If you cast a spell without a staff:
say:
You are a lvl 25 Char.
You cast a lvl 20 Spell.
<manacost>/<spell>+<lvl>=<mana-cost>
100 / 10 = 10
100 / 10+10 = 5
Here's the example.
If you cast a spell costing (normally) 100 mana,
you divide on your Char. Lvl, which makes it cost ten, but with a focus staff, you might double your lvl, and the spell cost 5.
This is only an example on how it could be calculated. I'm not saying this is the way it's calculated specifically, but these are the basics.
- W.Haven