1. Field of the Invention
The present invention relates generally to automatic electronic flash, and particularly concerns the automatic electronic flash capable of automatic adjustment of amount of flashed light when photographic scenery is of rear light.
2. Description of the Prior Art
Automatic electronic flash, which has a function of automatically controlling amount of flashed light in response to the light reflected from a scene, is very useful to make good picture for an amateur photographer.
In an automatic electronic flash photographing for a rear light scene for instance in outdoor scene with portrait in a bright sky, namely in a fill-in flash photographing, there are the following problems.
When the automatic electronic photographing for the rear light scene is executed on trial, most probable operation sequence is: firstly, brightness of scene is measured by exposure measuring system of a camera for the photographic scene angle for a shutter speed appropriate for strobe synchronization, thereby to obtain suitable F-stop value for the scene, and secondly, F-stop number of the automatic electronic flash and the stop of the camera are adjusted to the above-mentioned suitable stop value.
When a rear light scene is considered, in most cases the back scene of the object is a vacant space, or even when not the vacant space, something to reflect light is at a very far distance. Accordingly, unlike the ordinary indoor flash photographing with automatic electronic flash, amount of light incident to light sensor of the automatic electronic flash during the photographic flash is very small. In other word, unlike the indoor photographing where lights are reflected from various matters surrounding the photographic object, in case of a rear light photographing, for instance in outdoor scene, there is substantially no reflection of light of the flash, since there are no surrounding matters in not far distance other than the photographic object. As a result, in the rear light photographing, the amount of light incident to light sensor of the automatic electronic flash becomes considerably smaller than that in the case of indoor flash phographing with the same automatic electronic flash.
Accordingly, when the automatic photographing of outdoor is carried out in the above-mentioned operation sequence, the photographing naturally results in an overexposuring, thereby making the resultant photograph whitish.
According to the experimental study of the inventors, it has been found that, for fill-in flash photographing for such scenes with mountain or sea as backgound, the photograph becomes overexposured by a degree of 1-2 F-stops as converted into the stop value, irrespective of the stop value used within the usually used stop value range of F1.4-F22.
Accordingly, it has been believed that the fill-in flash photographing is not satisfactorily made with automatic electronic flashing, and instead a manual flash apparatus has been used as follows: firstly shutter speed of the camera is set usually to 1/60 sec. and the brightness of the photographic scene is measured by appropriately setting film sensitivity in the camera or in an exposure meter, thereby to measure suitable stop value. And secondly, distance between the camera and the photographic object is measured and a product of the distance and the above-mentioned stop value is calculated and a guide number dial of the manual flash apparatus is adjusted to the value of the product.
The above-mentioned conventional manual setting of the flash apparatus, however, is troublesome for amature photographer of small experience, and the above-mentioned sequence of manual setting is not well understood, or setting of the guide number by the product is difficult for him or been forgot by him. Accordingly there are many liability of failure of the flash photography in backlight. And therefore, the rear light photography is considered difficult to produce good picture.
Furthermore in some case, even when the user can understand and operates the above-mentioned sequence of the manual flash photographing, it is necessary that the calculated guide number is always available on the flash apparatus, and in such case there is a necessity to change distance between the camera and the object or in some time the photographing of the object becomes impossible.
On the other hand, in order to solve the above-mentioned inconvenience, there has been many proposals for automatic electronic flashes easily usable for amateur photographer, but these modern devices are limited in a parmanent combination with camera. In view of the above-mentioned problem, there is a strong demand for a satisfactory automatic electronic flash capable of photographing even for rear light scenery without troublesome manual operation and calculation.