I've probably seen it more on the ocular lens than the objective lens, but it is always my fault for either breathing on the lens when I'm about to take a shot or resting a cold rifle across my thighs and the heat off my legs condenses on the cold surfaces. I've pretty well solved the problem by using those flip up Butler Creek Storm covers (the ones with the clear glass windows) and by hanging my rifle on a limb or peg away from my body heat. Fogging in our scuba masks was solved by using some liquid stuff they sell or by spitting on the insides of our masks and rubbing it around. I not sure what that would do to a scope coating, so proceed with caution.
