Last night, the moon happened to be in a good phase (not full) and a good location (fairly high up at around 10pm) in the sky to photograph. I took a stream of images with the 600 and put them together in an animated GIF and you can see just how poor the viewing was. There is a shimmering or rippling effect over the surface of the moon and is this is an example of somewhat poor Astronomical Seeing.
I did manage to stack the 9 images I captured in Photoshop and then did some careful sharpening to try to extract detail. Pictured above is my result.
Technical Specs: Canon 1D3, 600 f/4 IS + 2x + 1.4x TCs (1680mm equiv.), f/11, 1/80s, ISO 800 (9 image stack).