How to choose your flash

Some essential features you need in a flash, are TTL-metering, bounce capability, and its Guide Number. With TTL flash, exposure is calculated automatically. You may need to make some adjustments, but with medium tone subjects, you should get correct exposure. Bounce heads let you control light to some degree. You can create softer portraits, prevent redeye, get more even light, or remove shadows. The Guide Number of flash is an important feature. Buy a flash that has enough power for the type of photography you do. You don't need to buy a very powerful flash if you'll be shooting at close range most of the time. A flash with a high Guide Number is good if you shoot sports from a distance, but for still-life or most portraits smaller flash units will work fine. 

Some other features to look for are, flash duration, multiple power levels, and built-in slave. Faster flash duration are better for stopping action in sports or wildlife photography. Power levels let you use lower or higher settings to save battery and control recycling time. If you are close to your subject or need to shoot in continues mode, use a lower setting. Switch to a higher setting for distant subjects. Built-in slaves are used for off camera operations. You can use your flash off the camera for better aiming and control, even macro photography. Off camera flash produces more natural looking macro shots than macro flashes. Several flash units can also be used with flashes that include a slave unit. Auto off is also a good feature, but not essential. It turns off your flash automatically if you forget, and saves battery. 

A wide-angle adapter is useful for wide-angle lenses. These snap on to the flash head and spread the light. Some models include a wide-angle adapter. Flash ready and OK (exposure confirmation) is another useful but not essential feature. AF assist beam is a good feature in low light situations. It helps the camera to focus faster and more accurately. A zoom head, either manual or motorized, can be adjusted for different focal length lenses. Both camera manufacturers and independent flash models are available. Independent flash units are lower in price and may lack some of the features of the camera manufacturers models, but they can usually work with different types of cameras. Camera manufacturers own flash units are also fully dedicated and may include motorized zoom heads, and are more solid.

Canon EOS D-30, Tamron 70-210mm f-2.8 zoom, 1/60 sec at f-4, Canon Speedlite 420EX flash, handheld.

Rrecommended Flashes

Canon Speedlite 580EX Flash

Nikon SB-800 AF Speedlight