Tokina AT-X 165 PRO DX AF 16-50 mm f/2.8 review - Vignetting

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Tokina AT-X 165 PRO DX AF 16-50 mm f/2.8

9 June 2010

Arkadiusz Olech

8. Vignetting

Here we get to the next very serious Tokina’s problem. Combining a wide angle, a sensible focal range and good fastness, while keeping moderate dimensions and low vignetting is always a task difficult to achieve. The Tokina didn’t carry out that task in a way you can call, say, acceptable.

At 16 mm focal length and by f/2.8 the light fall-off in the frame corners amounted to as much as 49% (-1.94 EV). Applying f/4.0 we see it decrease to still distinctly visible level of 31%. On further stopping down there’s some improvement but quite unsatisfactory. By f/5.6 the vignetting is 23%, by f/8.0 it reaches still 17% and it decreases to more or less acceptable level of 14% only by f/11.

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Fortunately in the middle of the focal range the situation is significantly better. The vignetting, amounting to 26% (-0.88 aperture value), is bothersome only at the maximum relative aperture. By f/4.0 it decreases to 13% and by f/5.6 it becomes negligible - only 9%.

At 50 mm focal length the problem is also visible because by f/2.8 it reaches 28% (-0.95 EV). Luckily by f/4.0 it decreases to 14% and by f/5.6 it is just 8%.

Canon 20D

The smaller size of the Canon sensor should have the biggest influence on the results in the vignetting category. And indeed it does. At the most difficult combination of 16 mm and f/2.8 the brightness loss in the frame corners amounts to 35% (-1.26 EV), which is still high but it doesn’t put the Tokina in a bad light when you compare it to its competitors – only the Sigma 18-50 f/2.8 Macro fared better. On stopping down to f/4.0 we see the vignetting decrease to 22% and by f/5.6 it is 14%. Only by f/8.0 though the vignetting becomes imperceptible.

In the middle of the focal lengths range the situation is much better. At the maximum relative aperture the light fall-off in the frame corners amounts to 17% (-0.55 EV) and it becomes imperceptible already by f/4.0, where it decreases to 10%.

A slight worsening of the results we observe at 50 mm where, by f/2.8, the vignetting reaches 26% (-0.88 EV) and it decreases to 12% by f/4.0; by f/5.6 it is already at a negligible level (5%).

The chart below shows the comparison between the results of the Tokina and the other lenses, tested mainly on the Canon 20D sensor. It is obvious that although it features the widest angle at 16 mm focal length, the Tokina fares really well here.