Choosing an External Flash: What Really Matters

An external flash, far more powerful and versatile than a camera’s built-in one, opens up possibilities that available light alone can’t always provide — as long as you choose a model suited to how you actually shoot, rather than the most expensive or feature-packed one on the shelf.

The guide number, a measure of power

The guide number measures the flash’s maximum output: the higher it is, the farther the flash can reach or the brighter a scene it can compete with. For everyday use (portraits, small events), a modest guide number is more than enough — maximum power only really matters in large venues or with distant subjects.

A tilting, swiveling head, close to essential

A flash whose head swivels and tilts lets you bounce the light off a ceiling or a wall instead of firing it straight at the subject — indirect light that is far softer and more flattering than direct flash, which flattens faces and casts harsh shadows. It’s probably the single feature that most improves the quality of flash photos.

TTL, so you no longer compute exposure yourself

TTL mode (through-the-lens metering) automatically calculates how much flash power the scene needs, much the way regular exposure metering does for ambient light. It makes day-to-day use far simpler — though manual mode remains preferable for anyone who wants full, repeatable control, particularly in the studio.

Compatibility above all

A flash designed for a different brand than your camera body may work in basic manual mode, but it generally loses TTL and automatic communication with the camera. Checking exact compatibility with your body before buying spares you plenty of disappointment — flashes from your camera’s own brand remain the safest bet, though well-regarded third-party alternatives can offer excellent value for money.