Canon EF 16-35mm f/4L IS USM Review
Sharpness at 20mm
The sharpness tests for this review were carried out using a real-world subject rather than a test chart. The Canon EF 16-20mm f/4L IS USM lens was attached to a Canon 5D Mark III body, which in turn was mounted on a sturdy tripod. Self-timer mode was activated. Slight tonal changes are due to slight changes in natural light during the session.
The full frame at 20mm
Center and edge sharpness are excellent wide open at f/4 and nothing short of outstanding between f/5.6 and f/11. At f/16 and f/11 sharpness across the frame is beginning to drop-off due to diffraction, but is still commendably high.
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