"Afton has a minor shielding skill, but it is limited by the fact that he cannot project it outside of himself. He has the ability to make himself invisible to attackers, but someone with a strong focus can see through the illusion. A person standing directly behind him can be hidden, too, but this is not a very reliable safeguard."
Afton's power allows him to be unseen by others. This power is mainly an illusion that works by making pursuers think he is invisible or unable to see him when they look his way.
It can also be used to hide someone if Afton is directly standing in front of them, but this protection isn't as reliable as a defensive power that provides protection for other people.
Limitations
It has been explained that this power is very limited and much weaker than a real shield in that it can only "shield" the user. And if someone has a strong ability of focus, he can easily see past the invisibility. Since this power takes place in the mind, it most likely has no effect against Bella's shield.
History
Afton's gift provided him a position within the lowest ranked guards of the Volturi. However, his position was kept permanent due to his more powerfully gifted mate, Chelsea, who maintains the coven's organization with her power to control emotional bonds between people, which makes her a key member to the coven's functionings.
Bella Swan's power is to block any power that affects the mind. These two powers are similar in a way that they are both made to protect the bearer. Since Afton's power works on a mental basis, it can most likely be rendered impotent by her shield.
Fred's ability of physical repulsion causes a person to not be able to look at him making him, in a sense, invisible to that person. He can also use this power to make his targets unable to think of him.
Renata's power to divert physical attacks by making the attacker want to go the other way. This power is similar in its defensive way where it makes an attacker unable to run in his target's direction without losing his focus.
