I'm still very new to photography, but I've been reading a lot of reviews of lenses lately. It seems to make sense when thinking about future lens purchases to always take away ~2 stops from the lens' advertised aperture. Does this make sense, and is this just how it is with lenses? Are there any lenses that are sharp wide open? I should add that I read reviews of Canon lenses only, and at that I don't generally spend time on L glass as it's out of my price range, but I have read a few and they seem to generally follow suit. I am more interested in consumer glass rather than professional, though. Just curious, thanks everyone.