To measure geometric distortion we photographed a test chart consisting of a grid pattern with perfectly straight lines. The lenses were tested with their apertures set to f8 using a Pentax K10D in Aperture Priority mode; the DA 18-55mm was tested at both 18 and 55mm focal lengths. The images were analysed with Imatest using 5th Order line calculation and the full areas presented here at a reduced resolution.

As you'd hope for higher quality fixed focal length short telephoto lenses, the 40 and 70mm Limited editions exhibit relatively low geometric distortion. Interestingly the 40mm exhibits slight barrelling, whereas the 70mm exhibits the more usual pincushion distortion associated with this kind of focal length. The 70mm suffers from the least distortion here.