Flash: Red-eye

Another common problem when photographing people using a hot-shoe mounted flash gun is red-eye. This shows as a distinctive red glow in the centre of the subject’s eyes.

Red-eye is caused by the flash illumination being reflected off the blood vessels at the back of the eye. If the Speedlite is close to the lens axis, these rays are reflected straight back to the camera.

Red-eye is most likely to occur in low-light situations, when the pupils of the eye are dilated (wide open). Photographing people at parties and wedding receptions can also be a problem, as alcohol has a similar effect on the pupils.

Many EOS cameras have a red-eye reduction feature. This works by shining a bright light at the subject for a second or two before the shutter fires. The light makes the pupil contract, reducing the risk of red-eye. However, the bright light can be distracting, and the delay between pressing the shutter release and the shutter firing inconvenient.

It helps if you can increase the level of light in the area before taking pictures. If this is not possible, try asking your subject not to look directly at the camera.

However, the real cause of red-eye is the close proximity of the flash unit to the axis of the camera lens. You can eliminate red-eye completely by using the Speedlite further away from the camera − often no more than 15cm to 30cm is enough. This can be done using the Canon Off Camera Shoe Cord.

If it is essential to use a Speedlite attached to the camera, and red-eye appears in some of your images, digital photography provides another solution. It is relatively easy to retouch the red areas, giving the eye a natural appearance, using imaging software such as Adobe Photoshop.