X & M

Some flashes have a delay (time lag) before reaching the peak of their light output. To function properly, flashes therefore need to be synchronised precisely to the opening of the shutter. When using a flash with a leaf shutter rangefinder, it is important to select the correct setting for full synchronisation at all shutter speeds. The Flash Setting Selector should be changed to “M”, “F”, or “X”, according to the flash type. Unless you have found some obsolete bulbs at auction, it’s more than likely today that you will be using an electronic flash (X).

X (xenon) Electronic flash
Zero time delay; flash responds instantly and coincides exactly when the shutter is fully open.

M (medium) Flash bulbs
20 millisecond delay between the start of the flash and the shutter opening fully, to allow the bulb to reach peak brightness before exposing the film.

F (fast) Flash bulbs
5 millisecond delay between the start of the flash and the shutter opening fully, to allow the bulb to reach peak brightness before exposing the film.