Can Mage Armor be used as a backup to regular armor?

[Cao Phen]

With the spell, Mage Armor, you gain a +4 AC (Armor) bonus that can effectivly be used against incoporeal creatures because it is a force effect.

Now let us say you have a Full Plate armor on your clunky fighter. I understand that if you cast Mage Armor, the only AC that applies is the highest bonus, the Full Plate. Now if a ghost smacks the clunky fighter with a touch attack, and the fighter has both the Full Plate and Mage Armor up, will the fighter gain the +4 AC from the Mage Armor since the touch attack effectivly ignores the Full Plate?

And if this is also possible, how about the same fighter with a Tower Shield and a Ring of Force Shield? If the Tower Shield becomes ineffective, will the ring kick in? Moreover, would the fighter with Shield Focus and Greater Shield Focus effectivly make that ring into a Ghost Touch Tower Shield?

[Grimmy]

As far as I know they overlap but don't stack but yes, the mage armor is still in effect vs incorporeal attacks.

[Mortalis]

I may be wrong about this, but I don't believe you can use a ring of force shield and a regular shield simultaneously, as the text states that you have to wield (i.e hold) the force shield.

As for whether or not you can apply shield focus to it, I'm not sure. I'd allow it, because it's not exactly game breaking. If you want to invest two feats and a ring slot to gain a weightless ghost touch shield that is otherwise unenchantable, go right ahead.

[Craig Frankum]

Theory on Mage Armor & Full Plate are correct.

You would have to choose the Tower Shield or the Ring of Force Shield. Either are wielded, though the option of either saves you a good bit on adding Ghost Touch to your tower shield.

[Cao Phen]

Ok, now with that, let us say you have the Tower Shield in one hand, the Ring of Force Shield in the other. With the description of the Heavy Shield, it states that because it is too heavy, you can not use your hand to do anything else. However, with the Ring of Force Shield, it is a weightless and emcumberance-free item. So would that mean a fighter with a longsword can carry thier gear like so?

Right Hand: Tower Shield
Left Hand: Longsword with Ring of Force Shield

[Mortalis]

Ring of force shield also says it's treated as a heavy shield, so I'm gonna say you can't to that. It's not so much about the weight of the shield, as the amount of control necessary to wield it, and the amount of space in your hand it uses up.

Kind of like if you wanted to hold a sword and carry a platter full of food palm up in the same hand.

You could always drop the longsword as a free action though, and with a leather weapon cord retrieve it as a free action.