eli5 how old camera flashes were timed

Question

flash powder. there’s been movies where the camera flash was a powder, ignited on a stick the camera operator is holding.

the powder burns very fast, so how did they have the photo to be in time with the flash? wouldn’t the long exposure time also make it difficult?

In: 2

Answer 1

If your film is slow enough, the ambient light does not matter much.

That means that you can open the shutter, fire the flash, close the shutter.

To compensate for the film being really slow, the flashes were quite powerful, too — the guide number of a typical electronic flash is 20 – 60, the guide number of a magnesium bulb was easily around 200-300. This means that the ambient light would matter much less.