This is an overlay of the 18mm and 55mm images (a factor of three change in focal length), using the "difference" layer mode in Photoshop Elements. Note that the greatest error between the two images occurs around the perimeter of the 55mm overlay. There is about a 7 pixel mismatch--about 0.23 percent of the image width--which can be explained by different amounts of barrel distortion at 18mm and 55mm and a not quite perfect scaling between the two images.

To within the errors of the testing methodology and equipment, the two images are perfect overlays. There is no detectable change in perspective between the two, even with a factor of three difference in focal length.