What flashgun features do I really need?

Question: I want to invest in a flashgun as I’ve outgrown my camera’s pop-up flash. To be honest, I’m not sure what all the features do and which ones I’ll actually find useful. Please can you shed some light on it?

Answer: Your camera’s built-in flash is adequate for getting you out of a difficult situation, but it’s never going to give you very attractive results. Not only is the light extremely harsh and unflattering, but it always comes directly from the camera, so your creativity is limited. An external hotshoe-mounted flashgun, on the other hand, opens up all sorts of lighting possibilities, and can enable you to achieve very professional results. Before you invest in a new flashgun though, there are some important things you should consider.

Guide number
A flashgun’s guide number, often written as GN, describes its power output. It represents the maximum distance, in metres, at which you can correctly expose a subject, assuming a hypothetical aperture of f/1 and an ISO of 100. It’s important to understand that guide numbers are measured on a logarithmic scale, so if one flash has double the guide number of another, it kicks out 4x the light. Most pop-up flashes have a GN of around ten, whereas decent external units are more like  40-60. Some manufacturers like to muddy the waters a little by using feet instead of metres, and higher ISO settings, which of course results in an inflated guide number. Be aware of this and check the specifications carefully. Look for a flash with a guide number of at least 35.

Bounce flash
Most external flashguns have a tiltable head, allowing you to bounce the light upwards towards a white ceiling. This is then reflected back down onto the subject. Bounce flash is generally more flattering than direct flash, as it vastly increases the effective size of the light source for softer shadows. Light coming from above also mimics normal daylight so it looks very natural. Some more advanced flashguns have heads that tilt side to side as well, allowing you to bounce light off a wall.

Recycle time
When shooting at or around full power, it can take several seconds for some flashgun units to recharge for the next shot. Others can recycle in less than a second. If you’re shooting in a fast-paced environment, such as at a wedding, a very fast recycle time is important, so it’s worth checking the spec sheet before you buy.

Zoom ability
On most premium flashguns, the bulb is able to move backwards and forwards within the head to adjust the angle of the beam of light. For further away subjects, for example, the angle narrows so that all the light is concentrated on the subject. Most zoomable flashes have a zoom range of 24-105mm, and in TTL mode will actually adjust automatically to match the focal length of your lens. So if you’re shooting at 50mm, your flash will adjust to ensure no light is wasted. Some photographers use the zoom function manually for creative effect. By zooming in on the flash but using a wide focal length, you can achieve a spotlight effect.

Wireless control
Most flashguns won’t fire off-camera without the use of a cable or wireless triggers. But some have a built-in wireless control so you can fire it off-camera. This is especially useful for portraits, as it allows you to use more flattering lighting patterns. Some flashes can be fired in a slave mode, which means the flash has a sensor on it that will fire the flash when it detects another flash firing.