Sigma A 24-35 mm f/2.0 DG HSM
8. Vignetting
| Canon 50D, 24 mm, f/2.0 | Canon 50D, 24 mm, f/2.8 |
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| Canon 50D, 28 mm, f/2.0 | Canon 50D, 28 mm, f/2.8 |
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| Canon 50D, 35 mm, f/2.0 | Canon 50D, 35 mm, f/2.8 |
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The vignetting can be noticed by and large only at the maximum relative aperture. At 24, 28 and 35 mm focal lengths it amounts to, respectively, 17% (−0.52 EV), 20% (−0.63 EV) and 23% (−0.76 EV). On stopping down the lens to f/2.8 the problem disappears almost completely, fluctuating between 6% (−0.18 EV) at 24 mm and 9% (−0.26 EV) at the 35 mm focal length.
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Far more problems we expected on full frame. Let’s start with examining the appropriate thumbnails.
| Canon 5D MkIII, 24 mm, f/2.0 | Canon 5D MkIII, 24 mm, f/2.8 |
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| Canon 5D MkIII, 28 mm, f/2.0 | Canon 5D MkIII, 28 mm, f/2.8 |
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| Canon 5D MkIII, 35 mm, f/2.0 | Canon 5D MkIII, 35 mm, f/2.8 |
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As you can see the problems are really distinct here. At a difficult combination of 24 mm and f/2.0 the light fall-off in the frame corners amounts to 59% (−2.56 EV) – it is really a very high value. On stopping down the aperture to f/2.8 it decreases to 37% (−1.32 EV). Only after employing f/4.0 the aberration becomes moderate, getting to 22% (−0.73 EV). By f/5.6 and f/8.0 the vignetting level is already low but still noticeable; our measurements provided the following values: 16% (−0.52 EV) and 14% (−0.44 EV).
In the middle of the focal range the vignetting level is a bit lower but still there are a lot of reasons to complain. At the maximum relative aperture it reaches 56% (−2.39 EV) and then it decreases to 34% (−1.18 EV) on stopping down the aperture to f/2.8. Further stopping down, this time to f/4.0, is able to limit that aberration to 19% (−0.61 EV). By f/5.6 and f/8.0 apertures the brightness loss in the frame corners amounts to just 14–15%.
When you progress to the maximum focal length you observe no big changes. By f/2.0 the vignetting is 55% (−2.31 EV), by f/2.8 it reaches 32% (−1.13 EV), and by f/4.0 it decreases to 20% (−0.64 EV). By f/5.6 and f/8.0 the results we got were almost the same, getting to 14% (−0.44 EV).
Below you can find a function graph of an averaged light fall-off presented in concentric circles, depending on the distance from the frame centre. The percentage value in every of the pictures states the size of an area limited at the top and on the right by the 100% value and at the bottom by that curve. It indicates how much light is overall lost due to the vignetting. Please, do not mix those percentages with the ones you saw at the beginning of this chapter; these two values are not connected in any direct way.
You can complain about the Sigma’s 24–35 mm vignetting and it completely deserves to be criticized here; still you should also keep in mind the performance of other lenses. For instance the vignetting of the Canon 2/35 IS at the maximum relative aperture reaches a huge value of 66% (over 3 EV!). The Nikkor AF-S 28 mm f/1.8G, when stopped down slightly to f/2.0, loses 48% of light in the corners so is better than the Sigma by just 8%.
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