Is it me or is this turning into an optical design discussion? > I read the posts of people about if some lens has very much linear > distortion, but not so much barrel distortion..... > > I am an ignorant and I don't know what does that imply..... can > someone explain it to me?? > > Are there other types of distortion?... As I would use the terms... Linear distortion isn't an aberration - it is a consequence of perspective when using wide angle rectilinear lenses. (nb you can tweak this in the design but it introduces other problems) Barrel and pincushion distortion are normally considered aberrations. If you have an image of a square, cantered in the image plane (on the primary axis of the lens), then if the sides of the box bend outwards then we have barrel distortion, and if they bend inwards you have pincushion distortion. The occurrence of pincushion or barrel distortion is closely related to field curvature. Are their others ... well not that actually have names in common usage. The names we normally use are the "primary aberrations" (astigmatism, spherical aberration, coma etc.), there are higher order terms which are usually much smaller and so have not got names in common usage. Of course it is possible to introduce other distortions into your images - just try imaging through a piece of non-flat glass. Andy Shaw
