I had been wanting to try this since I got the Mk II. This is a composite to 8 images shot with the 400mm f2.8L IS + 2.0X + 1.4X TCs. Add this to the 1D Mk II's 1.25X FOV crop and the FOV is similar to a 1400mm telephoto on a normal 35mm Camera.
The problem is that the Earth rotates and the Moon goes through the field of view very fast when magnified this much. To counter that, I shot at ISO 3200 so I could keep a rather fast 1/250 second shutter speed while still shooting at f14 to keep the lens at an optimal sharpness. These 8 shots were then pixel mapped in PanoTools and averaged to help cancel out any random noise. I would estimate the noise levels are similar to ISO 640. A substantial gain.
Note that I had originally done 4 images even though I had take 8. I had problems with PT doing optimizations on 8 image and it took awhile to figure out how to get the optimizer to work right (As great as PT is, there are some bugs in the optimizer that makes it go unstable at times)