Voigtlander Super Wide Heliar 15mm f4.5
v Sigma 12-24mm f4.5-5.6

 

f16 Centre Frame Crops (100%)

Voigtlander 15mm at f16	Sigma 12-24mm at 15mm/f16

As you might expect, by f16 there's not much to separate them. In fact, the Voigtlander 15mm is showing diffraction softening but the Sigma 12-24mm is just starting to look comfortable!

 

f16 Upper Right Corner (100%)

Voigtlander 15mm at f16	Sigma 12-24mm at 15mm/f16

...and still the Voigtlaner vignettes. This particular sample of the Sigma 12-24mm actually renders a reasonable corner by f16 (not all do) and of course is much more useful out of the box that the 15mm prime which requires anti-vignetting correction at all apertures.

Page 4: f11 Performance <  > Page 6: Distortion + Conclusion