A Moment of Science

Why Red Eye?

What causes those glowing red eyes in photographs?

red_eye_flash

Photo: reedfish (flickr)

So, is there any way to avoid red eye?

What causes those glowing red eyes in photographs?

Well, the flash is the problem. The eye’s retina contains a crisscross of red blood vessels. Sometimes, when the light from a camera flash reflects off the retina it bounces back to the camera lens carrying a red tint from the blood vessels and from a brownish pigment in a few layers of the retina.

So, is there any way to avoid red eye?

You can always edit it out, if you’re taking a digital picture. If not, some cameras come with a double flash that can reduce or get rid of red eye. The first flash happens before the camera takes the picture. It makes the pupil contract, which means that less light reflects off the retina during the second flash, when the picture is actually taken.

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