Red Eye Effect

Retina - The inner most layer that senses light in our eyes is responsible for the red eye appearance in photographs. When a powerful light like flash-light hits the retina, the light bounces back and the rich blood vessels in the retina gives the red color. The pupil of the eye naturally contracts when our eyes are exposed to bright light. Since, the light from a camera flash is quick, the pupils do not contract immediately. Hence the red eye effect.

Different ways to reduce "Red Eye Effect" are:
1. Many cameras have "red eye reduction" feature. When this feature is enabled, the flash produces two ro more subsequent flash-lights. This first flash will make the pupil to contract and the next flash is when the actual photo is taken.
2. Using a detached flash or a flash mounted away from the lens. This causes the light to enter the eyes in angle which is away from the axis of the lens thus the light reflected from the retina do not enter the lens.
3. Professional photographers prefer flash diffusers or reflectors (ever wondered why those umbrellas lying around in a studio!) that bounces the flash light and only allow softened light thus eliminating "Red Eye" as well as providing a natural lighted subject.
4. Many photo editing softwares provide "Red Eye" reduction technique.