300mm f/4 L issues with 5DII body
The lens is about 2.5 years old. I tried to recreate the problem by leaving the lens and camera outside for a few hours in cold temps and then tested it indoors, and it still worked fine. I'm just not sure what's going on here.
It may very well be the Iris however, since when I tested indoors, the lens was most likely wide open, and my wife often uses it wide open or one stop down at most to keep the shutter speeds high.