[[1ponders] (Paul)]

here are a couple of sites to have a look through.

http://www.skywatchertelescope.net/s...1=1&class2=102
http://www.saxon.com.au/m_refr.html
http://www.telescope.com/control/pro...oduct_id=09895
http://www.skywatchertelescope.net/s...1=3&class2=302