Ilkka , Feb 17, 2011; 09:19 p.m.
I did not understand one word of your Leica description, even though I have three Leica cameras, one that opens from the bottom.
But I think the fact of the matter in flash lights is really very simple. Focal plane shutter takes time to cross the film gate. The fastest speed that can be acheived with the gate fully open is about 1/250s at best, with most cameras at 1/125s and older ones at 1/60s (or 1/50s for Leica) while many medium format focal plane shutter cameras can be as miserable as 1/30s. For any exposure shorter than this, the film or sensor is only partially exposed to light at any given time, ie. the second curtain follows the first one so that a narrow open band sweeps across the sensor. This works well with continuous light, whether from lamps or sunlight. Flash of light is a very fast burst, typically less than 1/1000s, if subject is close or aperture is wide, it can be 1/30 000s. So practically instantaneous, when compared with the shutter speed. There are only two ways you can combine the two: 1-you must use a shutter speed that opens the sensor gate compoletely to light before firing the flash (ie. 1/125s or so shutter speed), or 2-you must make the flash last longer. This is where the modern pulsing flash systems come from. Nikon may have made them a few years before Canon, not sure of that, but there is no way to get an old flash to operate this way without major internal rebuild. Some old flash units were able to shoot some 5 frames per second, at lowest power setting, but that is not enough to cover the film gate with a 1/2000s exposure. The whole internals of the flash would need to be changed so that it does not store and release the power in the original way but becomes a stroboscope of sorts.