JP5332304B2 - Camera and flash method - Google Patents

Description

  The present invention relates to a camera, a flash device, an imaging device, and a flash method.

  When preliminary light emission is performed with a flash device and the main light emission amount is determined based on the reflected light from the subject, if the main light emission amount is insufficient, the sensitivity of the image sensor is increased by the shortage, and the light emission amount is insufficient. There is known a camera that compensates for (see, for example, Patent Document 1).

Prior art documents related to the invention of this application include the following.
JP 2005-115160 A

  However, in the conventional camera described above, since the main flash emits light at the maximum light emission amount that the flash device can emit, continuous flash photography cannot be performed, and the light emission energy for the next shooting is accumulated. There is a problem that it takes a long time to take a photo opportunity in sports photography.

According to the first aspect of the present invention, there is provided a camera having an image pickup means for picking up an image of a subject, flash light means for performing preliminary light emission before flash photography and main light emission at the time of flash photography, and subject brightness measured at the time of preliminary light emission of the flash means. Based on the first light emission amount and the determination means for determining the imaging sensitivity of the imaging means, and the second light emission that is smaller than the maximum light emission amount that can be emitted by the flash means by a predetermined amount set according to a predetermined condition. Second light emission amount calculating means for calculating the amount, determination means for determining whether or not the first light emission amount is larger than the second light emission amount, and the first light emission amount is determined by the determination means as the second light emission amount. When it is determined that the flash amount is larger than the amount, the flash unit is caused to perform main light emission with the second light emission amount, and is determined by the determination unit according to a difference between the first light emission amount and the second light emission amount. and control means for increasing the imaging sensitivity Characterized in that it obtain.
According to a ninth aspect of the present invention, there is provided a flashing method comprising: an imaging unit that captures a subject image; and a light emitting unit that performs preliminary light emission and main light emission at a predetermined light emission amount. Based on the first light emission amount and the imaging sensitivity of the imaging means, and a second light emission amount that is smaller than the maximum light emission amount that can be emitted by the light emitting means by a predetermined amount set according to a predetermined condition. Calculating, determining whether or not the first light emission amount is greater than the second light emission amount, and determining that the first light emission amount is greater than the second light emission amount; The main light emission is performed with two light emission amounts, and the imaging sensitivity determined by the determination unit is increased according to a difference between the first light emission amount and the second light emission amount.

  According to the present invention, continuous flash photography can be performed even when flash photography is performed by increasing the imaging sensitivity of the imaging device in order to compensate for the lack of light emission during flash photography.

  An embodiment in which the present invention is applied to a single-lens reflex digital camera in which an interchangeable lens and a flash device are mounted on the camera body will be described. The present invention can be applied not only to a single-lens reflex digital camera but also to a compact camera with a built-in flash device, for example.

  FIG. 1 is a cross-sectional view showing a configuration of a camera according to an embodiment. The light beam from the subject passes through the photographing optical system 101, is reflected upward by the quick return mirror 102, and is guided to the finder screen 103 to form an image. This subject image is guided to the photometric sensor 106 via the penta roof prism 104 and the photometric re-imaging optical system 105, and the subject image is re-imaged on the light receiving surface of the photometric sensor 106. The control device 107 determines camera control information such as exposure and imaging sensitivity based on the subject luminance output from the photometric sensor 106. The photometric sensor 106 can be a CCD or CMOS.

  When the release switch 108 is pressed, the control device 107 flips the click return mirror 102 upward, opens the shutter 109 and guides the subject luminous flux from the photographing optical system 101 to the image sensor 110. Then, a subject image is captured by the image sensor 110.

  A flash device 111 is detachably mounted on the top of the camera. The flash device 111 charges a capacitor with electric power of a built-in battery to store light emission energy, and discharges a discharge tube with the light emission energy to emit light. Further, preliminary light emission is performed prior to the main light emission, and the light emission amount during the main light emission is determined based on the amount of reflected light from the object field during the preliminary light emission.

  FIG. 2 is a flowchart showing the flash photographing operation of the camera according to the embodiment. In step 201, when the release switch 108 is pressed, the control device 107 starts this photographing operation. In step 202, preliminary light emission is executed by the flash device 111, and photometry of the object scene is performed by the photometric sensor 106 to detect subject luminance.

In step 203, based on the photometric output of the photometric sensor 106, the provisional light emission amount GN during the main light emission of the flash device 111 is determined by the following equation.
GN = Power√2 (−Log2 (Vo) + Gnconst) (1)
In Expression (1), Power√2 () is a function that returns the power of the argument of √2, and Log2 () is a function that returns the logarithm of the argument with 2 as the base. Vo is a value corresponding to the subject brightness output from the photometric sensor 106 during preliminary light emission, and is a value proportional to the amount of reflected light from the object scene. Gnconst is a constant term for calculating the provisional light emission amount GN. Note that the value in parentheses on the left side of the equation (1) is an APEX unit system, and the calculated unit of the provisional light emission amount GN is a guide number. When the light emission amount is doubled, the guide number is doubled.

In step 204, it is determined by the following formula whether or not there is a sufficient margin in the light emission capability of the flash device 111 with respect to the provisional light emission amount GN.
Log√2 (Gnmax / GN) <Svconst (2)
In equation (2), Log√2 () is a function that returns a logarithmic value of an argument with √2 as the base. Gnmax is the maximum light emission amount of the flash device 111, Svconst is a positive offset amount for calculating the sensitivity change amount of the image sensor 110, and the unit system is APEX. When the formula (2) is affirmed, there is no sufficient margin for the light emission capability of the flash device 111, and when the formula (2) is negated, there is a margin for the emission capability. The offset amount Svconst is a value indicating a margin of light emission capability, and a method for setting this value will be described later.

  When performing the main light emission with the provisional light emission amount GN, if there is a sufficient margin in the light emission capability of the flash device 111, the process proceeds to step 207, the quick return mirror 102 is flipped up, and the shutter 109 is opened. In the next step 208, photographing is performed by the image sensor 110, and at the same time, the main flash is performed by the flash device 111. When the flash photography is finished, in step 209, the shutter 109 is closed and the quick return mirror 102 is returned to the photographing optical path. In step 210, it is confirmed whether or not the power of the camera is turned off. If not turned off, the process returns to step 201 to repeat the above-described processing.

On the other hand, if it is determined by the above formula (2) that there is no sufficient margin in the light emission capability of the flash device 111 with respect to the provisional light emission amount GN, the process proceeds to step 205. In step 205, it is preferable to change the sensitivity of the image sensor 110 because there is no sufficient margin in the light emission capability. Therefore, the sensitivity change amount ΔSV of the image sensor 110 is calculated by the following equation and the sensitivity is changed.
ΔSV = Log√2 (GN / Gnmax) + Svconst (3)
In equation (3), Log√2 () is a function that returns the logarithmic value of the argument with √2 as the base. The sensitivity change amount ΔSV is the same APEX unit system as Svconst.

Here, for example, when the set sensitivity of the image sensor 110 when the release switch 108 is pressed is ISO 100, the set sensitivity After ISO in consideration of the sensitivity change amount ΔSV calculated by the above equation (3) is obtained by the following equation.
After ISO = ISO100 · Power2 (ΔSV) (4)
In Expression (4), Power2 () is a function that returns the power of two arguments. The set sensitivity After ISO calculated by the equation (4) is a unit system of ISO sensitivity.

Next, in step 206, the provisional light emission amount GN is changed to obtain the official main light emission amount AfterGN by the following equation.
AfterGN = GN.Power√2 (−ΔSV) (5)
In equation (5), Power√2 () is a function that returns the argument power of √2. The calculated main light emission amount AfterGN is smaller than the maximum light emission amount Gnmax of the flash device 111, and can be flashed without any problem.

  When the main light emission amount AfterGN is determined, the process proceeds to step 207 where the quick return mirror 102 is flipped up and the shutter 109 is opened. In the next step 208, photographing is performed by the image sensor 110, and at the same time, the main flash is performed by the flash device 111. When the flash photography is finished, in step 209, the shutter 109 is closed and the quick return mirror 102 is returned to the photographing optical path. In step 210, it is confirmed whether or not the power of the camera is turned off. If not turned off, the process returns to step 201 to repeat the above-described processing.

  FIG. 3 is a diagram illustrating a relationship between the light emission amount of the flash device 111 and the imaging sensitivity of the imaging element 110. 3A to 3C, the graph on the left side shows the relationship between the temporary light emission amount GN and the main light emission amount AfterGN (hatched bar graph in the figure) with respect to the maximum light emission amount Gnmax of the flash device 111, and the graph on the right side. Indicates the relationship of the set imaging sensitivity AfterISO (hatched bar graph in the figure) to the maximum imaging sensitivity of the imaging device 110. A method for setting the offset amount Svconst will be described with reference to FIG.

  The graph on the left side of FIG. 3A shows a state where the provisional light emission amount GN calculated by the above equation (1) exceeds the maximum light emission amount Gnmax of the flash device 111. At this time, it is assumed that the imaging sensitivity of ISO 100 is set in the imaging element 110. Since the light emission amount necessary for flash photography is larger than the maximum light emission amount Gnmax of the flash device 111, it is impossible to perform flash photography with bright illumination of the object scene.

  As described above, in the conventional camera, when the provisional light emission amount GN exceeds the maximum light emission amount Gnmax, as shown in FIG. To compensate for the lack of light emission. Certainly, flash photography is possible with this method, but since the light is emitted with the maximum light emission amount Gnmax of the flash device 111 at the time of the main light emission, the electric charge (accumulated power) of the capacitor that stores the light emission energy is used up, and the flash light continues. In order to shoot, it is necessary to store the light-emitting energy by accumulating in a capacitor with a battery. That is, it takes a long time to store electricity, and continuous flash photography cannot be performed.

  Therefore, in one embodiment, even when the provisional light emission amount GN exceeds the maximum light emission amount Gnmax and the light emission amount of the flash device 111 is insufficient, the flash device 111 does not emit light at the maximum light emission amount Gnmax, and FIG. As shown in FIG. 5, the image sensor 110 performs imaging by setting the light emission amount smaller than the maximum light emission amount Gnmax by a predetermined amount as the main light emission amount at the time of flash photography and reducing the light emission amount by the predetermined amount as necessary. Increase sensitivity. It is preferable to change the imaging sensitivity after the preliminary light emission during one imaging operation and before the imaging by the imaging device 110 is started. The offset amount Svconst described above corresponds to this predetermined amount. As a result, it is possible to avoid using up the capacitor charge (storage power) that stores the luminescence energy during the main light emission, and the remaining charge (storage power) of the capacitor can be used for the next flash photography. The storage time for flash photography is shortened, and preparations for the next flash photography can be made quickly.

  If the offset amount Svconst is increased, the consumption of the electric charge (accumulated power) of the capacitor that stores the luminescence energy is reduced, so that flash photography can be repeated as fast as that. Since the imaging sensitivity of 110 must be increased, noise included in the image signal output from the image sensor 110 may increase, and image quality may deteriorate.

  Therefore, in this embodiment, the offset amount Svconst is set according to the selected shooting mode. For example, when the continuous shooting mode is selected, the offset amount Svconst is set larger than when the single shooting mode is selected. Further, when a mode that requires continuous shooting performance such as a sports mode is set as the shooting mode, the offset amount Svconst is set larger than that in a mode that does not require continuous shooting performance such as a landscape mode.

  Further, during the main light emission, the maximum light emission amount of the flash device 111 decreases as the charge voltage of the capacitor that stores the light emission energy of the flash device 111 decreases. Therefore, the offset amount Svconst increases as the charge voltage of the capacitor decreases. .

  As described above, the flash device 111 stores light emission energy in the capacitor by the power of the built-in battery. Therefore, the lower the power supply voltage of the built-in battery, the lower the charging voltage of the capacitor, and the maximum light emission amount of the flash device 111 decreases. Therefore, the offset amount Svconst is increased as the power supply voltage of the built-in battery of the flash device 111 is lower.

  The flash irradiation direction of the flash device 111 is variable, and the flash is irradiated toward the ceiling obliquely above the front of the camera from the flash irradiation direction that directly illuminates the subject, that is, the subject is indirectly illuminated ( Bound illumination) Up to the flash irradiation direction can be arbitrarily changed according to the shooting conditions. Since indirect illumination such as bounce illumination requires a large amount of main light emission, a large provisional light emission amount GN may be calculated, and the offset amount Svconst is made larger than in the case of direct illumination.

  Furthermore, since the exposure determined based on the subject luminance, that is, the shorter the shutter time, the larger the main light emission amount is required, there is a possibility that a large temporary light emission amount GN may be calculated, and the shutter time is short. The offset amount Svconst is increased.

  As described above, according to one embodiment, a flash amount that is smaller than the maximum flash amount of the flash device by a predetermined amount is set as the main flash amount at the time of flash shooting, and the flash shooting determined based on the reflected light amount at the time of preliminary flash emission. When the temporary light emission amount at that time is larger than the main light emission amount, the flash device is made to emit main light at the main light emission amount, and the imaging sensitivity of the image sensor is increased according to the difference between the temporary light emission amount and the main light emission amount. As a result, flash photography can be performed continuously even if the imaging sensitivity of the image sensor is increased to compensate for the lack of light emission during flash photography, and is determined by the main light emission quantity and imaging sensitivity. The balance between continuous flash photography performance and image quality can be set optimally.

The figure which shows the structure of one embodiment The flowchart which shows the flash photographing operation of one embodiment The figure for demonstrating the setting method of offset amount.

Explanation of symbols

106; Photometric sensor, 107; Control device, 110; Image sensor, 111; Flash device

Claims (9)

Imaging means for capturing a subject image;
Flash means for performing preliminary light emission before flash photography and main light emission during flash photography,
Determining means for determining the first light emission amount and the imaging sensitivity of the imaging means based on the subject brightness measured during the preliminary light emission of the flash means;
Second light emission amount calculating means for calculating a second light emission amount smaller than a maximum light emission amount that can be emitted by the flash means by a predetermined amount set according to a predetermined condition;
Determination means for determining whether or not the first light emission amount is larger than the second light emission amount;
When the determination means determines that the first light emission amount is greater than the second light emission amount, the flash means causes the main light emission at the second light emission amount, and the first light emission amount and the second light emission amount. And a control means for increasing the imaging sensitivity determined by the determination means in accordance with the difference between the camera and the camera. The camera of claim 1,
A camera, further comprising changing means for changing the predetermined amount in accordance with a predetermined condition. The camera according to claim 2,
The control unit causes the flash unit to perform main light emission with the first light emission amount when the determination unit determines that the first light emission amount is equal to or less than the second light emission amount. The camera according to claim 2 or 3,
It further comprises mode selection means for selecting and setting the continuous shooting mode and the single shooting mode,
The change means changes the predetermined amount so that the predetermined amount when the continuous shooting mode is set is larger than the predetermined amount when the single shooting mode is set. . In the camera according to any one of claims 2 to 4,
The camera according to claim 1, wherein the changing unit increases the predetermined amount as a charging voltage of a capacitor for storing light emission energy of the flash unit decreases. In the camera according to any one of claims 2 to 5,
The camera according to claim 1, wherein the changing unit increases the predetermined amount as the power supply voltage of the flash unit decreases. In the camera according to any one of claims 2 to 6,
The flash means is capable of bounce illumination and direct illumination,
The camera is characterized in that the changing means changes the predetermined amount so that the predetermined amount becomes larger when the bounce illumination is performed than when the flash means performs the direct illumination. In the camera according to any one of claims 2 to 7,
The change means increases the predetermined amount as the set shutter speed is shorter. Imaging means for capturing a subject image;
Using a light emitting means for performing preliminary light emission and main light emission at a predetermined light emission amount,
Based on the subject brightness measured at the time of preliminary light emission of the light emitting means, determine the first light emission amount and the imaging sensitivity of the imaging means,
Calculating a second light emission amount smaller than a maximum light emission amount that can be emitted by the light emitting means by a predetermined amount set according to a predetermined condition;
Determining whether the first light emission amount is greater than the second light emission amount;
When it is determined that the first light emission amount is larger than the second light emission amount, the light emitting unit is caused to perform main light emission with the second light emission amount, and the difference between the first light emission amount and the second light emission amount is determined. Accordingly, the flashing method is characterized in that the imaging sensitivity determined by the determining means is increased .

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