Yes Tournesol, more curve deviates from the zero (thick black) line, more it distorts straight shapes. However, my test procedure has one flow, and it is to close camera to target distance. So this is why I've recorded mostly negative values (barell distortion). Manufacturers design lens distortion in a way that both negative and positive distortions are "balanced". So I believe it is the case with those two lenses as well, but definitely 17-70 has less distortion than 18-50 at the same focal length.
Tournesol
28-Feb-2006 08:58
Not sure how to read this, but does the Sigma 17-70 have less distorition than the 18-50?
