Image sensing device and control method thereof

An image sensing device allows to shoot an image using correct object distance information and light emitting amount when the main light emitting amount upon shooting an object image is calculated by making the pre-light emission after the auto-focusing process. When a predetermined button independent of a release button is operated, a focusing process is executed first. Then, photometry is made while inactivating a strobe, and an exposure value is determined based on an object distance. Then, pre-light emission is made, light reflected by the object in the pre-light emission is measured, and the photometry result under the available light is subtracted from that in the pre-light emission, so as to obtain a brightness value of object reflected light of only the pre-light emission.

FIELD OF THE INVENTION

The present invention relates to a technique for shooting an image after making pre-light emission toward an object in order to obtain an appropriate exposure value.

BACKGROUND OF THE INVENTION

Upon shooting a picture with strobe, automatic light control is normally executed by making a pre-light emission, measuring the objects reflected light, and determining the amount of main light needed on the basis of the photometry result.

Normally, a series of these processes are done depending on the operation state of a release switch (SW). More specifically, main light emission is performed after pre-light emission, photometry, and determination of the main light emitting amount are made while the release SW is pressed at the full stroke position.

Also, an automatic light control camera is known (e.g., Japanese Patent Laid-Open Nos. 61-156239, 61-156240, and 60-61733). That is, a member independent from the release SW makes pre-light emission and photometry of object reflected light by the pre-light emission, so as to determine a light emitting amount of a strobe in advance, and main light emission is then made by the release SW. According to these patent references 1 to 3, since the light emitting amount of the strobe can be determined in advance, even when a light control area is located at the center of the visual field and an object is not located at the center, pre-light emission is made while locating the object at the center upon pre-light emission. After that, even when shooting is made by changing the composition (shooting direction, field angle), an appropriate exposure value can be obtained upon shooting.

However, when automatic exposure shooting is performed by controlling object reflected light of the strobe, and a sub object with a high reflectance such as glass, a mirror, or the like is present near a main object, the exposure value is determined under the influence of the sub object with the high reflectance and, consequently, the main object is underexposed.

As a measure to be taken against this problem, an automatic light control camera which makes a strobe perform pre-light emission immediately before shooting under the assumption that a main object is located at an in-focus distance is known (e.g., Japanese Patent Laid-Open No. 3-287240). This technique uses a photometry sensor which divides a shooting area into a plurality of areas, and can make photometry on respective areas. Reflected light returning from an object is measured, and when the photometry result of a given area is higher than the brightness calculated from a shooting distance, it is determined that a high-reflecting object is present in that area, and the area is excluded from the light control areas, thus minimizing the influence of abnormal reflection.

In the automatic light control cameras disclosed in patent references 1 to 3, the strobe light control amount can be determined in advance. However, since pre-light emission is made to determine the main light emitting amount of the strobe irrespective of the in-focus state of the camera, the exposure value often becomes inaccurate. That is, since the open f-number of a lens changes depending on the extension position of the lens, when the extension amount becomes large in e.g., macro shooting, the exposure value is often changed by about one level due to variations of the open f-number upon extension. When an abnormal reflecting object such as glass or the like is present upon pre-light emission, underexposure occurs due to that influence. In patent reference 4, the influence of underexposure when an abnormal reflecting object such as glass or the like is present can be minimized, but it is difficult to obtain an appropriate exposure value when an object falls outside the light control range.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the aforementioned problems, and has as its object to provide a technique for shooting an image on the basis of an appropriate exposure value by eliminating the influence of a change in optical condition due to the lens extension position. It is another object of the present invention to provide a technique that allows appropriate strobe shooting which is hardly influenced by the reflectance of an object.

In order to achieve the above objects, an image sensing apparatus according to the present invention comprises the following arrangement. That is, there is provided an image sensing device which has light emitting unit for emitting light toward an object or can connect the light emitting unit, comprising:

a first instruction unit adapted to issue a pre-light emission instruction by the light emitting unit;

a second instruction unit adapted to issue a main light emission instruction by the light emitting unit, the second instruction unit being independent of the first instruction unit;

a control unit adapted to receive the pre-light emission instruction of the first instruction unit, determine a light emitting amount upon main light emission by executing an auto-focusing process for an object to attain an in-focus state, performing pre-light emission after the in-focus state is attained, and controlling predetermined photometry means to measure reflected light from the object by the pre-light emission, receive the main emission instruction of the second instruction unit, perform main light emission by driving the light emitting means in accordance with the light emitting amount, and shoot an image.

This invention allows to shoot an image using correct object distance information and light emitting amount when the main light emitting amount upon shooting an object image is calculated by making the pre-light emission after the auto-focusing process. To this end, when a predetermined button independent of a release button is operated, a focusing process is executed first. Then, photometry is made while inactivating a strobe, i.e., under available light, and an exposure value is determined based on an object distance. Then, pre-light emission is made, light reflected by the object in the pre-light emission is measured, and the photometry result under the available light is subtracted from that in the pre-light emission, so as to obtain a brightness value of object reflected light of only the pre-light emission. This brightness value is corrected to be equal to lower than an allowable maximum value depending on the object distance to compute a main light emitting amount. After that, when the release button is operated, the strobe is driven on the basis of the determined main light emitting amount, and shooting is made using the determined exposure value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a sectional view of an optical system when a strobe is mounted on a single-lens reflex camera according to this embodiment.

Referring toFIG. 1, reference numeral1denotes a camera body, on the front surface of which a shooting lens11is mounted. The camera body1houses optical members, mechanical members, an electric circuit, a film or image sensing element such as a CCD or the like, and so forth, and can shoot a photo or image. Reference numeral2denotes a main mirror, which is obliquely inserted into a shooting optical path in a viewfinder observation state, and escapes outside the shooting optical path in a shooting state. The main mirror2is a half mirror, which passes about half light rays of those coming from an object toward a focus detection optical system (to be described later) when it is obliquely inserted into the shooting optical path, i.e., in the viewfinder observation state.

Reference numeral3denotes a focusing screen which forms a viewfinder optical system and is arranged at a prospective image formation plane of lenses12to14(to be described later); and4, a pentagonal prism for changing a viewfinder optical path. Reference numeral5denotes an eyepiece. A photographer can observe a shooting frame by observing the focusing screen3via this eyepiece5. Reference numerals6and7denote an image formation lens and photometry sensor, which are used to measure the object brightness within the viewfinder observation frame. The image formation lens6keeps the focusing screen3and photometry sensor7in a conjugate state via a reflection optical path in the pentagonal prism4.

Reference numeral8denotes a focal plane shutter. Reference numeral9denotes a photosensitive member, which comprises a silver halide film or an image sensing element such as a CCD or the like. Reference numeral25denotes a sub mirror, which is obliquely inserted into the shooting optical path together with the main mirror2in the viewfinder observation state, and escapes outside the shooting optical path in the shooting state. The sub mirror25bends light rays transmitted through the obliquely inserted main mirror2downward, and guides them toward a focus detection unit (to be described later).

Reference numeral26denotes a focus detection unit, which comprises a secondary image formation mirror27, secondary image formation lens28, focus detection line sensor29, focus detection circuit (to be described later), and the like. The secondary image formation mirror27and secondary image formation lens28form a focus detection optical system, and form a secondary image formation plane of the shooting lens11on the focus detection line sensor29. The focus detection unit26detects a focusing state of the shooting lens11by a so-called phase difference detection method, and outputs the detection result to an automatic focusing device that controls a focusing mechanism of the shooting lens.

Reference numeral10denotes a mount contact group which serves as a communication interface between the camera body1and shooting lens11.

Reference numerals12to14denote lenses. The first lens group (to be referred to as a focusing lens hereinafter)12adjusts the focus position of the shooting frame when it moves back and forth along the optical path. The second lens group13changes the focal length of the shooting lens11when it moves back and forth along the optical axis. The third lens group14is fixed in position. Reference numeral15denotes a stop. Reference numeral16denotes a drive motor, which is a focus drive motor for moving the focusing lens12back and forth in the optical axis direction in an auto-focusing operation. Reference numeral17denotes a stop drive motor for changing the aperture size of the stop15. Reference numeral18denotes a distance encoder, which reads the position of the focusing lens12and generates a signal corresponding to an object distance when a brush19attached to the focusing lens slides. More specifically, the distance encoder18, the brush19, and a lens microcomputer112(to be described later) form an object distance detection means which reads the position of the focusing lens12after focus adjustment, and outputs a signal (object distance information) obtained by converting that position into an object distance at that time.

Reference numeral30denotes a strobe detachable from the camera body1. The strobe30is mounted on the camera body1and performs light emitting control in accordance with a signal from the camera body1. Reference numeral31denotes a Xenon tube (to be abbreviated as an Xe tube hereinafter), which converts current energy into light emitting energy. Reference numeral32denotes a Fresnel lens; and33, a reflector. The Fresnel lens32and reflector33serve to efficiently focus the light emitting energy toward the object. Reference numeral37denotes a glass fiber which guides some light components of light emitted by the Xe tube31to a first photodetector38such as a photodiode or the like so as to monitor the light emitting amount of the Xe tube31. In this way, the light amounts of pre-light emission and main light emission of the Xe tube31can be monitored.

Reference numeral35denotes a second photodetector such as a photodiode or the like for monitoring light emitted by the Xe tube31. Based on the output from the second photodetector35, the light emitting current of the Xe tube31is limited to control flat light emission. Reference numerals34and36denote light guides which are integrated with the reflector33, and reflect and guide some light components of light coming from the Xe tube31to the second photodetector35or fiber37.

Reference numeral39denotes a strobe contact group which serves as a communication interface between the camera body1and strobe30.

The circuit arrangement of the strobe shooting system will be described below usingFIG. 2. Note that the same reference numerals inFIG. 2denote elements common to those inFIG. 1.

The circuit arrangement in the camera body1will be explained first.

To a camera microcomputer100, a focus detection circuit105, the photometry sensor7, a shutter control circuit107, a motor control circuit108, a switch sense circuit110, and a liquid crystal display circuit111are connected. The camera microcomputer100exchanges signals with a lens control circuit (lens microcomputer)112arranged in the shooting lens11via the mount contact group10, and also exchanges signals with a strobe microcomputer200arranged in the strobe30via the strobe contact group39.

The focus detection circuit105performs accumulation control and read control of the focus detection line sensor29in accordance with signals from the camera microcomputer100, and outputs pixel information to the camera microcomputer100. The camera microcomputer100A/D-converts the information to detect a focusing state based on the phase difference detection method, and then exchanges signals with the lens microcomputer112to attain focusing control of the shooting lens11.

The photometry sensor7outputs brightness signals in both a steady state in which the strobe makes pre-light emission toward an object and a pre-light emitting state. The camera microcomputer100A/D-converts the brightness signals, and calculates an aperture value and shutter speed to adjust an exposure value for shooting, and also calculates a strobe main light emitting amount upon exposure.

The shutter control circuit107performs energization control of a shutter first curtain drive magnet MG-1and shutter second curtain drive magnet MG-2which form the focal plane shutter8in accordance with signals from the camera microcomputer100so as to drive shutter first and second curtains, thus attaining an exposure operation. The motor control circuit108controls a motor M in accordance with a signal from the camera microcomputer100to perform up/down movements of the main mirror2, shutter charge, and the like.

Reference numeral SW1denotes a switch which is turned on by a first stroke (half stroke) operation of a release button (not shown) to start photometry and AF (auto-focusing). Reference numeral SW2denotes a switch which is turned on by a second stroke (full stroke) operation of the release button to start a shutter drive operation, i.e., an exposure operation. Reference symbol SWFELK denotes a switch which makes pre-light emission, and is enabled upon depression of a button by the user independently of the release button. The camera microcomputer100reads, via the switch sense circuit110, state signals of respective switches such as the above switches SW1, SW2, and SWFELK, and operation members (not shown) including an ISO speed setting switch, aperture setting switch, shutter speed setting switches, and the like.

The liquid crystal display circuit111controls an intra-viewfinder display24and external display42in accordance with signals from the camera microcomputer100.

The electrical circuit arrangement in the shooting lens11will be explained below.

The camera body1and shooting lens11are electrically connected to each other via the lens mount contact group10. The lens mount contact group10includes a contact L0as a power supply contact of the focus drive motor16and stop drive motor17in the shooting lens11, a power supply contact L1of the lens microcomputer112, a contact L2for clocks used to make serial data communications, a contact L3for data transmission from the camera body1to the shooting lens11, a contact L4for data transmission from the shooting lens11to the camera body1, a motor ground contact L5for a motor power supply, and a ground contact L6for a power supply of the lens microcomputer112.

The lens microcomputer112is connected to the camera microcomputer100via the lens mount contact group10, and operates the focus drive motor16for driving the focusing lens12and the stop drive motor17for driving the stop15in accordance with signals from the camera microcomputer100, thus controlling the focus and aperture of the shooting lens11. Reference numerals50and51denote a photodetector and pulse disk. The lens microcomputer112counts the number of pulses to obtain the position information of the focusing lens12upon focusing (in-focus operation). In this way, focusing of the shooting lens11can be attained.

Reference numeral18denotes the aforementioned distance encoder. The position information of the focusing lens12read by this encoder18is input to the lens microcomputer112, which converts the input information into the object distance information and supplies it to the camera microcomputer100.

The photometry sensor7will be described below usingFIG. 3.

The photometry sensor7is an integrated circuit including photodetectors such as silicon photodiodes or the like, an amplifier for amplifying photocurrents generated by the photodetectors, and the like, andFIG. 3shows photo-receiving portions of the photometry sensor7viewed from an entrance surface.

The photometry sensor7receives light within a two-dimensional range which is nearly the same as the frame of the image sensing element (or film)9, and its photo-receiving surface is formed by photo-receiving portions arranged on a plurality of areas (35 areas inFIG. 3), as indicated by P(0,0) to P(6,4) inFIG. 3. The respective photo-receiving portions are photodetectors such as silicon photodiodes or the like, and generate currents according to the light amount upon reception of light. The current outputs are sent in the same order as a raster scan, i.e., in turn from the upper left one inFIG. 3, to the camera microcomputer100via a known log compressing amplifier. The camera microcomputer100can measure the brightness values at respective positions of the two-dimensional area of the photometry sensor7as digital values by A/D-converting the outputs from the respective photodetectors.

The arrangement of the strobe30will be explained below usingFIG. 4.

Referring toFIG. 4, reference numeral200denotes a strobe microcomputer which controls the operation of the entire strobe30; and201, a power supply battery. Reference numeral202denotes a DC/DC converter which boosts a battery voltage to several hundred V. Reference numeral203denotes a main capacitor which stores light emitting energy. Reference numerals204and205denote resistors, which divide the voltage of the main capacitor203to a predetermined ratio. Reference numeral206denotes a coil used to limit a light emitting current;207, a diode which absorbs a counter electromotive voltage generated upon stopping light emission; and31, the Xe tube mentioned above. Reference numeral211denotes a trigger generation circuit; and212, a light emitting control circuit such as an IGBT or the like.

Reference numeral230denotes a data selector which selects D0, D1, or D1in accordance with a combination of Y0and Y1, and outputs it to a terminal Y. Reference numeral231denotes a comparator which controls the light emitting level of flat light emission; and232, a comparator which controls the light emitting amount upon flash light emission (strobe light emission).

Reference numeral35denotes the second photodetector such as a photodiode or the like, which serves as a photo-receiving sensor used to control flat light emission. The second photodetector35monitors a light output of the Xe tube31. Reference numeral234denotes a photometry circuit which amplifies a small current flowing through the second photodetector35, and converts a photocurrent into a voltage. Reference numeral38denotes the first photodetector such as a photodiode or the like, which serves as a photo-receiving sensor used to control flash light emission. The first photodetector38monitors a light output of the Xe tube31. Reference numeral236denotes an integration circuit which log-compresses a photocurrent flowing through the first photodetector38, and compresses and integrates the light emitting amount of the Xe tube31.

Reference numeral39denotes the strobe contact group provided to a hot shoe used to communicate with the camera body1. Reference numeral242denote a power switch used to turn on/off the strobe30.

Respective terminals of the strobe microcomputer200will be explained below.

Reference symbol CNT denotes a control output terminal which controls charging of the DC/DC converter202; COM2, a control output terminal corresponding to the ground potential of the switch242; OFF, an input terminal selected upon power OFF of the strobe30; and ON, an input terminal selected upon power ON of the strobe30. Reference symbol CK denotes an input terminal of sync clocks used to make serial communications with the camera body1; DO, a serial output terminal used to transfer serial data from the strobe30to the camera body1in synchronism with the sync clocks; and DI, a serial data input terminal used to transfer serial data from the camera body1to the strobe30in synchronism with the sync clocks. Reference symbol CHG denotes an output terminal used to transfer a light emitting OK/NG signal of the Xe tube from the strobe30to the camera body1; and X, an input terminal which receives a flash light emitting command from the camera body1.

Reference symbol INT denotes an integration control output terminal of the integration circuit236; AD0, an A/D conversion input terminal used to read an integrated voltage indicating the light emitting amount of the integration circuit236; and DA0, a D/A output terminal used to output a comparison voltage (threshold voltage) of the comparators231and232. Reference symbols Y0and Y1denote output terminals of the selection state of the aforementioned data selector230; and TRIG, a light emitting trigger output terminal.

The arrangements of the camera body1, lens11, and strobe30in this embodiment have been explained.

The processing sequence of the camera microcomputer100of the camera body1in this embodiment will be described below with reference to the flowchart shown inFIG. 7. Note that a variable FLAG to be described below is assured in a RAM included in the camera microcomputer100, and stores information indicating whether or not a flash exposure value (FE) lock process is executed.

After the power switch of the device is turned on, respective circuits are initialized in step S11, and the flag FLAG is reset to “0” in step S12.

It is checked in step S13if the switch SWFELK is ON, i.e., an FE lock instruction is issued. If the switch SWFELK is ON, the flow advances to step S20; otherwise, the flow advances to step S14. A case will be explained below wherein the switch SWFELK is OFF, and the flow advances to step S14.

It is checked in step S14if the flag FLAG is “1”. If FLAG=“1”, the flow advances to step S23; if FLAG=“0”, the flow advances to step S15. The following description will be given when the flag FLAG is “0”.

When the flow advances to step S15, it is checked if the switch SW1is ON, i.e., the release button is at the half stroke position. If NO in step S15, the flow advances to step S16to execute other processes. Note that “other processes” include selection of a shooting mode (auto, shutter speed priority, aperture priority, and the like), setting of parameters (shutter speed and aperture values), selection of photo-receiving portions of the photometry sensor7upon photometry (the central photo-receiving portion as a default), ON/OFF of normal strobe shooting, and the like. If the camera of this embodiment is a digital camera, a browse process of sensed images stored in a memory card (not shown) and the like are also included in these processes.

If the release button is at the half stroke position (the switch SW1is ON), the flow advances to step S17to execute an auto-focusing (AF) process according to a known sequence. It is then checked in step S18if the switch SW2is ON, i.e., if the release button is at the full stroke position. If the switch SW2is ON, the flow advances to step S19to shoot an image in accordance with the parameters determined in step S17.

As described above, when the switch SWFELK is OFF and the flag. FLAG is “0”, the same processes as in normal shooting are performed.

On the other hand, when the switch SWFELK is ON and the flag FLAG is “1”, the processes unique to this embodiment are performed. The flag FLAG becomes “1” when it is determined that the switch SWFELK is ON. Hence, the processes when it is determined that the switch SWFELK is ON will be explained first.

In this case, the flow advances from step S13to step S20. In step S20, a flash light amount (FE) lock process is done. In the FE lock process, AF (in-focus process) to an object is executed, and an exposure value (shutter speed and aperture value) and the light emitting amount of the strobe30are determined, as will be described in detail later.

Upon completion of the FE lock process, the flag FLAG is set to be “1” in step S21, and time measurement of a timer (not shown) is started in step S22. Then, the flow returns to step S13.

If the operator does nothing in this state, the processes in step S13, S14, S23, and S24are repeated. If a time-out is determined in step S24, the flag FLAG is reset to “0” in step S25. That is, if the operator does not perform any processes for pressing the release button to its full stroke position and so forth when a predetermined period of time has elapsed after the FE lock process in step S20, data obtained in the process in step S20are discarded. In this embodiment, the predetermined period of time is 5 sec. However, this value may be set by the operator.

On the other hand, if the operator presses the release button to its full stroke position, i.e., he or she turns on the switch SW2while the flag FLAG=“1”, the flow advances to step S26to make strobe shooting. Upon completion of the shooting process, the flag FLAG is reset to “0” in step S27even before the predetermined period of time elapses. Note that the reason why whether or not the release button is at the half stroke position is not checked when the flag FLAG=“1” is that the auto-focusing process has already been done in step S20.

When the operator looks into, e.g., the eyepiece5while the flag FLAG is “1” in the above process, a mark indicating that the flash exposure amount is locked is displayed outside the shooting visual field. Such display can inform the operator that a flash shooting process is done when he or she presses the release button to the full stroke position while this mark is displayed. The same applies to a case wherein the camera body1is a digital camera. In case of the digital camera, since the camera body1normally has a liquid crystal display used to confirm a sensed image on its back surface, a similar mark may be displayed on that liquid crystal display.

As described above, if the release button is pressed to its full stroke position (switch SW2is turned on) within the predetermined period of time after the switch SWFELK is turned on, strobe shooting is forcibly made in step S26.

The processing contents in step S20in the above process will be described below with reference to the flowchart ofFIG. 5.

When the switch SWFELK of the camera body1shown inFIG. 2is turned on, an AF control process is executed from step S100. Note that the camera microcomputer100performs focus detection by a known method on the basis of a defocus of an object image formed on the focus detection line sensor29in the focus detection unit26including the focus detection circuit105so as to compute a lens drive amount to an in-focus position, and outputs the lens drive amount to the lens microcomputer112via serial communication lines LCK, LDO, and LDI mentioned above. Upon reception of the lens drive amount, the lens microcomputer112drives the focus drive motor16to read the rotation of the pulse disk51, which is directly coupled to the motor16, using the photodetector50, thus driving the focus drive motor16by the designated drive amount. This operation is repeated to attain in-focus control until a defocus of the object image formed on the focus detection line sensor29is removed. Note that the stop is in an open state (minimum f-number) during the in-focus process, and until the process inFIG. 5ends.

Upon completion of the in-focus control, the flow advances to step S101, and the camera microcomputer100instructs the photometry sensor7to measure brightness values Ba(0,0) to Ba(6,4) of a plurality of areas P(0,0) to P(6,4) obtained by dividing an object field under steady light. The photometry results are log-compressed and converted into voltage values by the log compressing amplifier (not shown) in the photometry sensor7, and are input to the camera microcomputer100. The camera microcomputer100temporarily stores digital brightness values BVa(0,0) to BVa(6,4) of the respective photo-receiving portions obtained by sequentially reading the values from the areas P(0,0) to P(6,4) via an A/D input terminal, and adding open FNo (AVo) and open correction (AVc) values of the shooting lens11in its internal RAM (not shown).

In step S102, the camera microcomputer100determines an exposure value (BVs) by a known method on the basis of the brightness values BVa(0,0) to BVa(6,4) of the respective measured areas. Then, the camera microcomputer100determines a shutter speed value (TV) and aperture value (AV) in accordance with the set camera shooting mode.

When the flow advances to the next step S103, the camera microcomputer100issues a pre-light emitting command to the strobe microcomputer200via a serial communication using communication terminals S0, S1, and S2. In response to the pre-light emitting command, the strobe microcomputer200performs a pre-light emitting operation with a predetermined light emitting amount.

The pre-light emitting operation in this embodiment will be described below.

The strobe microcomputer200sets a predetermined voltage at the terminal DA0in accordance with the predetermined light emitting level designated by the camera body1. The strobe microcomputer200outputs Hi and Lo to the terminals Y1and Y0to select the input D2. At this time, since the Xe tube31does not emit light yet, almost no photocurrent of the first photodetector35flows, and the monitor circuit (photometry circuit)234does not generate any output to be input to the inverting input terminal of the comparator231. Hence, since the output of the comparator231is Hi, the light emitting control circuit212is enabled.

When a trigger signal is output from the terminal TRIG, the trigger circuit211excites the Xe tube31that generated a high voltage, thus starting pre-light emission.

The strobe microcomputer200issues an integration start instruction to the integration circuit236. Upon reception of this instruction, the integration circuit236begins to integrate the output from the monitor circuit234, i.e., the log-compressed photoelectric output of the first photodetector38for light amount integration, and a timer that counts a light emitting time is started.

After pre-light emission starts, the photocurrent from the second photodetector35for light emitting level control of flat light emission increases, and the output from the monitor circuit234rises. When the output from the monitor circuit234becomes higher than a predetermined comparison voltage set at the non-inverting input of the comparator231, the output from the comparator231is inverted to Lo, and the light emitting control circuit212cuts off the light emitting current of the Xe tube31. In this way, a discharge loop is disconnected, but the diode209and coil206form a reflux loop. Thus, the light emitting current gradually decreases after an overshoot due to a circuit delay settles.

Since the light emitting level lowers with decreasing light emitting current, the photocurrent of the second photodetector35decreases, and the output from the monitor circuit234also decreases. When the output from the monitor circuit234decreases to be equal to or lower than the predetermined comparison level, the output of the comparator231is inverted to Hi again, the light emitting control circuit212is enabled again to form the discharge loop of the Xe tube31, and the photocurrent increases, thus increasing the light emitting level.

In this way, the comparator231repeats an increase/decrease in light emitting level at short cycles to have the predetermined comparison voltage set at DA0as the center, and flat light emitting control for keeping light emission at nearly a constant light emitting level is consequently made.

After an elapse of a predetermined light emitting time counted by the aforementioned timer, the strobe microcomputer200sets Lo and Lo in the terminals Y1and Y0. As a result, D0, i.e., an Lo level input is selected as the input of the data selector206, and its output is forcibly set at Lo level. The light emitting control circuit212cuts off the discharge loop of the Xe tube31. In this manner, pre-light emission (flat light emission) ends.

Upon completion of light emission, the strobe microcomputer200A/D-converts the output of the integration circuit236that integrates the pre-light emitting amount by reading it from the A/D input terminal AD0, thus reading the integrated value, i.e., the light emitting amount upon pre-light emission as a digital value.

During the pre-light emission, an object reflected light photometry operation based on the pre-light emission is performed at the same time in step S104. InFIG. 5, the process in step S104is performed after the pre-light emission for the sake of convenience. The pre-light emitting process in step S103and the process in step S104are parallelly done.

In the process in step S104, object reflected light of the pre-light emission is received by the photometry sensor7of the camera body1via the shooting lens11. As a result, object brightness values BVf(0,0) to BVf(6,4) are measured as in step S101described above. In step S101, the brightness values of object reflected light without pre-light emission of the strobe30, i.e., those of available light are obtained. However, in step S104, object brightness values in the pre-light emission (flat light emission) by the strobe30are obtained unlike in step S101.

The flow advances to step S105, and the camera microcomputer100extracts brightness values dF(x, y) (x=0 to 6, y=0 to 4) of only reflected light component of the pre-light emission by subtracting the object bright values BVa(x, y) (x=0 to 6, y=0 to 4) obtained in step S101from the object brightness values BVf(x, y) (x=0 to 6, y=0 to 4) upon pre-light emission.

In step S106, object distance information (which is obtained by detecting the position of the focusing lens12by the distance encoder18and the like, and converting it onto an object distance; to be also referred to as distance information hereinafter) is acquired from the shooting lens11.

In step S107, photometry level LVL1corresponding to appropriate exposure is calculated by:
LVL1=PRG−log2(infinity-side distance)+K0
where PRG is a pre-light emitting guide number, and K0is a constant.

In step S108, determination level LVL2used to determine an abnormal reflection area is determined by:
LVL2=LVL1+K1
where K1is a constant, and LVL2can be a threshold value which is used to determine abnormality when the brightness value is higher than LVL2. In other words, LVL2can be also an allowable maximum value.

It is checked in step S109if a light control area suffers abnormal reflection due to glass or the like. For the sake of simplicity, the following description will be given under the assumption that the light control area upon FE lock is the central photometry area P(3,2) inFIG. 3.

The photometry value dF(3,2) of the photo-receiving portion P(3,2) obtained in step S105is compared with LVL2calculated in step S108. If dF(3,2)>LVL2, a correction process for replacing the value of dF(3,2) by LVL2is performed. Let dF′(3,2) be the corrected value of dF(3,2). We have:

In step S110, a main light emitting amount γ of the strobe30is calculated on the basis of the corrected photometry value dF′(3,2) of the photometry area P(3,2) by:
γ=BVt−dF′(3, 2)
where BVt is calculated from the TV and AV values calculated in step S102by:
BVt=TV+AV−SV
(where SV is the shooting sensitivity value.)

In step S111, the TV and AV values determined in step S102are displayed on the intra-viewfinder display24and external display42, and the mark indicating FE lock is displayed, as described above, thus ending this process.

The process in step S26inFIG. 7will be described below. Note that this process is executed when the release button is pressed to the full stroke position (SW2=ON) within a predetermined period of time after the FE lock process.

When the release button is pressed to the full stroke position, and the switch SW2is turned on, the camera microcomputer100sends the main light emitting amount γ calculated in step S110to the strobe microcomputer200via a serial communication using the communication terminals S0, S1, and S2in step S121, and the flow advances to step S122.

When the flow advances to step S122, it is checked if the shutter speed is equal to or lower than a sync speed. If the shutter speed is equal to or lower than a sync speed, the flow advances to step S123, and the camera microcomputer100transmits a flash light emitting mode to the strobe microcomputer200. On the other hand, if the shutter speed is higher than the sync speed, the flow advances to step S124, and the camera microcomputer100transmits a flat light emitting mode and flat light emitting time (a time as the sum of the shutter speed and curtain travel speed) to the strobe microcomputer200.

In step S125, the main mirror2is flipped up to be retracted from the shooting optical path, and the camera microcomputer100issues a stop-down instruction of the stop15to the lens microcomputer112at the same time. In step S126, the control waits until the main mirror2is completely retracted from the shooting optical path. After the main mirror2is completely retracted from the shooting optical path, the flow advances to step S127, and the camera microcomputer100energizes the shutter first curtain drive magnet MG-1to start an open operation of the focal plane shutter8.

It is then checked in step S128if the light emitting mode is a flat (FP) light emitting mode. If the light emitting mode is a flat light emitting mode, the flow advances to step S130. On the other hand, if the light emitting mode is a flash light emitting mode, the flow advances to step S129, and the control waits until the first curtain of the focal plane shutter8is completely open, and the contact X (not shown) is turned on. After the contact X is turned on, the flow advances to step S130.

In step S130, the strobe microcomputer200performs main light emitting control according to the light emitting mode designated by the camera microcomputer100. That is, the strobe microcomputer200starts flat light emission in the flat light emitting mode, or flash light emission in the flash light emitting mode.

The flash light emitting control will be described below.

When the shutter speed of the camera is equal to or lower than the strobe sync speed, the flash light emitting control is done. In this case, the strobe microcomputer200outputs a control voltage corresponding to a set manual light emitting amount to the terminal DA0. This voltage is obtained by adding a control voltage corresponding to a light amount difference between the pre-light emission and main light emission to the output voltage, i.e., the integrated voltage of the integration circuit236which has been explained in the pre-light emission.

For example, let V1be the integrated voltage when the pre-light emission is made with a light amount 1/32 of a full light emitting amount. When the main light emitting amount is the same value as in the pre-light emission, i.e., 1/32 of the full light emitting amount, light emission can be stopped when the same integrated voltage is output. Hence, V1is set as the comparison voltage of the comparator232. Likewise, when the main light emitting amount is 1/16 of the full light emitting amount, light emission can be stopped when an integrated voltage one step larger than that upon the pre-light emission is output. Hence, the sum of the integrated voltage upon the pre-light emission and a voltage corresponding to one step is set as the comparison voltage of the comparator232.

The strobe microcomputer200outputs “0, 1” to the terminals Y1and Y0to select the flash light emitting control comparator232connected to the input D1of the data selector230. Since the Xe tube31does not emit light yet, nearly no photocurrent flows in the first photodetector38. For this reason, no output of the integration circuit236is generated, and the potential of the − input terminal of the comparator232is lower than its + input terminal. Therefore, the output voltage of the comparator232goes to high level, and the light emitting control circuit212is enabled. At the same time, the strobe microcomputer200outputs a Hi signal from the terminal TRIG for a predetermined period of time. In response to this signal, the trigger generation circuit211generates a high trigger voltage. When the high voltage is applied to the trigger electrode of the Xe tube31, the Xe tube31starts light emission.

After the Xe tube31starts light emission, a photocurrent flows in the first photodetector38, and the output from the integration circuit236rises. When the output from the integration circuit236has reached the predetermined voltage set at the +input terminal of the comparator232, the output voltage from the comparator232is inverted to low level, and the light emitting control circuit212is disabled, thus stopping light emission.

At this time, the Xe tube31generates a predetermined light emitting amount and stops light emission, and a light amount required for strobe shooting is obtained.

The flat light emitting control will be explained below.

When the shutter speed of the camera is higher than the strobe sync speed, the flat light emitting control is made. The strobe microcomputer200outputs a control voltage corresponding to a set manual flat light emitting amount to the terminal DA0. This voltage is obtained by adding a control voltage corresponding to a light amount difference between the pre-light emission and main light emission to the voltage set as the comparison voltage of the comparator231upon the pre-light emission.

For example, let V1be the control voltage when the pre-light emission is made with a light amount 1/32 of the full light emitting amount. When the main light emitting amount is the same value as in the pre-light emission, i.e., 1/32 of the full light emitting amount, flat light emission can be made at the same control. Hence, V1is set as the comparison voltage of the comparator231. Likewise, when the main light emitting amount is 1/16 of the full light emitting amount, a control voltage one step larger than that upon the pre-light emission can be set. Hence, the sum of the integrated voltage upon the pre-light emission and a voltage corresponding to one step is set as the comparison voltage of the comparator231.

The strobe microcomputer200outputs “1, 0” to the terminals Y1and Y0to select the flat light emitting control comparator231connected to the input D2of the data selector230. After that, the flat light emission is made by the same operation as the aforementioned pre-light emitting operation. After an elapse of the predetermined period of time designated by the camera microcomputer100, the terminals Y1and Y0of the strobe microcomputer200are set to be “0, 0”, thus ending the light emitting process.

Referring back toFIG. 6, after an elapse of the predetermined shutter release time, the flow advances to step S131, and the camera microcomputer100energizes the shutter second curtain drive magnet MG-2to close the second curtain of the focal plane shutter8, thus ending exposure. If the light emitting mode is the flat light emitting mode, light emission continues until the second curtain is closed completely. Upon completion of a series of shooting sequences, the flow advances to step S132to move the main mirror2downward, thus ending shooting.

According to the aforementioned embodiment, when the pre-light emitting switch SWFELK is operated, auto-focusing is made prior to pre-light emission (step S100inFIG. 5), the pre-light emission is made after completion of the auto-focusing operation (step S103inFIG. 5), and reflected light from an object is measured (step S105inFIG. 5). Then, the main light emitting amount is calculated in accordance with the photometry result of the reflected light from the object (step S110inFIG. 5).

Furthermore, in the above operation, the distance information of the object is calculated from the position of the focusing lens12(distance encoder18, brush19, lens microcomputer112), appropriate photometry level LVL1is calculated from the distance information (step S107inFIG. 5), and identification level LVL2used to identify an abnormal reflection area is calculated (step S108inFIG. 5). The photometry value of the light control area (more specifically, that inFIG. 3) is compared with identification level LVL2to determine if the light control area is an abnormal reflection area. If abnormal reflection is detected, the photometry value is replaced by that calculated from the object distance (step S108inFIG. 5), thus computing a correct main light emitting amount according to the detected object distance (step S110inFIG. 5).

Therefore, underexposure due to the influence of an abnormal reflection area when correct light control can be made under the optical conditions (distance information, aperture value, and the like) in an in-focus state can be prevented, and optimal strobe light emitting control can be made.

When viewed from the object side, only two light emissions, i.e., the pre-light emission and main light emission of the strobe are required, and uncomfortable feeling can be reduced.

In the above embodiment, a case wherein the release button is pressed to its full stroke position while the flag FLAG=“1” is set as the condition for advancing the flow to step S26inFIG. 7. However, the present invention is not limited to such specific condition. For example, when the switch SWFELK is turned on, the aforementioned FE lock process is executed. After that, when the release button is pressed to its full stroke position while the switch SWFELK is kept ON, the flow may advance to step S26. In this case, the need for measuring the time by the timer can be obviated.

In this embodiment, the optical system of the camera body1has been explained on the basis of that of a single-lens reflex camera. However, the present invention is not limited to such specific camera type. In this embodiment, the strobe and camera body have been explained as independent devices. However, when the camera body incorporates a strobe, that strobe may be used. In the above embodiment, the pre-light emission and main light emission are attained by the single strobe, but they may be attained using independent light emitting devices. Furthermore, as can be seen from the description of the above embodiment, the camera can be either a silver halide film camera or digital camera.

In the above embodiment, a button that instructs the switch SWFELK and the release button are independently provided. However, the present invention is not limited to such specific arrangement. For example, a means for selecting a shooting mode that selects strobe shooting using the FE lock process of this embodiment (e.g., a switch itself, selection from a menu display, or the like) may be provided. If this shooting mode is selected, the same process as that of the switch SWFELK may be executed in the half stroke state of the release button.

According to the arrangement of the present invention, since the main light emitting amount upon shooting an object image is calculated by making the pre-light emission is made after the auto-focusing process, shooting can be made using the correct object distance information and light emitting amount.

CLAIM OF PRIORITY

This application claims priority from Japanese Patent Application No. 2004-133914 filed on Apr. 28, 2004, which is hereby incorporated by reference herein.