Sigma 24-70 mm f/2.8 EX DG HSM
8. Vignetting
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Usually, the most difficult part comes when we want to combine the widest angle and the fastest aperture possible (24 mm by f/2.8 in this case). Here we get an 11% vignetting level ( -0.35 EV) so hardly visible. By f/4.0 it decreases by next 2%.
At 45 mm wide open, the level of vignetting reached 13% ( -0.40 EV) and by f/4.0 it dropped to 7%. Similarly, at maximum focal length by f/2.6 we get 15% vignetting (-0.48 EV), but by f/4.0 it’s just 6%.
It’s worth notice, that these results are very much the same as the results of the Nikkor 24-70 mm, a bit better than those of the Zeiss/Sony 24-70 mm and significantly better than those of the Canon 24-70 mm.
Full frame is a law unto itself. The vignetting results, obtained on the Nikkon D3x are a very fine example of that truth. For the 24 mm and f/2.8 combination the illumination loss in the frame corner is exactly 50% (-2.00 EV). What’s important, the level of the aberration decreases on stopping down but not as fast as we were accustomed to dealing with small detectors. By f/4.0 the vignetting is 36%, by f/5.6 its level amounts to 31%, by f/8 it reaches 27%, by f/11 it’s still 23%.
The situation is much better for the middle focal lengths. There, at maximum relative aperture, the vignetting reaches 24% ( -0.80 EV). After closing the aperture by one stop the vignetting stops being a problem, because it decreases to 11%.
Unfortunately, for maximum aperture the problem returns. By f/2.8 the illumination loss in the corners of the frame reaches as much as 43% ( -1.61 EV) and for f/4.0 it amounts to 26%. The aberration is still visible by f/5.6 because its value, measured by us, was still 19% and it disappears almost completely only for f/8.0 and f/11, with the results of 14% and 9% respectively.
