Conditions:
- bright sun, clear skies, 87F
- dry newspaper, 1 week old
- Leitz Summicron 50/2
Procedure:
- focused lens at infinity, f/2, focus sun on paper ~10 sec
- focused lens at infinity, f/16, focus sun on paper ~10 sec
Results:
- no burning
My previous belief that the lens will burn a hole in the shutter appears to be wrong, although I cannot explain at this time why.
Leica doesn't explain what "long periods" are, perhaps I didn't hold focus long enough.