Wayne, the scope has a much bigger objective lens. The fixed f/stop is 7.5, but somehow the scope does something nice to an image. I can't quite put my finger on it, but they are subtly different. And I use ISO 160. The Bigma shots are at ISO 320. It's just an experiment, rainy day and all that. 
Hmmm, I wonder if the scope being bigger, plus having the Kenko tube on, plus the length of the adapter, [maybe 100mm longer than the telescope eyepiece would be], has something to do with the angle the light hits the sensor? That would explain a lot.