Stan. I did go to a retailer, London Camera Exchange, but I didn't take a wide angle, but a 50mm f1.8 and aimed towards a book shelf and the books. I shifted the focus point from far left to far right and top to bottom, zoomed in on that point on each image and all were sharp. I guess that's not perhaps the same test, but I think it was a sensible attempt. When I got home I tested it with my 16-35mm at 16mm and all was fine.