting a voltage of the main capacitor  331  is integrated as a component of the boost circuit, not shown, and it is possible to determine whether or not the main capacitor  331  is in the charge completed state, using this resistor. If the main capacitor  331  is not in the charge completed state (NO to the step S 502 ), the process returns to the step S 501 , and this determination is repeated until it is determined that the main capacitor  331  is in the charge completed state. If the main capacitor  331  is in the charge completed state (YES to the step S 502 ), the process proceeds to a step S 503 . 
     In the step S 503 , the strobe controller  311  acquires the temperature information Tth from the temperature sensor  323  disposed in the vicinity of the LED  322 . 
     In a step S 504 , the strobe controller  311  determines whether or not the temperature information Tth acquired in the step S 503  is equal to or higher than a first charge completion signal temperature threshold value Tlim_BAT1. If the acquired temperature information Tth is equal to or higher than the first charge completion signal temperature threshold value Tlim_BAT1 (YES to the step S 504 ), the process proceeds to a step S 505 , wherein the LED  322  is controlled not to be lit, followed by terminating the present process. On the other hand, if the temperature information Tth is lower than the first charge completion signal temperature threshold value Tlim_BAT1 (NO to the step S 504 ), the process proceeds to a step S 506 . 
     In the step S 506 , the strobe controller  311  determines whether or not the acquired temperature information Tth is equal to or higher than a second charge completion signal temperature threshold value Tlim_BAT2 lower than the first charge completion signal temperature threshold value Tlim_BAT1. If the acquired temperature information Tth is equal to or higher than the second charge completion signal temperature threshold value Tlim_BAT2 (YES to the step S 506 ), the process proceeds to a step S 507 . On the other hand, if the temperature information Tth is lower than the second charge completion signal temperature threshold value Tlim_BAT2 (NO to the step S 506 ), the process proceeds to a step S 508 . 
     In the step S 507 , since the acquired temperature information Tth is equal to or higher than the second charge completion signal temperature threshold value Tlim_BAT2, it is necessary to protect the LED  322  from heat. For this reason, the strobe controller  311  provides a lighting instruction to the LED  322  for emitting light with a light amount ½ Rmax_initial which is half of the maximum light emission amount Rmax_initial. Then, the process proceeds to a step S 509 . 
     On the other hand, in the step S 508 , since the acquired temperature information Tth is lower than the second charge completion signal temperature threshold value Tlim_BAT2, the strobe controller  311  provides a lighting instruction to the LED  322  for emitting light with the maximum light emission amount Rmax_initial. Then, the process proceeds to the step S 509 . 
     In the step S 509 , the strobe controller  311  causes the LED  322  to start intermittent light emission at intervals of approximately one second according to the lighting instruction provided in the immediately preceding step (i.e. the step S 507  or S 508 ), and then proceeds to a step S 510 . 
     In the step S 510 , the strobe controller  311  determines whether or not an instruction for starting flashlight emission from the flashlight emitting tube  321  (flashlight emission start instruction) has been received from the transmitter  400 . If the flashlight emission start instruction has been received (YES to the step S 510 ), the process proceeds to a step S 511 , whereas if the flashlight emission start instruction has not been received (NO to the step S 510 ), the process returns to the step S 501  and continues to wait to receive the flashlight emission start instruction. 
     In the step S 511 , the strobe controller  311  terminates intermittent light emission of the LED  322  and proceeds to a step S 512 . 
     In the step S 512 , the strobe controller  311  causes the flashlight emitting tube  321  to emit flashlight according to the flashlight emission start instruction received from the transmitter  400  in the step S 510 . After the flashlight emission, the process returns to the step S 501 . 
     Lighting of the LED  322  as the charge completion signal in a case where the main capacitor  331  has been shifted to the charge completed state is intermittent lighting at intervals of one second, and hence the temperature rise is gentle, compared with the case where the LED  322  is continuously lit as the video light. For this reason, the first charge completion signal temperature threshold value Tlim_BAT1 for determining the availability of the LED  322  for the charge completion signal is set to be higher than the temperature threshold value for determining the availability of the LED  322  as the video light (the same value as the first modeling lamp temperature threshold value Tlim_mod1). Similarly, the second charge completion signal temperature threshold value Tlim_BAT2 for determining the light emission amount of the LED  322  for the charge completion signal is set to be higher than the temperature threshold value for determining the light emission amount of the LED  322  as the video light (the same value as the second modeling lamp temperature threshold value Tlim_mod2). 
     As described above, in the present embodiment, when the light emitting device  300  is a strobe slave device, and the main capacitor  331  has been shifted to the charge completed state, the LED  322  disposed in the strobe body section  310  is caused to intermittently emit light for indicating charge completion. This makes it possible to notify a user that the light emitting device  300  as the strobe slave device can be used as a video light and the flashlight emitting tube  321  can be used. Further, similar to the first embodiment, also in the present embodiment, it is possible to perform proper light emission control of the LED  322  for each use by setting the different temperature threshold values according to the uses. According to the present invention, it is possible to cause the LED  322  to exhibit sufficient performance for the respective uses of the case where the LED  322  is used as the video light and the case where the LED  322  is used as a flickering light for indicating charge completion, while ensuring the temperature reliability of the LED  322 . 
     Note that although in the present embodiment, the description is given of the case where the light emitting device  300  is a strobe slave device, this is not limitative. That is, the third light emission mode may be a mode in which the LED  322  disposed in the strobe body section  310  is caused to perform intermittent light emission to notify a user of charge completion when the main capacitor  331  has been shifted to the charge completed state. 
     Next, a description will be given of a third embodiment of the present invention. In the first and second embodiments, the flashlight emitting tube  321  which is formed by a xenon tube or a quartz tube and emits flashlight is mounted in the strobe head section  320 . On the other hand, in the third embodiment, a case where the light emission mode of the LED  322  has a fourth mode in which the LED  322  emits flashlight. That is, the present embodiment has the same configuration as the first embodiment except that the flashlight emitting tube  321  and the main capacitor  331  are not mounted in the light emitting device  300  but an LED flashlight dedicated circuit is mounted instead so as to cause the LED  322  to emit flashlight. Therefore, the same components of the present embodiment as those of the first embodiment are denoted by the same reference numerals, and redundant description thereof is omitted. 
       FIG.  8    is a block diagram showing a hardware configuration of a camera system  1   b  according to the present embodiment. 
     As shown in  FIG.  8   , in the present embodiment, the flashlight emitting tube  321  and the main capacitor  331  are omitted from the configuration of the first embodiment, and the LED flashlight dedicated circuit, not shown, is added so as to cause the LED  322  to emit flashlight. This is because the current value to be applied to the LED  322  is different between the normal light emission, such as the modeling light emission and the AF assist light, and the flashlight emission, and hence another circuit is required to be provided for flashlight emission. 
     Further, to perform the following LED flashlight emission process, a temperature threshold value (a first LED flashlight temperature threshold value Tlim_flash1 and a second LED flashlight temperature threshold value Tlim_flash2 lower than the first LED flashlight temperature threshold value Tlim_flash1) in the fourth light emission mode are set by the strobe controller  311  (second setting unit). 
       FIG.  9    is a flowchart of the LED flashlight emission process. 
     The present process is executed by the strobe controller  311  that loads an associated program stored in the ROM, not shown, disposed in the strobe body section  310  into the RAM, not shown, also disposed in the strobe body section  310 . 
     In a step S 601 , the strobe controller  311  receives an LED flashlight emission instruction for causing the LED  322  to emit flashlight from the image capturing apparatus  100 . 
     In a step S 602 , the strobe controller  311  reads out an elapsed time Interval. Here, the elapsed time Interval is an elapsed time after the last LED flashlight emission, which is counted by the strobe controller  311 . However, in a case where the LED flashlight emission has never been performed, the value of the elapsed time Interval is set to 0 sec. 
     In a step S 603 , the strobe controller  311  acquires the temperature information Tth from the temperature sensor  323  disposed in the vicinity of the LED  322 . 
     In a step S 604 , the strobe controller  311  determines whether or not the temperature information Tth acquired in the step S 603  is equal to or higher than the first LED flashlight temperature threshold value Tlim_flash1. If the acquired temperature information Tth is equal to or higher than the first LED flashlight temperature threshold value Tlim_flash1 (YES to the step S 604 ), the process proceeds to a step S 605 . On the other hand, if the acquired temperature information Tth is lower than the first LED flashlight temperature threshold value Tlim_flash1 (NO to the step S 604 ), the process proceeds to a step S 607 . 
     In the step S 605 , the strobe controller  311  determines whether or not the elapsed time Interval acquired in the step S 602  is equal to or shorter than a first light emission interval Interval_1. If the elapsed time Interval is equal to or shorter than the first light emission interval Interval_1 (YES to the step S 605 ), the process proceeds to a step S 606 , wherein the LED flashlight emission is performed, followed by terminating the present process. Note that this is the time at which the LED flashlight emission is started, the strobe controller  311  starts counting the elapsed time after this LED flashlight emission, as the elapsed time Interval. On the other hand, if the acquired elapsed time Interval is longer than the first light emission interval Interval_1 (NO to the step S 605 ), the present process is immediately terminated without causing the LED  322  to emit light. 
     In the step S 607 , the strobe controller  311  determines whether or not the acquired temperature information Tth is equal to or higher than the second LED flashlight temperature threshold value Tlim_flash2. If the acquired temperature information Tth is equal to or higher than the second LED flashlight temperature threshold value Tlim_flash2 (YES to the step S 607 ), the process proceeds to a step S 608 . On the other hand, if the acquired temperature information Tth is lower than the second LED flashlight temperature threshold value Tlim_flash2 (NO to the step S 607 ), the process proceeds to the S 606 , wherein the LED flashlight emission is performed, followed by terminating the present process. 
     In the step S 608 , the strobe controller  311  determines whether or not the acquired elapsed time Interval is equal to or shorter than a second light emission interval Interval_2 shorter than the first light emission interval Interval_1. If the elapsed time Interval is equal to or shorter than the second light emission interval Interval_2 (YES to the step S 608 ), the process proceeds to the step S 606 , wherein the LED flashlight emission is performed, followed by terminating the present process. On the other hand, if the acquired elapsed time Interval is longer than the second light emission interval Interval_2 (NO to the step S 608 ), the present process is terminated without causing the LED  322  to emit light. 
     As described above, in the LED flashlight emission process in the present embodiment, in a case where the acquired temperature information Tth becomes equal to or higher than a temperature threshold value, the number of times of light emission of the LED  322  is limited by performing the LED flashlight emission at a light emission interval determined according to the temperature threshold value. However, this is not limitative insofar as it is possible to suppress temperature rise within the LED  322  in the LED flashlight emission process. For example, in a case where the acquired temperature information Tth becomes equal to or higher than a temperature threshold value, the light emission amount may be set to an amount of LED flashlight emission, which is determined according to the temperature threshold value. 
     Further, similar to the first embodiment, in the configuration of the present embodiment, it is also possible to use the LED  322  as the modeling light emission and the AF assist light. Further, similar to the second embodiment, in a case where the LED  322  is mounted in the central portion of the strobe body section  310 , it is also possible to use the LED  322  as the video light and the flickering light for indicating charge completion. 
     Further, as for the settings of the temperature threshold value used for the LED flashlight emission process, the temperature threshold value may be calculated from the maximum energy total sum EN applied to the LED light emission, as described in the first embodiment, or may be determined from a material heat-resistant temperature of peripheral components. 
     According to the present invention, the light emission amount and the light emission interval of the LED  322  are controlled in accordance with each of uses of the LED  322 , such as the modelling lamp, the video light, the AF assist light, the flickering light for indicating charge completion, and the LED flashlight. With this, it is possible to suppress temperature rise within the LED  322  and cause the LED  322  to exhibit sufficient performance for each use while ensuring the reliability of the LED  322 . 
     Other Embodiments 
     Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     The processor or circuit can include a central processing unit (CPU), a micro processing unit (MPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA). Further, the processor or circuit can include a digital signal processor (DSP), a digital flow processor (DFP) or a neural processing unit (NPU). 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2021-181023 filed Nov. 5, 2021, which is hereby incorporated by reference herein in its entirety.