For awhile i've been thinking about this question. how do i trade off sweet spot vs noise for the best picture quality. Especially in a picture that DOF doesn't really matter. As most of the lens the "sweet spot" is about 1 stop from the wide open( i don't want to hear how such and such lens is super sharp at wide open neither.), sometimes, with the given shutter speed, should i step down and crank the iso up, for best picture quality. My general take is that as long as ISO is 800 or less, i'm will to trade for the sharpness and crank up the ISO, any personal opinion, or you guys experience on that?
I just want to hear how you guys would do in that situation, given that extra light is not available. I do day/night landscape/portrait indoor/outdoor.

and then never worry about ISO again !
