This gallery lists 100% crops from images taken with a Canon EOS350D and this lens + a Sigma 2x
Tele Converter. All shots were taken with an external flash (National PE-387S) with GN of 38
Please note that some of the closed apperture shots were taken at a higher (up to ISO1600) sensor sensitivity, hence some additional noise.
As it can be seen, the medium apperture (f11~f16) shots @ 400mm and equivalent @800mm exhibit high contrast and detail.