Thank you all for your answers.
David, I did the first focus at F5, shot, and then, without moving the focus back to shoot F10. With a tripod, mirror up.
I did other tests shooting at a building that was considerably farther, more than 30 meters. And the result was the same. In the corners the quality was very poor at F5.
Finally I/ve returned the lens. I want to believe that its quality is higher, like the HC150 and HC80 already have.
I don't know if waiting for the new zoom HC 35-90.
What do you think David? Does the quality of the new 35-90 match for prime lenses like the HC50? What's price and availability of purchase?
Thanks very much.