What causes red-eyes in photos?
AsstProf is correct. I would like to add another reason for red eye is the location of the flash with respect to the lens of the camera. Red was not as much of a problem with older photography systems which were larger and had separate flash units connected to them. As cameras have gotten smaller the flash is placed very close to the camera lens. This creates a very small angle between the flash and lens with respect to your eye. With such a small angle the flash travels nearly straight out bounces off your retina and travels nearly straight back to the camera lens. Older cameras had the flash further away from the camera lens or the flash could be detached and held in one hand even further away. Basically this created a larger angle. The flash bouncing off your eye with this larger angle would send the reflected light off at an opposite angle and not directly back to the camera lens. Consider why you do not see as much red eye in old photos as you do now in old pictures when flash uni
