What causes red-eye in photos?

Question

Red-eye makes photos look rubbish, but what exactly causes it to happen in the first place? How come some people are more prone to getting red-eye in photos than others? Does the colour of your eyes make a difference? Is there any way of avoiding this when taking photos?

Answer 1

As others have said it's the reflection of the light from the flash off the retina at the back of the eyeball. It's nothing to do with the colour of your eyes, which is the colour of the iris at the front of the eye. Some people are more prone because some people's pupils (the hole in the iris that allows light into the eye) are naturally bigger than other people's in their resting state.

There are four ways of reducing it. As ambient light increases the iris constricts making the pupil smaller to protect the eye from excessive light entry. So if you take a picture somewhere that is brighter eg turn the light on in a room, the pupil constricts so less redeye. Also if your camera (digital or film) has a redeye reduction flash, this is a pre-flash which aims to get your eye to close down the pupil thus achieving the same thing. Thirdly, if the subject looks slightly away from the camera the reflection off the retina becomes less directed at the camera. Fourthly, get a camera with a separate flash unit or at least a camera which has its built-in flash positioned as far from the lens as possible. This will once again result in the reflection off the retina being less directed at the camera and reduce redeye.

Answer 2

Normally the inside of your eyes look black (the pupil of the eye being the window to the interior), but red-eye essentially reveals that given enough light, they're balls of transparent jelly with red walls. Here's why.

A camera flash happens faster than the iris of the eye can close the pupil (you can see the pupil's of people's eyes getting smaller if you happen to be looking at their eyes when they walk from a dark room into a sunny outdoors). The lens of the eye focuses the light from the flash onto the retina at the back of the eyeball, which is red because of all the blood vessels in it.
People with blue or grey eyes get worse red-eye because their pupils have less melanin in them (the pigmentation that makes brown eyes brown and moles on your skin dark).

Some animals, such as cats, have green- or yellow-eye instead of red. This is because they have a light-reflecting layer behind the retina, to help their night vision. It affects the colour of the reflected light.

You can do various things to improve red-eye. You can use a separate flash unit and point the flash at a nearby reflective surface, instead of straight at the subject of the photo, which is what pros usually do. Many modern cameras have a red-eye reduction feature, which sets off a small series of low-power flashes before the main flash, causing the pupil to contract in advance. You can ask people not to look at the camera, which is probably a good idea anyway as it tends to make them look better. There are other things you can do, like processing the film in certain ways, or using software to digitally process out the red-eye.

Or, of course, you can just not use flash.

Answer 3

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

This happens when you take a picture in a dark environment. In this relative darkness, your iris opens so that more light enters in your eye and you can see better. It must have happened to you when you enter a dark place, you can't see a thing at first but slowly your eyes get 'accustomed' to the darkness and you can see better. That's your iris opening. Now if someone had to take you a photo, the flashlight will find your iris wide open and red will reflect back to the camera. Newer cameras have a pre-flash (also called red-eye!!) which lights up just before the main exposure lights up and the shutter opens, thus forcing the iris to close down, thereby eliminating the red-eye. Also by turning slightly your head, so as not to face directly the camera, seems to help. What makes some people more prone than others is the colour of their eyes especially brown. Also age, in older people their reflexes are a bit slower and their iris takes longer to adjust. Hope this helps. Ciao

Answer 5

Hi,
It is down to retinal reflection, that is in flash photography, the burst of light reflects back to the film. Red, as the red is due to the high blood concentration. Colour of the pupil does not make for a bit of difference, other than, having fairly bright green eyes myself, a bit of red in the middle looks nicely bizarre.
Fust for fun, stick a green lens on the flash - it makes folks & things look a bit surreal. Or different colour filters.
Of course, if you are taking digital pics, the software always comes with a remove red-eye thing at a click or two.
If you have your subject facing a bright sunshine, the pupil will close up a bit, and usually lose the reflection.
Landscapes etc don't have eyeballs, but I know what you mean.
All the best,
Bob

Answer 6

Redeye is mostly a function of where your flash is in relation to the lens of your camera. That's why compact cameras have such problems with redeye. The flash is necessarily too close to the camera lens. What happens is the light from the flash enters the eye and reflects off the back of the retina. In humans, this reflection is red. Other animals have different colored retinas (for example, cats are green). In order for you to see this on the photo, the reflection has to be angled back in such a way that it enters the lens of the camera relatively directly. If your flash is up high or off to the side, this can't happen. If your camera has problems with this and has a hotshoe, buy a seperate flash for it and it will solve the problem. When buying a camera, look for one where the pop up flash rises high, away from the lens (as it does in better cameras).

If you have a compact camera, you are SOL. Use the preflash (which will reduce redeye by causing your subjects pupils to contract) and/or use photoshop to color the redeye something else.

Answer 7

You are not taking the picture correctly.
Nothing to do with where the subject looks.
Nothing to do with the media.
You can't change the cause so forget it
All eyes are the same if they in line with the flash.
Its only red because of the media.
Use Infra Red and it will be white, and you will see a man's beard under the skin. Horrible.

Daylight? Then choose fill in flash if digital
If Film choose shutter speed and aperture and rate
your film the next setting up if Iris Shutter.
If focal plane shutter use 1/60 sec and change the
aperture to suit

Darkish? Use the Red eye feature if digital
For Film & Iris set the film speed the next
setting down and point your flash at the ceiling.
For focal plane open the aperture by one setting
and point your flash at the ceiling

Forgetting about the different types of camera.
If you have manual control always increase the shutter speed if you open up the aperture and vice versa.
Red eye always comes if the flash is inline with the eye's pupil.
Forget about the focal plane bit with film unless your camera has a blind moving across it when you release the shutter with no film in it. If this speed is then above 1/60th of a second with flash you will lose the right hand side of your picture.
Sorry to be long winded but you did not say what type of camera you are using.

Answer 8

Light reflecting back from the back of the eye has a red color due to the color of the retina.

The size of the pupil is usually what governs it for the most part but having lighter eyes also plays a role.

Some cameras fire a burst of flashes that make our pupul contract. This usually reduces it significantly.

You can use a photo editing program to fix red-eye in digital pictures.

Answer 9

Reflection from the back of the eye. Don't look directly at the camera, If your camera has a preflash use it. This causes the eye to close down before the main flash and can reduce red eye or buy a flashgun that will allow the flash to be bounced off ,say the ceiling (if your camera has the facility to accept such a flashgun ) or buy a flashgun that connects to the camera with a cable which will allow you to hold the flashgun away from the camera so that the subject is not looking directly at the flash (again your camera must have the facility to allow connection of such a flash gun

Answer 10

Its due to the light from the flash reflecting off the eye's retinas, our pupils open more when light levels are low to help us to see, so there is more of the retina exposed to the flash. In brighter light our pupils contract to protect the retina, but a flash goes off too quickly to allow the pupil to react in time, so you get red eye.

Some cameras have a red eye reduction button which flashes the flash for a few seconds before actually blasting it at you and taking the picture, this gives your pupils time to react and close against such a bright light source, so less light penetrates the eye and bounces off the retina.

If you dont look directly at the camera, the light hits the retina at the wrong angle to allow the reflection to cause red eye.