Some of the examples on this page were taken with the Canon EOS 1D Mark III, a 10.1-megapixel camera with a 1.3X field-of-view crop sensor ( 1.3X Sensor Crop ). Others were taken with the full-frame 21.1-megapixel Canon EOS 1Ds Mark III ( ).
Stopping down to f/11 or f/16 is needed to pull the corner sharpness into bounds due to curvature of field. Unfortunately, stopping down past f/8 drops image contrast just a bit, and this can be seen in the areas that are already optimal at f/8. See also Diffraction at diglloyd.com.
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EOS 1D Mark III, ISO 50, 0.5 sec @ f/8 <=> f/11