The principle of smoking old camera.

Smoking flashlights, the old flashlights use magnesium as filament, and after being electrified, magnesium violently oxidizes and burns in the air to produce strong light.

The smoke you see is produced when magnesium is oxidized, so it is also called magnesium light. The bulb of this kind of lamp is disposable, and it needs to be replaced once it flashes. Modern flashlights can be used repeatedly by using the principle of high voltage discharge, and will not produce smoke when flashing.

Because the old cameras before the 1950s needed a flash when taking indoor photos (or subjects with dim light), the electronic flash didn't come out at that time.

A spotlight was used. At the moment of taking pictures, the magnesium powder of the magnesium lamp is ignited, which will give off dazzling light and give off a "bang". Almost at the same time, magnesium powder emits light blue smoke after burning. This is the phenomenon of smoking when we take pictures.

Extended data:

Before 1950s, old cameras needed to use flash when taking indoor photos (or dimly lit objects). The electronic flash hasn't come out yet. It's a magnesium light.

At the moment of taking pictures, the magnesium powder of the magnesium lamp is ignited, which will give off dazzling light and give off a bang. When magnesium powder is burned, it will emit light blue smoke. This is the phenomenon of smoking when we take pictures.