Shutterbug Strasse

Posted by pipetman (A) on June 29, 2004 at 10:42:15

In Reply to: How to avoid "wonky distortion"?" - non-parallel lines posted by dvb on June 28, 2004 at 16:44:44:

Pincushion or barrel distortion is usually caused by lens aberrations and most visible when using wide angle lenses. Diverging parallel lines, however, are caused by perspective distortion. Your camera is not responsible for this distortion, but the way you take your pictures. If you want to avoid converging/diverging of parallel lines the object plane, the lens plane and the film (or sensor) plane all have to be oriented in parallel (look for a tutorial on large format camera photography for more in-depth info about this subject). With large format cameras you can adjust the lens and film plane independently and thus, correct for perspective distortion.
With a regular 35 mm camera it gets a little more tricky. As mentioned before you can do it through software (I use Picture Window Pro, which has a very neat feature for perspective correction, but PSP or PS should be able to do the same. Its not the same as pincushion or barrel distortion correction, though). You can also do it, when shooting. Imagine taking a picture of an amp. You want all the lines framing the faceplate to be be parallel, yet the sidepanels and the top should be visible. Imagine, pointing your camera straight at the faceplate, the camera/filmplane is parallel to the faceplate and so there is no distortion. Now move the camera to the left and up without tilting or rotating it (you have to step back far enough, so the faceplate doesn't fill the entire frame)!!! The side and top panels become visible, but since your camera is still parallel to the faceplate, there is no perspective distortion of the lines framing the faceplate. Your amp will be in the lower right corner of the picture, though and you have to crop away most of the picture that doesn't show the amp. Hope, that wasn't too confusing...