I have been working on moon shots. I tried the 400mm with 1.4x and 2x tc's stacked the night before. I was not happy with my result. I had a lot of CA. On this shot I used my 300 f/4 IS with IS turned off. I tried it with 1.4x +1.4x stacked, 1.4x + 2x stacked, and 1.4x + 1.4x + 2x stacked. It seems that less is better. The 2x degrades the image too much. This one was 300mm +1.4x +1.4x tc (camera only reports 1 tc). I used a tripod, manual focus, mirror lock-up, and remote shutter release. A good ballhead seems key to being able to lock the heavy lens down tight. Any creep in the ballhead degrades the image. You have to work fast as you just get the setup tightened down, but the moon is rising fast, and it has now moved partially out of the frame! --start over.

Steve Mcsweeny has written me that keeping the shutter speed over 1/80 has worked for him. I imagine that would vary by the lens and tripod sturdiness. I'm going to give it a try next month.