Lens review

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

6. Distortion

In most kit lenses and their substitutes the distortion causes problems only at the widest angle. When you increase the focal length it decreases very quickly, becoming zero near 24-30 mm and transforming into a not very bothersome pincushion distortion. Of course the wider the focal range and angle of view the bigger challenge constructors face. In the case of the Tokina 16-50 mm the task was not easy because this lens features one of the widest angles of view in its class. The distortion values, measured at 16, 30 and 50 mm focal length amounted to 4.1%, -0.22% and 0.69% respectively (with the measuring error around 0.1%). How does the lens compare to its competitors? It is shown in the chart below.

	Canon 17-55 IS	Nikkor 18-70	Sigma 18-50 Macro	Tamron 17-50	Tokina 16-50
beginning	-2.47%	-4.50%	-3.90%	-3.70%	-4.10%
middle	1.06%	0.20%	-0.77%	0.24%	-0.22%
end	1.38%	0.90%	0.11%	0.97%	0.69%

The most expensive Canon 17-55 mm sticks out in a positive sense among all these instruments. The Nikkor 18-77 mm differs in a negative way for a change but it might be explained by its wider range of focal lengths. The Sigma and the Tamron seem to fare equally well. The Tokina is a bit worse than them but it features 16 mm focal length, not 17 or 18 like its rivals. We can state that the three lenses from independent companies are on a similar level.

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Compared to the Nikon, on the Canon 20D the distortion level didn’t change. At the widest angle it amounts to –4.03% and it decreases to 0.2% in the middle of the range, to reach 0.73% at the end. Such results are, within the margin of error, the same as on the D200.