Hellashot wrote in post #2958772
The only thing about your test is that the Bigma is very likely already at f6.3 at 200, 300, and 400mm because it never reports a minimum appeture of f6.3 so that your camera will be able to autofocus with it since the camera will "think" the appeture is f5.6 when it is really f6.3
Incorrect. The Bigma DG on my 20D test body reports (in Av mode) exactly what I posted at my main test page [max apertures of]: 100mm f5, 200mm f5.6, 300mm f5.6, 400mm f5.6, and 500mm f6.3. Again, only at around 460mm and on does it report f6.3.
Also, the 1-4 and Bigma, in Av mode, report identical shutter speeds when set to corresponding apertures, under identical lighting conditions. It isn't at f6.3 until around 450mm-460mm +.