Tokina AT-X PRO SD 14-20 mm f/2 (IF) DX
8. Vignetting
| Canon 50D, 14 mm, f/2.0 | Canon 50D, 14 mm, f/2.8 |
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| Canon 50D, 17 mm, f/2.0 | Canon 50D, 17 mm, f/2.8 |
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| Canon 50D, 20 mm, f/2.0 | Canon 50D, 20 mm, f/2.8 |
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The combination of the 14 mm focal length and f/2.0 aperture is very difficult so we expected a lot of vignetting problems in that place. The result of the Tokina surprised us very positively because the brightness loss in the frame corners amounted here to 26% (−0.92 EV) which is just a moderate value. Still the fact that the vignetting decreases so slowly on stopping down is a flaw : by f/2.8 it is 21% (−0.68 EV), by f/4.0 it reaches 16% (−0.49 EV), and by f/5.6 it gets to 12% (−0.39 EV). Further stopping down doesn’t have any measurable influence on vignetting.
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In the middle of the focal range the situation is very much the same. At the maximum relative aperture the vignetting reaches 25% (−0.84 EV) and by f/2.8 it drops to 20% (−0.66 EV). By f/4.0 and f/5.6 the results we got amount to 15% (−0.49 EV) and 12% (−0.38 EV) respectively.
When you change the focal length to 20 mm you see practically no differences in the vignetting performance. By f/2.0 that aberration amounts to 26% (−0.87 EV), by f/2.8 it decreases to 20% (−0.66 EV), and by f/4.0 it drops to 15% (−0.38 EV). By f/5.6 you deal with a level of 12% (−0.38 EV) which doesn’t change on further stopping down.
To sum up the Tokina managed the correction of vignetting well enough, taking into account its parameters. For example the Sigma 18-35 mm f/1.8 had maximum results of 34-37% in that category and by f/2.0, the Tokina’s maximum aperture, it reached near 30%. Both lenses constitute a similar challenge for its constructors (the Sigma is a bit faster and features a wider focal range but the Tokina provides noticeably wider angles of view) so the fact that the Tokina performed a bit better in this category is the proof that you deal here of a lens of a very good quality.
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