Interesting replies. I thought I was pretty clear about how I compared the lenses. ha, ha.
I'm probably not any good at manual focusing though. I only did it for 15 years with a Nikon FE and Bronica SQA... So I'm sure that must be it.
Look, I have no doubt there are good, if not great, copies of this lens out there. Why else would I have bought it? The examples, like those posted above (even though they are examples with lots of light and I question whether they were shot wide open ? ) are what steered me toward this lens.
At f8, the lens was arguably as good as my 55-250 wide open at 5.6 - which is very good. At f11, the lens was tack sharp.
But I don't know who would buy a 100-300 f4 lens (a pretty heavy lens) knowing they'd have to use it at f8 or f11. Not me.
For those that say it was something I was doing wrong, let me ask you something...
How do you explain the lens got progressively sharper from f4 to 5.6 to 8 and then to 11 If you want to claim focusing errors, then how do you explain that nothing in the field of view, ahead or behind the front edge of the bird house, was in focus?
It was razor sharp at f11, so the lens was capable of producing a sharp image. Just not below f8 where I need it.