Want to buy a lens for the 100d super that can be used in low light without a flash. Considering the older Pentax 50 mm f/1.4 or the newer 40 mm pancake lense. To be used for general purpose walking around photograpy where flash may not be permitted. A little concerned about the 50mm lens as there are some comments about it being too sharp (focusing problems) and also a lens that was not designed for DSLRs. Will it auto-focus with the 100D super? Does anybody have any thoughts on the subject or another lens recommendation?