So, I promised to come back to this topic when my Kenko 3x extender got in. And its in. Its throwing lens errors however, so I had to fiddle around a lot before I could get it to make pictures.
When no lens is attached it errors, and with the Tamron 150-600 it errors. It does however work fine with the 85mm. So i'm not sure whats going on.
I ended up taping up all the pins on a 12mm extension tube, and put that between the body and the kenko.
The moon is still a bit low right now for the best shots (humid air and all that), but I shot a video to show what the field of view is on this combo.
Here is the link: http://youtu.be/Xhz4ux7F8BQ
Moon is bit higher now. i did a shot with and without the kenko from the same position. Lens fixed on the tripod.
The fringing on both setups is about the same. These shots were set to b&w because I like the moon best that way. Apart from that and cropping I did nothing.
Just to point out...the moon is out of focus there. Which is expected, since you used an extension tube...that kills infinity focus in favor of closer focus than the lens' default MFD. You wont' be able to sharply focus the moon until you remove the extension tube.
I noticed twisting off the lens a bit also allows for shots to fire, as the lens error is no longer present.
What would you say should be my f stop on the lens with the 3x attached? I think I can go pretty low with the shutter speeds, about 1/160 to only counter the moons movement, as I have a pretty sturdy tripod.