Canon EF 11-24 mm f/4L USM
8. Vignetting
| Canon 50D, 11 mm, f/4.0 | Canon 50D, 11 mm, f/5.6 |
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| Canon 50D, 17 mm, f/4.0 | Canon 50D, 17 mm, f/5.6 |
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| Canon 50D, 24 mm, f/4.0 | Canon 50D, 24 mm, f/5.6 |
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The image which can be observed here is surprisingly good. At a very difficult combination of 11 mm and f/4.0 you lose only 26% (−0.88 EV) of light in the corners. That value decreases to 11% (−0.32 EV) on stopping down the aperture to f/5.6 and by f/8.0 it drops even further to just 9% (−0.28 EV).
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The situation is even better at the 17 mm focal length where, at the maximum relative aperture, the vignetting reaches 20% (−0.64 EV). It becomes almost entirely imperceptible on stopping down the aperture to f/5.6 where it amounts to just 9% (−0.28 EV).
At 24 mm there are no problems almost at all, even with the lens wide open where the brightness loss in the frame corners amounts to 16% (−0.51 EV). By f/5.6 that aberration vanishes almost completely (8% i −0.26 EV).
Of course we expected far more problems on full frame but first let’s have a look at the appropriate thumbnails.
| Canon 5D MkIII, 11 mm, f/4.0 | Canon 5D MkIII, 11 mm, f/5.6 |
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| Canon 5D MkIII, 17 mm, f/4.0 | Canon 5D MkIII, 17 mm, f/5.6 |
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| Canon 5D MkIII, 24 mm, f/4.0 | Canon 5D MkIII, 24 mm, f/5.6 |
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The combination of the 11 mm focal length and the f/4.0 relative aperture already shows you the scale of the problem the Canon optics constructors had to deal with. The vignetting reaches here a very high level of 62% (−2.81 EV). That aberration is still pretty visible by f/5.6 where you got a value of 41% (−1.53 EV). A sensible level can be seen only by f/8.0 where the result amounted to 26% (−0.89 EV). By f/11 and f/16 the vignetting value remained on the same level of 20% (−0.66 EV).
The middle of the focal range is better but it doesn’t mean the vignetting won’t be noticed there. Quite the opposite is true – by f/4.0 it is 41% (−1.54 EV) so it can be perceived without any problems. Only by f/5.6 you deal with a moderate value of 23% (−0.75 EV). By f/8 that aberration level decreases to 17% (−0.55 EV), and by f/11 to 15% (−0.48 EV). Further stopping down doesn’t have any measurable influence over the vignetting results.
The fewest problems with the vignetting you’ll experience at the maximum focal length where, by f/4.0, the light fall-off in the frame corners amounts to 32% (−1.12 EV). On stopping down to f/5.6 it decreases to 23% (−0.74 EV) and by f/8.0 it gets even lower, to 19% (−0.61 EV). The results by f/11 and f/16 are respectively 15% (−0.47 EV) and 13% (−0.42 EV).
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