Device for detecting sharp focusing

An image focusing device which comprises:

• a light-beam projection means comprising an auxiliary flash unit which is incorporated in an electronic flash device having a main flash unit comprising a power supply, a first main flash capacitor, a first electronic flash lamp and a first trigger circuit, said auxiliary flash unit comprising said power supply, a second main flash capacitor, a second trigger circuit and a second electronic flash lamp;
• an optical transmission means for transmitting light emitted from said auxiliary flash unit into said photographic lens;
• and
• a reflecting mirror which is disposed to redirect the light emitted from said auxiliary flash unit through said optical transmission means toward the object, the angular position of said reflecting mirror being controlled in response to the output from said lens-group displacement detection means,
• a photodetection means which is disposed within a camera body at such a position spaced apart from a main mirror by the same distance between the mirror and the film plane at which said photodetection means can intercept the light beam passing through said photographic lens along the optical axis thereof and at which said photodetection means will not interfere with the formation of the image of the object through said photographic lens upon a film plane,
• a driver-control means which includes an actuating switch and which, upon closure of said actuating switch, can drive said light-beam projection means, and
• a detection circuit which drives a display means responding to the output from said photodetection means to detect whether or not said photographic lens is sharply and correctly focused at the object.