More detailed weight painting? Hi i was weight painting for a finger and I couldn't help but notice it doesn't paint anything until i hit a certain spot and even then it paints all around it!

apparently brush size doesn't help. any ideas?
Weight paining is actually just assigning weights to vertices.  So you will need to add more geometry to your mesh.  I would recommend going into edit mode on your mesh, selecting all with A, and hitting W > subdivide or subdivide smooth.