I'm practicing rigging a finger. Why is the tip getting smaller when I rotate it? And hopefully someone has tips on rigging a hand/fingers.
If vertices of the tip of your finger were weighted 1.0 to the last bone and 0.0 to every other bone in the rig, you would have your tip moving exactly with the tip bone. As I can see in your screenshot, the tip vertices of your finger do not follow the bone completely: surely they are weighted to some other bones, and this is the reason why they get distorted. Also if a vertex is weighted 0.1 to one bone and 0.0 to every other bone, it will exactly follow the movement of that bone(Blender always introduces a "normalization" of values: even 0.001 is infinitely higher than 0.0). So, select all the tip vertices, assign them a weight of 0.0 relative to all others bones, and you will have no deformations at all of the tip and exact following of the tip bone movement.
a good topology is very important for smooth joints transformations (try to model your finger as pictured below and you'll see how smooth it bends)
a proper mesh weights assigment is crucial for realistic bend movement (I suggest you using the With Automatic Weights parenting option. Select your mesh, then the bones and press Ctrl+P-->With Automatic Weights. This'll automatically aassign the proper, blended weights for all bones)