The present invention relates to a lens-fitted film unit with a built-in electronic flash unit.
Since a lens-fitted film unit is featured to be simple and inexpensive, no function of exposure adjustment has been provided, a diaphragm has had only an open aperture of a camera lens, and only one shutter speed of about 1/125 sec has been provided in the lens-fitted film unit. In addition, an f-number of the open aperture of the camera lens is about 10 (T-number based on the transmittance of the lens and the lens number is about 11), which means that the lens has a large f-number. Accordingly, if a film having the speed of ISO 100 is used, photographing is limited to that in the daytime on a fine day. Therefore, a film having the speed of ISO 400 is loaded so that photographing can be carried out in lower luminance.
For example, when it is assumed that the shutter speed is 1/125 sec and an aperture is represented by T-number 11, an exposure for ISO 100 is EV 14. Therefore, if a film of ISO 400 is used, an EV value is 12, and it is possible to photograph in a luminance range from the daytime on a fine day to gloomy morning and evening.
However, it is still impossible to photograph indoors or at night. Therefore, there is available a lens-fitted film unit which houses therein an electronic flash unit to make it possible to photograph in low luminance. An electronic flash unit which emits brighter light, namely, the one which has larger capacity is desired so that the electronic flash unit makes it possible to photograph in the dark room. In the lens-fitted film unit, however, it is difficult to realize a large capacity electronic flash unit which makes it difficult to make a camera small and causes high cost. It is therefore common to use an electronic flash unit whose guide number for ISO 100 is about 10, as an electronic flash camera emitting the most bright light among those which do not cause the problems stated above.
However, even in this case, there have occurred frequently problems that a user felt an object distance in stroboscopic photographing to be insufficient. For example, when a film of ISO 400 is used and a T-number is made to be 11, an object distance for appropriate exposure is 1.8 m which is relatively short, and even if it is possible to compensate insufficient exposure up to EV 1.5 with latitude such as a film, the object distance up to about 3.0 m is a limit.
To extend an object distance in stroboscopic photographing, therefore, there is available on the market a lens-fitted film unit with a built-in electronic flash unit in which a film of ISO 800 is loaded. As a result, an object distance for appropriate exposure is 2.5 m under the same condition as in the foregoing, and the object distance is extended to 4.3 m if exposure insufficiency up to that of EV 1.5 is allowed.
However, it has been found that further problems are caused if the speed of the film is raised and electronic flash light is made to be of higher intensity (namely, capacitor capacity of an electronic flash unit is raised), for the purpose to make indoor or night photographing to be possible and to extend an object distance.
In stroboscopic photographing, an object distance for appropriate exposure is fixed to one point, and when a major object such as a person is set to that distance, an object which is closer than that major object is subjected to over-exposure, while, an object in the background which is farther than the major object is subjected to under-exposure. In particular, in the case of indoor photographing, electronic flash light does not arrive at an object and a possibility of under-exposure is high in broad rooms in European and American homes and in broad rooms such as hotel lobbies, or in the outdoors where illumination is poor, although under-exposure for an object in the background is reduced in a relatively narrow room like those in Japanese homes where illumination other than electronic flash light plays a part in exposure.
For example, in some of conventional lens-fitted film units which house a film of ISO 800, an f-number of an open aperture is 10.3, shutter speed is 1/110, a guide number of an electronic flash unit is 11.6 for ISO 100. Accordingly, appropriate exposure for photographing by external light results at EV 10.5, while appropriate exposure for photographing by electronic flash light results at the distance of 3.2 m.
When this lens-fitted film unit is used for stroboscopic photographing in a broad room such as a hotel lobby or in the outdoors where illumination is poor, by placing a major object at the distance of 3.2 m, there results appropriate exposure on the major object. On the other hand, a remote background at which electronic flash light does not arrive is exposed by only external light, and if the remote background is sufficiently bright, the background can be recognized on the finished photograph. In a broad room such as a hotel lobby or in the outdoors where illumination is poor, however, brightness is not sufficient for the conventional lens-fitted film unit in many cases, and when a print is made under that condition so that appropriate exposure may result on a major object photographed with electronic flash light, the background turns out to be dark on the photograph. Namely, there has been a problem that a remote background recognized visually by human eyes can not be recognized at all on the finished photograph.
Further, for example, in an ordinary camera, a user can select an EV value within a relatively wide range, and the user sets a shutter speed and an aperture value in accordance with the situation, to conduct stroboscopic photographing with an EV value established by the user in broad rooms or in the outdoors where illumination is poor. However, this is very hard to understand for those who have no good knowledge about a camera, and they can sometimes photograph properly, while they can not photograph properly on the other occasion, to be inconsistent. On the other hand, a constant EV value has been employed in a lens-fitted film unit as stated above, because the primary object of the lens-fitted film unit is that it can be used simply for photographing even by a user having no good knowledge about a camera. The value, however, has not been preferable as stated above in stroboscopic photographing in broad rooms or in the outdoors where illumination is poor. Namely, a fixed EV value has been established for attaining that it is possible to photograph simply, but for that reason, there has been a problem that photographing under low brightness is difficult.