I've been taking photos with a newly acquired PL 20mm mounted to my E-P3, and noticed the focus lag of this lens, particularly in low light. Since one of the primary reasons I bought the lens was for low-light shooting of candids, I'm now debating whether to return it for the 12mm or the PL 25mm. Before I did so, I want to make sure this is a lens issue and not a weakness of the m43 format contrast detection autofocus system. I thought it may be the lens since my kit zoom seems to snap into focus much more quickly. Is it the lens? Would the newer generation prime lenses be superior in autofocus speed?