We maintain that the single most important accessory for your DSLR is a full-featured TTL flash unit. With “lightning in a bottle,” you can freeze action solid, mimic studio lighting, tame harsh midday sunlight, balance (or unbalance) the color in a scene, and produce wild and weird effects—with no software required. Here we present a primer on portable flash theory and practice.

Photo: Using a Canon Speedlite 540 EX  high on a tripod, Gary Williamson made these sunflowers pop against a dark sunsett.

Don’t fear “unnatural” fill. For example, a 2-stop ambient underexposure combined with full flash exposure can dramatically isolate a human figure or foreground object.