Patent Description:
Flash devices controlled through wireless communication with an image capturing apparatus (wireless strobes) have been known for some time. Wireless strobes have the advantage of being easier to install than strobes connected using wires. However, the lower reliability and greater latency than wired communication are issues that must be addressed.

<CIT> discloses a technique in which the reliability of communication is ensured by sending timing information, which instructs the timing at which the strobe is to fire, multiple times from an image capturing apparatus to a wireless strobe. Furthermore, according to <CIT>, the timing of the firing is varied from timing information to timing information so that the wireless strobe fires at the same timing regardless of which of the timing information sent multiple times the firing is based upon.

If the shutter speed or exposure period is determined prior to shooting, the strobe can be fired in synchronization with the shutter release using the method disclosed in <CIT> by instructing the firing timing in accordance with delay taken by communication, the timing of shutter operations, and the like. The method disclosed in <CIT> can implement front curtain synchronous firing control, in which the strobe is caused to fire immediately after the front curtain fully opens, and rear curtain synchronous firing control, in which the strobe is caused to fire immediately before the rear curtain closes, in a focal plane shutter or electronic shutter combination.

However, in rear curtain synchronous firing control realized through radio wave control, operations from the start of the firing sequence to the end of the firing are linked to the timing at which the rear curtain of the shutter closes. Accordingly, after a long exposure, the communication link between the communication device and the wireless strobe may be lost between the start of the exposure and the time when the strobe fires immediately before the rear curtain closes, and it therefore may not be possible to cause the wireless strobe to fire synchronously with the rear curtain.

Specifically, the communication device must instruct the wireless strobe to obtain charge completion information, communicate a light amount setting, and set a firing trigger for the wireless strobe without any skew, in a period from when a signal for the image capturing apparatus to start shooting is made to when the wireless strobe stops firing. The issuing of beacon packets is therefore stopped.

A "beacon" is a signal that ensures communication between a communication device and a wireless strobe, and normally, a link is maintained by the sending-side communication device issuing a beacon packet periodically, e.g., every one second, and the wireless strobe receiving the beacon packets. The wireless strobe is designed so that the link is cut if a beacon is not received within a predetermined amount of time, e.g., five seconds. As such, with long exposure times such as times over five seconds, the link will be cut and the wireless strobe will be unable to fire synchronously with the rear curtain. Further background is disclosed in <CIT> "Flash Control Device, Flash Control Method, Flash, Image Capture Apparatus, and Image Capture System", <CIT> "Stroboscope Control System and Stroboscope Control Method" and <CIT> "Image Apparatus, Flash Device, and Control Method Thereof".

Having been achieved in light of the foregoing issue, the present invention improves the reliability of firing control when controlling a strobe wirelessly.

According to a first aspect of the present invention, there is provided a control apparatus as specified in claims <NUM>-<NUM>.

According to a second aspect of the present invention, there is provided an image capturing apparatus as specified in claim <NUM>.

According to a third aspect of the present invention, there is provided a control method of controlling a strobe as specified in claim <NUM>.

According to a fourth aspect of the present invention, there is provided a computer-readable storage medium as specified in claim <NUM>.

<FIG> is a schematic diagram illustrating a strobe control camera system according to a first embodiment of the present invention. The strobe control camera system according to the present embodiment is a wireless strobe system constituted by a digital single-lens reflex camera (called simply a "camera" hereinafter) <NUM>, a communication device (called a "transmitter" hereinafter) <NUM> connected directly to the camera <NUM>, and a strobe ("flash device") <NUM> independent from the camera <NUM>.

The transmitter <NUM>, which is connected directly to an external accessory attachment part <NUM> of the camera <NUM>, is capable of communicating with the camera <NUM> via the external accessory attachment part <NUM>, and incorporates a wireless communication circuit and a wireless antenna. The strobe <NUM>, which is independent from the camera <NUM>, also incorporates a wireless communication circuit and a wireless antenna, like the transmitter <NUM>. The transmitter <NUM> and the strobe <NUM> communicate wirelessly through a known wireless communication standard, such as IEEE <NUM>.

<FIG> assumes shooting using a strobe in a photography studio, and illustrates the camera <NUM> being held in place by a tripod <NUM> with respect to a subject <NUM> and a screen <NUM>. In the present embodiment, the transmitter <NUM> connected to the camera <NUM> serves as a master device and the strobe <NUM> independent from the camera <NUM> serves as a slave device, and a firing timing of the strobe <NUM> is synchronized with a shutter timing of the camera <NUM>. Strobe-synchronized shooting is performed as a result.

Although the transmitter <NUM> connected to the camera <NUM> is described as the master in the present embodiment, it is also possible to use a strobe capable of wireless communication as the master instead of the transmitter <NUM>. Alternatively, if the camera itself incorporates a wireless communication circuit and a wireless antenna, and is capable of wireless communication, the camera may serve as the master and send instructions directly to the strobe <NUM> through wireless communication.

<FIG> are a schematic vertical cross-sectional view (a vertical cross-sectional view including an optical axis) and a rear view of the camera <NUM> and the transmitter <NUM> according to the present embodiment. Note that of the configurations included in the camera <NUM>, only the configurations required for describing the embodiment are illustrated in <FIG>.

The camera <NUM> and a shooting lens <NUM> are connected by a mount <NUM>, and the shooting lens <NUM> is an interchangeable lens which can be removed from the camera <NUM>. The shooting lens <NUM> includes a lens group <NUM>, and forms an optical image of a subject on an image capturing surface of an image sensor <NUM>.

The image sensor <NUM> is a CMOS image sensor, for example, and has a plurality of photoelectric conversion elements arranged two-dimensionally. The image sensor <NUM> converts the optical image formed by the shooting lens <NUM> into an electrical signal (an image signal) using the plurality of photoelectric conversion elements. The amount of the electrical signal (a voltage value) relative to the same amount of light received can be changed by changing the sensitivity of the image sensor <NUM>.

A shutter <NUM> is disposed in front of the image sensor <NUM>, and includes a front curtain and a rear curtain that travel up and down. The front curtain will also be called a "first curtain" and the rear curtain will also be called a "second curtain". Assuming a state in which the optical path is blocked is "fully closed" and a state in which the optical path is open is "fully open", exposure of the image sensor <NUM> starts when, in a state where the rear curtain is fully open and the front curtain is fully closed, the front curtain travels in a direction that opens the front curtain. Then, when the rear curtain is fully closed after a predetermined amount of time has passed, the exposure of the image sensor <NUM> ends. As the exposure time shortens, the rear curtain begins traveling before the front curtain becomes fully open, and the image sensor <NUM> is exposed through a slit-shaped opening formed between the front curtain and the rear curtain.

A camera microcomputer <NUM> includes, for example, a programmable processor and memory, and controls operations of the camera <NUM>, the shooting lens <NUM>, and external accessories by loading programs stored in non-volatile memory into system memory and executing the programs.

A lens control unit <NUM> of the shooting lens <NUM> includes, for example, a programmable processor and memory, and controls operations of the shooting lens <NUM> by loading programs stored in non-volatile memory into system memory and executing the programs. Operations of the shooting lens <NUM> include driving an aperture stop <NUM>, driving a mobile lens included in the lens group <NUM>, and the like. A focus lens, a magnification lens, and the like are included in the mobile lens. The lens control unit <NUM> can communicate with the camera microcomputer <NUM> through the mount <NUM>, and controls operations of the shooting lens <NUM> in response to instructions, requests, and the like from the camera microcomputer <NUM>, sends information of the shooting lens <NUM> to the camera microcomputer <NUM>, and so on.

The camera microcomputer <NUM> can execute automatic exposure control ("AE" hereinafter) for determining exposure control values (aperture value, shutter speed, shooting sensitivity) on the basis of brightness information of an image shot by the image sensor <NUM>, for example. The camera microcomputer <NUM> can also execute automatic focus adjustment ("AF" hereinafter) for controlling the focal distance of the shooting lens <NUM> so as to focus on a predetermined area within a shooting range, on the basis of contrast information of the image shot using the image sensor <NUM>.

Note that the configuration is not limited to one in which the camera microcomputer <NUM> implements the AE and AF, and any publicly known configuration can be used, such as a configuration in which an AE sensor, an AF sensor, and the like are used.

A display unit <NUM> is constituted by a liquid crystal display, an organic EL display, or the like, and displays images shot using the image sensor <NUM>, information about the camera <NUM> (various types of setting values, remaining battery power, a number of shots that can be recorded, and the like), displays a GUI, and so on. The display unit <NUM> may be a touch screen.

A mode selection unit <NUM> is an operating member for selecting a shooting mode of the camera <NUM>. "Shooting mode" refers to modes having different methods for setting the exposure control values, and includes an aperture priority mode, a shutter speed priority mode, a program mode, and an auto mode. The modes may also include a shooting mode for setting exposure control values appropriate for a specific subject or situation, such as shooting a moving body, shooting a person, or the like.

A shooting instruction unit ("shutter button" hereinafter) <NUM> includes a switch (release switch) SW1 which turns on in a half-pressed state, and a switch (release switch) SW2 which turns on in a fully-pressed state. The camera microcomputer <NUM> recognizes the half-pressed state (the switch SW1 being on) as a shooting preparation instruction, and recognizes the fully-pressed state (the switch SW2 being on) as a shooting start instruction. Upon recognizing the shooting preparation instruction, the camera microcomputer <NUM> executes AE and AF. Additionally, upon recognizing the shooting start instruction, the camera microcomputer <NUM> starts still image shooting processing, which includes driving the shutter <NUM>, controlling the lighting of a strobe, and the like.

Operating members of the camera <NUM>, such as the mode selection unit <NUM> and the shutter button <NUM>, are electrically connected to the camera microcomputer <NUM>. The camera microcomputer <NUM> monitors the states of the operating members, and upon detecting a change in the state of an operating member, executes operations in response to the detection.

When a long exposure mode (bulb mode) is selected by the mode selection unit <NUM>, the camera microcomputer <NUM> drives the shutter <NUM> upon recognizing the shooting start instruction, and exposes the image sensor <NUM> by setting the front curtain and the rear curtain to be fully open. The camera microcomputer <NUM> continues to expose the image sensor <NUM> while the shooting start instruction is continuously being recognized. Once the shooting start instruction is no longer recognized, the camera microcomputer <NUM> ends the exposure of the image sensor <NUM> by setting the front curtain and the rear curtain of the shutter <NUM> to be fully closed. In another shooting mode, the camera microcomputer <NUM> controls the exposure time of the image sensor <NUM> through automatic exposure control, or in accordance with a shutter speed set by a user.

The external accessory attachment part <NUM> is what is known as a "hot shoe", to which external accessories such as the transmitter <NUM>, an external strobe, a microphone, and the like are mechanically and electrically connected. The external accessories attached to the external accessory attachment part <NUM>, such as the transmitter <NUM> and the strobe <NUM>, can communicate with the camera microcomputer <NUM>, and the settings, operations, and the like of the external accessories can be controlled by the camera microcomputer <NUM>.

A transmitter microcomputer <NUM> of the transmitter <NUM> includes, for example, a programmable processor and memory, and controls the operations of the transmitter <NUM> by loading programs stored in non-volatile memory into the system memory and executing the programs. By connecting to the external accessory attachment part <NUM> of the camera <NUM>, a camera mounting part <NUM> of the transmitter <NUM> is mechanically and electrically connected to the camera <NUM>, and the transmitter microcomputer <NUM> and the camera microcomputer <NUM> can communicate as a result.

<FIG> is a block diagram illustrating an example of the functional configurations of the camera <NUM> and transmitter <NUM> illustrated in <FIG>. Elements also illustrated in <FIG> are given the same reference signs, and redundant descriptions will not be given.

In the shooting lens <NUM>, an aperture drive unit <NUM> includes a motor, an actuator, and the like that drive the aperture stop <NUM> of the shooting lens <NUM>, and adjusts the extent to which the aperture stop <NUM> opens by driving the aperture stop <NUM> under the control of the lens control unit <NUM>.

A lens drive unit <NUM> includes a motor, an actuator, and the like that drive the mobile lens in the lens group <NUM> of the shooting lens <NUM>, and adjusts the focal distance, focal length (angle of view), and so on of the shooting lens <NUM> by driving the mobile lens under the control of the lens control unit <NUM>.

In the camera <NUM>, a shutter drive unit <NUM> includes a motor, a spring, and the like that drive the front curtain and the rear curtain of the shutter <NUM>, and executes shutter charging, causes the shutter curtains to travel, and so on under the control of the camera microcomputer <NUM>.

A signal processing unit <NUM> applies various types of processing to the image signal output by the image sensor <NUM>, including noise removal, white balance adjustment, color interpolation, various types of correction, resolution conversion, generating evaluation values used for AF and AE, and the like. The signal processing unit <NUM> generates an image signal for display and outputs that signal to the display unit <NUM>, generates an image data file for recording and outputs that file to the camera microcomputer <NUM>, and the like. The signal processing unit <NUM> also detects a predetermined region of the subject, such as a person's face, detects subject movement, and the like. Furthermore, the signal processing unit <NUM> encodes and decodes image data as needed.

A recording unit <NUM> is a memory card, for example, and the camera microcomputer <NUM> records the image data file for recording, obtained from the signal processing unit <NUM>, in the recording unit <NUM>. The recording format, the format of the image data file, and the like are determined in advance.

In the transmitter <NUM>, a wireless circuit <NUM> performs wireless communication with the strobe <NUM> (described later) through a wireless antenna unit <NUM>. The transmitter microcomputer <NUM> communicates with the camera microcomputer <NUM> through the external accessory attachment part <NUM>. Firing timing of the strobe <NUM> is controlled on the basis of a firing timing instruction from the camera <NUM>, through wireless communication performed by the wireless circuit <NUM> and the wireless antenna unit <NUM>.

<FIG> is a vertical cross-sectional view schematically illustrating an example of the configuration of the strobe <NUM>, which can communicate wirelessly with the camera <NUM>, and <FIG> is a block diagram schematically illustrating an example of the functional configuration of the strobe <NUM>. In both drawings, only part of the configuration of the strobe <NUM> is illustrated.

A light emitting unit <NUM> includes a flash lamp, a capacitor, and the like, and emits light under the control of a strobe microcomputer <NUM>. The strobe microcomputer <NUM> controls the firing timing, emitted light amount, and so on of the light emitting unit <NUM> on the basis of instructions from an external device, instructions made through operating members, and so on. A camera mounting part <NUM> is capable of mechanically and electrically connecting to the external accessory attachment part <NUM> of the camera <NUM>. The strobe can communicate with the camera microcomputer <NUM> through the camera mounting part <NUM>, and settings, operations, and the like of the strobe can be controlled by the camera microcomputer <NUM>. A stand <NUM> is a support member for enabling the strobe <NUM> to stand on its own, and is configured to support the camera mounting part <NUM> of the strobe <NUM>.

In <FIG>, a wireless circuit <NUM> of the strobe <NUM> performs wireless communication with the transmitter <NUM> through a wireless antenna unit <NUM>. The strobe microcomputer <NUM> receives information (instructions) for controlling the firing timing, the emitted light amount, and the like from the camera <NUM> through the wireless circuit <NUM>, the wireless antenna unit <NUM>, and the transmitter <NUM>.

Although the method for wireless communication between the transmitter <NUM> and the strobe <NUM> is not particularly limited, radio wave-based wireless communication using the <NUM> band is assumed to be used in the present embodiment. Operations of an image capturing system configured so that the camera <NUM>, the transmitter <NUM>, and the strobe <NUM> are capable of wireless communication will be described hereinafter.

<FIG> is a flowchart pertaining to firing control method selection processing performed by the camera microcomputer <NUM>. This processing can be executed at any desired timing prior to recognizing the shooting start instruction.

In step S101, the camera microcomputer <NUM> determines whether to perform normal front curtain synchronous firing control or rear curtain synchronous firing control. "Front curtain synchronous firing control" is synchronous strobe firing control which causes the strobe to fire immediately after the shutter front curtain has become fully open. "Rear curtain synchronous firing control" is synchronous strobe firing control which causes the strobe to fire immediately before the shutter rear curtain travels. Which firing control is to be performed is assumed to be set in advance through user operations.

In the case of front curtain synchronous firing control, in step S102, front curtain synchronous shooting is registered in the camera microcomputer <NUM>, and the selection of the firing control method ends.

When rear curtain synchronous firing control has been determined in step S101, the camera microcomputer <NUM> confirms the shooting method in step S103. Specifically, the camera microcomputer <NUM> confirms whether the shooting mode which is set is a bulb shooting mode, in which the shooting is performed with an indefinite exposure period, or as another shooting mode. Shooting modes aside from the bulb mode will be collectively called a "normal shooting mode".

In the case of bulb shooting, in step S104, bulb shooting and rear curtain synchronous firing control are registered in the camera microcomputer <NUM>, and the shooting method selection then ends.

In the case of normal shooting, in step S105, rear curtain synchronous firing control in normal shooting is registered in the camera microcomputer <NUM>, and the shooting method selection then ends.

Operations performed when the shooting mode of the camera <NUM> is a mode that causes the strobe <NUM> to perform rear curtain synchronous firing in the normal mode (step S105) will be described next with reference to the flowchart in <FIG>. <FIG> illustrates operations performed by the camera <NUM>, <FIG> illustrates operations performed by the transmitter <NUM>, and <FIG> illustrates operations performed by the strobe <NUM>.

To facilitate descriptions, the present embodiment assumes that a shutter speed Tv, an aperture value Av, an ISO sensitivity, and a strobe emitted light amount are all set to manual before shooting. However, these values may be determined using AE (automatic exposure) and a strobe automatic adjustment system.

Additionally, the present embodiment will describe strobe synchronized shooting in which the transmitter <NUM> and the strobe <NUM> connected to the camera <NUM> are in a one-to-one relationship, as illustrated in <FIG>. It is furthermore assumed that the transmitter <NUM> and the strobe <NUM> are already registered with each other as communication partners through a known wireless pairing method.

When the transmitter <NUM> is powered on and is set to a strobe firing mode, the transmitter microcomputer <NUM> of the transmitter <NUM> controls the wireless circuit <NUM> to scan for channels across different wireless frequencies. Through this, the transmitter <NUM> searches for the strobe <NUM> to serve as a communication partner. When the strobe <NUM> is powered on, the strobe <NUM> controls the wireless circuit <NUM> in the same manner as the transmitter <NUM>, sets a channel to be used, and enters a state of being able to respond to the search performed by the transmitter <NUM>.

When the transmitter <NUM> discovers the strobe <NUM> through the search, the transmitter <NUM> serves as a network coordinator and establishes a network by starting the periodic issuance of beacon packets (beacon signals). The strobe <NUM> acts as a network device, establishing a link with the transmitter <NUM> as a communication partner so as to be capable of communication at any time.

Operations of the camera <NUM> performed after a wireless communication system constituted by the transmitter <NUM> and the strobe <NUM> has been started in this manner will be described with reference to the flowchart in <FIG>.

In step S201, the camera <NUM> enters a state of standing by for a release operation made by the user (a switch SW1 on standby state).

When the switch SW1 turns on in step S201, focus adjustment operations begin in step S202, and in step S203, the camera stands by for the switch SW2 to turn on.

In step S203, the camera microcomputer <NUM> determines whether or not the switch SW2 has turned on in response to a user operation. When the switch SW2 turns on, in step S204, the transmitter <NUM> is notified that the switch SW2 has turned on through a connection unit constituted by the external accessory attachment part <NUM> of the camera <NUM> and the camera mounting part <NUM> of the transmitter <NUM>. The notification that the switch SW2 has turned on simultaneously serves as a trigger for instructing the transmitter <NUM> to obtain charging information, which indicates a charging state of the strobe <NUM>, through wireless communication between the transmitter <NUM> and the strobe <NUM>.

In step S205, the camera <NUM> receives the charging information, indicating the charging state of the strobe <NUM>, through the transmitter <NUM>. Then, in step S206, it is determined whether or not the strobe can fire.

When it is determined in step S206 that the strobe can fire, in step S207, the camera <NUM> performs communication for setting a pre-set emitted light amount in the strobe <NUM> through the transmitter <NUM>, under the control of the camera microcomputer <NUM>. Having received the emitted light amount setting, the strobe <NUM> returns an Ack (acknowledgment) packet for acknowledging the reception, and the camera <NUM> receives that packet through the transmitter <NUM>. If it is determined in step S206 that the strobe cannot fire, the sequence returns to step S203, where the camera once again stands by for the switch SW2 to turn on.

Next, in step S208, under the control of the camera microcomputer <NUM>, the camera <NUM> controls the aperture stop <NUM> to cause the front curtain of the shutter <NUM> to begin traveling, and controls the image sensor <NUM> to begin accumulation.

In step S209, under the control of the camera microcomputer <NUM>, the camera <NUM> makes a notification of a rear curtain travel start time of the shutter <NUM>. The timing of the notification is immediately before the rear curtain travels. Specifically, the processing time is calculated by taking into account the shutter speed Tv value set before the start of shooting, the processing time of the firmware in the camera, and the time from when a firing instruction is made by the camera to when the firing of the strobe <NUM> ends, and the timing of the notification is set to be greater than or equal to an amount of time equivalent to this processing time prior to the start of the rear curtain travel.

In step S210, under the control of the camera microcomputer <NUM>, the camera <NUM> notifies the transmitter <NUM> that a firing trigger is to be set. Operations performed in the period from when the transmitter <NUM> receives the firing trigger setting notification to when the strobe <NUM> fires will be described in detail later with reference to <FIG> and <FIG>, but the strobe <NUM> fires starting at the firing trigger setting notification (firing trigger signal) made in step S210.

After the strobe <NUM> has fired, in step S211, the camera <NUM> causes the rear curtain of the shutter <NUM> to travel under the control of the camera microcomputer <NUM> as per the rear curtain travel start time notification (step S209).

Then, in step S212, the image sensor <NUM> is controlled to switch from an accumulation state to a readout state, and the readout of shot image data is started. At the same time, in step S213, the strobe <NUM> is notified, through the transmitter <NUM>, that a camera shooting sequence in strobe synchronized shooting is complete. The strobe <NUM> also returns an indication that the strobe has fired normally.

In this manner, the camera shooting sequence ends, and the camera <NUM> returns to an idle state.

Operations performed by the transmitter <NUM> will be described next with reference to <FIG>.

In step S301, in a state where a wireless communication system constituted by the transmitter <NUM> and the strobe <NUM> has been started, the transmitter <NUM> issues a beacon packet every one second to establish communication with the strobe <NUM>. Setting the interval at which the beacon packets are issued to a comparatively long time of one second makes it possible to reduce the frequency of reception operations performed by the wireless circuit <NUM> of the strobe <NUM>. This in turn makes it possible to reduce the power consumption of the strobe <NUM>.

In step S302, the transmitter <NUM> receives a notification that the switch SW2 of the camera <NUM> has turned on, i.e., an instruction to obtain the charging information of the strobe <NUM>, and a firing sequence is then started. "Firing sequence" refers to a series of operations by the transmitter <NUM>, including communication between the transmitter <NUM> and the strobe <NUM> during a period leading up to the strobe firing, which is started in response to the shooting start instruction from the camera <NUM>, i.e., in response to the switch SW2 turning on (step S203).

In step S303, having received a notification that the switch SW2 has turned on, the transmitter <NUM> stops (suspends) the issuing of the beacon packets.

In step S304, the transmitter microcomputer <NUM> starts counting the time for which the beacons are stopped.

In step S305, the transmitter <NUM> queries the strobe <NUM> for the charging information through wireless communication, on the basis of the instruction to obtain the charging information, indicating the charging state of the strobe <NUM>, from the camera <NUM> (step S204). Once the strobe <NUM> returns the charging information (step S402; see <FIG>), the transmitter <NUM> returns the charging information of the strobe to the camera <NUM> through the connection unit.

Next, in step S306, the transmitter <NUM> receives the notification of the setting of the emitted light amount, made in step S207, from the camera <NUM>, and sends the emitted light amount setting value to the strobe <NUM> through wireless communication. Communication indicating that the emitted light amount setting has been correctly received is then received from the strobe <NUM>.

In step S307, the transmitter microcomputer <NUM> determines whether or not the time for which the beacons have been stopped, the counting of which started in step S304, is greater than or equal to a predetermined amount of time. The predetermined amount of time is set to an amount of time at which the wireless network will not be cut off due to the beacons being stopped during the exposure period (i.e., the connection will be maintained). For example, if the wireless network is set to be cut off after five seconds, the predetermined amount of time is set to four seconds.

When the beacons have been stopped for greater than or equal to the predetermined amount of time in step S307, in step S308, the transmitter <NUM> suspends the firing sequence and resumes issuing the beacon packets.

In step S309, the notification of the setting of the firing trigger, made in step S210, is received from the camera <NUM>, and in step S310, the transmitter <NUM> stops issuing the beacon packets and resumes the firing sequence.

In step S311, the transmitter <NUM> sequentially sends a plurality of firing triggers, including the timing information, to the strobe <NUM>, and varies the timing information included in each firing trigger in accordance with the order of the sending. Of the plurality of firing triggers sent sequentially from the transmitter <NUM>, the strobe <NUM> fires in accordance with the timing information included in the first firing trigger which has been successfully received. As soon as any one firing command packet is received, the remaining firing command packets no longer need to be received, and the reception operations of the strobe <NUM> are therefore ended.

When, in step S307, the time for which the beacons are stopped is less than the predetermined time, the sequence moves to step S314. In step S314, the notification of the setting of the firing trigger, made in step S210, is received from the camera <NUM> before resuming the beacons. The beacons are not yet resumed, and thus the sequence moves directly to step S311.

In step S312, the notification that the camera shooting sequence has ended, made in step S213, is received from the camera <NUM>, and the transmitter <NUM> notifies the strobe <NUM> of the end of the camera shooting sequence through wireless communication. Next, an Ack signal indicating whether or not the strobe <NUM> has fired normally is received from the strobe <NUM>, after which the camera is notified and the firing sequence is ended.

In step S313, the transmitter <NUM> resumes the operations of periodically issuing beacon packets every one second, and returns to an idle state of standing by for the switch SW2 to turn on.

The operations performed by the strobe <NUM> will be described next with reference to <FIG>. These operations start upon the wireless communication system constituted by the transmitter <NUM> and the strobe <NUM> starting.

In step S401, the strobe <NUM> continuously receives the beacon packets sent from the transmitter <NUM> to ensure that the communication is not cut off.

In step S402, the transmitter <NUM> queries the strobe <NUM> for the charging information through wireless communication, after which the strobe microcomputer <NUM> checks the charging information of the strobe <NUM> itself and returns the charging information to the transmitter <NUM>.

In step S403, a notification of the emitted light amount is received from the camera <NUM> through wireless communication by the transmitter <NUM>.

In step S404, the strobe <NUM> receives a firing command from the camera <NUM> through wireless communication by the transmitter <NUM>. The strobe <NUM> performs control for main firing as soon as this reception is complete.

In receiving this firing command, unlike normal communication, after receiving the emission command packet, the strobe <NUM> does not return an Ack packet to the camera <NUM> in order to prepare for the main firing and avoid performing any unnecessary operations. However, the Ack packet may be returned. Returning the Ack packet stops the camera <NUM> from sending subsequent firing command packets, which makes it possible to cut down on wasteful wireless communication.

In step S405, of the plurality of firing command packets sent by the transmitter <NUM>, the first packet that was received is analyzed, and the timing of the main firing is controlled by changing a clock count number in accordance with the timing information included in that packet. Regardless of which packet is ultimately received, the strobe <NUM> can perform the main firing at the same timing, and thus the camera <NUM> and the strobe <NUM> can be synchronized at a precise timing.

In step S406, the strobe <NUM> receives a notification of the end of the shooting sequence from the camera <NUM> through the transmitter <NUM>, and sends an Ack packet indicating that the firing has ended normally.

<FIG> is a diagram illustrating the operations in the flowcharts of <FIG>, <FIG>, and <FIG> in timing chart format. These operations are assumed to start from a state in which the wireless communication system constituted by the transmitter <NUM> and the strobe <NUM> is started.

The transmitter <NUM> issues a beacon packet every one second. In accordance with this, the strobe <NUM> controls the wireless circuit <NUM> to perform reception operations every one second so that the beacon packets can be continuously received. It takes several milliseconds to receive a beacon packet, and particularly in the idle state where there is no need to communicate, the wireless circuit <NUM> on the strobe side does not need to operate from the end of the receiving operation until the next receiving operation, which makes it possible to conserve energy (Start to T0).

When the switch SW1 turns on (T0), the camera <NUM> adjusts the focus (step S202).

When the switch SW2 of the camera <NUM> turns on (step S203), the transmitter <NUM> detects that the switch SW2 has turned on through the external accessory attachment part <NUM>, and stops the issuing of beacon packets (T1). Next, the transmitter <NUM> sends a packet requesting the charging information to the strobe <NUM>. The strobe <NUM> checks its own charging state, and if the strobe <NUM> is in a state where firing is possible, the strobe <NUM> notifies the transmitter <NUM> to that effect. The charging information of the strobe <NUM> is then transmitted to the camera <NUM> through the transmitter <NUM>. The strobe <NUM> is also set to a state in which wireless packets can always be received.

After entering this state, the camera <NUM> sends a light amount notification for the strobe firing, set in advance, to the strobe <NUM> via the transmitter <NUM>, using wireless communication. Then, when rear curtain synchronous firing is set, the firing sequence of the transmitter <NUM> is temporarily suspended, and the issuing of the beacon packets is resumed.

Next, the camera <NUM> causes the front curtain of the shutter <NUM> to begin traveling (T2), and controls the image sensor <NUM> to enter the accumulation state (step S208).

Once the rear curtain travel time is near, a rear curtain travel start time notification is made within the camera <NUM>, and the camera <NUM> makes a firing trigger setting notification to the transmitter <NUM> (T3). Upon receiving the firing trigger notification from the camera <NUM>, the transmitter <NUM> stops the issuing of the beacon packets in order to resume the firing sequence (step S310), and sends a firing countdown to the strobe <NUM>.

If the strobe <NUM> can receive any one of the plurality of firing command packets from the transmitter <NUM>, the strobe <NUM> performs the main firing. As soon as any one firing command packet is received, the remaining firing command packets no longer need to be received, and the reception operations of the strobe <NUM> are therefore ended.

The camera microcomputer <NUM> causes the strobe <NUM> to fire on the basis of the firing timing communicated by the last firing command sent to the strobe <NUM> (T4), and causes the rear curtain of the shutter <NUM> to travel using the shutter drive unit <NUM> (T5). The exposure of the image sensor <NUM> ends as a result. Note that in order to reliably end the exposure after the strobe <NUM> has fired, the camera may cause the rear curtain to start traveling after receiving a response from the strobe <NUM> indicating that the firing has ended.

Then, when the travel of the rear curtain of the shutter <NUM> is complete, the image sensor <NUM> is controlled to switch from the accumulation state to the readout state, and the readout of image data is started. At the same time, a packet indicating that the camera shooting sequence has ended is sent to the strobe <NUM> through the transmitter <NUM>. When the strobe <NUM> has received the firing command packet and fired successfully, the camera <NUM> is notified to that effect. The camera <NUM> determines that the image shot now is an image shot when the strobe has fired normally, adds an indication to that effect to the image data as information on shooting conditions, and records the resulting data as an image file. Conversely, if the strobe shooting could not be performed normally, an indication to that effect is added to the image data, and the data is recorded as an image file.

Once the camera shooting sequence has ended in this manner, the camera <NUM> and the strobe <NUM> return to the idle state of standing by for the switch SW1 to turn on. In other words, the transmitter <NUM> once again periodically issues the beacon packets every one second, and the strobe <NUM> correspondingly operates the wireless circuit <NUM> to receive the packets in one-second intervals.

As described thus far, according to the present embodiment, when shooting using rear curtain synchronous firing, the transmitter <NUM> stops, resumes, and re-stops the issuing of beacon packets in conjunction with the operations in the firing sequence, and issues the beacon packets until immediately before the rear curtain travels. By operating the wireless circuit <NUM> to receive the packets in response, the strobe <NUM> can maintain a wireless communication system with the transmitter <NUM> even during long exposure times, which makes it possible for the wireless strobe <NUM> to perform rear curtain synchronous firing.

Additionally, when beacon packets and firing commands are issued simultaneously, there has been a risk of the beacon packets interrupting the reception of the firing command packets, which is to be prioritized in the strobe <NUM> receiving the packets, and causing a shift in the firing timing. However, by stopping the beacons immediately before the rear curtain travels and only issuing the firing command packets, the strobe <NUM> can be caused to fire in synchronization with the rear curtain at a reliable timing.

Although the embodiment assumes that a shutter having mechanical front and rear curtains is used, the front curtain may be configured as a rolling shutter (electronic front curtain) in which the accumulation of the image sensor is started on a line-by-line basis. Alternatively, instead of the front and rear curtains, a global electronic shutter in which the start and end of accumulation are controlled digitally may be used.

The present second embodiment will describe rear curtain synchronous firing control performed in bulb shooting. In the second embodiment, only the operations of the camera <NUM> (the camera microcomputer <NUM>) are different from the first embodiment, and thus the configurations of the camera <NUM>, the transmitter <NUM>, and the strobe <NUM> will not be described.

Operations of the camera <NUM>, when the shooting mode of the camera <NUM> is the bulb shooting mode and the strobe <NUM> is caused to fire in the rear curtain synchronous firing control (step S104 in <FIG>), will be described with reference to the flowchart in <FIG>. In the rear curtain synchronized firing control in the bulb mode according to the present embodiment, the user can complete the shooting at any desired timing, and therefore the camera microcomputer <NUM> cannot know the timing at which the shooting will be complete beforehand. The descriptions will therefore assume that it is not possible to automatically adjust the light emission, and the user manually sets the emitted light amount, aperture value, ISO sensitivity, and so on before the bulb shooting.

In <FIG>, steps in which the same operations as in the first embodiment are performed are given the same reference numerals as those in <FIG>, and will not be described here. Furthermore, in the present embodiment, the processing from step S201 to step S208 is the same as the processing from step S201 to step S208 in the first embodiment, and will therefore not be described.

As in the first embodiment, in step S208, under the control of the camera microcomputer <NUM>, the camera <NUM> controls the aperture stop <NUM> to cause the front curtain of the shutter <NUM> to begin traveling, and controls the image sensor <NUM> to begin accumulation. However, in bulb mode, the end of shooting is determined by the photographer, and thus at this point in time, the timing at which the shooting ends is unknown from the perspective of the camera <NUM>.

Next, in step S1201, the switch SW2 of the camera <NUM> is deactivated. In bulb mode, the deactivation of the switch SW2 serves as the timing for making a notification of the rear curtain travel start time, and in step S1202, a notification of the rear curtain travel start time is made in the camera. The rear curtain travel start time is determined by calculating the processing time required before the rear curtain travels, taking into account the processing time of the firmware in the camera and the time from when the firing instruction is made by the camera to when the firing of the strobe <NUM> ends. Note that the shutter speed Tv value is not included in this calculation.

The subsequent operations from step S210 to step S213 are the same as step S210 to step S213 in the first embodiment, and will therefore not be described.

The operations of the transmitter <NUM> and the strobe <NUM> during bulb shooting are the same as when not performing bulb shooting.

<FIG> is a diagram illustrating the flowcharts of <FIG>, <FIG>, and <FIG> in timing chart format. Processing parts that are the same as in the first embodiment will not be described.

The camera <NUM> causes the front curtain of the shutter <NUM> to begin traveling (T2), and controls the image sensor <NUM> to enter the accumulation state (step S208).

When the user deactivates the switch SW2 to end the shooting, the rear curtain travel start time notification is made within the camera at the same time (step S1201, T3').

When the rear curtain travel start time notification is made, the camera <NUM> makes a firing trigger setting notification to the transmitter <NUM> at the same time. Upon receiving the firing trigger notification from the camera <NUM>, the transmitter <NUM> stops the issuing of the beacons in order to resume the firing sequence (step S310), and sends a firing countdown to the strobe <NUM>. The subsequent operations are the same as the processing in the first embodiment.

The first and second embodiments describe a wireless strobe system in which the transmitter <NUM> serves as the master and the strobe <NUM> serves as the slave. However, the system may instead be a wireless strobe system in which a strobe attached directly to the camera <NUM> serves as a master, and the strobe <NUM> can be controlled as a slave.

Claim 1:
A control apparatus (<NUM>) configured to be connected to an image capturing apparatus (<NUM>) and configured to control a strobe (<NUM>) to fire in synchronization with an end of a long exposure period of the image capturing apparatus (<NUM>), the control apparatus (<NUM>) comprising:
wireless communication means (<NUM>, <NUM>) configured to communicate wirelessly with the strobe (<NUM>); and
control means (<NUM>) configured to control the wireless communication means (<NUM>, <NUM>),
characterized in that
the wireless communication means (<NUM>, <NUM>) is further configured to:
issue periodically beacon signals to establish a communication link with the strobe (<NUM>);
suspend the issuing of the beacon signals after receiving a shooting start instruction from the image capturing apparatus (<NUM>);
when a time for which the beacon signals have been stopped is equal to or greater than a predetermined amount of time, resume periodically issuing the beacon signals, and suspend the issuing of the beacon signals again after receiving a firing trigger setting notification from the image capturing apparatus (<NUM>) immediately before the end of a long exposure period,
wherein the predetermined amount of time is set to an amount of time at which the communication link with the strobe (<NUM>) will not be cut off due to the beacon signals being stopped during the long exposure period.