John,
I fully agree that low light levels are a major contributor to the redeye
problem. But I have to wonder, how does the film speed/flash level play into
this. Given a certain level of darkness and 2 film samples of different ASA,
if the exposure is correct, wouldn't the proportion of reflectance from the
retina to reflectance of the subject's face be the same? And wouldn't that
net the same image level on the film? Of course, changing the f-stop would
affect the depth of focus, and the shadow depth, but I suspect the redeye
would be constant in intensity.
My understanding is that the darker the room, the wider the subjects
iris's are dilated, thus making red-eye more of a problem. This would
be regardless of film speed etc. In other words, dark room, pupils
wide open - bad red-eye. More light in the room, pupils contracted,
less potential for red eye. Still a good idea to use off camera flash
if possible and also to soften the light by bouncing or diffusing.
Does anyone know if it is true that the "red" is caused by the blood
capillaries in the back of the eye?
peter
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