That's great to know, thanks. That explains the nice colour of the sky. I feared I might lose too much light with a CP filter, resulting in too slow a shutter speed. But appearently that won't be an issue. I'll be shooting with a 50D too and a 300mm f2.8 with drop-in CP filter, likely with 1.4x or possibly 2x extender. I missed all the recent local air shows, so I'll have to wait until next year.