Sigma A 85 mm f/1.4 DG HSM
8. Vignetting
| Canon 50D, f/1.4 | Canon 50D, f/2.0 |
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The vignetting is not bothersome even at the maximum relative aperture because it reaches just 22% (−0.72 EV). The problem disappears completely on stopping down the aperture to f/2.0 where its value decreases to 8% (−0.25 EV).
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Now let’s check the situation on full frame.
| Canon 5D III, f/1.4 | Canon 5D III, f/2.0 |
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| Canon 5D III, f/2.8 | Canon 5D III, f/4.0 |
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In this case, at the maximum relative aperture the vignetting is high, reaching 49% (−1.92 EV). Should you criticize the Sigma A 1.4/85 for it? Perhaps you should but not very harshly. It still fares noticeably better than both Zeisses and, within the margin of error, is exactly as good as the Nikkor AF-S 1.4/85G. What’s interesting, the older Sigma EX 1.4/85 remains a role model in this category as it is still the best of all the group.
Fortunately by f/2.0 the vignetting becomes slight, reaching just 27% (−0.89 EV) and by f/2.8 the problem becomes negligible (15% and −0.46 EV).
Further stopping down of aperture doesn’t influence the brightness loss in the frame corners in a significant way. By f/4.0 and f/5.6 we got an identical result of 11% (−0.34 EV).
Below we present averaged out values of brightness loss shown in concentric circles as you move further away from the frame centre. The numerical value expressed in percents for every image shows the area limited from the top and right by 100% and from the bottom by the presented curve. The area shows how much light overall is lost due to the vignetting effect. Please don’t mix these percentages with the values given at the beginning of the chapter because they aren’t directly connected.
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