I should not let my fingers get ahead of my brain, I missed an important part of only using 1 tube and 1 extender. It all validates everything you had said earlier.

The initial test was on a 70-200 f2.8L IS with a 2x, 12mm, and a 1.4x and my camera, a 5D2, which read 5.6..

My wide open comment was regarding the 400/5.6 with a 12mm and 1.4x and it still read 5.6. If I changed the setup to a 12mm and the 2x it still read 5.6. I am also using Kenko tubes with the AF electronics. This surprises me because I expected it to pass through the information. I also wasn’t sure if the body would play into any part of this.

Thanks again for all the information you provide!

You are welcome. The above makes sense. Whenever you put an extension tube onto the lens the camera will show as wide open even with a TC behind it. Why? The tube cuts off communication between the camera and the lens. What is interesting is that the exposure will not be affected. And in the situations that you describe, you will always lose the ability to focus on infinity. Lastly, you are welcome artie

#1: No matter which TC you put on the lens it should not be reading wide open….

#2: If you put the 2X on the lens with the 1.4X TC on the camera with the 12mm tube in between you should be able to focus on the well muted sun…. At 93 million miles that qualifies as infinity to me….