Based on a casual survey of photos posted on Facebook and Flickr, it wouldn’t be crazy to assume that the demon population has skyrocketed: Red eyes are everywhere. The dreaded red-eye effect, of course, owes its existence to a far more mundane phenomenon than occult forces of evil. Red eyes usually pop up in photos taken in low light, an ambient condition in which people’s eyes naturally dilate to let in as much light as possible. But when the pupil is wide open, the eye's retina is fully exposed to the camera lens; and when your camera flash-fires, the light bounces off the retina and appears in your photo as the creepy dot of red so familiar from snapshots and horror movies.
The good news? Understanding what causes the problem puts you in a position to eliminate it from your photos. Here are some key recommendations to help you capture better, red-eye-free photos.
Shoot in a well-lit room: The easiest way to avoid red-eye in your photos is to avoid having your subjects' pupils dilate to begin with—and that means not taking pictures of people in dimly illuminated environments. Try instead to shoot in a well-lit location. You can move your subject near a window (turn them so that they face the window), turn on lights, or shoot outdoors. Of course, this advice won’t help if it’s night, or if you’re shooting in a location where you have no control of the lighting (such as a restaurant or night club). If that’s the case, no worries—you can still triumph over red-eye by using one of the following strategies.
Use your camera’s red eye mode: Most digital cameras come equipped with a handy red-eye reduction mode. Check your flash’s settings; you should be able to cycle through modes such as fill flash, slow shutter, and red-eye (hint: the icon looks like an eyeball). When you use red-eye mode, the flash will “prefire” several times, rapidly, before taking the actual photo. The purpose of this behavior to cause your subject’s pupils to contract, thus reducing the intensity of the red-eye effect. How well does it work? The answer depends on the setting—how dark the location is—and on your subject. Not everyone’s eyes respond quickly to changes in light. In general, though, this approach produces good (but not perfect) results.
Bounce the flash or take it off the camera: This generally isn’t a viable option with point-and-shoot cameras; and indeed, one reason that serious photographers step up to a digital SLR is to gain the ability to move the flash. If your camera has an external flash, you can angle the flash so that the light bounces off the ceiling for indoor photos.
Why does this work? Remember that red-eye occurs because the flash reflects off your subject’s eyes and back into the camera lens. But if the light from the flash doesn’t travel directly along the axis of the lens, it won’t bounce back along the same path. Similarly, if you can remove the flash from the camera’s hot shoe and hold it off to the side, you'll avoid directly reflecting light into the camera lens, and thus defeat the red-eye effect.
Fix it on your computer: Your last line of defense against images of eerie possession is to edit out the red-eye effect, using your favorite photo-editing program. Pretty much every photo editor has some sort of red-eye removal tool; working with it is as simple as selecting the tool and clicking the affected eyes.
Most such tools fiddle with the colors and exposure in the eye to mask the red. The result isn’t perfect in any event, and it works most effectively if the eyes are relatively small in the photo. But if you've taken an otherwise lovely portrait that's haunted by glaring red eyes, resorting to a red-eye removal tool is certainly better than doing nothing.