I picked up a second hand 17-40L passing through Bangkok and am using it on my 5D3. I had a bit of a play with it in the shop and thought it was pretty sharp and it is in the centre. Looking at photos I've been taking in my travels (still on the road so not well placed to post any) I've found the corners lack any real sharpness at 17mm until I stop down to around F9 and F11 for decent sharpness. Actually I expected that for the wide end, but I didn't expect the substantial border (and not just the extreme borders) softness I get at the long 40mm end... I'm worried there might be some sort of misalignment as I find softness on the left side when focussed on infinity and on the right side when focussed on close objects. Again I need to stop down to around F11 to even this out, but by then it's as much at the expense of centre sharpness as uplift on the borders.
Anyone else experience something like this or think normal? Unfortunately no chance to take it back so I either live with it or get is serviced?