« on: October 22, 2014, 03:46:59 PM »
For canon, exposure for a 400mm 5.6 on a crop (640mm 5.6) is the SAME exposure as a 400mm 5.6 on a full frame. By using a crop sensor the aperture doesn't magically shrink. Just like taking the center section of a full frame image to give the same view as a crop sensor does not shrink the aperture.
That is because correct photographic exposure is dictated by the intensity of light, not volume. So you are of course right that the exposure for a given f stop lens will be ( more or less depending upon the efficiency of the lens) the same irrespective of sensor size or image circle, but when you begin talking about Achieving the same result on different formats you must deal with equivalence in all areas if you want to be correct - not just the 400 to 640 bit