I recently put the 600mm prime to use in the garden one night. It was a little experiment to see what the lens looked like with the 1.4 & the 2x converters.

The first shot was with the 2x converter on the lens. The second is with both converters stacked. The 1.4 converter keeps autofocus, but with moon shots I prefer to use manual focus anyway. With the 2x converter on the lens you lose autofocus anyway.

With the full-frame sensor the moon doesn’t appear as large in the frame as it would on a cropped sensor, but there is plenty of detail on these uncropped shots. I just have to try again with the moon in different phases to see how the shadows effect the detail on the surface of the moon.