Reducing that red-eyed look

Press, 23 July 1986, Page 21

Reducing that red-eyed look

If your friends look redeyed when you photograph them using flash, is it because of the late nights they have had, the film, the processing, or some mistake you have made? None of these. The red is a reflection from the retina, the light-sensitive layer at the back of the eye. Those most likely to show red-eye are children and fair complexioned people. Dogs and cats eyes reflect blue. Since the reflection is from the back of the eye, the light must go in and out through the pupil, which is actually a hole in the iris (the coloured ring round the pupil). If the flash is very close to the lens, the reflection will be picked up by the lens; otherwise, it will go to one side and the red-eye effect will not appear on the film. The larger the pupil, the greater the likelihood that the reflection will be caught by the lens. Pupils are larger in dim light, so if the flash is close to the lens (as in all compact cameras and many others), the surrounding light should be as bright as possible to cause the subject’s pupils to contract. The flash does not Itself affect the pupil size as it strikes too quickly for the Iris to respond. Red-eye is more likely to appear at a distance from the camera than close to it, as the angle from flash to subject to lens decreases as the subject moves away. This effect must be weighed against the general need to get in close (to capture the subject rather than the background), but not too close (to avoid facial distortion and the “tadpole effect’’ — receding parallels). Red-eye can be reduced, and perhaps prevented, by putting a diffuser over the flash element. A handkerchief or tissue will probably be adequate. There are many pitfalls, however.

For one thing, the diffuser must cover the element and that alone,

else it is liable to cover such things as the lenses of the automatic systems and maybe a part of the main lens. For another, many flash units have a fixed output; with these, cutting down the illumination of the subject is likely to result In serious underexposure. On the other hand, the diffuser makes the light from the flash much less directional, so filling the shadows which can be very harsh with bare flash. A further warning, though: do not use a diffuser if the walls or other surfaces are highly coloured, or your photograph will be tinged with that colour. Red-eye is less obvious, and may disappear altogether, if the subject is not looking at the camera. If you are photographing one of your friends you will mostly want him/her to look at least in the general direction of the lens; but an alternative style is when the subject is engaged in some typical interest, when the pupils will be sideways-on and so admit much less light. The key element in minimising the chance of red-eye is to distance the flash from the axis of the lens. A flash element which is to the side of the camera, or pops up, is better than an element which is squarely in the upper corner of the camera front.

Popping up is in fact the best, for another reason. We are used to light coming from above — in fact, lighting from below is a stock stage method of pointing up the villain. On SLR cameras there is normally a hot shoe which carries an independent flash unit, taking the element sufficiently far from the lens axis to avoid red-eye. Possibilities and problems associated with off-the-camera flash will be dealt with in a future article.