Sigma 30 mm f/1.4 EX DC HSM
5. Chromatic aberration
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Despite quite an advanced for a standard prime construction, designed for small sensors, and using low-dispersion elements, correcting chromatic aberrations doesn’t work well for Sigma.
Most of all, the level of this aberration doesn’t depend on the aperture used at all, staying on the borderline of medium and large level everywhere. What’s interesting, you can see distinct differences between specified systems. You can understand it knowing about two things. Firstly, we can’t exclude small differences between specified copies. We’re dealing with Sigma for 1 300 zl and not Leica for 20 000 zlotys, in which every element is examined separately. In the latter there are no differences between copies, in the former there are for sure. The second thing is the dependency, of showed by us aberration, on pixels size. When the pixels are smaller it’s easier to see this aberration. The observed effect is no coincidence, then, showing the smallest aberration for Canon (the biggest pixels), the same for A100 and D200 (the same pixels, but smaller than in Canon) and the biggest in Olympus E-3 with the smallest pixels. As a matter of fact, the biggest aberration is displayed in Pentax, which has the same pixels as Nikon and Sony, which, again, disconcerts us. Because either we’re dealing with the weakest lens copy (if this is so, then why do we record such high resolution?), or K10D manipulates RAW files, which effects in both distorting the resolution results and chromatic aberration. Truth be told, the second alternative is more possible, although, again, it’s a subject for a discussion on camera tests, not the lens.
