1. Field of the Invention
The present invention relates to an image capture apparatus dividing a photographed screen into a plurality of photometry areas to perform the photometry of the luminance of an object in each photometry area, and a control method thereof.
2. Description of Related Art
Japanese Patent Application Laid-Open No. H03-223821 has proposed the following image capture apparatus.
First, a field (or a photographed screen) is divided into a plurality of photometry areas, and the luminance of each area is detected. The plurality of photometry areas is grouped into groups of concentric circles around focus detection areas according to a selection of the focus detection areas detected at a plurality of points of the field, and the photometry value (or the luminance value) of the whole field is operated by changing weighting to the average luminance of the grouped areas. The image capture apparatus aims to perform highly accurate photometry in such a way.
The prior art invention will be simply described with reference to FIGS. 4A, 4B and 4C.
As shown in FIG. 4A, the field (or the photographed screen) is divided into 15 photometry areas S01-S15, and a photometry output signal can be acquired from each of the photometry areas S01-S15. On the other hand, there are three distance measurement points SL, SC and SR, which are areas in which their focus states can be detected. In the case of the distance measurement point SC, the operation of the obtaining of the photometry value is performed by providing performing the operation of a weighted average with larger weighting to the photometry area S08, and an exposure value is determined to perform control. Such photometry is called evaluation photometry.
In a photographing scene in which the main object is dark and the background thereof is bright as shown in FIG. 4B, in order to acquire a photometry output, weighting is provided to the dark main object by providing larger weighting on the photometry area S08 because the distance measurement point is SC. An appropriate exposure amount is acquired for the whole photographed screen by performing the weighting in such a way without the main object becoming inky black.
However, as shown in FIG. 4C, in the case where the dark main object does not cover the whole photometry area S08, which is the photometry area at this time, although the scene is similar to that shown in FIG. 4B, the photometry output becomes high because the photometry value of the photometry area S08 is primarily influenced by the luminance of the bright background. As a result, an exposure value which is considerably high in comparison with that of the case shown in FIG. 4B is obtained. When the exposure value changes greatly in this way in spite of similar scenes, it becomes difficult for a photographer to grasp the peculiarity of the automatic exposure of a camera, and the camera appears to be difficult to use.
Accordingly, the prior art has designed the sensitivity distribution in the field of a photometry sensor to be gentle. FIG. 5B is a diagram showing the sensitivity distribution of the photometry area S08 shown in FIG. 5A in a horizontal one-dimension. The sensitivity distribution of the photometry area S08 is designed to be gentle in such a way, which is equivalent to the use of an optical filter. By using such an optical filter, the change quantity of the photometry values in the photometry area S08 between the scenes of FIGS. 4B and 4C becomes small. Not only is the change in the photometry value of the photometry area S08 small, but also the change in the photometry values of the whole photometry area become small when the framing of the field is subtly shifted with an optical filter. Consequently, the image capture apparatus becomes one having a small change quantity of a final exposure value to be easy for the photographer to use.
However, when the photographer selects a spot photometry mode with the intention of determining an exposure based on only the photometry value of the center photometry area S08 of the photographed screen, the sensitivity distribution of the spot photometry becomes wide in turn owing to the optical filter. Consequently, the photometry value is subjected to a lot of influence of the background luminance of the areas other than the area which the photographer aimed at.
In order to realize a camera which is easily used when the photographer has selected the spot photometry mode, the sensitivity distribution in a photometry area in a photographed screen must be a sharp one as shown in FIG. 5D. If the sensitivity distribution is set in such a way, there is contrary caused a problem of the increase of a change of the exposure amount at the time of subtly shifting the framing of a field in the case of the evaluation photometry mode, which makes the camera appear to be difficult to use.
In order to solve the problem, Japanese Patent Application Laid-Open No. H05-53169 has proposed an image capture apparatus using an area sensor such as a CCD to make it possible to acquire an optimal exposure value independent of the photometry mode.
However, because the area sensor is a charge accumulation type sensor, this sensor has a problem of responsiveness in low luminance conditions, and the use of the area sensor cannot be a good settling method.