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.
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![Pentax smc DA 17-70 mm f/4.0 AL [IF] SDM - Distortion](upload2/13417_pen17-70_dys17.jpg "Pentax smc DA 17-70 mm f/4.0 AL [IF] SDM - Distortion")
![Pentax smc DA 17-70 mm f/4.0 AL [IF] SDM - Distortion](upload2/13418_pen17-70_dys30.jpg "Pentax smc DA 17-70 mm f/4.0 AL [IF] SDM - Distortion")
![Pentax smc DA 17-70 mm f/4.0 AL [IF] SDM - Distortion](upload2/13419_pen17-70_dys50.jpg "Pentax smc DA 17-70 mm f/4.0 AL [IF] SDM - Distortion")
![Pentax smc DA 17-70 mm f/4.0 AL [IF] SDM - Distortion](upload2/13420_pen17-70_dys70.jpg "Pentax smc DA 17-70 mm f/4.0 AL [IF] SDM - Distortion")
