Sigma A 24-70 mm f/2.8 DG OS HSM
8. Vignetting
| Canon 50D, 24 mm, f/2.8 | Canon 50D, 24 mm, f/4.0 |
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| Canon 50D, 45 mm, f/2.8 | Canon 50D, 45 mm, f/4.0 |
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| Canon 50D, 70 mm, f/2.8 | Canon 50D, 70 mm, f/4.0 |
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There is really no need to worry. At a difficult combination of the 24 mm focal length and f/2.8 aperture the brightness loss in frame corners amounts to just 15% (−0.48 EV); then it decreases to 11% (−0.34 EV) on stopping down the aperture to f/4.0. The middle of the focal range is even better – at the maximum relative aperture the vignetting reaches 13% (−0.40 EV) and it decreases to 8% (−0.24 EV) on stopping down the aperture to f/4.0.
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The maximum focal length doesn't differ much from the performance in the middle of the range. By f/2.8 the vignetting is 14% (-0.44 EV) and by f/4.0 it decreases to an imperceptible value of 7% (-0.22 EV).
Now let's check how the tested lens performed on full frame of the Canon 5D Mark III.
| Canon 5D III, 24 mm, f/2.8 | Canon 5D III, 24 mm, f/4.0 |
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| Canon 5D III, 45 mm, f/2.8 | Canon 5D III, 45 mm, f/4.0 |
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| Canon 5D III, 70 mm, f/2.8 | Canon 5D III, 70 mm, f/4.0 |
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There far more problems at that point. The combination of wide angle and the maximum relative aperture means the loss of 57% (−2.41 EV) of light in frame corners. It is a result worse than that of the stabilized Nikkor, a tad weaker than that of the Tokina but better than that of the Canon and the Tamron. The Sigma's vignetting levels decrease slowly on stopping down. By f/4.0, f/5.6, f/8.0 and f/11.0, we got respetively: 44% (−1.66 EV), 36% (−1.31 EV), 32% (−1.10 EV) and 27% (−0.92 EV).
In the middle of the focal lengths range the vignetting is lower so at the maximum relative aperture it amounted to 31% (−1.05 EV). On stopping down the lens to f/4.0 its level decreased to 21% (−0.68 EV) and by f/5.6 it got to 15% (−0.47 EV); further stopping down didn't produce any measureable effect.
The maximum focal length means the return of vignetting problems – by f/2.8 that aberration reaches 52% (−2.14 EV) constituting, next to the Tamron, the worst result among all lenses compared here. By f/4.0 it decreases to 30% (−1.05 EV) and by f/5.6 it is 16% (−0.52 EV). By f/8.0 and f/11.0 the brightness loss amounts to just 13% (−0.39 EV).
| Canon 5D Mk III, 24 mm, f/2.8 |
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| Canon 5D Mk III, 45 mm, f/2.8 |
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| Canon 5D Mk III, 70 mm, f/2.8 |
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