Last night I stood out on my deck with my Nikon D800 and Nikkor 200-400 lens, and took a few photos of the moon. This wound up being one of my favorite images.
ISO 400, 1/400 second at f/11. Lens racked out to 400 mm, with camera set on DX crop for an effective focal length of 600mm. Image was cropped in Photoshop and sharpened slightly.
I tried adding my 2x teleconverter for an effective focal length of 1200mm, but no matter what I did, I wasn’t able to get a reasonably sharp image.