Lens review

Pentax smc DA 17-70 mm f/4.0 AL [IF] SDM

6. Distortion

The Sigma 17-70 mm distortion changed from –4.0% at 17 mm to 0.7% at 70 mm. Pentax gets very similar results. For the shortest focal length the distortion is –3.82%, it decreases rapidly and changes the sign, reaching at 30 mm the level of 0.55%, then it increases slowly, reaching 1.07 % at 50 mm and 1.09 % at 70 mm.