One guy showed me this Canon SX50 when I was testing out my 640 at zoo yesterday. He said he could reach 1200mm and get a crystal clear shot closer than my 600mm.
I did some reseach on that sub $500 Canon today and is very impressed with the telephoto capability.
Here is a link to some moon shots done by SX50
http://www.flickriver.com/photos/tedsla/tags/canonpowershotsx50hs/
Here is a Youtube video
http://www.youtube.com/watch?v=rU5zVcCCDBc
what do you think? The SX50 is small and light, much better than that 640 to carry on a Africa Safari.