Sigma 12-24 mm f/4.5-5.6 II DG HSM
4. Image resolution
If you expect here sensational and record-breaking results, be warned – there will be none of this. It is obvious without even testing the lens. Resolution records usually occur by f/4.0-5.6 and only for such lenses where these values are away from their maximum relative aperture by about 2-3 EV. Such a reserve is needed to stop the aperture down a bit, limiting the influence of optical aberrations efficiently, which are present in every optical instrument to a higher or lesser degree. In the case of the Sigma 12-24 mm the f/4.5-5.6 apertures are nothing less than the maximum relative aperture. It would be difficult to get any records here because the aforementioned aberrations are still present. When we start to stop the Sigma down the apertures enter the values of f/8-11 where the influence of diffraction, limiting MTF values, makes itself felt.
Let’s finish the theorizing now and check how the tested lens fared in the frame centre at 12,18 and 24 mm.
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This graph is nothing the Sigma should be ashamed of, mainly because, at the maximum relative aperture, contrary to the performance of its predecessor, the lens reaches the decency level at every focal length. We hoped that the new lens would have better results after a slight stopping down though and here we were disappointed. The previous model was tested on the Canon 20D and that camera provides MTF values almost the same as those from the D3x, to an accuracy of 1-2 lpmm, so they are easily comparable. It is clearly seen that the current model and its predecessor reach a similar maximum level. Something which was satisfactory ten years ago might be not sufficient anymore.
Of course you still should maintain the right frame of reference. The image the Sigma provides in the frame centre is good – but nothing else. Our slight disappointment stems from the fact that we counted on the possibility that the Sigma 12-24 mm II might come closer to the level of 40 lpmm. Of course we didn’t expect it to exceed it for reasons described at the beginning of this chapter.
The previous model performed weakly already on the edge of the APS-C/DX sensor where it had problems with exceeding distinctly the level of 30 lpmm. How its successor fares here? Let’s look at a graph below.
After taking into consideration the measurement errors we can state boldly that the performance of the new lens is almost the same as that of the old lens. It’s a pity there is no improvement but, defending the tested Sigma, you should also notice that at all focal lengths the results are even and very close to the decency level.
It wouldn’t be hard to guess that the edge of full frame sensor is the most problematic here. It is unavoidable with such a wide angle. Let’s look at a graph below.
The official decency level is reached nowhere, even after stopping down. Taking into account the price of the Sigma 12-24 mm II there are too many average or weak results here. Below we present some crops of our test chart photos taken from JPEG files in the frame centre.
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