Originally Posted by
Lenny Eiger
It does. I once had it explained to me by a physicist. (I am not a physicist, so this is for explanation only, I can't say I did this test myself.)
Here's what he said: It has to do with the difference between what happens to one of these grains of silver salts from being hit by photons. If they are hit by enough photons, they move from the "undevelopable" to a "developable" state. We know what happens in the developer....
However, at some levels of energy (less photon strikes) the grain moves to a third state, which is "I don't know". It may like the bowling pin that gets hit by the ball but not with enough force and so tips back and forth, and will either fall over, or right itself.
In the case of "not enough light" this third state rules. Some of the grains move back from the precipice of being developable and become undevelopable again.
The less the amount of light, the more of them are in the state where they might change back, and so there is a predictable rate of reciprocity failure. I don't care what AA said, it's a failure of a grain to turn to the developable state by being hit with photons. Failure is a fine word, IMO. I think the distinction is fairly meaningless.
At any rate, I hope this helps you understand what happens at the toe of the curve, at least. What happens at the top is a different matter.
Regards,
Lenny