Quote Originally Posted by MattKing View Post
Actually ...

The DIN and ASA standards were combined into the modern ISO standard. It continues to be correct to specify film sensitivity as 100/21 where 100 is the arithmetic sensitivity (as ASA was) and 21 is the logarithmic sensitivity (as DIN was).

We most commonly see just the arithmetic part.
A question just flickered across my frontal cortex: it seems odd that DIN should be a base 3 logarithm... is it associated with the dB concept that 3dB is the difference in amplitude that is detectible by the human ear..( I dunno, not a physicist)

David