JP4406954B2 - Flash control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flash control device that optimally controls the flash emission amount.
[0002]
[Prior art]
A flash control device that performs automatic light control of a flash light emitter (hereinafter referred to as SB) mainly used in a single-lens reflex camera is a so-called TTL light control method. In this method, a light beam emitted from SB and reflected from a subject is measured in real time through a photographing lens, and SB emission is stopped when the light emission amount reaches an appropriate amount. This method measures the light flux that has passed through the photographic lens, so there is no deviation (parallax) between the area to be photographed and the area to be metered, and the photographer can set the aperture value freely. ing.
[0003]
In addition, the flash control device is a flashmatic system mainly used in compact cameras and the like. In this method, the subject distance X, the aperture value F, and the guide number GN of the SB light satisfy the relationship of the following formula 1, and the subject distance X at the time of shooting and the SB of the camera are provided. The aperture value F at the time of shooting is calculated from the guide number GN.
[0004]
GN = X · F (1)
[0005]
However, the former TTL dimming method has a disadvantage in that an exposure error occurs due to the reflectance of the subject because the SB light reflected from the subject is controlled to an appropriate amount. However, since the photographer cannot freely select the aperture value in the flashmatic system, it cannot be adopted for a high-function camera such as a single-lens reflex camera.
[0006]
Therefore, in the apparatus disclosed in Japanese Patent Laid-Open No. 3-692828 by the present applicant, in the TTL dimming method, as in the algorithm shown in FIG. 22, immediately before shooting (# 1), prior to the main light emission (# 6). Preliminary light emission is performed (# 2), reflected light from the shutter curtain surface is divided and metered (# 3), and weighting calculation is performed based on the amount of received light to obtain the reflectance of the subject (# 4), and according to the reflectance Thus, a technique for obtaining an appropriate exposure regardless of the reflectance of the subject by adjusting the SB light emission level during exposure (# 5) (# 6 to # 8) is disclosed.
[0007]
Japanese Patent Application Laid-Open No. 4-88762 discloses a technique for increasing the gain of an image sensor at the time of pre-emission higher than the gain at the time of main emission in an imaging apparatus that performs preliminary emission and main emission.
[0008]
[Problems to be solved by the invention]
However, in the above-described apparatus disclosed in Japanese Patent Laid-Open No. 3-692828, since the light emission amount during preliminary light emission is small, the photometric output is small and the reliability of the photometric value may not be obtained sufficiently. In particular, in the so-called guide number control method in which the light emission amount at the time of shooting is determined in advance based on the photometry output at the time of preliminary light emission, the photometric accuracy at the time of preliminary light emission is directly fed back to the light emission accuracy at the time of shooting. Therefore, sufficient exposure accuracy may not be obtained.
[0009]
In addition, in the apparatus disclosed in Japanese Patent Laid-Open No. 4-88762, no disclosure is made as to how much the gain at the time of preliminary light emission is increased, and the problem regarding the optimum gain setting method has not been solved.
[0010]
Therefore, in the present invention, even if the light emission amount during preliminary light emission is small, the photometric accuracy is ensured, and as a result, the flash light control capable of accurately calculating the main light emission amount and improving the exposure accuracy during flash photography. The object is to provide a device.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention of claim 1 includes a flash light emitting unit (30) for performing preliminary light emission having a first light emission amount upper limit value and main light emission having a second light emission amount upper limit value, and the preliminary light emission unit (30). A flash metering unit (31) for metering reflected light from a light emitting subject; The farthest light reachable distance that can give a proper exposure when the flash light emitting part emits light at the second light emission amount upper limit value. Sensitivity value (Formula 4) , The first light emission amount upper limit value Gain correction value so that the detection limit distance of the photometric output of the flash photometric unit when it is made to emit light is substantially equal to the light arrival distance And a gain setting unit (28) for setting the gain of the flash photometry unit.
[0012]
According to a second aspect of the present invention, in the flash control device according to the first aspect, the gain setting unit includes: Set the gain to reduce the gain according to the subject distance A flash control device characterized by the above.
[0013]
The invention of claim 3 is claimed in claim 1. Or 2 In the flash control device according to claim 1, the gain setting unit includes: Set the gain to decrease the gain when the subject brightness increases. A flash control device characterized by the above.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing an optical system of a flash control device for a camera according to an embodiment of the present invention. The light beam that has passed through the photographing lens 1 is bent by the quick return mirror 2 and forms an image on the diffusion screen 3 once. Thereafter, it reaches the eyes of the photographer through the condenser lens 4, the pentaprism 5, and the eyepiece lens 6. On the other hand, a part of the light beam diffused by the diffusing screen 3 is re-imaged on the photometric element 9 for stationary light through the condenser lens 4, the pentaprism 5, the photometric prism 7, and the photometric lens 8.
As the photometric element 9, for example, a light receiving element such as SPD (silicon photo diode) is used. As shown in FIG. 3, the object field is divided into five areas B1 to B5, and the photometry is performed. It has a structure that can output photometric values.
[0017]
At the time of shooting, first, the aperture 10 is reduced to a predetermined value, and at the same time, the quick return mirror 2 is flipped up. Thereafter, during preliminary light emission, a part of the light beam that is substantially imaged and reflected on the shutter 11 is re-imaged onto the light control element 13 through the light control lens 12, and during the main light emission, the shutter 11 is opened. A light beam is imaged on a light receiving surface of an image sensor 14 constituted by a CCD (charge coupled device) or the like.
[0018]
The dimming element 13 is composed of SPD and a capacitor for accumulating the photocurrent from the SPD, an amplification amplifier, and the like. As shown in FIG. 4, the dimming element 13 has substantially the same divided shape as the photometry element 9 for stationary light. The regions S1 to S5 correspond to B1 to B5 in FIG. The quick return mirror 2 is a half mirror that transmits a part of the light, and a part of the transmitted light beam is bent downward by the sub mirror 16 and guided to the focus detection unit 17. The focus detection unit 17 detects the focus state of the focus detection areas F1 to F5 of the object scene shown in FIG. 3, and drives the photographing lens 1 until the focus of any one of the areas is in focus. Which focus detection area is focused depends on manual selection by the photographer, close selection, and the like.
[0019]
FIG. 2 is a block diagram showing a schematic configuration of the embodiment of the present invention.
As shown in FIG. 3, the stationary light metering unit 21 is a circuit that measures light by dividing the object scene into five parts, and the photometric output is output to the exposure calculation unit 22.
The exposure calculation unit 22 is a lens such as an output from the stationary light metering unit 21 and an open F value, focal length, and exit pupil position of the photographing lens stored in a lens microcomputer 25 that is a microprocessor provided in the photographing lens. Based on the information, the sensitivity information of the image sensor 14 from the sensitivity setting unit 29, etc., an appropriate exposure value related to the steady light exposure is calculated, and is decomposed into an aperture value and a shutter value and output to the sequence control unit 20.
[0020]
In response to the release signal from the release switch 27, the sequence control unit 20 raises / returns the quick return mirror 2 shown in FIG. 1, narrows / returns the aperture 10, and performs preliminary light emission / main light emission to the flash light emission unit 30. A series of operations such as instruction and control of the shutter 11 are controlled.
[0021]
The gain setting unit 28 is based on the photometry information from the steady-light photometry unit 21, the aperture value information from the exposure calculation unit 22, and the sensitivity information from the sensitivity setting unit 29. The gain of the amplifier etc. that amplifies the output from the element is calculated, and the gain setting of the flash photometry unit 31 is performed. The flash metering unit 31 integrates the subject reflected light at the time of preliminary light emission with the gain set in the gain setting unit 28, and outputs the integrated value to the light emission amount calculation unit 32. The light emission amount calculation unit 32 includes a preliminary light emission integral value from the flash photometry unit 31, a photometric value from the steady light photometry unit 21, a focus distance value from the lens microcomputer 25, an aperture value from the exposure calculation unit 22, and a sensitivity setting unit 29. The main light emission amount is calculated based on the sensitivity value and the like, and the value is output to the flash light emitting unit 30.
[0022]
The flash light emitting unit 30 performs preliminary light emission and main light emission based on the timing signal from the sequence control unit 20. In the preliminary light emission, a small light emission of a predetermined light emission amount is performed by the number of instructions from the sequence control unit 20, and the main light emission is performed with a light emission amount according to information from the light emission amount calculation unit 32.
The focus detection unit 23 detects the focus state of the subject in the focus detection area based on the instruction signal from the sequence control unit 20, and drives the lens optical system 26 to the in-focus position by the lens driving unit 24.
[0023]
Here, the operations of the exposure calculation unit 22, the gain setting unit 28, the light emission amount calculation unit 32, and the sequence control unit 20 are realized by internal calculation of a one-chip microprocessor 100 (hereinafter referred to as a microcomputer).
[0024]
FIG. 3 is a diagram showing the division state of the photometric element 9 and the focus detection area of the focus detection unit 17 in comparison with the object scene. The photometric element 9 can measure the light by dividing almost the entire surface of the object field into five and output the respective photometric values B1 to B5. Further, the focus detection unit 17 can detect the focus states for the five regions F1 to F5.
[0025]
FIG. 4 is a view showing the optical system of the flash photometry unit 31 and the divided shape of the photometry area. The optical system of the flash metering unit 31 re-images the subject image that is incident on the shutter surface and formed on the light control element 13 by the three light control lenses 12, and divides the image into five regions S1 to S5. Thus, the respective photoelectrically converted charges are stored. Here, the relationship between each area of S1 to S5 and the number corresponds to the number of each area of the photometric areas B1 to B5 in FIG.
[0026]
FIG. 5 is a diagram illustrating the terminals of the light control element 13 and their roles in an easy-to-understand manner. C1 to C5 are external capacitors for storing the photocurrents of the regions S1 to S5, SC is an external capacitor for adding and storing the photocurrents of S1 to S5 to output a stop signal, and Vref is proportional to temperature. A voltage output terminal, stop is a stop signal output terminal, and CSR, CSG, and CLK are terminals for switching the setting of the amplifier gain and the readout channel. The setting method will be described with reference to FIGS. IS is a terminal for starting / ending accumulation, DA is a terminal for inputting an amplifier / gain of each area, and AD is an output terminal for a photometric integration value of each area.
[0027]
FIG. 6 is a diagram illustrating a method of setting the amplifier / gain of each region of the light control element 13. The channel is switched in synchronization with the fall to the L level when the CSR terminal is lowered to the L level while the CSG terminal is kept at the H level and then the clock signal is input to the CLK terminal. The gain of the channel is set by setting the DA terminal to a voltage level corresponding to the set gain while the CLK terminal is at the L level. Ch1 to Ch5 correspond to S1 to S5, respectively.
[0028]
FIG. 7 is a diagram illustrating a method of reading the photometric integration value of each region of the light control element 13. When the clock signal is input to the CLK terminal after the CSR and CSG terminals are lowered to the L level after the CSR and CSG terminals are lowered, the channel is switched in synchronization with the fall to the L level, and the photometric integration value of each region is a voltage level corresponding to the photometric value. And output to the AD terminal.
[0029]
FIG. 8 is a diagram for easily explaining the operation at the time of preliminary light emission. When the release signal is input and narrowing down is completed, the gain setting unit 28 performs gain setting for preliminary light emission (gain setting 1). The method for calculating the gain will be described in detail later. After that, after warming up the flash emission unit 30 and the flash photometry unit 31, the chop emission two shots are performed, then the IS terminal is lowered, and preliminary emission integration (integration 1) starts. At the same time, the first preliminary light emission is performed.
[0030]
Preliminary light emission ends when the photometric integration value reaches an appropriate level or when the number of chopped light emission reaches a predetermined value, and after the integral value is read out (readout 1), the IS terminal is started up and integrated. Reset the value. Since the integral value at the time of the preliminary light emission includes the stationary light component in addition to the reflected light of the SB light, integration of only the stationary light is performed after the preliminary light emission is completed, and the stationary light component is calculated in the subsequent calculation processing. Subtraction is performed from the preliminary light emission integral value. In gain setting 2, gain setting for steady light integration is performed, and then the IS terminal is lowered and steady light integration (integration 2) is performed as in the case of preliminary light emission. The gain setting and integration time for stationary light integration will be described later.
[0031]
When the steady light integration is completed, the integrated value is read out (readout 2), and then the IS terminal is raised to reset the integrated value. Thereafter, the main light emission amount is calculated by an algorithm described later, and the value is communicated to the flash light emitting unit 30. The main light emission control is performed simultaneously with the photographing, and the photographing is completed.
[0032]
FIG. 9 is a diagram showing the relationship between the aperture value (unit AV) of the lens and the output logIG of the flash photometry unit 31. log IG is the logarithm of the output IG of the flash photometry unit 31. In this case, the gain of the flash photometry unit 32 (hereinafter simply referred to as gain) is unchanged with respect to changes in AV. Thus, the output decreases as the AV value increases, that is, as the aperture is reduced. This is because the amount of light incident on the sensor is reduced to narrow down.
[0033]
FIG. 10 is a diagram showing the relationship between the shooting distance (unit: m) and the output logIG of the flash photometry unit 31. logIG is the same as in FIG. Again, the gain is invariant to changes in distance. As shown in the figure, the output decreases as the distance increases. This is because the amount of reflected light decreases in inverse proportion to the square of the distance.
[0034]
FIG. 11 is a diagram showing the relationship between the gain change (unit: ratio to the reference gain) and the output logIG of the flash photometry unit 31. Increasing the gain increases the output proportionally. Note that the gain decreases as the horizontal axis moves to the right in FIG. 11 because, as will be described later, when the voltage is set low, the gain increases.
[0035]
FIG. 12 is a diagram illustrating a sensitivity change (unit: SV) and a gain change of the image sensor 14. In the case of A, the gain is constant with respect to the change in SV, and in the case of B, the gain is also changed in accordance with the change in SV.
[0036]
FIG. 13 is a diagram showing the relationship between the sensitivity of the image sensor 14 (unit: SV) and the reach of SB light (unit: logarithm of distance) in the case of A and B in FIG. is there. The reach distance of the SB light is the farthest distance at which the SB light can give an appropriate exposure under a given photographing condition (for example, aperture value) in the case of the main light emission. In this case, the flash metering unit 31 is the farthest distance at which the reflected light integral value can be detected.
[0037]
As shown in FIG. 13, in the case of the main light emission and B, as SV increases, that is, as the sensitivity increases, the reach distance increases, but in the case of A, it is constant. If the preliminary light emission is performed by the method A, the reflected light of the preliminary light emission can be measured within the range of the main light emission reach distance when the SV is smaller than the point O equal to the main light emission reach distance. When SV becomes larger than O, the preliminary light emission arrival distance becomes closer to the main light emission arrival distance, and the preliminary light emission integral value cannot be obtained. As a result, the main light emission amount cannot be calculated within this SV range.
[0038]
On the other hand, in the case of B, since the gain is changed according to the SV value, the reach distance is extended according to the SV value as in the case of the main light emission. In FIG. 13, the reach distance of B is always closer to the front than the main light emission. This is because the gain setting of the flash photometry unit 31 changes in accordance with the SV, but does not take into account the light amount difference between the preliminary light emission amount and the main light emission amount.
[0039]
FIG. 14 is a diagram showing the relationship between the ratio (GN ratio) between the main light emission guide number GNhon and the preliminary light emission guide number GNpre and the gain. In the case of C, the gain is constant with respect to the change in the GN ratio, and in the case of D, the gain is changed in accordance with the change in the GN ratio. Here, GNhon and GNpre are the maximum amount of light that can be emitted in each case. If a plurality of types of SBs can be mounted and the GNpre is constant regardless of the mounted SB, the GN ratio varies depending on the GNhon.
[0040]
FIG. 15 is a diagram showing the relationship between the main emission guide number (unit: GN) and the SB light reach distance (unit: logarithm of distance) in the case of C and D in FIG. . The definition of the reach distance of the SB light is as described in FIG. As shown in the figure, in the case of the main light emission and D, the reach distance increases as GN increases, that is, the light emission amount increases, but in the case of C, it is constant.
[0041]
If the preliminary light emission is performed by the method C, if the GN is smaller than the point P equal to the main light emission reach distance, the reflected light of the preliminary light emission can be measured within the range of the main light emission reach distance. When GN becomes larger than P, the preliminary light emission arrival distance becomes closer to the main light emission arrival distance, and the preliminary light emission integral value cannot be obtained. As a result, it is impossible to calculate the main light emission amount within this GN range.
[0042]
On the other hand, in the case of D, since the gain is changed according to the GN of the main light emission amount, the arrival distance is extended according to the GN as in the case of the main light emission even when the preliminary light emission amount is constant. In FIG. 15, in order to make the drawing easier to see, the reaching distance is slightly closer to D than the main light emission, but it should be theoretically matched by appropriately adjusting the gain correction amount with respect to the GN ratio. Is possible.
In the above description, A and C correspond to the prior art, and B and D correspond to the present invention, respectively.
[0043]
FIG. 16 is a flowchart showing a program of the microcomputer 100. When the release switch 27 of the camera is pressed halfway, the camera is turned on and this program is executed. First, in step S100, communication is performed with an SB microcomputer (not shown) provided in the flash light emitting unit 30, and the SB full light emission guide number GN and the guide number GNp1 per preliminary light emission (both at ISO 100). Is read. In step S101, communication is performed with the lens microcomputer 25 provided in the photographing lens, and information such as the open F value, focal length, and exit pupil position of the photographing lens is read. In step S102, the sensitivity value set manually or automatically is read from the sensitivity setting unit 29. Further, in step S103, stationary light photometry is performed by the photometric element 9, and the luminance information of B1 to B5 is obtained by performing correction using the lens information read in step S101. Based on the value, stationary light is measured by a known method. An exposure calculation is performed to obtain an appropriate exposure value BVans. In step S104, an aperture value and a shutter value at the time of shooting are calculated from BVans and the film sensitivity value.
[0044]
In step S105, focus detection is performed by the focus detection unit 23, and the lens optical system 26 is driven by the lens driving unit 24 until the defocus amount calculated in step S106 becomes zero. In step S107, the focus distance of the photographing lens at the in-focus position is regarded as the subject distance, and the value is read from the lens microcomputer 25. In step S108, it is determined whether or not the release switch 27 is fully pressed. If the release switch 27 is fully pressed, the process proceeds to step S109. If not, the process jumps to step S119. In step S109, the quick return mirror 2 is flipped up and the diaphragm 10 is narrowed down to the value obtained in step S104.
[0045]
After setting the gain of preliminary light emission in step S110, preliminary light emission is performed in step S111, and photometric integration values IGpre [1] to IGpre [5] in S1 to S5 are calculated. The gain setting method and the preliminary light emission method will be described in detail later. When the preliminary light emission ends, in step S112, steady light integration is performed to read integration values IGTei [1] to IGTei [5]. Steady light integration sets the gain setting and integration time equal to the preliminary light emission. That is, in FIG. 8, tpre = ttei.
In step S113, GV [1] to GV [5] in each of the dimming regions S1 to S5 are calculated from the integrated value obtained by preliminary light emission or the like. GV [i] (i = 1..5) is a variable related to the subject reflectance in each region, and is expressed in unit EV. The calculation method of GV [i] will be described in detail later. In step S114, based on the result of GV [i] and the like, a main light emission amount at the time of photographing is calculated by a method described later, and in step S115, the value is transmitted to the flash light emitting unit 30 by communication.
[0046]
In step S116, the shutter is opened, and in step S117, the flash emission unit 30 controls the light emission amount of the main light emission. After the main light emission is completed, the shutter, aperture, and mirror are returned to the initial positions in step S118. In step S119, it is determined whether or not a predetermined time has elapsed after the half-press timer is activated. If it is within the predetermined time, the process returns to step S101 to repeat the process, and if the timer has expired, the process ends.
[0047]
FIG. 17 is a subroutine flowchart showing a gain calculation method set by the gain setting unit 28. By executing step S110 of FIG. 16, this subroutine is called and executed. First, in step S201, a high brightness cut area is detected. This is a process of excluding from the dimming area in advance a high-luminance area that adversely affects the reflected light integration during preliminary light emission by referring to the values of the steady light metering values B1 to B5. Specifically, an area exceeding BVcut_th, which is a threshold for high-intensity cut, among B1 to B5 is set as a cut target area. However, when there are three or more cut areas, the three areas from the darker are set as the light control areas.
[0048]
Next, in step S202, Gav [i] (unit: EV, i = 1..5) which is a main variable for determining the gain is calculated. Gav [i] is calculated for each of the five dimming regions, and the gain increases by 1 EV each time the value increases by one. The calculation method of GaV [i] will be described in detail later. Next, in step S203, a numerical value T proportional to the current temperature output from the dimming element 13 is read.
[0049]
Next, in step S204, the gain DApre [i] that is actually set in the light control element 13 is calculated by the following formula 2.
DApre [i] = (pre_level [i] −GaV [i] * pre_gamma) * T / Tref, (i = 1 to 5) (2)
Where pre_level [i]: reference value of the pre-flash dimming level
pre _gamma: Gamma adjustment value
T: Current temperature
Tref: Temperature during adjustment
pre_level [i], pre_gamma, and Tref are data stored in a non-illustrated nonvolatile memory (EEPROM or the like) in the camera.
[0050]
The reason for being negative with -GaV [i] is that the gain increases as the DA terminal voltage of the light control element 13 shown in FIG. By the way, in the case of normal TTL light control, the SV value, which is equivalent to the film sensitivity (hereinafter simply referred to as film sensitivity), is substituted for GaV as it is, and if the film sensitivity increases by one step, the gain increases by one step. The stop signal is controlled so as to be output at half the image plane exposure amount.
[0051]
However, in step 201, the gain DApre [i] of the area subject to the high-intensity cut is set to the minimum so that the area is not actually measured.
[0052]
Next, a method for calculating GaV [i] in step S202 of FIG. 17 will be described. GaV [i] is a main variable that determines the gain set for each region of the light control element 13, and is obtained by the following Equation 3.
Gav [i] = SvV + GnV-XmV-BvV + MvV-Sa [i] where i = 1..5 (3)
Here, each variable on the right side will be described.
[0053]
SvV is a correction value corresponding to the sensitivity of the image sensor 14. If the sensitivity is high, light will reach far away even if the amount of light emitted during the main light emission is the same. Therefore, the gain at the time of preliminary light emission is increased to increase the integrated output, and the preliminary light emission reaches far. Specifically, it is given by Equation 4 below.
SvV = SV-5 (4)
Here, SV is a sensitivity value (unit: SV) of the image sensor 14. The reason why 5 is subtracted is to make SVv = 0 when SV = 5, that is, when the sensitivity is ISO100.
[0054]
GnV is a correction value of the guide number difference between the main light emission GN and the preliminary light emission GN of the mounted SB, and is obtained by the following Equation 5.
GnV = log2 (GN / GNp1 / √ (Qpre_max)) ^ 2, where GnV <GnVmax (5)
Where GnVmax: GnV upper limit
log2: Represents the logarithm of base 2.
GN: Guide number for full flash at ISO100
GNp1: Guide number per preliminary light emission at ISO100
Qpre_max: Maximum number of preliminary flashes
[0055]
In addition, √ () is a square root in (), and ^ is a symbol representing power. GnV is a variable for canceling the light amount difference between the maximum GN of main light emission (at the time of full light emission) and the maximum GN of preliminary light emission (when chopped light emission of GNp1 per light emission is performed Qpre_max times). The reason why the numerical value in the logarithm is squared is that GN changes by 1 EV by √2. However, if the gain is increased too much, the S / N characteristic of the integral value deteriorates, so GnV limits its upper limit value by GnVmax.
[0056]
XmV is a gain correction value based on the distance signal, and is obtained by the following Equation 6.
XmV = kxm * log2 (GN * 2 ^ {(SV-5) / 2} / {X * F}) ^ 2 (6)
Where kxm: distance correction coefficient
log2: Represents the logarithm of base 2.
GN: Guide number for full flash at ISO100
^ 2: represents square
SV-5: ISO sensitivity value (Unit: SV)
(5 is subtracted because the GN value is based on ISO100)
X: Shooting distance at that time (unit: m)
F: Aperture value at that time (unit: F number)
[0057]
GaV is set to a gain according to the ISO sensitivity at that time and the maximum reachable distance of the main flash by GN, depending on SvV and GnV, but the actual shooting distance is usually closer than that. If it is as it is, the gain may be too large and the integral value may overflow. Therefore, the gain is lowered according to the subject distance by XmV. kxm is a correction coefficient for preventing overcorrection, and a numerical value of about 0.5 is used.
[0058]
BvV is a correction value for preventing a stop signal from being generated due to the influence of ambient light when the ambient light is bright, such as during daytime synchronization. The influence of ambient light increases as the brightness increases and the distance increases, so that these are used as parameters to obtain the following Expression 7.
BvV = BVave -BVofset + log2 (X ^ 2), but 0 <BvV <BvVmax (7)
BVave: Average brightness value of all dimming areas that are not cut with high brightness (unit: BV)
BVofset: Offset adjustment value
log2: Represents the logarithm of base 2.
^ 2: represents square
X: Shooting distance at that time (unit: m)
BvVmax: Brightness correction upper limit
A number of about 9 (unit: BV) is used for BVofset, and a number of about 2 (unit: EV) is used for BvVmax.
[0059]
MvV is a gain correction value corresponding to the number of effective areas, and is obtained by the following Equation 8.
MvV = log2 (1 / mval) (8)
mval: number of valid areas
[0060]
Normally, the gain is set on the assumption that all five areas S1 to S5 are effective, and a stop signal is output when the sum of the photocurrents in the five areas reaches a predetermined value. However, if there is a cut area, the photocurrent from that area does not enter, so that the gain of the other area is increased by that amount so that a stop signal is output with the same light emission amount. The number of effective areas (mval) is the total number of areas that are not cut with high luminance, which is obtained by detecting the high luminance cut area in step S201.
[0061]
Sa [i] is a value for correcting the non-linearity of (aperture value) versus (integral output value), and is a function of the aperture value. In addition, the value is different for each region (mainly the center and the periphery). Since the value of Sa [i] depends on the optical system and the like of the flash photometry unit 31, it is desirable to actually calculate the relationship between the aperture value and the integrated output value.
[0062]
FIG. 18 is a subroutine flowchart showing a control method at the time of preliminary light emission. By executing step S111 in FIG. 16, this subroutine is called and executed. First, in step S302, the amplifier gain DApre [i] for preliminary light emission obtained in FIG.
[0063]
Next, in step S303, after the light emission is performed twice for warming up the arc tube of SB, in step S304, a variable Qpre indicating the number of times of preliminary light emission is set to 0, and the preliminary light emission time tpre1 is counted. And the IS terminal of the light control element 13 is set to L to start integration.
[0064]
In step S305, 1 is added to Qpre. In step S306, preliminary light emission is performed at the guide number GNp1, and in step S307, it is determined whether or not a stop signal has been output. If not, the process proceeds to step S308, and it is determined whether or not the number of preliminary light emission times Qpre has reached the maximum number of times Qpre-max (standard value 16). When Qpre-max has been reached, the preliminary light emission is terminated and the process proceeds to step S309. Otherwise, the process returns to step S305 and the preliminary light emission is repeated. Since the upper limit of the sum of the preliminary light emission amounts is provided, it is possible to reliably secure the light emission amount during the main light emission.
[0065]
When the preliminary light emission ends, the time measurement of the preliminary light emission time tpre is ended in step S309. In step S310, the integral values IG1 (1) to IG1 (5) corresponding to the light control regions S1 to S5 are read out, and the process is terminated.
[0066]
FIG. 19 is a flowchart for explaining the method of calculating GV [i] shown in step S113 of FIG. As described above, GV [i] (i = 1..5) is a variable related to subject reflectance in each region, and guides SB light that gives an appropriate exposure amount to a subject with standard reflectance. The number is represented by unit EV.
First, in step S401, 0 is substituted for a variable i that designates an area. Next, in step S402, it is determined whether or not the area i is a high-luminance cut area. If so, the area is not subject to dimming, and in step S405, the area GV [i Substitute 99 for].
[0067]
In step S403, the net integral value IG [i] is calculated using Equation 9.
IG [i] = IGpre [i] −IGtei [i] (9)
That is, by subtracting the value integrated with only ambient light without preliminary light emission from the integral value during preliminary light emission, the integrated value of reflected light with only preliminary light emission is obtained.
[0068]
In step S404, it is determined whether IG [i] is 0 or less. If it is 0 or less, GV [i] cannot be calculated, and the process proceeds to step S405. If GV [i]> 0, GV [i] is calculated in step S406. GV [i] is obtained by the following Equation 10.
[0069]
GV [i] = log2 (GNrtn [i]) ² …(Ten)
Here, GNrtn [i] is obtained by the following Expression 11.
[0070]
GNrtn [i] =
GNp1 * √ (Qpre) * √ (2 ^ (Gav [i] + Sa [i]) * √ (IGstop / mval / IG [i])… (11)
However, GNp1: Guide number per preliminary light emission (ISO100 conversion)
Qpre: Pre-flash count
IGstop: Sum of each IG [i] (i = 1..5) value when the stop signal is output.
mval: number of valid areas
IG [i]: Net integrated value of preliminary light emission in each area
[0071]
The meaning of GNrtn [i] is that if the GNrtn [i] emits light, the area i has a reference exposure amount (0.1 Lx with ISO 100). ^Four s) is obtained. That is, when the subject has the standard reflectance, the following Expression 12 is established for the distance X and the aperture F.
[0072]
GNrtn [i] = X * F (12)
Therefore, GV [i] is obtained by converting the guide number that gives the reference exposure amount to the unit EV for the standard reflectance subject. Further, GV [i] can be obtained from Equations 10 and 12 by the following Equation 13 without calculating GNrtn [i].
[0073]
GV [i] =
log2 (GNp1 ^ 2 * Qpre) + (Gav [i] + Sa [i]) + log2 (IGstop / mval / IG [i])… (13)
Thereafter, after i is incremented in step S407, it is determined whether or not i exceeds 5 in step S407. If i is 5 or less, the process returns to step S402, and if i> 5, the process ends.
[0074]
Next, the main light emission amount calculation method in step S114 of FIG. 16 will be described. First, the subject reflectance RefEV [i] of each region is calculated using Equation 14 using GV [i] of each region obtained by Equation 13.
[0075]
RefEV [i] = 2 * X + AV−GV [i], (i = 1..5) (14)
Where X: shooting distance (unit: m)
AV: Shooting aperture value (unit: AV)
[0076]
Here, RefEV [i] is a variable that is 0 when the reflectivity is a standard value, +1 when the reflectivity is +1 step higher than the standard, and similarly -1 at -1 step. is there. Next, using RefEV [i], a weighting number RefG [i] for each region corresponding to the reflectance is calculated using Equation 15.
[0077]
RefG [i] = 1 / (2 ^ (Abs (RefEV [i]))), (i = 1..5) (15)
However, Abs () is a function for obtaining an absolute value in (). As shown in FIG. 20, RefG [i] is a variable that is 1 when the reflectance of the subject is a standard value, and decreases as the distance from the standard value increases.
[0078]
Next, RefG [i] is normalized by Expression 16, and the weight wt [i] for each region is calculated.
wt [i] = RefG [i] / (RefG [i]), (i = 1..5)… (16)
However, () is a function for calculating the sum of the variables RefG [i] (i = 1..5) in (). Next, the reflectance correction value RefMain for the entire object field is calculated by Equation 17 again using RefEV [i] obtained by Equation 14.
[0079]
RefMain = log2 ((wt [i] * 2 ^ RefEV [i])), (i = 1..5)… (17)
However, () is a function similar to Equation 16, and log 2 is a function representing the logarithm of 2. The main light emission amount correction value deltaY is calculated by Equation 18 using RefMain.
[0080]
deltaY = krm * RefMain (18)
The relationship between reflectance and deltaY is shown in FIG. Here, krm is a constant for adjusting the degree of correction of the reflectance, and a numerical value of about krm = 0.5 is used, but it may be changed as necessary.
[0081]
When wt [i] and deltaY are obtained from Expressions 16 and 18, the actual light emission quantity multiple Kgn is calculated by Expression 19.
[0082]
Kgn = IGstop / mval / (IG [i] * wt [i]) * GH * DY (19)
IGstop is used in Equation 11, and GH and DY are obtained by Equations 20 and 21 below.
[0083]
GH = 2 ^ (Gav [i] + Sa [i]) (20)
DY = 2 ^ (deltaY-SV + 5) (21)
Here, the symbol ^ is a function representing a power, and SV, GnV, XmV, and BvV are those used in Equation 11.
[0084]
Kgn is a variable representing how many times the main light emission amount is to be increased as compared with the preliminary light emission, as shown in Equation 22.
GNhon = GNpre * √ (Kgn) (22)
However, GNhon: Main light emission GN
GNpre: preliminary light emission GN
The reason why √ is applied to Kgn is that GN has a property of changing 1 EV when √2 times.
[0085]
As described above, according to this embodiment, there are the following operations and effects.
(1) The gain setting unit 28 does not perform gain setting using the aperture value as a parameter as in the prior art, but as shown in Formula 3, the sensitivity value SvV, the first light emission amount upper limit value, and the second light emission amount The gain of the flash metering unit 31 is set using at least one of the ratio GnV to the upper limit value, the shooting distance XmV, the subject brightness MvV, and the like. The exposure accuracy at the time can be improved.
[0086]
(2) When the gain setting unit 28 emits light at the second light emission amount upper limit value, the farthest light arrival distance SvV that can provide appropriate exposure is expressed using the sensitivity value SV as shown in Expression 4. Since the gain setting is performed using the gain correction value so that the detection limit distance of the photometry output of the flash photometry unit when the light is emitted with the first light emission amount upper limit value is substantially equal to the light arrival distance, A gain correction value can be obtained by calculation.
[0087]
(3) The gain setting unit 28 calculates a gain correction value (GnV) corresponding to the ratio between the first light emission amount upper limit value (GNp1) and the second light emission amount upper limit value (GN), as shown in Equation 5. To set the gain. For example, as shown in FIG. 14, the gain is changed in accordance with the ratio between the guide number for main light emission and the guide number for preliminary light emission. For this reason, as shown in FIG. 15, it can correct | amend so that an arrival distance may be extended as the ratio (light emission amount) becomes large.
[0088]
(4) As shown in Formula 6, the gain setting unit, when the light is emitted with the second light emission amount upper limit value, the farthest light arrival distance (GN / F) that can give appropriate exposure, and the shooting distance (X The gain is set by using a gain correction value corresponding to the ratio to (). That is, when the ratio increases, the gain is corrected in a decreasing direction. Therefore, accurate correction can be performed even if the shooting distance changes.
[0089]
(5) Since the gain setting unit sets the gain so as to decrease the gain when the subject brightness increases as shown in Equation 7, even when the ambient light is bright such as during daytime synchronization, The influence can be prevented.
[0090]
The present invention is not limited to the embodiment described above, and various modifications and changes are possible, and these are also within the equivalent scope of the present invention.
For example, regarding the relationship between the first and second light emission amount upper limit values, the second light emission amount upper limit value is determined based on the maximum light emission amount of the arc tube (for example, the amount if the charge is 90%) Although it is used to mean an upper limit value obtained by subtracting the light emission amount used at the time of light emission (first light emission amount upper limit value), the second light emission amount upper limit value is originally the maximum light emission amount of the arc tube, for example, a guide number. It may be considered that the amount of light used during preliminary light emission is subtracted from the above.
[0091]
Although the example using the first and second light emission amount upper limit values has been described, when only one of them is obtained, it is a constant (typical value, for example, a value when fully charged). May be treated as
Further, the ratio of the second light emission amount upper limit value to the first light emission amount upper limit value is used, but conversely, the ratio of the first light emission amount upper limit value to the second light emission amount upper limit value may be used.
[0092]
【The invention's effect】
As described above in detail, according to the present invention, the photometric accuracy is ensured even when the light emission amount during the preliminary light emission is small, and as a result, the main light emission amount is accurately calculated, and the exposure accuracy during flash photography is improved. It becomes possible to improve.
[Brief description of the drawings]
FIG. 1 is a diagram showing an optical system according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of an embodiment of the present invention.
FIG. 3 is a diagram illustrating a division shape and a focus detection unit of a stationary light photometry unit according to the present embodiment.
FIG. 4 is a diagram showing an optical system and divided shapes of a flash photometry unit of the present embodiment.
FIG. 5 is a diagram showing the terminals of the dimming element according to the present embodiment and their operations in an easy-to-understand manner.
FIG. 6 is a diagram showing the terminals of the dimming element of this embodiment and their operations in an easily understandable manner.
FIG. 7 is a diagram showing the terminals of the dimming element according to the present embodiment and their operations in an easy-to-understand manner.
FIG. 8 is a diagram for easily explaining the operation at the time of preliminary light emission according to the embodiment.
FIG. 9 is a diagram briefly showing the relationship between various conditions and the integral output.
FIG. 10 is a diagram briefly showing the relationship between various conditions and an integral output.
FIG. 11 is a diagram briefly showing the relationship between various conditions and an integral output.
FIG. 12 is a diagram briefly showing the relationship between various conditions and gains.
FIG. 13 is a diagram briefly showing the relationship between various conditions and the reach of SB light.
FIG. 14 is a diagram briefly showing the relationship between various conditions and gains.
FIG. 15 is a diagram briefly showing the relationship between various conditions and the reach of SB light.
FIG. 16 is a flowchart showing an algorithm of the present embodiment.
FIG. 17 is a flowchart showing an algorithm of the present embodiment.
FIG. 18 is a flowchart showing an algorithm of the present embodiment.
FIG. 19 is a flowchart showing an algorithm of the present embodiment.
FIG. 20 is a diagram briefly showing the relationship between reflectance and each variable.
FIG. 21 is a diagram briefly showing the relationship between reflectance and each variable.
FIG. 22 is a diagram showing a conventional technique.
[Explanation of symbols]
1 Photo lens
2 Quick return mirror
3 Diffusion screen
4 condenser lens
5 Penta prism
6 Eyepiece
7 Photometric prism
8 Photometric lens
9 Photometric element
10 Aperture
11 Shutter
12 Light control lens
13 Light control element
14 Image sensor
15 Flash emission part
16 Submirror
17 Focus detector
21 Stationary light metering unit
22 Exposure calculator
23 Focus detection unit
24 Lens drive unit
25 Lens microcomputer
26 Lens optics
27 Release switch
28 Gain setting section
29 Sensitivity setting section
30 Flash emission part
31 Flash metering section
100 microprocessor

Claims (3)

A flash light emitting unit for performing preliminary light emission having a first light emission amount upper limit value and main light emission having a second light emission amount upper limit value;
A flash metering unit for metering reflected light from the preliminary light emission subject;
Using the sensitivity value , the farthest light arrival distance that can provide appropriate exposure when the flash light emitting portion is caused to emit light at the second light emission amount upper limit value is used to emit light at the first light emission amount upper limit value . And a gain setting unit for setting the gain of the flash photometry unit using a gain correction value such that the detection limit distance of the photometric output of the flash photometry unit is substantially equal to the light arrival distance. . The flash control device according to claim 1,
The flash control device, wherein the gain setting unit performs gain setting so as to decrease the gain according to a subject distance . The flash control device according to claim 1 or 2 ,
The flash control device according to claim 1, wherein the gain setting unit performs gain setting so as to reduce the gain when the subject brightness increases .

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