How sharp is it at f/4? F/2.8?Do you really think we didn't thought about that?
The comparison is between the 70-300 L and the 55-250. I believe it is surprising that the 55-250 is sharper at equal apertures and focal length, I really would like to understand why it is the case. Do you know why the 70-300 L is not as sharp as the lightweight 55-250 STM?