After checking several boxes and confirmed that the aim was indeed defective, I used the Amazon exchange procedure.
Three mouse click, a small comment on the problem and in the moment Amazon sent me a new lens received after 48h.
It is thanks to this reactivity and professionalism that I buy here with confidence. Five stars to Amazon.
Regarding the new objective received, it is perfectly consistent with the required quality. A purchase of an exellent value for money. Focus quickly and accurately, if a little noisy, and good image quality to excellent depending on the focal length settings / remote MAP / opening. Five star.