Hi Steve

Would suggest to test you lens Its easy. Set up a target like a newspaper and check results. Would try wide open and stopping down always with enough shutter speed. btw test both close up and far away ... there could be a variation.

Mine is very sharp and have no problem acquiring focus for bif. Have been nailing purple martins !!! btw the lens will even produce sharp results with converters contrary to popular belief.

When the lens first came out, years ago, there were some that were soft. Current crop seems fine.