I'm trying to learn rigging, so I started with very very simple character model. But when I weighted head vertexes and tried to rotate bone, the head became deformed as top of the head had lower weight then the bottom part of head.
Head bone rotated to front site:

Any idea what did I do wrong? I tried to follow video tutorial on youtube, where it worked correctly right away, but with a bit complicated character model.
Thanks a lot for all help!
