With a DxOMark score of 22 points the Canon EF16-35mm f/4L IS USM is generally a good performer. It has good peak sharpness, particularly in the center at 16mm from f/4 onwards, reasonable transmission of 4.5Tstops and low vignetting, though it’s still noticeable wide-open, particularly in the extreme corners at 16mm and more generally in the periphery at 35mm. Sharpness varies throughout the zoom range, as you might expect with a zoom but thanks to some curvature of field this lens has a rather complicated optical performance. At 28mm the lens has somewhat soft corners at full aperture, a marked increase in sharpness across the field at f/5.6 and then at f/8 a return to the lower edge performance seen at f/4. Geometry is good though (particularly at 20mm); there’s no difficult to correct moustache type distortion, only some barrel distortion at 16mm and slight pincushion from 24mm.
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