Question on : What does M and X mean on the barrel of my old camera?
"M" indicates the connection is for a flash bulb. M refers to (medium) sync [there are others: F (fast) sync and FP (focal plane) sync] "X" is the connection for electronic flash units. Source(s): digiPro
	Answer by Ctownbro

Question on : What does M and X mean on the barrel of my old camera?
There are two types of flash that are still used on manual cameras (and some automatics that can be over ridden). The M button or contact is used for Manual flash ie photographic bulbs, the X is for electronic flash. It's all to do with their synchronisation with the shutter, the light output of a bulb lasts approximately 1/25 of a second and there is a fraction of a second delay in the shutter opening and the full intensity of the bulb being reached. Typically an electronic flash lasts about 1/10,000 of a second and for all intents and purposes is instantaneous. In some cameras the X and M are replaced by symbols, as in one of my old cameras (Minolta Autocord). In 1963 when I stopped using bulbs, I glued this camera in the X position to prevent accidents, if it was in the wrong position, no photograph!!
	Answer by Galdiii

Question on : What does M and X mean on the barrel of my old camera?
X sync fires the flash when the shutter is open. This was used for electronic flash typically or for flash bulbs used at fairly slow shutter speeds, like 1/25 of a second or longer. M was used for a certain class of flashbulbs so that the flash circuit would fire just before the shutter fully opened, allowing the flash bulb to begin burning and come to a full brightness at the same time that the shutter was open.
	Answer by 44katty

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