Canon Ultrawide Lenses Compared (Full-Frame)
Canon 16-35mm f/2.8 L II (2007-today)
Canon 16-35mm f/2.8 L (2001-2007)
Canon 17-40mm f/4 L (2003-today)
Canon 17-35mm f/2.8 L (1995-2001)
Canon 20-35mm f/3.5-4.5 USM (1993-2007)
Canon 20mm f/2.8 USM (1992-today)
Canon 20-35mm f/2.8 L (1989-1995)
Tokina 17-35mm f/4 (2011-)
Canon Ultrawide Comparison Table top
*Corners are sharper than even the newest 16-35 f/2.8 L II, but look out: the 20mm f/2.8 USM's deliberate field curvature will make the region midway between corners and center less sharp for flat subjects, but make then even sharper for subjects which get closer to the camera in that region.
For a much tougher professional lens at about the same size and weight, the 20mm f/2.8 USM (1992-today) is excellent with a lens profile on my 5D Mark III. The 20mm f/2.8 USM is the smallest and lightest Canon ultrawide sold today.
The Canon 17-40mm f/4 L is unbeaten optically, and the lightest of the zooms sold today.
If you demand the best and don't mind the size, weight and expense, the Canon 16-35mm f/2.8 L II (2007-today) is the best that Canon's ever made.
The Canon 16-35mm f/2.8 L II is the biggest, heaviest and most expensive lens here, and the best optical performer. It's the best ultrawide zoom available for Canon, but still soft in the corners at f/2.8. If you need better, use Zeiss fixed lenses.
The previous Canon 16-35mm f/2.8 L is even softer in the corners, but it's not that big a deal unless you're a pixel counter, as opposed to a professional photographer. All of these lenses are best in the corners stopped down to about f/11.
The Canon 17-35mm f/2.8 L (1995-2001) is Canon's lightest f/2.8 ultrawide zoom ever, has a metal filter thread and great ergonomics with instant manual-focus override and a great focal length range. Its optics are about as good as the Canon 16-35mm f/2.8 (2001-2007).
The 20-35mm f/2.8 L (1989-1995) is the smallest and toughest Canon professional ultrawide zoom ever — with the least distortion. It's the only all-metal lens here, but since Canon offers no lens profile for use with the 5D Mark III, its uncorrected lateral color fringes will degrade its optical performance compared to all the other Canon lenses. For use on 35mm film, this of course doesn't matter; but the lack of instant manual focus override might.
The Canon 20-35mm USM (1993-2007) is the lightest and smallest lens here, but that's because it's built instead to very good amateur standards instead of pro. It has the best ergonomics of any lens here, and with full automatic lens profile correction on the 5D Mark III, suddenly offers similar optical performance to the heavy and expensive pro lenses. With the ultra-high ISO capability of the 5D Mark III, f/2.8 is no longer needed for low-light use, so this older consumer lens suddenly is much more useful than ever.
The 20mm f/2.8 USM (1992-today) is a professionally tough lens, as well as being small and light and fast. If you don't need to zoom, want small and demand a well-made lens, this enduring classic is also much less expensive than any of the other Canon ultrawides today. With a lens profile on the the 5D Mark III, it is excellent optically.
The Tokina 17-35 is an off-brand lens. It's built out of tough plastic and offers good enough optical quality, but there is no lens profile available for use with the 5D Mark III, so its performance probably will be worse than the Canon 20-35mm USM.
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