Voigtlander Super Wide Heliar 15mm f4.5
v Sigma 12-24mm f4.5-5.6
f5.6 Centre Frame Crops (100%)
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| Voigtlander 15mm at f5.6 |
Sigma 12-24mm at 15mm/f5.6 |
These are both s-l-o-w lenses: for each, f5.6 is only about one stop down. However, at this aperture the Voigtlander is much sharper and has transmitted a lot more information: the above JPEGs are 61K and 53K respectively. Note also the typical Sigma yellow/warm cast.
f5.6 Upper Right Corner (100%)
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| Voigtlander 15mm at f5.6 |
Sigma 12-24mm at 15mm/f5.6 |
So where's the chromatic aberration we were expecting? This is a 15mm lens one stop down, and an extreme corner crop from a full frame. Very impressive. However, the Voigtlander is here being handed something of an advantage in this instance: though the Sigma 12-24mm has predictably lousy corners at this aperture, what it doesn't have is vignetting - I mean, practically nil.
To give a fairer comparison, here's the top right corner which is drawn in far less flattering light for the Voigtlander.
f5.6 Upper Right Corner (100%)
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| Voigtlander 15mm at f5.6 |
Sigma 12-24mm at 15mm/f5.6 |
So while the Voigtlander wins the resolution race, it really does suffer from pronounced vignetting at this aperture. In sky, I like vignetting. Vignetting helps. Vignetting is good. Vignetting works. But I don't want to see it in brickwork, thanks.