Thank you, some good reading there, and it answers my questions, well most of them. It doesn't touch on what panoptics or radians are, how they compare with other designs, when to use them, strengths/weaknesses etc.
I found this page as well, which talks about exit pupils and other things, and is quite good (at least I think so):
http://www.bpastro.org/index.php?pag...ting-eyepieces
Dave