HELLO ALL,HOPE SOMEBODY OUT THERE CAN HELP,IF POSSIBLE DOES ANYBODY KNOW WHAT THE DIFFERENCE IS BETWEEN THE CANON EF400MM F2.8 MK1 LENS TO THE CANON EF400MM F2.8 MK2 LENS,GOT A MK1 OFFERED,AND JUST WONDERED IF I SHOULD LOOK FOR A MK2 VERSION.ANY OFFERS OF INFO WILL BE GREATLY ACCEPTED.CHEERS PAUL