Digital Photo Advisor

Forget rocket science – that's child's play compared to taking good flash photos. Want proof? When I read about a bunch of guys who build a 21-foot long replica of a Star Wars X-Wing fighter and launch it several hundred feet in the air, only to watch it disintegrate, I'm not surprised. But when I get 30 e-mails – yes, 30 – in the same week from people asking how to take better flash photos, that's just business as usual.

The most common problem with flash photos is the dreaded "supernova in the cave" effect – your subject is properly exposed, or even too bright, but the background is a black hole. That's what we'll fix.

Understanding the Flash Controls

Unfortunately, I've never found a camera smart enough to take great flash photos all the time, even when set to fully automatic or a fancy "through the lens" flash exposure mode.

Good flash photos take a little human intervention. One reason for this is the fact that most flash photos include a huge range of light levels. The flash has a meaningful effect only on the foreground, fairly close to the camera. Everything else in the photo – the rest of the room, people milling about in the background, tables, chairs, paintings, the occasional puppy dog – gets exposed by whatever ambient light happens to be available.

So how do you deal with that? In general, there are three important settings that you can use to control any flash photograph: ISO, aperture, and shutter.

ISO. You probably know that ISO is the camera settings that controls the camera sensor's sensitivity to light. The higher the ISO, the brighter your picture will be, all other things being equal.

Aperture. Controlled by the camera's "f/stop" setting, the aperture is the size of the opening in the lens through which light hits the sensor. The bigger the opening (which, counter intuitively, is the smaller the f/stop number), the brighter your foreground subject will be. The camera's aperture setting is mainly responsible for exposing the foreground – whatever your flash is striking.

Shutter. The camera's shutter speed is usually set to somewhere between 1/60 and 1/250 second for flash photos. The shutter speed handles the overall light level in the background of the photo, which is too far away for the flash to have any effect. The slower you set the shutter speed, the brighter your background will be.

Applying Our Secret Knowledge

So what do we do with this information? You could, for example, set your camera to its manual exposure mode and fiddle separately with all the controls. But frankly, that's too much work.

Most cameras do an okay job of exposing the foreground subject, so I'd leave the aperture setting alone. If you don't like your camera's usual results, you can try changing the ISO or, if your camera has a flash power or flash compensation control, you can use those settings to fine-tune the exposure on your subject. For more on tweaking the ISO, read "Use ISO to Take Low-Light Photos".

It's the background that generally needs your help. Try setting your camera to Shutter Priority mode and experimenting with a variety of speeds. The slower the shutter speed, the more light you'll have a chance to soak up in the background. Even if you pick a really slow shutter speed – like an entire second – the foreground will remain sharp because it's exposure is based on a rapid burst of bright light from the camera flash.

Consider these examples:

I shot this first photo using a shutter speed of 1/60 second, and you can see that the background is very dark.

I told my kids not to move, then quickly reset the shutter speed to 0.5 seconds.

The second photo captures the foreground more or less the same as in the first photo, but the background is dramatically better.