Response to Whoops, half this negative is overexposed

John Hicks is correct. If these were flash pictures it is nearly assured that this is the problem. A focal plane shutter varies shutter speed by changing how closely the first shutter curtain follows the second shutter curtain across the film. The closer the first follows the second, the faster the shutter speed. Most people don't realize that with a focal plane shutter at the faster shutter speeds the film is not all exposed at the same instant. Since the light of a flash unit is many times faster (about 1/10,000 of a second) than the fastest shutter speed, only the sliver of film showing at the time the flash pops will be exposed. For most focal plane shutters 1/60th of a second is the fastest shutter speed at which the film is completely exposed all at the same instant, thus it is used as the "flash sync" speed, although slower shutter speeds work just fine also. Those of us who use LF and MF cameras with leaf shutters don't have this problem (although I never use a flash!) because leaf shutters at any shutter speed have an instant at which the entire film is exposed. Good luck with your class.

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