Wednesday, March 15, 2006

What Is "Red Eye" and How Do You Get Rid of It?

Many thanks to Bruce for asking me these questions in an e-mail.

We've all experienced the dreaded "red-eye" in photos when taking flash photos. The red-eye makes your subject look demon-possessed or crazy, often ruining what would otherwise be a good photograph.

Red-eye is caused by light reflecting off the back of the eye towards the lens of the camera. We've all seen this effect with animals like cats or dogs with glowing eyes in the dark when lit with a flashlight or headlight. The retina of the human eye is nowhere near as reflective as the retinas of many animals, so we don't see reflections under the same conditions.

However, when taking a flash photo, the intense light of a strobe flash is strong enough to reflect off the back of the human eye. In dim light, the pupil of your subject will be wide open to let in more light, and the iris will not close quickly enough when the flash goes off. So, with red eye, what you're actually doing is taking a flash photo of the backs of your subject's eyes!

This effect is much more likely to occur when the light souce--your strobe flash--is near your lens. This is because the light is shining directly into the eye, bouncing off the back, and bouncing directly into the camera lens. In technical terms, it's because the angle from the flash to the subject and back to the lens is pretty small.

Here's the conditions which cause red-eye:
  • Dim lighting, causing the pupil of your subject(s) to be wide open.
  • Use of a strobe flash, close in line with the lens of the camera.

So, the obvious solutions to red-eye: 1) eliminate the dim lighting or 2) move the flash farther from the lens.

Eliminating the dim lighting may be as simple as turning on more lights, causing the pupil to be smaller. Some cameras have "red-eye reduction" which amounts to using the flash to send out pulses of light to make the pupils of your subject's eyes smaller. However, red-eye reduction doesn't always work, and it slows down camera operations and takes battery power.

Moving the flash farther from the lens is the best way to reduce or eliminate red-eye. Even a few inches will make a tremendous difference. However, this requires you to have a camera where you can add an external flash. Many point and shoot cameras don't have the necessary hot shoe. And if you are shooting flash at an extreme distance, even a flash in a hotshoe may not eliminate red-eye, as the flash effectively becomes more in the same line as the lens when the subject is far away. However, in such an instance of distance flash use, it's unlikely that the flash is significantly lighting your subject; all it's likely to be doing is just causing red-eye.

If you have a point and shoot camera, take a look at how close the strobe is to the lens. If it's very close, that's probably why you keep getting red-eye. You'll want to activate the red-eye reduction mode of your camera, often by simply pressing the button with the lightning bolt until the camera display shows an eye (indicating red-eye reduction is on).

If you have an SLR and you're getting red-eye, you need to use a flash in the hot shoe instead of a built-in popup flash. Another option is to use a flash bracket and cable, which raises the flash even further away from the lens.

If you've got photos with red-eye, you can "fix" them in a number of ways. Most digital viewing programs/software now include red-eye elimination as an option. If you've got prints, there are pens for covering up the red-eye.

Red-eye is annoying, but it is preventable and even if it occurs, it's fixable. It's more likely to occur with the small point and shoots that are easy to carry around, but don't let that deter you from getting a once in a lifetime photo. You may never again be able to capture the moment.


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