With a DxOMark score of 22 points the Canon EF16-35mm f4L IS USM is generally a good performer. It has good peak sharpness, particularly in the center at 16mm from f4 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 f5.6 and then at f8 a return to the lower edge performance seen at f4. 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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Adding stabilization in a lens like this is targeting videographers more than stills photographers, where the wide field of view and steadying effect can be put to good use, but it’s a welcome addition all the same. The imaging performance is good, very good in fact, but it’s not without some shortcomings, particularly at the longer end where field curvature provides some unexpected results. Once those are understood and either avoided or worked around, the lens can be a very satisfying performer and at $1,199 this new model doesn’t seem over priced.
http://www.dxomark.com/Reviews/Canon-EF16-35mm-F4L-IS-USM-lens-review-Canon-s-best-wide-angle-zoom-yet