What causes the red eye effect in pictures?

Answer 1

"I think we are all familiar with that picture that is lovely except for the horrible red spot in the center of the subject’s eyes, Red-Eye. The first thing to note is that it only occurs in flash pictures and the darker the room the more pronounced the effect. Fortunately, digital photo editing programs can greatly reduce the problem, but it is still best to eliminate the problem at the source when possible.

The effect is caused by the light from the flash reflecting off of the rear of the eye, the retina, which contains translucent blood carrying capillaries. Thus, the reflected light is red. The reflected light is passed back out of the eye and imaged by the camera. In dark surroundings, the iris of the eye, like that of the camera, opens to pass more light, thus the more pronounced the effect. Professional photographers deal with the problem by offsetting the flash source 6-10 inches from the plane of the camera lens. In this case, the reflected red light is offset so it does not pass through the camera lens. The amateur photographer does not want to carry around such a bulky contraption, so another solution has been developed. Unfortunately, it does not work very effectively. In this case just before taking the picture the camera sends out one or more preflashes in hopes of making the eye’s iris small enough that little light is passed back to the camera even though the flash and lens are very nearly on the same axis. Unfortunately, the preflashes are seldom strong enough or long enough to cause the iris to constrict before the main flash and may cause the person to blink at the wrong time. This feature often does considerably reduce battery life but little else.

What can the photographer do? Only use the flash when there is no other way to sufficiently light the subject. Turn on additional lights and open drapes. Remove lamp shades from lamps out of view of the camera. If you must use the flash, place a bright light source in the direction the subject will be looking, thus constricting the subject’s iris. Have the subject look at an object off camera.

If all of this fails to give acceptable results, then obtain a retouching program that has a good Red-Eye Retouching feature"

http://www.tpcug.org/newsletter/nl_2002/april2002/red_eye.htm

Answer 2

It happens when your flash is too close to your lens. This causes the light from the flash to bounce off a person's retinas at just the right angle that it can be seen in the picture. Human retinas reflect back the color red. To solve the problem, use the preflash (causes pupils to constrict, blocking the flash), use software to color the red something else, have the person look somewhere else besides directly into the camera or simply mount a flash on the camera's hotshoe, which is usually well away from the lens.

Answer 3

We've all see photographs where the people in the picture have spooky red eyes. These are photos taken at night with a flash. Where do the red eyes come from?

The red color comes from light that reflects off of the retinas in our eyes. In many animals, including dogs, cats and deer, the retina has a special reflective layer called the tapetum lucidum that acts almost like a mirror at the backs of their eyes. If you shine a flashlight or headlights into their eyes at night, their eyes shine back with bright, white light. Here is what Encyclopedia Britannica has to say about the tapetum lucidum:

Among many nocturnal vertebrates the white compound guanine is found in the epithelium or retina of the eye. This provides a mirrorlike surface, the tapetum lucidum, which reflects light outward and thereby allows a second chance for its absorption by visual pigments at very low light intensities. Tapeta lucida produce the familiar eyeshine of nocturnal animals.

Humans don't have this tapetum lucidum layer in their retinas. If you shine a flashlight in a person's eyes at night, you don't see any sort of reflection. The flash on a camera is bright enough, however, to cause a reflection off of the retina -- what you see is the red color from the blood vessels nourishing the eye.

Many cameras have a "red eye reduction" feature. In these cameras, the flash goes off twice -- once right before the picture is taken, and then again to actually take the picture. The first flash causes people's pupils to contract, reducing "red eye" significantly. Another trick is to turn on all the lights in the room, which also contracts the pupil.

Another way to reduce or eliminate "red eye" in pictures is to move the flash away from the lens. On most small cameras, the flash is only an inch or two away from the lens, so the reflection comes right back into the lens and shows up on the film. If you can detach the flash and hold it several feet away from the lens, that helps a lot. You can also try bouncing the flash off the ceiling if that is an option.

Answer 4

Too much reflection of the light (coming from your camera's flash) on subject eye retinas = "red eye".

It is all about the too small angle between the Flash (which generate the light) , the subject's eye (where the reflection ocurr) and the Camera Main Lens (which capture the "red eye" effect). When the angle is small you have "red eye".

Unfortunately because this days the cameras are soo small, the built in flash is too close to the Main Lens = the angle is too small = "red eye". To compensate this few camera have "red eye" mode = multiple flashes before the picture is recorded or a pop-up built in type flash.

Ideal is to use a far away from the Main Lens flash (external flash on hot shoe - as SLR/DSLR style).

Answer 5

Light [usually from your flash bulb] reflecting of the back of an eye causes red-eye. Shine a torch at your subject to reduce pupil dilation.

Answer 6

It is the light hitting the back of your eye,

Answer 7

The blood vessels behind the cornea.

Answer 8

Simply put. a reflection.

Answer 9

i think she coppied that off of a web site.. but that's pretty much all it is...

Answer 10

It only seems to happen on people with blue eyes.