Resolving Power
The finest detail a lens or film can distinguish, traditionally expressed in line pairs per millimetre.
Measured in
lp/mm
In depth
Resolving power alone is a poor guide to how a lens looks, because a lens can separate very fine lines while rendering them at such low contrast that they are invisible in a print. This is why MTF has largely replaced raw lp/mm figures in serious testing. The number is also limited by whichever is worse, the lens or the recording medium.
Examples in practice
A fine-grain film resolving 150 lp/mm is wasted behind a lens that manages only 60 lp/mm.