> just a quick interjection - this rule applies to a point source light, no > debate whatsoever but unfortunately it doesn't apply when a lens or > collimator of any desription is involved. Karl Absolutely and uncategorically right!. The "inverse square law" has as much clout as the "rule of thirds" when it comes to real world photography. It's a good starting point but it's far from the whole truth. A little bit of knowledge and all that :o) It does indeed only apply to hypothetical point sources of light. Obviously, for very small real sources a long way away it's a good approximation. A light meter is a better one :o) Bob
