DIY Network

Avoiding Photo Red-Eye: Pre-Flash and External Slave From "The Whole Picture" episode DTWP-109

	The all-too-common problem of red-eye can ruin what would otherwise be a good picture.
	An external slave-flash, which removes the flash slightly away from the camera itself, is one way to help reduce red-eye. A sensor on the slave triggers the external flash when you press the shutter.

NOTE: Images on this page may be enlarged for enhanced viewing simply by clicking on them.

Do a number of your photos feature that unintended "special effect" known as red-eye? Professional photographer Erin Manning understands how the red glare in a subject's eyes can essentially ruin an otherwise perfect picture. In this digital-photography lesson, she explains what causes red-eye and provides suggestions for several ways of avoiding it. Specific topics include the red-eye reduction feature on digital cameras, how to use an external slave-flash and the advantage of using a bounce flash to illuminate a room.

But even if you master all these techniques for avoiding red-eye, what about those pictures you've already taken in which your subjects' eyes look like little red traffic-reflectors? Even for those, all is not lost. In the "digital darkroom" portion of the lesson, Erin shows how eliminating red-eye can be just as simple as the click of a mouse.

Materials used in this episode:

Digital camera with pre-flash mode
Camera owner's manual
External slave flash, adjustable for bounce-flash
Computer with image-editing software

advertisement

Figure A

Whence the Red Eye?

The phenomenon of red-eye is particularly prevalent when shooting with an on-camera flash in low-light situations. In these cases, the pupils of your subject's eyes dilate in order to adjust for vision in the absence of bright light (figure A).

When you photograph people in this situation, particularly if they are looking straight toward the camera, the light of the flash is actually reflected off the reflective retinal surface at the back of the eye. The reflection shows up in the resulting photo as a red "glow"--sometimes subtle, but sometimes quite distinct and distracting.

Simple point-and-shoot cameras are particularly susceptible to causing red-eye because the flash is so close to the lens (figure B). One relatively "low-tech" technique that may help is to use a diffuser of some sort over the flash (figure C). Experiment with some digital shots in low-light using a diffuser to see if this helps.

Another simple way to reduce the occurrence of red-eye is to bring up the lights in the room. In that way, your subjects pupils will narrow and the reflection will be less likely to occur. Of course, if the lighting is bright enough you may be able to shoot without a flash. But depending on the shooting situation or the effect you're trying to achieve, these may not be viable options.

Figure B

Figure C

Figure D

Using Pre-Flash

One simple tool for reducing the chances of red-eye effect is the use of built-in red-eye reduction feature on your camera. This works by giving off a quick pre-flash of light just before the actual flash that accompanies the activation of the shutter. The intended effect is that the pre-flash causes a reduction in the size of your subject's eyes an instant before the picture is taken, thus minimizing the red-eye effect. This feature is simple to use. Simply navigate through your camera's menu to locate the red-eye or pre-flash selection (figure D).

Using pre-flash can help reduce the occurrence of red-eye, but it's hardly fool-proof. While the pre-flash is intended to reduce the size of the pupils, often its effect may be to cause your subjects to blink. When the actual flash goes off, you get closed eyes instead of red ones.

Instead of a pre-flash, some cameras shine a bright light into the subjects eyes seconds before the actual flash goes off (figure E). You may find this to be an effective way of capturing your subjects without red-eye (figure F).

Figure E

Figure F

Figure G

Unfortunately, this may cause the same result as pre-flash--catching the subject while blinking (figure G).

Another reason these techniques are not foolproof is that some peoples' pupils react more slowly than others. For some subjects, the pupils may still be dilated when the actual flash fires.

Pre-flashes also limit you when it comes to taking candid shots. The bright flash warns the subject that a picture is about to be taken, so you end up loosing some of the spontaneity.

In short, pre-flash or built-in red-eye reduction features are handy, but they may not solve the problem entirely. But as always with digital photography, it costs little or nothing to take lots of test shots. Experiment with different lighting situations using the pre-flash and with it turned off. See what works best for the types of pictures you take. You can always discard the ones that you don't like.

Red-eye caused by direct flash.

Using the pre-flash or red-eye reduction feature on your camera may help prevent red-eye in some cases.

	Figure H
	Figure I

Using an External Slave Flash

As mentioned, most digital point and shoot cameras come with a built-in flash, and that's part of the problem when it comes to red-eye. The flash being so close to the lens is what is creating the unwanted reflection. One solution might be an external slave flash. This is a great accessory, especially for photographers who take a lot of nighttime pictures or deal with low light.

A slave flash is an external, self contained, battery-operated flash unit (figure H). It has a built in system that triggers the external flash when your camera's internal flash goes off. Most connect easily to your digital camera using an included bracket. The idea is to get your flash further away from the lens, which will help eliminate red-eye by not firing the flash directly into your subjects' eyes. Since the slave-flash is battery operated, you'll want to carry extra batteries to make sure you don't miss that perfect shot.

In some cases, you may need to cover your camera's internal flash with a diffuser or with translucent paper (figure I) to make sure that it doesn't reflect off your subjects' eyes.

	Figure J
	Figure K

The slave-flash is typically triggered by the camera's internal flash by means of a sensor on the slave unit. Most can be used either on or off the camera bracket.

Some slave flashes will work only if your camera's pre-flash feature is turned off, while others work in conjunction with the pre-flash. Some models require that you set the slave flash according to how many flashes or pre-flashes your camera fires (figure J).

Check the owners manual to see how yours works. Also, before purchasing a slave flash, do your homework and make sure that the one you select is compatible and will work with your particular camera.

Try taking some pictures using the external slave flash and see if you get better results (figure K). Remember, the further away the flash is from the lens, the less likely you'll get red eyes looking back at you.

Pro Tip: Professionals typically prefer to use slave-flashes that work only when the pre-flash function is turned off. In that way, the spontaneity of candid shots is not lost.

RESOURCES :

PC Photo magazine
Website: www.pcphotomag.com
Online version of the magazine devoted to digital photography and related technologies.

The Complete Idiot's Guide to Digital Photography
Model: 002864235X
Author: Steven Greenberg
Order this book from Amazon.com.
Prentice Hall
Paramus, NJ 07652

Digital Photography For Dummies
Model: 0764506463
Author: Julie Adair King
Order this book from Amazon.com.
Hungry Minds, Inc.

Complete Digital Photography
Model: 1584500077
Author: Ben Long
Order this book from Amazon.com.
Charles River Media
Website: www.charlesriver.com/