Distortion was measured at 15, 30, 50 and 85 mm focal lengths. At the widest angle it’s barrel like and reaches a large level of -4.52%. Then it decreases quickly, zeroes, changes its sign to be pincushion like at 30 mm with 0.75% level. Later on, the aberration decreases slowly. At 50 mm it amounts to 0.75% and at 85 mm 0.64%.
How does Canon come off compared to its rivals? You can say that it’s medium at the most. Zeiss 16-80 mm (tested on a sensor of 1.5x factor, so giving the same angle of view as Canon at 15 mm) gave the maximum distortion of -3.98%, which later decreased quickly to a low level 0.16%-0.64%. Zeiss performs better than Canon at every focal length, then.
In a duel with Nikkor 16-85 mm VR is closer to a draw. Nikkor performs slightly better at the shortest focal length than Canon, and at longer ones slightly worse.
