The Red Eye Phenomenon.
- What it is
- Why it appears
- What to do about it

The Red Eye phenomenon is, as earlier mentioned here on E2, something that occurs when you take a picture of someone. If you have a compact camera and you've taken a few rolls of pictures, chances are that you have stumbled across the phenomenon.

Why does this happen?

If an eye had absorbed all light, then this wouldn't happen. In fact, if an eye had been theoretically flawless, the red eye effect would not have existed at all. What happens when you see the red eyes on pictures, is that the flash is reflected in someone's eye. The reflection is red because of all the blood vessels inside the eye.

A bit more technical, please. Why does this happen?

(this is a bit of a non-medical explanation, but I hope it is written in such a fashion that everyone can understand it)

When light shines straight into an eye, thereflection is in the shape of a cone. This can be illustrated by holding a piece of cardboard with a hole in it up in front of a mirror. Shine a flashlight into the hole, and see if you can see a reflection.

When you take pictures, in particular if you take pictures with a compact camera, the flash (source of light) and the lens (the observer) are fairly close to each other. This is our equivalent of holding the flashlight right next to your head - you will clearly see the flashlight coming back at you.

So.. How do we avoid red eyes?

Removing the red eye effect can only be done by posing a change somehow, so the light from the flash doesn't bounce back into the lens.

If we go back to our flashlight-and-cardboard, there are several obvious ways we can avoid the reflection:

  • Turn off the flashlight. This is the point most people forget about. Obviously, if you can do without a flash, either by increasing the light in the room, by switching to a film that has a faster ISO value*, or using a faster lens**.
  • Diffuse the flashlight. If you hold a piece of (white) cloth in front of the flashlight, you will notice that the intensity of the flashlight is only a little decreased. It does, however, seem less piercing to your eyes. This is not a coincidence - if you hold a piece of thin white cloth in front of your flash, you can often drastically decrease the problem with red eyes.
  • Move the flashlight further away from your eyes. This is a bit harder with compact cameras, but if you have an SLR, you should definitely get an external flash that goes in the hotshoe of your camera. For one thing, these flashes are a lot more sophisticated than the internal ones. Besides, they are significantly further away from the lens.
  • Make the hole smaller. Put away your piece of cardboard, and take one that's got a smaller hole in it. Try the same trick with the flashlight. As you will see, you will get a reflection in much less of the cases. Making peoples irises smaller isn't that hard.
    • One, you could try to turn on the anti-red-eye function that probably exists on your camera. This function usually sends off a few short flashes, or it will shine some other sharp light into your victims' eyes. This makes their irises smaller, and the problem diminishes.
    • Turn on more lights. This has the same effect as above, but it also has some other advantages: One, you get more even light, two, depending how sophisticated your camera is, it might fire a less strong flash, giving a more natural light. Three: you might get away without using a flash alltogether.
    • Make sure your subjects aren't drunk. Have you ever noticed that if you take a roll of film at a party, how there seem to be more and more occurences of the red eyes? Not a coincidence. People who start to become intoxicated have slower reactions - this applies to eyes as well. The eyes just won't contract, leaving you with red-eyed pictures.

*) ISO value: "Normal" film is 100 or 200 ISO. If you go to a store and buy some 800 film, the film will be more sensitive to light, and you will in many situations get away with not having to use a flash.
**) Switching to a faster lens on a compact camera is obviously not possible. What few people realize, however, is that many of the entry-level zoom compact cameras have lenses that gather light much better when it is fully zoomed out. In low light, you should therefore consider zooming out and go closer instead of using the zoom to frame your pictures. On an SLR camera, look for a camera with a larger aperture.

So.. What do I do if I get red eyes after all?

Most photo editing programs have great tools for removing these. Some processors will remove them for you (if you ask) and quite a few photo stores sell pens specifically designed for "colouring over" red eyes (not recommended).