Red-eye occurs when light from the built-in flash of a camera bounces off the subject's retinas and reflects back to the camera lens. Along the way, the light takes on the tint of the blood vessels in the eye, which causes the eyes to appear to be glowing red in the picture. In animal pictures, eyes often have a white, yellow, or green glint.
Red-eye can result from any camera with a built-in flash, not just a digital camera. Why just a built-in flash? Because a built-in flash is positioned very close to the camera lens. When people look into the lens, they're also looking directly at the flash, which means that their retinas pick up and reflect almost all of the light from the flash. When you use an external flash head, you can position the flash farther from the lens and also angle the flash so that it's not aimed directly at the eyes.
Most digital cameras don't have connections for attaching an external flash head, unfortunately. Using a slave flash - a flash unit that is designed to work in tandem with a built-in flash - isn't always a solution, either, because your camera's built-in flash needs to fire to trigger the slave flash. If you stand at a distance from your subject, the built-in flash may be far enough away to prevent red-eye, but if you want to get a close-up, you're right back in red-eye zone. So what's the casual photographer to do?
A couple of tactics help reduce - but may not entirely eliminate - red-eye:
- Indoors, turn on as many lights as possible. In response to the additional light, your subject's eyes will constrict a little, so less flash light will be reflected back to the lens. (This is why you can usually use flash in the daytime without creating red-eye.) Most cameras also adjust flash output based on the ambient room lighting, so the brighter the setting, the weaker the flash needs to be.
- If you're shooting indoors during daylight, position your subjects next to a window. The daylight coming through the window will have the same effect as turning on additional room lights.
- Switch the flash to red-eye reduction mode. In red-eye reduction mode, the camera fires a brief, preflash light in advance of the main flash. The idea is the same as turning on lots of room lights - the eyes constrict in response to the preflash so that when the main flash fires, less light is reflected from the retinas. Keep in mind, though, that it's called red-eye reduction and not red-eye prevention mode for a reason: That little preflash can do only so much, so you may still wind up with some red-eye areas.
- Consider posing your subjects so that they're not looking directly into the camera lens. A profile shot can be every bit as captivating as a regular, face-forward image, as illustrated by Figure 1. You also can ask your subjects to look off to one side or slightly up or down. Because the flash light won't be heading straight for the eyes, red-eye reflections will be minimized.
Despite your best efforts though, some pictures will still be marred by the red-eye effect. The good news is that you can fix the problem easily in your photo editor.
Figure 1: Consider shooting subjects in profile to avoid red-eye in flash pictures.
- http://tech.yahoo.com/gd/avoiding-red-eye-in-digital-photography/153011;_ylt=Agqhu7K9Y3jGyw1kf2dF1lYvLZA5
