Questions

How does electronic flash work?

Electronic flash is a controlled discharge of electricity in a flash tube to make a short burst of lighting. As the duration of the light is short, it freezes action. They use a battery or other power source to charge a capacitor. When the flash it triggered, the power in the capacitor is sent to the flash tube.

• The electric energy from a battery or accumulator is converted to high voltage (300 volts or more) and is used to charge a capacitor. The converter generally makes a high pitched noise when the unit is charging.
• The capacitor is permanently connected to two electrodes in a glass tube filled with xenon gas. Another small capacitor is charged at the same time as the big one.
• When the flash needs to fire, this small capacitor is discharged through a transformer, which generates a pulse of very high voltage.
• This voltage is applied to a third electrode in the xenon tube.
• The high voltage pulse causes the gas to ionize. Ionization makes the gas conductive, and the big capacitor starts to discharge through the xenon gas.
• Bright light is released by the xenon gas during this process. The discharge is rapid due to the resistance of the gas being low at this stage.
• About 1/1000 – 1/200 seconds later the capacitor is empty, and the voltage has dropped so low that the xenon stops to conduct electricity, and the light pulse dies off.
• At this point the process restarts from the beginning again.
  

Describe/define electronic flash synchronisation

Electronic flash synchronisation is the timing of a flashgun and a camera so that the flash is making the most light while the shutter is open.

Identify your cameras synchronisation speed

Canon EOS 20D

external speedlites – 1/250 or faster

non canon flash units – 1/250 or slower

large studio flash – 1/125 or slower

(settings described in user manual)