I've just read on another thread that most lenses are sharpest around their middle range of apertures eg f8 or f11. I agree that this is the case. My 2 L lenses both have a constant aperture of f2.8 and i use them at that end quite a lot. But in order to get the sharpest image from my lenses, i should set my aperture to around f8 as previously mentioned. The problem is then the light. At f2.8 light isn't so much of an issue. But at f8 it is. So i could easily increase the ISO to compensate. I know there are times i'd want f2.8 and others i'd want f8 so i'm talking about general, run of the mill shots on my 24-70 L lens. The 5D has incredibly low noise even at 1600 but the question i have is this: Would i be better to shoot at f2.8/3.2 and ISO 100 or get a sharper image at f8/f11 but have higher ISO eg 1000 or 1200?? if i get a chance i'll try a comparison over the next day or so and post them but what do you guys think?