Red Eye Explained (And How To Prevent It)


Red Eye, as you probably are aware, is the phenomenon in which the human subjects (or even animal subjects) in your photos appear to have red pupils.  While the “demon child” look might be amusing for a short while, the reality is that Red Eye has ruined more photos of your loved ones than you’d like to admit.  Thanks to the digital world, fixing this in post processing is fairly easy.  Most cameras also have a red eye reduction flash setting.  But the phenomenon itself is often misunderstood, and many find the fix in post processing.  But it doesn’t have to be that way.  There are several ways to prevent red eye, but first you need to understand why the phenomenon occurs.

What Causes Red Eye?

Red Eye is caused by the light from your flash reflecting off the back of the retina of the eye.  The light traveling into the eye is reflected back at the same angle in which it hit the retina.  When the flash is mounted too close to the lens, the reflection angle is very small and the camera lens picks up the reflection.  The effect happens more often in dim light when your subject’s pupils are wide open.  The human eye works very much like a camera lens (an obvious design influence, the eye).  In low light conditions, the eye responds by opening up its iris, which is pretty much like the eye’s aperture.  By doing so, the iris appears larger, and more light can be let in.  Inversely, more light can be reflected back at your camera, and the red eye is much more prominent.  So now that you understand what causes red eye, let’s talk a little bit about how to prevent it in the camera.


Preventing Red Eye

There are many ways in which we can prevent red eye.  There are advantages and disadvantages to each solution.  Depending on your current situation, one solution may be more appropriate than the other.  Understanding all of the possible solutions will only help you to select an appropriate method which will result in a better photograph.

Red Eye Reduction Flash – Almost all digital cameras containing a built-in flash have a red eye reduction flash option (though some may call it by a different name).  A red eye reduction flash actually consists of several short flash bursts before the main flash fires.  The shutter only opens for the last flash.  The purpose of the first few flashes is to constrict the pupil so that less light can be reflected off the retina.  There is still a chance that a small amount of red eye will occur, but more often than not, this will eliminate the phenomenon all together.  There are two disadvantages to this method.  First, your subjects will be confused by the red eye reduction flash.  I’m sure most people are aware of the flash by now, but you will still find people that break their smile after the first flash.  Or worse, the shutter might open mid-blink and closed eyes are far worse than red eye.    The other disadvantage is a psychological one:  Wide open pupils appear warm and welcoming whereas small pupils appear cold – I feel they look almost evil.  If you’re close enough to clearly see the pupils, red eye reduction flash shouldn’t be your first choice.

Off Camera Flash – An after-market off-camera flash (be it a studio strobe or a portable flash) is one of the best and easiest ways to solve the red eye problem.  When an aftermarket flash is mounted to your hot shoe, the reflection bounces off the retina at a much wider angle, and the chance that your lens will pick up the reflection is greatly reduced.  Better yet, if you bounce the flash off the ceiling, there is almost no chance of retina reflection.  Even better still, get the flash off your camera entirely.  Not only will you avoid the red eye problem, but you’ll get better lighting.  The disadvantages here are cost and compatibility.  From a pure financial perspective, an aftermarket flash or studio strobe is going to cost you some extra cash.  This is, in my opinion, a minor disadvantage as the benefits far outweigh the cost.  As for compatibility, I’m sorry to say that those of you with a point-and-shoot camera, and even some of the bridge cameras, will not have this option as aftermarket flashes will not sync with your cameras.

Diffusers – Diffusers are readily available for your aftermarket flash or studio strobe, but you can also fashion a diffuser for your on-camera flash out of tissue paper or sheets of diffuser gels that you can cut to size.  Not as professional looking, but it works.  Diffusers soften the light by splitting it up in all directions.  The light through a diffuser is not unidirectional in nature, so less light is actually bouncing off the retina.  Red eyes disappear..

Natural Light – Natural light from the sun is probably the best and easiest way to avoid red eye all together.  If you have a choice, use natural light and a few reflectors.  You’ll avoid the red eye problem, and you’ll end up with better quality light.

Final Thoughts

Regardless of which technique you use, you must always consider the comfort of your subject.  Bright light, in general, is discomforting to humans.  The best thing you can do is to keep your subject informed.  If they can expect multiple flashes, let them know.  It doesn’t hurt to do a few test shots so they know what to expect.

I hope this helps clarify the issue of the red eye phenomenon.  It is my hope that you will take a few of these thoughts into consideration the next time you’re shooting portraits, formal or informal.  As always, if you have anything to add or if you have any additional thoughts, feel free to reply to this post.


About Author

D. Travis North is a professional Landscape Architect, a Freelance Photographer and founder of Shutter Photo. Ever since he picked up his first SLR, his father's Nikon N2000, he's been hooked on photography. Travis likes to photograph urban environments, architectural details and has a new-found interest in close-up photography. His work can be found at D. Travis North Photography. Follow Travis on twitter: @dtnorth.

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