Many compact cameras and some SLR cameras have built-in-flash. The flash cannot be detached from these cameras and may result in “red-eye” that is, the pupils of a subject’s eyes appear red-in colour photographs.
Red-eye occurs when light from the flash is reflected off the back of the retina. (Subjects pupils are dilated and the On-camera flash actually illuminates the blood vessels in the eye). The only way to avoid this is to close down the pupils (contract the iris) by raising the room lights, or using “red-eye reduction flash mode”.
The feature is available in sophisticated compacts. This mode fires a pre-flash or a bright lamp prior to exposure, which makes the iris contract and close down the pupils, thereby reducing the effect. In compacts where there is no red-eye reduction feature, the following technique may be employed to reduce the red-eye effect. The flash light may be bounced off the ceiling or wall, before it reaches the subject.