My budget was a bit lower than Symtex's, so I got the Baader solar film. Reflects most light and what's left over directly from the sun is comfortable (and safe!) for imaging.
It comes in an A4 sheet, so I followed their instructions and mounted it on cardboard to fit a 78mm filter as used on the 100-400 but easy to step up to if I want to use something else later. That used about half a sheet, I'm not sure I got enough left over to do the same for my scope now. Doh!
Anyway, here's two samples for now.
100-400L x2 for 800mm. f/11 1/1000s ISO800 cropped and resized.
100-400L x2 for 800mm. f/11 1s ISO100 resized.
The second one was for fun. There was patchy cloud getting in the way most of the time.
Side note: I accidentally left the light pollution filter on from last night at first. I think that gave a better contrast detail than after I removed it, but I've not looked into it in more detail yet.