Binoviewers - internal optical structure

[Avocette]

I have been searching on all posts about binoviewers to try to get to grips with the optics involved. Their performance with different types and models of scopes seems to be difficult to predict and even when trial and error is used, the results (apparent magnification/back focus distance etc.) seem unexpected. Can someone explain what the various optical elements are please? It seems likely that there is a half silvered light path splitter and some prisms but what about lenses?

[Avocette]

I've found the first answer to my question http://en.wikipedia.org/wiki/File:Binoviewer.png but would welcome any further info!

[YKSE]

You may find some info in links in the end of this review:

http://www.iceinspace.com.au/42-717-0-0-1-0.html

[Avocette]

Thanks Yong - a very good resource!