Does anyone have any samples of this lens at 18mm f/2.8? I've seen some shots that show its super sharp at 50mm at like f/2.8 but thats pointless for me as I have the Canon 50mm f/1.8. I'd be buying it to have the f/2.8 constant aperture through out the 18-50mm range. The samples I've seen online kinda make me wonder. I haven't actually seen a sharp shot at 18mm. I've seen some stunningly sharp shots from the 24-70 so I'm more tempted by that lens but I would prefer the range of the 18-50.