Sigma 50-150 mm f/2.8 APO EX DC OS HSM
8. Vignetting
At the shortest focal length and the maximum relative aperture the light fall-off in the frame corners reaches 27% (-0.92 EV). It is a moderate value. What’s more important, on applying f/4.0 the problem disappears practically completely because then the vignetting is just 9% (-0.28 EV).
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In the middle of the focal range the situation is even better. At the maximum aperture we get 24% (-0.80 EV) and by f/4.0 – only 8% (-0.25 EV).
The highest level of that aberration you can notice at 150 mm. In that case applying f/2.8 aperture will make you lose 34% (-1.21 EV) of light in the frame corners. On stopping down the lens to f/4.0 you can decrease the level of this aberration to 17% (-0.55 EV). The problem disappears almost completely by f/5.6 and f/8.0 where the vignetting is respectively 10% and 4%.
To tell you the truth when I first saw the Sigma 50-150 mm OS and its huge elements I was almost sure it was secretly a full frame device. I also thought that perhaps the vignetting level on full frame would be really high, reaching 3-4 EV but still you would be able to use the lens with the bigger detector. Unfortunately I was wrong. All my delusions were dispelled after attaching the Sigma to the Canon EOS 1Ds MkIII. The results of that experiment are presented in thumbnails below. You get black corners at every focal length – it proves that the lens image circle is noticeably smaller than that of typical full frame devices.
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