Tokina AT-X 116 PRO DX II AF 11-16 mm f/2.8
8. Vignetting
As you can notice the image circle of the lens is too small to cover a full frame detector in the range from 11 to 14 mm. If you use those focal lengths, the corners of the frame will be black, no matter what aperture. The situation changes at 15 mm. Here the image circle is bigger than the sensor and the vignetting decreases with the increase of the aperture. By f/2.8 it still reaches a huge value of almost -6 EV, by f/4.0 you get a result of -4.2 EV, by f/5.6 it amounts to -3 EV and by f/8.0 it gets to already sensible -2.2 EV.
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The 16 mm focal length already features more sensible vignetting levels: at the maximum relative aperture this aberration reaches -3 EV and it decreases to -2 EV on stopping down to f/4.0. By f/5.6 the vignetting gets to -1.35 EV and by f/8.0 it approaches -1.1 EV.
It is evident that at 15-16 mm focal length the Tokina can be used with a full frame camera. Is it important, though? In my opinion – not really. At 15 mm and on full frame the edges are dark and of very low quality. At 16 mm the situation is significantly better – there you get an angle of view of 107 degrees. It is really a lot but the same Tokina, attached as it should to a body with an APS-C sensor, provides 102 degrees at 11 mm. Apart from that you don’t have to tackle a level of 3 EV vignetting there – we are going to present more detail it in a moment.
As we already announced the description of the performance on a smaller sensor, let’s check how the Tokina 11-16 mm fares on the Canon 50D.
Applying 11 mm focal length and the maximum relative aperture you must take into account a vignetting level of 33% (-1.17 EV). If you stop down the aperture to f/4.0 the problem becomes just moderate, decreasing to 18% (-0.59 EV). By f/5.6 the situation is even better because the vignetting reaches 13% (-0.42 EV). Further stopping down doesn’t make it decrease any lower.
In the middle of the focal range the number of vignetting problems diminishes. At the maximum relative aperture it gets to 24% (-0.81 EV) and it becomes almost imperceptible by f/4.0, where it reaches just 13% (-0.41 EV). What’s interesting, further stopping down doesn’t help at all.
The best situation can be observed at 16 mm. The maximum vignetting level you’ll have to deal with there amounts to 19% (-0.63 EV). It is a low value – in order to be sure of that let’s remind the result of the Tokina 16-50 mm f/2.8 which, at the combination of 16 mm and f/2.8, had 35% of the light fall-off in the corners of the frame. On stopping down to f/4.0 the vignetting of the Tokina 11-16 mm can be considered as negligible (12% and -0.36 EV).
Vignetting is a category in which the Tokina 11-16 mm definitely gets the upper hand over its ultra wide-angle rivals. The good aperture fastness makes it possible to close it to f/4.0 without any qualms and by that aperture the vignetting is not bothersome, reaching just a dozen or so percent. With the competitors the f/4.0 constitutes the maximum relative aperture or an area near it, where the vignetting typically gets to a significant level of 30-40%.
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