Photography – With object illumination for exposure – Having preexposure illumination
Reexamination Certificate
1999-12-22
2001-08-07
Parkey, W. B. (Department: 2851)
Photography
With object illumination for exposure
Having preexposure illumination
Reexamination Certificate
active
06272292
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Application No. 10-363732 filed Dec. 22, 1998
Japanese Patent Application No. 11-153253 filed Jun. 1, 1999
Japanese Patent Application No. 11-220264 filed Aug. 3, 1999
1. Field of the Invention
The present invention relates to an electronic flash control apparatus that achieves optimal control of the electronic flash output.
2. Description of the Related Art
Electronic flash control apparatuses that implement automatic flash control on flash light emitters (hereafter referred to as SBs) mainly employed in single lens reflex cameras adopt the TTL auto flash control method. In this method, real-time metering is performed through the taking lens on a light flux emitted by the SB and reflected from the subject, and the SB light emission is stopped when the flash output reaches the correct level. The method is particularly advantageous in that since metering is performed on light flux having passed through the taking lens, there is no misalignment (parallax) between the area being photographed and the area over which metering is performed and in that the photographer can freely set the aperture value.
In addition, there are electronic flash control apparatuses that employ the “flashmatic” method, a flash-priority system mainly adopted in compact cameras and the like. In this method, by using the relationship expressed in numerical expression (1) below achieved among the subject distance X, the aperture value F and the SB light guide number GN, the aperture value F is calculated for a photographing operation based upon the subject distance X during the photographing operation and the SB guide number GN provided at the camera.
GN=X·F
(1)
However, the TTL auto flash control method described earlier has a problem in that since control is implemented to ensure that the correct quantity of SB light reflected from the subject is achieved, an exposure error may occur depending upon the reflectivity of the subject. The flashmatic method, on the other hand, which does not allow the photographer to freely select the aperture value, cannot be adopted in an advanced-function camera such as single lens reflex cameras.
Accordingly, Japanese Laid Open Patent Publication No. H3-68928 submitted by the applicant of the present invention discloses a technology whereby the correct exposure is achieved regardless of the reflectivity of the subject through the TTL auto flash control method by performing a pre-flash (#
2
) prior to the main exposure immediately before a photographing operation (#
1
), performing metering on light reflected at the divided regions of the shutter curtain (#
3
), determining the reflectivity of the subject through a weighted arithmetic operation using the quantity of received light (#
4
) and adjusting the SB flash output level during the main exposure (#
5
) in correspondence to the reflectivity thus determined (#
6
~#
8
) as indicated in the algorithm in FIG.
42
.
However, in the apparatus described above, a sufficient degree of reliability with regard to the metering value may not always be achieved due to a low or high metering output caused by an insufficient flash output (or an excessively large flash output) during the pre-flash or due to an incorrect gain setting at the metering unit. In particular, when the so-called guide number control method, in which the photographic flash output is determined in advance based upon the metering output obtained during the pre-flash is incorporated, the metering accuracy achieved during the pre-flash is directly fed back to the photographic flash output, which may result in an insufficient degree of accuracy.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an electronic flash control apparatus that is capable of achieving a higher degree of flash control accuracy by improving the accuracy in the flash metering operation performed during the pre-flash.
In order to achieved the object described above, the electronic flash control apparatus according to the present invention comprises a flash metering unit that measures the quantity of the light reflected by the subject during a pre-flash implemented immediately before a photographing operation, a decision-making unit that makes a decision as to whether or not a pre-flash is to be performed again based upon a signal output by the flash metering unit, a flash control unit that causes a pre-flash to be performed again in correspondence to the results of the decision made by the decision-making unit and a flash output calculation unit that calculates the electronic flash output for the photographing operation based upon the signal output by the flash metering unit.
The present invention may further comprise an electronic flash unit that emits light at a flash output corresponding to the results of the calculation performed by the flash output calculation unit.
In addition, according to the present invention, the flash metering unit having a photo-current storage portion that stores the photo-current generated by receiving light, engages in a new storage operation after discharging the electrical charge that has been stored during the initial pre-flash when another pre-flash is to be performed.
Alternatively, according to the present invention, the flash metering unit having a photo-current storage portion that stores the photo-current generated by receiving light, may engage in a new storage operation while retaining the electrical charge that has been stored during the initial pre-flash when another pre-flash is to be performed.
Furthermore, according to the present invention, when another pre-flash is to be performed, the gains used to amplify the photo-current generated at the flash metering unit by receiving light may be varied.
According to the present invention, regardless of the number of pre-flashes that have been performed, the flash metering unit performs a single metering operation on ambient light after the pre-flashes are completed.
According to the present invention, an upper limit may be imposed by the flash control unit with respect to the total light quantity of the flash light emitted by the electronic flash unit during a pre-flash operation by the electronic flash unit.
In addition, according to the present invention, the flash metering unit is capable of performing metering on individual areas in the photographic field achieved by dividing the photographic field into a plurality of areas, and the flash output calculation unit selects a set of signals that will achieve the highest possible metering accuracy among a plurality of sets of signals each obtained in the output from the flash metering unit resulting from one of a plurality of pre-flashes and calculates the electronic flash output for a photographing operation based upon the selected signals.
In addition, the present invention may comprise a flash metering unit that measures the quantity of reflected light from the subject during a pre-flash performed immediately before a photographing operation, a gain setting unit that sets gains used to amplify signals obtained through the measurement of the light quantity of the reflected light by the flash metering unit, a flash control unit that outputs a plurality of pre-flash commands to the electronic flash unit immediately before a photographing operation, a gain resetting unit that changes the gains set by the gain setting unit when a plurality of pre-flashes are performed in response to the output of the plurality of pre-flash commands from the flash control unit and a flash output calculation unit that calculates an electronic flash output for the photographing operation based upon the signal output by the flash metering unit.
Moreover, the present invention may be further includes an electronic flash unit that performs light emission at a flash output corresponding to the output from the flash output calculation unit.
REFERENCES:
patent: 5717963 (1998-02
Iwasaki Hiroyuki
Osawa Keiji
Nikon Corporation
Oliff & Berridg,e PLC
Parkey W. B.
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