Digital SLR Flash Glossary

Before you start comparing all the different flash units available for your camera, it will help if you understand some of the terms associated with digital SLR camera flash.

This digital SLR flash glossary will introduce you to the terms and technology associated with "off-camera" flash.

When I use the term "off-camera" to describe a flash unit, don't take it literally - it doesn't mean that the flash cannot be attached to the camera.

Off-camera is just a standard way of talking about flash units that are not built in to the camera body (which are also called pop-up flashes).

Off-camera flash units require their own separate power source and don't rely on the camera's battery the way the built in flash does.

Flash Terminology

Ready to dig into some terminology? A solid understanding of these terms will not only help you when you're trying to compare different flash units, it will also help you when you want to USE your flash effectively.

We'll get started by introducing two terms that are applicable to the flash unit:

Guide Number An indication of the power of a flash unit. A guide number tells you the maximum distance you can have between the flash and your subject.
Recycle Rate How quickly the flash can reach a full charge. This feature of an external flash is important if you want to use it for action photography, and need the flash to quickly achieve full power after it goes off.

There are two other flash terms that have an impact on your flash photography, but are features of the camera instead of the flash:

Flash Sync Speed The fastest shutter speed you can use with flash. Enabling a flash unit will place an upper limit on the shutter speed that your camera can use.
Slow Sync Flash A slow shutter speed in combination with the flash. Slow sync flash is a way to increase the brightness of a background when you're using an electronic flash or to create a motion blur effect.

If you feel pretty comfortable already about flash terminology or - you can admit it - have absolutely zero interest in learning this stuff, then you can jump ahead and start learning about external flash units.

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