1. Field of the Invention
This invention relates to an automatic flash limiting apparatus in a camera for dividing the object field into a plurality of photometry areas and limiting flash on the basis of a photometric output from each area.
2. Related Background Art
Apparatuses of this kind according to the prior art include an apparatus as disclosed in Japanese Laid-Open Patent Application No. 60-15626. This publication discloses an automatic flash control camera as will hereinafter be described.
The front face of a camera body is provided with a stroboscopic light emitting portion for main flashing, an infrared stroboscopic light emitting portion for preliminary flashing, and a photometry portion for receiving these stroboscopic lights. This photometry portion is formed so as to meter the reflected light from an object while dividing it into the central portion and the marginal portion of the picture plane.
First, in this camera, the infrared stroboscopic flash emitting portion is caused to emit light, and the infrared light is measured while the reflected light from an object is divided into the central portion and the marginal portion of the picture plane, and in which of the two areas the main object exists is judged from the difference therebetween. In conformity with this judgment, the photometric system of the photometry portion is changed over to one of central portion priority photometry, marginal portion priority photometry and average photometry.
Next, the stroboscopic light emitting portion for main flashing emits light in synchronism with a shutter operation. During this light emission, the reflected light from the object is divisionally metered by one of the above-mentioned photometric systems, and when the integrated value of this reflected light reaches a predetermined value, the stroboscopic light emitting portion stops emitting light.
However, in the prior art disclosed in this Japanese Laid-Open Patent Application No. 60-15626, no countermeasure has been taken for the reflected light from an object of high reflectivity which generally adversely affects TTL flash control, such as a mirror or a gold-leafed folding screen which exists in the area to be photographed, and this has led to the problem that this object cannot be distinguished from the main object with a result that in some cases, substantial under-exposure is effected.
Also, as a technique of controlling stroboscopic photographing, there has heretofore been a technique as shown in Japanese Laid-Open Patent Application No. 56-89728 wherein preliminary flashing is effected prior to main flashing and the quantity of relfected light from an object by the preliminary flashing is measured and the quantity of main flash during stroboscopic photographing is corrected from the result of the measurement.
In the prior art, however, the quantity of reflected light from an object has been small and accurate photometry has been impossible when the reflectivity of the object is small or when the object is far away.
Also, the quantity of reflected light from an object may be excessive and lead to waste of energy when the reflectivity of the object is great or when the object is near.
Further, in the prior art, accurate measurement has been impossible unless the reflectivity of an object is uniform and the reflectivity is standard. For example, when there is a mirror in the photographing picture plane, the quantity of reflected light by preliminary flashing may be too great to accomplish photometry.
Also, in such an apparatus, the distance to an object must be measured, and this has led to the disadvantage that a camera system other than a camera system having an automatic focus apparauts cannot be used.
USPTO Backgrounds
USPTO Backgrounds