Originally posted by Docrwm Thanks guys. Yes, on the K-x the maximum manual lens setting is also 800mm.
So if you use a 500mm and 2x TC, just enter 800mm anyway. That's close enough. Then put the rig on a tripod and switch-off SR, because 800-1000-1200mm is just about impossible to deal with handheld! My Rubinar Makpo 1000/10 mirror (1760g) *can* be handheld on a bright day, but it's not much fun.
Tripod, sandbags, whatever it takes to stabilize it, whew!
I haven't bothered putting the much smaller 500/8 on a 2x TC because 1) CIF doesn't work at f/16 and 2) I get better IQ with cropping than with a TC. Also note that LONG lenses aren't good for distance shots in warm / murky atmosphere -- air roils, particulates diffract, images are pale and fuzzy, etc. I mostly use my 500/8 for people-shooting in urban settings, with subjects usually less than 100ft away.