Would it be beneficial to test often used focal length settings of a zoom for the best aperture settings for those various lengths? For instance on a 14-42 take test pics at maybe 14, 20, 25, 35 at various aperture settings to see what gives the best pic for each. Reason I asked I took a pic at 25 and 35 at 5.6. 25 was surprisingly sharp, but 35 was not. Later read on SLgear that at 35 you need to step down to f8.