Canon 300mm F4 L IS at 300mm F8
Very interesting, Decided to see if it was worth spending anything on that Opteka 420mm-800mm fixed fstop manual focus lens.
Looks like more zoom on a softer lens will get you more detail, especially once sharpened up.
These images have all been slightly cropped to the exact same size to show the difference in magnification.
You may download the 100% originals from this gallery.