Flash Details

Flash Details

In manual mode most commercial hot shoe flashes like the Canon EX and NIkon AB start fully charged. They fire and then cut out when the selected fraction of full energy has been used for the flash, resulting in a short duration pulse of light. Fortunately, after discharging a small amount of energy, the flash will not take long to fully recharge. Rapid fire is possible and practical.

But, be aware, not all flashes operate in this manner. Some studio flashes will only charge up to the prescribed fraction of full energy and then when fired discharge this amount over a much longer period. You are safe using the Canon EX and Nikon AB type flashes, and also the Einstein Flashes in action mode. Note that the different models of these flashes, for example Canon 430EX, 550EX, 600EX, etc., differ in the maximum amount of energy they output, but conveniently, they will generate, for the same energy fraction, the same flash pulse duration. This also applies to the ring and macro flashes from these manufacturers. Use of these on-camera flashes for freezing motion will be covered in a subsequent post.

Often, but inaccurately, flash power and energy are referred to interchangeably. Flash energy is specified in watt-seconds, or joules. One watt-sec equals one joule. Flash power is the rate of delivering energy, for example, in watts.  A Canon 600EX flash delivers approximately 80 joules in 0.002 seconds: this is 40 kilowatts of power. A Prius, or other small car, generates about 100 kilowatts.

Probably the best value in terms of short flash duration and energy is the Einstein flash. At 5 watt-secs (or 1/128th full energy) this unit delivers a short duration flash equal to that of a Canon 600EX flash set at 1/32nd energy, but with 3 times the energy output. However, the Canon hot shoe flashes are more versatile. They have zoomable flash heads and output a beam that has a rectangular cross section that matches the image frame.