Before buying a flash for your camera, it's important to put some thought into what you will be doing with the flash. If you mainly take snapshots with friends and family, a fully automatic, less powerful flash may be all you need. Large powerful flashes can give you more options, but they also are heavy and cumbersome to carry around. This is why many photographers have a couple of flashes -- a small flash to brighten faces and other details indoors and a larger, more powerful flash for night shots outdoors.
Before You Start Shopping
Make sure your camera can accommodate a new flash. Point-and-shoot cameras usually rely on a built-in flash and don't have an option for adding a new one. If your camera doesn't have a shoe -- a metal bracket on the top -- to fit a flash, it probably can't use a new flash. Check your user guide to make sure.
Make a note of the make and model of your camera. Flashes for digital cameras are usually designed specifically for different brands. Read the description or specifications page for the flash to see which cameras it accommodates.
Decide on a budget and consider the uses you have for the flash. If you take night shots at distances of more than a few yards, you need a flash with a lot of power, a long flash duration and probably with manual settings. If you are planning to take studio shots, you may want a detachable wireless flash that can be placed in positions other than directly on top of the camera. Cameras with these options are more expensive than fully automatic flashes without extra features.
What to Look for
Compare the recycle times between different flashes to see how long you have to wait after each shot. Every time the flash is used, it needs to recharge by drawing power from the batteries. The times stated by the manufacturer usually include the shortest time using a partial flash and the longest time using a full flash. Times can range from a fraction of a second to 10 seconds or more. Recycle times become longer as a battery begins to drain or when you use the flash in cold weather. Picking up extra batteries is a good idea.
Compare the flash durations available with different models. A long flash duration indicates a more powerful flash that is able to fill a larger area with light at a longer exposure setting. If the flash doesn't tell you its durations, keep in mind that a flash with one or two batteries is seldom as powerful as a flash that requires four batteries.
Look at flashes that give you different bounce angles and allow you to manually control the flash if you want to control how much flash is used in different circumstances. A flash that can bounce at a 45-degree or 90-degree angle can give you softer effects without harsh shadows. If the flash has limited bounce angles, choose one that has a red-eye reduction setting.
Compare the guide numbers. Understanding guide numbers can be complicated, but what's important to remember is that a higher guide number indicates a more powerful flash. Guide numbers are determined by multiplying the f-stop number needed for a full exposure with the distance between the flash and the subject. Make sure the guide numbers are based on the same ISO setting, which is usually 100, and use the same unit of measurement, usually meters; otherwise the numbers can't be compared without doing some math.
Examine the flash's power-saving options if you plan to use your camera for more than a quick snapshot at a time. A flash with a continuous-on mode gives you the freedom to take pictures as needed without having to turn on the flash and wait for it to charge again every 10 minutes.
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