Well Sherlock is closer to him, I would believe his eyes would have an easier time focusing on him.<<<You know this was supposed to be a cute post<<everybody has the chance to make things a little more scientific<<<The Sherlock Fandom
When he shot Magnussen, it wasn't just to protect John. It was to protect the woman who shot him and lied to John. Because although she shot and lied and betrayed, John still loved her, therefore Sherlock loved her. The three of them are so amazing.