As part of our test of the Canon EF 400mm f/2.8 IS II USM we've shot our SFR Plus chart at every aperture to check for sharpness and fringing across the frame. The resulting images are then fed through the Imatest Master software.
The graph below shows the results of the test, with each of the coloured lines depicting the lenses performance at the centre of the frame (in blue), and an average of the results for the mid-range (pink) and edge (yellow) frame.
The graph shows that the Canon EF 400mm f/2.8L IS USM performs well across the aperture range. Despite the progressive fall towards f/22 the results for this lens are impressive with little drop in sharpness across the frame. The best results are achieved between f/2.8 and f/7.1.
This graph shows that signs of fringing are low across the aperture range, whilst results at the middle and edge frame are higher at the centre fringing is almost non-existent.