I have recently bought a couple of old (film era) wide-angle lenses for my infra-red photography. One thing that interested me was comparing the images produced by the old lenses with modern lenses. I took a photo, using a tripod, of a scene from my back garden, first using my good camera in colour, then switching cameras on the tripod to use the old lens in monochrome infra-red. I used a zoom lens to match, a close as possible, the focal length of the old lens.
What surprised me was how different the distortions were between the 2 lenses – the distortions made it impossible to line them up accurately. Here are slider comparisons for the 2 lenses. First is a 24mm lens:
Now I show the 21mm lens:
At this size the distortions are hardly noticeable but for some of the purposes I intend to use them for they would be obvious. Care is needed!