Armor Group Focus

ARMOR GROUP FOCUS [General]
Select one armor group which you are proficient with.

Prerequisite: Armor proficiency (selected armor group), character level 1st.

Benefit: You gain a +1 bonus to AC and DR/adamantine while wearing an armor from the selected weapon group.

Special: This feat can be taken multiple times; its effects can stack or apply to a new armor. Each time it is taken, its character level prerequisite increases by 5 for the purposes of stacking but not for selecting a new armor group.

Comments
The original Armor Focus feat is hardly beneficial and overlyfocused. A character wearing a chainshirt and trading it for chainmail could lose the benefits of their years of armor training. A better use of this feat would be to add to both attack and damage resistance as well as use the Armor Groups variant which merely classifies armor into six varieties: Light Leather, Heavy Leather, Light Mail, Heavy Mail, Light Plate, and Heavy Plate.
 * Light Leather: All light armor made of cloth, leather, wood, bone or other creature hides or vegetation.
 * Heavy Leather: All medium and heavy armor made of cloth, leather, wood, bone or other creature hides or vegetation.
 * Light Mail: All light armor made of chainmail, ringmail or scalemail.
 * Heavy Mail: All medium and heavy armor made of chainmail, ringmail or scalemail.
 * Light Plate: All light and medium armor made of plated metal or stone.
 * Heavy Plate: All heavy armor made of plated metal or stone.