Why Do People Have Red Eyes In Flash Photographs?
Like many answers to “scientific” questions, this one has a simple answer that will satisfy many people. However, there is also a more complex answer as well. In simple terms, the red color is caused by the flash from the camera being reflected by the retina (the area at the back of the eye).
A more complicated answer would mention such medical/scientific terms as “tapetum lucidum” and “epithelium.” The first is the substance that forms a reflective surface on the retina (also referred to as the epithelium).
Any light that shines into the eyes of animals will reflect this light so that it is visible to us as we look at it. For cats, dogs, deer and other animals, this is what produces the sometimes eerie shining of the eyes at night.
But why do human eyes show up as red? Because humans don’t have the reflective surface of tapetum lucidum on the retina. The flash of a camera or a flashlight shining into human eyes isn’t reflected back as white light from the mirror-like surface. The blood in the small vessels of the human retina is responsible for the color we see, simply because the camera flash is bright enough to light up all those tiny blood vessels. There are so many, so close together, that we see an almost solid red color.
How can we avoid getting “red eye” in our family pictures? Some of the newest cameras have been made with a pre-flash that causes the light to flash once to make the pupil of the eye contract, and then flash again when the photo is taken. Contracting the pupils will reduce “red eye” quite a bit, but there may still be a small amount of red in the photo.
It’s also possible to reduce or eliminate red eye in photos by pointing the flash slightly away from the people in the picture rather than directly at them (and their eyes). Photographers have also found that moving the flash away from the camera, if possible, will help with the red-eye problem.
These few suggestions are about the only way to reduce the red that shows up in the subjects’ eyes when a photo is taken. The blood vessels on the retina are a fact of life and the only way to get around it is to use the technology of new cameras or the tricks that photographers use when moving the flash to different positions.
The eye naturally tries to process the bright flash of light that makes its way into the eye suddenly. The retina works remarkably well with natural light and colors during the day. But the flash of a camera is just too intense and overpowers the eye, illuminating the blood as described earlier. The eye just doesn’t have time to adjust. The bright light of the flash may be too much for the eye even if it could make adjustments.
For photos that are already printed or on the computer screen, there are some ways to take the red out, with either a special pen for printed photos or computer software for the electronic version.
Category: Technology