My first try:

This one ended up being fairly simple. I didn't really plan the center part well, so that messed up my focus, but it was still nice to work on.

 

My 2nd try:

I thought more about what I wanted to draw for each ring. Even though I planned more, I ended up drawing almost all of this one directly with ink. I only penciled out a couple of rings.

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Note: I don't have a scanner right now, so I had to take pictures of the drawings, and try to fix the exposure in Photoshop. That's why parts of them look a little washed out.