Oh, I know this isn't what it is suppose to be used for. I was at a park using the lens at its intended range and just shot this right before putting my 100-400mm on my camera. Overall, I know it is not a birding lens that should be used for such distant shots and would never intentionally take a shot that would need this much cropping.
I would like it to be this sharp from 50-100mm. Some of my shots are ok at all ranges but some are less so. I think maybe I will keep it but send it to Sigma to be looked at and see if it can be improved on in the shorter range or maybe I am just expecting too much out of it.