For those that are not familiar with the term, it is the appearance of red colored pupils in the subject’s eyes in flash photographs.The example shown here is from an very definitive article on Red Eye at Wikipedia – Not all cases are this bad, but unless you are shooting a production of Dracula, even a little red eye can distract from a photo. The following example is a photograph of my granddaughter taken with a typical point & shoot camera. Although the amount of red eye in this photo is not all that bad, enlargements make it obvious.
Any cure for red eye should start with an explanation of why it happens. Red eye occurs when the light from the flash is reflected off the subject’s retina back into the camera lens. If you want to get more technical, check the Wikipedia article linked above. Anyhow, if you can avoid this reflection, you can solve the problem. A basic rule of thumb is that to avoid red eye you must separate the flash from the lens by 1/20 of the distance of the camera to the subject. It becomes more & more of a problem to do this as cameras get smaller because it becomes difficult to move the flash off axis with the camera lens. A few manufacturers have designed their flash heads so that they pivot or extend away from the body of the camera, but most built them into the face of the camera body. Cell phone cameras are particularly prone to producing red eye, but any compact camera will tend to have problems.
Some interesting things about red eye: It tends to be more of a problem in children & adults with light colored eyes. It is not the reflection of the blood vessels in the back of the eye; the color is determined by the color of the fundus, which is different in different animals. You may find green, amber, or even clear “red eye” reflections, depending on what animal you are photographing. Again, for people the reflection is red.
Some solutions:
- The solution most camera manufacturers use is to “pre-flash” just prior to the actual exposure. This first flash causes the subject’s iris to close, reducing the size of the opening to the eye, and a second flash a bit later is used to take the picture. The smaller the iris, the less light will be reflected. Although pre-flash is a simple solution, it can cause some problems. First, all your subjects will have small irises, whether or not that made sense in the overall image. It also makes it difficult to tell when the actual photograph is taken. If your subject drops out of the pose as soon as the flash goes off, and a pre-flash used to reduce red eye, the actual photograph taken a fraction of a second later may not be what you expect. It also adds more shutter delay between when you press the shutter button & when the actual photograph is taken. This can be a problem when shooting a moving target.
- Since the cause of red eye is a reflection of the flash into the camera lens, moving the flash away from the lens will help prevent it. While this may be impossible with a compact camera due to the limited size, using a fold out flash or, better yet, an off camera flash will help. Professional photographers often use flash brackets to move the flash unit well away from the lens.
- Many off camera flash units can be tilted so they do not directly illuminate the subject. The technique is called bounce flash since the flash head is usually aimed at the ceiling & the light bounced to the subject. This can be a very effective solution if your flash is powerful enough to provide adequate illumination after bouncing. You also need to insure that the color of ceiling or what ever you bounce you light from does not change the color of the flash. A red or blue ceiling may produce strangely colored faces!
- If you can’t bounce your flash, another helpful technique is to diffuse it. While there are commercial diffusers, you can also use theatrical diffusion material to make the apparent light source larger. A piece of theatrical “frost” taped over your flash works for just about any camera. Although a manufactured frost will work best, if it is not available a piece of plastic shopping bag, even a tissue can be used to cover the flash. Although you will end up spreading the light from your flash over a wider area, resulting in less light striking the subject, the diffused source will lessen red eye. This works well for close ups, however your on camera flash may not be powerful enough to use the technique for group images.
- Since the subject’s irises will be wide open, the worst cases of red eye occur when the subject and surroundings are dark. Increasing the level of the general lighting will cause the subject’s irises to close down, reducing red eye. This won’t work if your goal is to shoot a dark image with the subject’s irises wide open, but for general images avoid using flash in a dark room – turn on some lights!
- Finally, you might want to try to take the photograph without any flash. If the light level is so low the shutter speed ends up too slow for you to hand hold the camera without shake, use a tripod or brace the camera against a doorway, table, chair of other solid object. Natural lighting generally produces better photographs than the harsh shadows caused by the flash.
If you already have images with red eye, all is not lost. Most editing software includes fairly automatic red eye reduction actions. Even printing kiosks in your local drug store or Walmart will often have a red eye reduction mode. Although substuting black for red in the open part of the iris is better than nothing, it often results in unnatural looking eyes. Some better techniques with many of the major editing applications is available at the About.com page. In any case, there is little excuse for not fixing red eye, either during the picture taking process or with an editor afterwards.