What causes red eye?

Question

What causes red eye in photographs?

Just curious :]

Answer 1

Red eye is caused by the flash from your camera reflecting off the back of your subject's retina.  Meaning your flash shines off the back of the person's eyeball.

Red eye reducers on a camera work by having a mini-flash go off before the picture is taken, so the pupil will contract, and that prevents enough light to go in to create a reflection.

Answer 2

Redeye is caused by the reflection of a camera flash on the blood filled retina.



It can be reduced by increasing the distance between the lens and the flash. The close proximity of the flash and the lens increases the effect. That's why you often see cameras that have the flash mounted on an extendable flip top.

If the camera is a point and shoot, the anti-redeye feature is often a preflash, or stroble effect that causes the iris of the eye to close and reduce or remove redeye.