Yesterday I took quite a lot of photos with my 18-55mm kit, mostly I left the fairly wide, and with zooming, that means around f/4 - f/5 and I think I have noticed a trend. The sharpest photos seem to be when the focal length is around 30mm. Photos at 55mm are not as clear as at 30mm, but better than at 18mm. I was looking at dpreview's review of the , and they say is good 18 to 35mm "even wide open". A couple of questions come from this...
1. Since they say "even wide open", is it common for a to have problems wide open, and to benefit from stopping down?
2. Can different of the same model, have individual characteristics. I mean, could it be that mine does perform better at 30mm than at 18mm, even though the review doesn't mention it.
Also, all photos were taken with auto focus. Could it be that the auto focus got it a little wrong at 18mm more often than at 30mm, or is more likely a property as I have been thinking above? Maybe I need to do my own controlled testing. What would be a good method, and test subject. I imagine a and manual focus, then trying sets of focal lengths, each set at a different , all of the same subject?