Shield focus, Benefit: Increase the AC bonus granted by any shield you are using by 1.
the word using is key with this feat. Its not wearing, wielding or holding. Using definition is take, hold, or deploy (something) as a means of accomplishing a purpose or achieving a result; employ.
Spell are a form of deploying are they not?
Also if it was not a shield, why would it add this at the end of shield spell. "The shield has no armor check penalty or arcane spell failure chance." if it was not a shield.
Shield: A shield bonus improves armor class and is granted by a shield or by a spell or magic effect that mimics a shield. Shield bonuses stack with all other bonuses to AC except other shield bonuses. A magic shield typically grants an enhancement bonus to the shield’s shield bonus, which has the effect of increasing the shield’s overall bonus to AC. A shield bonus granted by a spell or magic item typically takes the form of an invisible, tangible field of force that protects the recipient. A shield bonus doesn’t apply against touch attacks.
In the end its up to the GM if they allow the extra +1 ac after that point it don't matter.
