Red Eye

Using a camera flash when a subject is looking directly at the camera often has the unfortunate effect of causing the eyes of the subject to appear an evil shade of read. The reason is the the eye muscles do not have enough time to react to the flash, restricting the size of the pupil before light has entered and left the eye. The back of the eye has a rich blood supply, so reflects red light.

Red eye can be avoided when a flash is used by taking pictures in brighter light or using a 'red eye reduction feature which emits short flashes of light Two give the eye muscles time to reduce the size of the pupil before the camera actually takes the picture.