I believe this lens is unusually prone to decentering defects. I am on my third copy, and all three have been far from ideal. The first one was blurry along the whole left edge of the frame, I returned it to the shop. The second was very blurry in the lower left corner, and the third and the current one is a bit "smudgy" in the lower right corner. I kept it since it was by far the best of the three, and simply learned to work around this flaw by never placing anything of interest into the affected part of the frame.