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Avoiding Red Eye – What Causes Red Eye?

written by: •edited by: Rhonda Callow•updated: 5/27/2010

It can be more than a little frustrating to find that an otherwise excellent photo is ruined by the subject having red eye. This two part article will explain briefly what red eye is and provide you with tips and techniques to avoid red eye without the use of an external flash.

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    What causes red eye and how can you avoid it? The culprit is your digital camera’s built-in flash. Unfortunately, in most compact digital camera’s the flash is positioned directly beside the lens, so the light from the flash bounces off the subject’s eyes and back to the camera’s lens, resulting in those evil looking red eyes, also know as the red eye effect.

    If you want a brief overview of the technical side of things, read on. If the technical side of red eye doesn’t interest you and you just want to get on with learning how to avoid red eye, then please see part two of this article.

    The Science of Red Eye

    Here’s a quick science lesson for you. The coloured part of your eye, called the iris, controls the levels of light which enter the eye by dilating and constricting the black center of your eye, called the pupil. Its function is very much like the lens aperture of a camera. When a flash on a camera is used, the light disperses so quickly that the iris doesn’t have time to constrict the pupil before the photo is taken. The result is this: the light travels through the choroid (which consists of layers of blood vessels), hits the retina (which lines the back of the eye) and bounces back through the blood-rich choroid and through the iris. The camera captures this light reflection all in a blink of an eye - indeed, that pun was intended – ultimately resulting in the red eye effect.

    If you’d like to see a diagram of the eye and read more about how the eye works, WebMD does a great job of explaining things in their article called: Eye Health: The Amazing Human Eye: Your Guide to How the Eye Sees.

    Did You Know?

    • Children and people with blue or grey eyes are more likely to suffer from the red eye effect. Children’s eyes are more reactive to light meaning their pupils don’t need to constrict as much as an adult’s in low light conditions. Fair coloured irises contain less melanin permitting more light to travel through to the retina.
    • Many animals, especially nocturnal animals have a layer behind their retina called the tapetum lucidum. This tissue increases the amount of light captured by the retina, allowing these animals to have superb night vision. The tapetum lucidum is what causes some animal’s eyes to appear blue, green, yellow or even pink in photographs.

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    Now that you know the cause of red eye and what it is, let’s move on to learn how to avoid red eye. To read part two, please see Tips and Techniques to Avoid Red Eye.

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The Red Eye Effect

This article series will explore the red eye effect. What causes red eye? How do you prevent red eye from showing up in your photos? Learn the answers to these questions and more by reading these photography tips and techniques.
  1. Avoiding Red Eye – What Causes Red Eye?
  2. Top 5 Tips and Techniques to Prevent the Red Eye Effect in Your Photos