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You can tell your son that the spooky red-eye effect common in many photographs taken with a flash is simply light being reflected off the retina. The retina is the light-sensitive membrane that lines the inner eye and sends messages to the brain via the optic nerve. Why do the eyes appear red? Because this is the color of the blood vessels that line your retina. Many animals have a reflective layer in their retina called a tapetum lucidum. This layer bounces light back into the eye, allowing it to pick up more information in lower levels of light. This helps
night predators spot prey, and prey react in turn. This reflective layer causes those strange glowing eyes in the snapshots of your favorite furry friend. Notice that the glowing-eye-Fido and red-eye-Johnny effects only happen in flash photography. This is because in both cases, usually shot in low ambient light, the pupils are dilated, allowing for a maximum amount of reflective retina area. There are several ways you can reduce red eye, such as moving the flash off the camera or increasing the light around your subject. Red-eye reduction features in cameras usually flash twice -- once to
reduce the pupil in the subject's eye, then again to take the photograph.
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