Sigma A 14-24 mm f/2.8 DG DN
8. Vignetting
| A7R II, APS-C, 14 mm, f/2.8 | A7R II, APS-C, 14 mm, f/4.0 |
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| A7R II, APS-C, 19 mm, f/2.8 | A7R II, APS-C, 19 mm, f/4.0 |
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| A7R II, APS-C, 24 mm, f/2.8 | A7R II, APS-C, 24 mm, f/4.0 |
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At the combination of 14 mm focal length and f/2.8 aperture you deal with a moderate level, that of 26% (−0.86 EV), which decreases to 18% (−0.58 EV) on stopping down the aperture to f/4.0. By f/5.6 vignetting is 12% (−0.38 EV) and further stopping down doesn't make it decrease anymore in a noticeable manner.
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In the middle of the focal range there are almost no problems at all. At the maximum relative aperture the brightness fall-off in the frame corners reaches 20% (−0.64 EV) and then it decreases to 12% (−0.36 EV) on stopping down the aperture to f/4.0. By f/5.6 the vignetting becomes imperceptible, reaching just 10% (−0.30 EV).
At 24 mm focal length and by f/2.8 brightness loss is 23% (−0.76 EV), but already by f/4.0 it becomes imperceptible, dropping to 9% (−0.27 EV).
Now let's check how the tested lens manages on full frame – below you can find appropriate images.
| A7R II, FF, 14 mm, f/2.8 | A7R II, FF, 14 mm, f/4.0 |
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| A7R II, FF, 19 mm, f/2.8 | A7R II, FF, 19 mm, f/4.0 |
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| A7R II, FF, 24 mm, f/2.8 | A7R II, FF, 24 mm, f/4.0 |
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This time there are far more problems because at 14 mm and by f/2.8 vignetting reaches a very high level of 62% (−2.79 EV). It is a result a bit higher than in the reflex camera model, which was 58%. Still, taking into account the fact that the mirrorless version is smaller and physically ligher, facing more serious telecentricity problems, these 4% of vignetting increase seem to be a small price to pay. It doesn't change the fact that both Sigmas 14-24 mm lose a lot of light on full frame, sad but true.
The problems don't end here. Because of the lack of telecentricity, mentioned before, vignetting hardly reacts to stopping down. By f/4.0 that aberration gets to 53% (−2.19 EV), by f/5.6 it is 49% (−1.93 EV), and by f/8.0 it amounts as much as 44% (−1.67 EV). Even by f/11 and f/16 you don't have any problems with noticing vignetting because, by these apertures, its level amounts to, respectively, 38% (−1.38 EV) and 33% (−1.17 EV).
At 19 mm focal length you can notice a distinct improvement of the performance but still the vignetting remains not especially susceptible to stopping down. By f/2.8 the brightness loss in frame corners amounts to 48% (−1.91 EV), by f/4.0 it reaches 36% (−1.30 EV), by f/5.6 it gets to 30% (−1.02 EV), and by f/8.0 it drops to 26% (−0.85 EV). Further stopping down doesn't have any measurable influence on vignetting any longer.
Very similar results you can observe at the maximum focal length. By f/2.8 we got a value of 46% (−1.78 EV) and it decreases to 29% (−0.98 EV) on stopping down the aperture to f/4.0. By f/5.6 vignetting amounts to 21% (−0.70 EV) and it doesn't change further even after a more pronounced stopping down of the aperture.
| Sony A7R II, 14 mm, f/2.8 |
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| Sony A7R II, 19 mm, f/2.8 |
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| Sony A7R II, 24 mm, f/2.8 |
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