How does the internal flash operate?
Aleksk measured the flash parameters. Heres a translation of his original post (in Russian): When the built-in flash of the camera fires, a very short pre-flash of a constant strength and duration (20μs) is fired first. It is used by the photosensor to rapidly estimate the amount of reflected light. Obviously, this high-speed exposure measurement method is designed to save battery life, since the energy of the pre-flash is weaker than that of the main one by more than an order of magnitude. The short duration is not sufficient for measuring the reflected light through the lens (the pre-flash is probably substantially longer in cameras that support TTL metering). The measured light affects the intensity of the main flash, which fires 98ms later. The duration of the main flash, when photographing remote objects, is 600μs and its intensity is 15% higher than of the pre-flash. It was possible to measure the main flash only when it was stronger than the pre-flash (photographing a far object
