No attempt was made to equalise the framing of the Leica 19mm and Olympus 18mm primes in this instance.
|Olympus 18mm f3.5 at f8 (full frame)|
The Zuiko 18mm has an excellent reputation for distortion control – users commonly report experience ‘no distortion’ for architectural work. As you see, Zones A and B are fairly neutral for a lens this wide, but there is an observable kink of positive distortion in Zone C.
|Leica 19mm Elmarit f2.8 at f8 (full frame)|
The Leica has a similar patten of distortion to the Olympus but it’s more severe in scale.
|Canon 16-35mm f2.8 Mark II at 18mm / f8 (full frame)|
The Canon 16-35mm II behaves like a less unruly version of the Mark I: the barrel distortion is uncomplicated and located only in Zones A and B. A simple Photoshop Spherize (-6%) does the trick without any degradation. In typical ultrawide zoom style, the 16-35 II progresses from barrel distortion at the wide end (at 16mm, it has the exactly same distortion as at 18mm), through to neutral (like the Nikon 17-35mm f2.8, it is dead neutral in the 20-22mm range), and onto pincushion from 24mm up, peaking at 28mm and flattening out somewhat by 35mm . . . like this:
Canon 16-35mm f2.8 L at 16mm (full frame)
Canon 16-35mm f2.8 L at 20mm
Canon 16-35mm f2.8 L at 24mm<
Canon 16-35mm f2.8 L at 28mm
Canon 16-35mm f2.8 L at 35mm