I don't know, Mark... Looking at the first image of Big Ben, I see both perspective distortion (the lean in the clock tower) and barrel distortion (the curve in the clock tower).


Here's an example from my recent trip, shot with the 5DII and EF 24-105mm f/4L IS @ 24mm, which has what photozone.de refers to as 'massive barrel distortion' at the wide end (measured as 4.3%). The left image is a DPP conversion with no corrections applied, the right image is a DxO conversion which corrects for the barrel distortion(DxO also improves the lighting). You can see that the perspective distortion is present in both images, but in the uncorrected image on the left the lines on the ceiling appear to converge (yes, perspective causes convergence too, but not over a distance of 15 feet), the transverse beams on the ceiling 'frown', the vertical columns bow outward, and the altar and table in front appear to 'smile'. Those effects are all due to the barrell dostirtion of the lens, and the spatial correction applied by DxO removes those effects.


[img]/cfs-file.ashx/__key/CommunityServer-Components-UserFiles/00-00-00-35-15/Barrel-Distortion.jpg[/img]