The 24mm World Cup
Group C: Regular f2.8 Prime Lenses

Canon 24mm f2.8 v Olympus 24mm f2.8 v Sigma 24mm f2.8 v Yashica ML 24mm f2.8:
Geometric Distortion

Here each frame has been reduced to 2000 pixels, and a sample taken from the extreme upper left corner, demonstrating part of the distortion pattern in the brickwork.

So that's four points to the Yashica, three each to the Olympus and Canon (the Zuiko's distortion is slightly more pronounced, but more regular and easier to fix without degrading the capture), and two for the Sigma. At this focal length, it seems that the greater the resolution, the worse the distortion.

Chromatic Aberration (see also f2.8 Performance Page)

2 points	4 points
Canon 24mm at f11 (corner)	Olympus 24mm at f11 (corner)
Sigma 24mm at f11 (corner)	Yashica ML 24mm f11 (corner)
2 points	3 points

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As indicated by the wide open performance, there is a touch of chromatic aberration in the Sigma and Canon captures; the Olympus and Yashica results are largely aberration-free.