Originally posted by Marc Sabatella I think my DA15 is probably my sharpest lens overall, followed by my DA70. While I have the DA40 and M50/1.7 and see them getting a lot of votes, I don't think mine quite compare to the 15 or 70. But like most here, I've never really done any sort of controlled test - I'm going mostly by the results I get in typical use and how they tend to strike me. It's images from the the 15 and 70 that are most likely to take me aback.
I've been thinking about this and looking at more images, and I'm going to amend this a bit. What impresses me most about the DA70 is the sharpness it can get at relatively large apertures, and this feeling ends up being enhanced by the shallow DOF I get from those apertures at that focal length. I think that's the source of much of the "wow" I get from this lens.
But stopped down to f/5.6 or f/8, the DA40 really does do at least as well. Unfortunately, my images from the M50/1.7 don't report aperture, but I know I tended to use it mostly for low light, so very few of the images I have from it would be at f/8. My A50/1.7 does report aperture, but I haven't used it nearly as much because I got it around the same time as my DA40, which I definitely prefer overall (just for the focal length, and of course size, AF, etc), so it's hard for me to include the 50/1.7 in the comparison.
I've found it interesting to search for all portraits & candids done with these lenses, find examples shot in good enough light to give me fast shutter speeds at low ISO, with the face filling the frame in roughly the same way, then examine them at 100%. Obviously, I'm shooting from different distances with different lenses in order to do this, but I'm pretty sure that's how you'd want to compare sharpness: with a subject the same size in the frame (that's how resolution tests are done, isn't it?). It is of course difficult to judge corners using portraits, but it's the one subject where I can easily find at least some reasonably comparable images from each lens. One thing that surprised me is finding the M28/2.8 noticeable sharper at f/8 than either the M100/2.8 or M135/3.5. Maybe it shouldn't have - I guess it's normal for wider lenses to have better resolutions scores than telephoto lenses.
And in fact, the more I look the more I'm convinced the DA15 really is my sharpest lens overall. Again, it's tough to judge corners by looking at portraits, but at the center, the DA15 is pretty equally amazing anywhere in the f/4 to f/8 range. Photozone's MTF scores show it actually doing better in the center at f/4 than f/8, and I can't dispute that. And it supposedly peaks at f/5.6, which now makes me want to shoot that aperture more than I otherwise would.
But of course as most people know, the DA15 has a reputation for much softer borders until f/8. I still haven't done any real controlled testing to see how much of this perception is just field curvature & DOF issues (photozone acknowledges it is an issue in their own measurements). But one thing I have noticed is that when I do happen to get something at the edge of the frame in focus at f/4, sharpness is really much better in the *middles* of the borders (ie, the 12:00, 3:00, 6:00, and 9:00 positions) than some sample images would lead you to believe. It's actually only the extreme corners where it seems to require more stopping down to get the kind of results one might want.
Anyhow, just some random thoughts.