Optics: measuring and testing – Photometers – Photoelectric
Reexamination Certificate
2001-09-07
2004-03-30
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Photometers
Photoelectric
C356S218000, C396S287000, C396S292000
Reexamination Certificate
active
06714293
ABSTRACT:
This application claims priority from Japanese Patent Application Nos. 2000-280381 and 2000-280382, the contents of which are hereby incorporated by references.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure meter which measures an illuminance of an object by detecting incident light to the object and detecting light reflected from the object.
2. Description of the Related Art
There are two types of conventional exposure meters, namely an incident light exposure meter and a reflected light exposure meter. The incident light exposure meter directly measures the intensity of the incident light illuminating an object. The reflected light exposure meter measures the intensity of the light reflected from the object. The incident light exposure meter or the reflected light exposure meter is selected for deciding exposure conditions such as a shutter speed and an aperture number of a taking lens of a camera depending on the type of the object and its photographic conditions.
When a contrast of the object is high, it is difficult to include the highlight portion having the highest illuminance value (or the largest exposure value) and the shadow portion having the lowest illuminance value (or the smallest exposure value) of the object within the photographic latitude of a film. In such a case, it is necessary to decide which range of the measured exposure values of the object should be within the latitude of the film. For this purpose, the exposure values must be measured by the reflected light exposure meter at several portions on the object.
It is impossible to use the incident light exposure meter to distinguish the exposure values on different points of the object, since a photo-sensing window of the incident light exposure meter is configured to face the light source. On the other hand, the reflected light exposure meter used for measuring local exposure values of the object has a disadvantage. That is, it cannot measure the illuminance of the object precisely, since the exposure calculation is based on an assumption that the reflectance of the object has a predetermined standard value, for example, 18%. When the reflectance of the object is higher than the standard value, such as is the case with a white object, the exposure value calculated by the reflected light exposure meter is larger than the proper exposure value so that the color of the object is too dark when a photograph of the object is taken under the calculated exposure value. Similarly, when the reflectance of the object is lower than the standard value, such as is the case with a black object, the exposure value calculated by the reflected light exposure meter is smaller than the proper exposure value so that the color of the object is too bright when a photograph of the object is taken under the calculated exposure value. Thus, it is preferable to determine a proper exposure condition of a camera based on the exposure values measured by both the incident light exposure meter and the reflected light exposure meter.
To take into account the exposure values measured by the incident light exposure meter and the reflected light exposure meter, the exposure value of the object is first measured by the incident light exposure meter, which is then used as a preliminary exposure value for calculating the latitude of the film to be used. Subsequently, the exposure values are measured by the reflected light exposure meter at several important portions on the object. Then, it is determined whether the exposure values measured by the reflected light exposure meter are included in the latitude of the film. Since the exposure values measured by the incident light exposure meter and the reflected light exposure meter are respectively displayed on different display devices of the exposure meters, it is troublesome and difficult to compare the exposure values and to recognize the relationship between them. Especially, when the exposure values measured by the reflected light exposure meter are not included in the latitude or barely included in the latitude, it is necessary to adjust the preliminary exposure value measured by the incident light exposure meter. In such a case, the exposure values displayed on the different the display meters make it difficult to perform such an adjustment of the preliminary exposure value.
SUMMERY OF THE INVENTION
A purpose of the present invention is to provide an exposure meter having both an incident light exposure meter and reflected light exposure meter so that the two types of exposure values measured by the two exposure meters can be compared easily. Another purpose of the present invention is to provide an exposure meter having both an incident light exposure meter and a reflected light exposure meter so that the exposure values measured by the reflected light exposure meter can be easily compared to a latitude of a light sensing member calculated based on the exposure value measured by the incident light exposure meter.
An exposure meter in accordance with an aspect of the present invention includes a first meter portion measuring an exposure value based on incident light illuminating an object, a second meter portion measuring an exposure value based on reflected light from the object and a display portion displaying the exposure values measured by the first meter portion and the second meter portion for comparison thereof.
In this configuration, the exposure values measured by the first meter portion and the second meter portion are displayed on the same display to compare easily the exposure values measured at several portions of the object based on the reflected light with the exposure value of the object based on the incident light.
A second exposure meter in accordance with an aspect of the present invention includes a first meter portion measuring an exposure value based on incident light illuminating an object, a second meter portion measuring an exposure value based on reflected light from the object and a calculator portion calculating a latitude of a light sensing member based on the exposure value measured by the first meter portion.
In this configuration, the latitude of the film, which is used for taking a photograph, is calculated by the calculator portion based on the exposure value measured by the first meter portion so as to compare easily the exposure values measured at several portions of the object based on the reflected light with the latitude.
As a result, it is easy to determine an exposure condition in which the highlight portion and the shadow portion of the object are included in the latitude of the film.
REFERENCES:
patent: 4203668 (1980-05-01), Chapman
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patent: 4364662 (1982-12-01), Yuasa et al.
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patent: 4748468 (1988-05-01), Fujino et al.
patent: 5486914 (1996-01-01), Denove et al.
patent: 5678079 (1997-10-01), Ogawa
patent: 5784654 (1998-07-01), Saito
patent: D432555 (2000-10-01), Mitsui
patent: 6509963 (2003-01-01), Oda et al.
patent: 707-15160 (1995-06-01), None
Goto Yasushi
Yuasa Yoshio
Font Frank G.
Lauchman Layla
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