How a Flash Fires

When broken down to its simplest elements, the flash consists of the following three systems:

•  Batteries

•  Capacitor

•  Flash tube

When you turn the flash on, the batteries fill the capacitor with energy (figure 3.3). Think of the capacitor as a water tank. When the capacitor is filled to the top, the batteries stop adding more energy. When you take a photograph, the flash uses energy from the capacitor and sends it to the flash tube (also called the flash head) where it makes a pulse of light. The camera’s TTL system controls the amount of power sent to the flash tube, and the matrix meter determines how much power the flash puts into the scene.

Figure 3.3 - Simple diagram of a flash. Energy from the batteries fills the capacitor. When you take a picture, the capacitor dumps the correct amount of power to the flash head (flash tube) to provide a good flash exposure.