Photography – Exposure control circuit – Color temperature compensation or detection
Reexamination Certificate
2000-12-08
2003-01-14
Perkey, W. B. (Department: 2851)
Photography
Exposure control circuit
Color temperature compensation or detection
C396S234000
Reexamination Certificate
active
06507709
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photometry device applicable to an SLR (Single Lens Reflex) camera, and more particularly to a photometry device with which exposure errors due to a difference of reflectivity of objects having different colors can be compensated.
Recently, in most of cameras, reflection type photometry devices are employed. The reflection type photometry device receives the light, which is reflected by an object and passed through an observing optical system of a camera, using a light receiving element, determines the brightness of the object based on the output of the measured value, and then calculates the exposure value of the camera based on the measured brightness. However, this type of the photometry device cannot detect the color of the object because of its structure. Accordingly, in such a device, the reflectivity of an object is generally assumed to be 18% and the exposure parameter is determined on this assumption. Therefore, regarding a whitish object whose reflectivity is greater than 18%, the brightness is measured as greater than the actual brightness. If the camera controls an exposure operation based on thus determined exposure value, the object is under exposed. A dark object whose reflectivity is less than 18% is measured to have a lower brightness. Therefore, such an object is over exposed. The difference of the reflectivity of the object may also occur depending on the color of the object. For example, when the color of an object is yellow, the reflectivity may be up to 70%. In such a case, if the standard exposure value is for the object whose reflectivity is 18%, the exposure value is approximately 2 Ev lower than necessary. If the object color is blue, the reflectivity is approximately 9%. In this case, the object is over exposed by approximately 1 Ev greater than necessary.
Therefore, in the conventional photometry device, photographer should guess the reflectivity of the object. Then, based on the reflectivity determined by the photographer, the exposure is controlled such that, if the object is a whitish or yellowish one having a relatively high reflectivity, it is to be overexposed, and if the object is a blackish or bluish one having a relatively low reflectivity, it is to be underexposed. With this operation, the above-described defects may be solved. However, to guess the reflectivity of the object and control the exposure can be done by only experienced and skilled photographers. It is impossible to require all the photographers to do such an operation. Further, it is not preferable that a manual operation of the photographer is required for exposure. Further, if such a manual operation is required, cameras become unsuitable for recent trend of the automatic photographing.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved photometry device with which appropriate exposure values can be obtained regardless of difference of reflectivity of the objects.
For the above object, according to an aspect of the invention, there is provided a photometry device for a camera, which is provided with a normal light metering system having spectral sensitivity characteristics close to visual sensitivity characteristics, a plurality of light metering systems having spectral sensitivity characteristics that are different from those of the normal light metering system, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light metering system, a colorimetry system that judges a color of the object in accordance with the outputs of the plurality of light metering systems, a compensation amount determining system that determines an exposure compensation amount in accordance with the color judged by the colorimetry system; and a controller that compensates for the exposure amount determined by the exposure amount determining system in accordance with the exposure compensation amount.
With this configuration, since the exposure amount, which is determined similarly to a procedure in the conventional art is compensated in accordance with the color of the object. Therefore, regardless of the color of the object, an appropriate exposure value can be obtained.
Optionally, the normal light metering system may include a normal light photometry sensor, the spectral sensitivity characteristic of which has a peak sensitivity at a wavelength within a range from 500 nm through 600 nm, and the colorimetry system may include at least a first photometry sensor and a second photometry sensor, the peak sensitivity of the spectral sensitivity characteristic of the first photometry sensor is on a shorter wavelength side with respect to the peak sensitivity of the normal light photometry sensor, and the peak sensitivity of the spectral sensitivity characteristic of the second photometry sensor is on a longer wavelength side with respect to the peak sensitivity of the normal light photometry sensor.
Further optionally, the calorimetric system may include, a blue light photometry sensor that meters blue light, a green light photometry sensor that meters green light, and a red light photometry sensor that meters red light.
The photometry device may be configured such that the colorimetry system judges at least yellow, blue and red from among yellow, magenta, cyan, blue, green and red, in accordance with the outputs of the plurality of photometry sensors, the compensation amount determining system determines the exposure compensation amount in an over exposure side if the colorimetry system judges the color is yellow, and the compensation amount determining system determines the exposure compensation amount in an under exposure side if the colorimetry system judges the color is blue or red.
In this case, the compensation amount determining system may determine the compensation amount is zero if the colorimetry system judges the color is magenta, cyan or green.
Still optionally, each of the normal light metering system, and the plurality of light metering systems has divided photometry areas, the exposure amount determining system and compensation amount determining system determining the exposure amount and the exposure compensation amount in accordance with the metering amount obtained for each of the divided photometry areas.
In such a case, the colorimetry system may judge the color of the object at each of the photometry areas, and the compensation amount determining system determines the exposure compensation amount for each of the photometry areas.
Further, the exposure amount determining system may determine an exposure compensation amount for the entire object by applying a predetermined calculation to the exposure compensation amounts obtained for the plurality of photometry areas.
Optionally, the normal light metering system and the plurality of light metering systems are arranged on an eyepiece optical system side of a pentagonal prism of an single lens reflex camera, at least the normal light metering system being arranged at an upper central portion of the pentagonal prism.
In such a case, at the upper central portion of the pentagonal prism, the normal light metering system and the green light metering sensor are arranged side by side, the blue sensor and the red sensor being arranged at right-and-left portions of the eyepiece optical system.
In a particular case, the green light metering sensor may double as the normal light metering system.
In this case, the green light metering sensor is arranged at the upper central portion of the pentagonal prism, the blue sensor and the red sensor being arranged at right-and-left portions of the eyepiece optical system.
According to another aspect of the invention, there is provided a photometry device for a camera, which is provided with a normal light metering system having spectral sensitivity characteristics close to visual sensitivity characteristics, the normal light metering system dividing a photometry area into a plurality of areas and performing photometry for each of
Hirai Isamu
Iida Yoshikazu
Greenblum & Bernstein P.L.C.
Pentax Corporation
Perkey W. B.
LandOfFree
Photometry device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photometry device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photometry device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3003626