Larry
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We’ve all seen that when some people or animals are photographed, the pictures turn out showing their eyes glowing red like they are possessed by demons. This can happen with all people in the right conditions, but it is more frequent in some than it is in others. Red-eye occurs mostly in people with light blue eyes, light skin, and light hair. It is also more frequent when using compact cameras since one of the factors that causes red-eye is using a flash too close to the camera lens in a low-light setting.
Red-eye results only when the flash is used. What happens is that the light from the flash travels into the eyes of the subject, reflects off the back of the eyeball, out the pupil, and into the camera lens. The main cause for the red color is that the back of the eye and the retina are rich in blood vessels. The eye also contains pigments that contribute to the redness, and when the light passes out of the pupil, the lens absorbs some of the blue and violet wavelengths of the light. The reason why red-eye happens more with light-skinned, light-haired people is because of the presence of melanin. Melanin is the pigment in skin and hair that makes it dark. This pigment is also in the space behind the eye where the light of the flash reaches. The melanin absorbs the light from the flash, so people with more melanin reflect less of the light.
If you or someone you know gets a lot of red-eye when a picture is taken, there are some ways to help prevent it. Professional photographers use flash reflectors so that the flash is not pointed directly at the subjects. A light colored ceiling or wall can act as an impromptu reflector, but your flash has to be able to swivel or tilt. Swiveling or tilting the flash moves the light out of the axis of the lens. If your flash is in a fixed position, you can have the subject look slightly to the side and not directly into the camera. Also, many modern cameras have red-eye reduction settings that can help.
 Posted 5185 day ago
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