Cost considerations aside, how do these three lenses rank on sharpness at f/2.8? I would be using them on a Canon 30D or 40D. Considering that I would be using them on a crop camera, would I really see any advantage that the Zeiss lens is renowned for in the corners? Is the Olympus lens usable at f/2.0? I would buy an appropriate focus confirmation adapter for whichever I choose. BTW, which brand of adapter do you recommend for $50-100? The things I would be using these lenses for would be daytime casual shooting (I like the 32 - 35mm perspective that these lenses will give better than a 'normal' 50mm perspective), daytime landscapes, low-light environmental portraits (where f/2.0 would really help), and most important, wide-field astrophotography (where the Olympus f/2.0 would also be great if usable at that aperture). I am still interested in differences at smaller apertures for daytime casual and landscape shooting, but the wide apertures are of key interest to me. As you may know, astrophotography will be the greatest test of these lenses' sharpness (light fall-off will also be very important here), particularly in the corners. Astigmatism in the corners ruins the sharpness of some supposedly sharp lenses--it turns pinpoint stars into seagulls. So considering these lenses will be used on a crop camera, which would you recommend? Has anyone tried all three, especially by any chance with astrophotography? Thanks.