Ed and I went out to Broemmelsiek in case any of my, or Stacey Thater's, students showed up for observing.  Jim and Yvonne arrived, and Jim showed us how to use the Jones-Bird 16" and its digital setting circle accessory.  WOW, large aperture with crisp images, can't be beat. 

Check out this link that discusses interesting optical paths http://members.chello.at/birkfellner/raytracing.html