Lens aberrations

Distortion

Camera lens manufacturers try to eliminate the distortion, which is a natural effect of lens projection. But the success of adjusting the distortion using aspherical lenses is limited by the high technical complexity, especially when the focal length of the lense is variable. With certain focal lengths even the most expensive lenses show distortion residues which particularly appear at the image edges and can induce very unwanted effects. This is particularly visible in photographs of straight lines or edges taken with zoom lenses adjusted to extreme wide angle (more barrel distortion) or to extreme telephoto (more trapezium distortion).

There is a lot of image processing software which enable the photographer to manually adjust these lens aberrations quite far for single images. Due to the fact that in most cases the distortion is a compound of the pincushion and the barrel distortion, this procedure needs quite a long time and it´s doubtful whether it is worth it. Anyway if the images shall be used for measuring distances or angles, the needed precision can hardly be achieved in the manual way.

Vignetting

Vignetting, which is a light fall-off at the image edges, is one more problem that appears with camera lenses. This effect mainly increases with lower f-stops and higher focal lengths. As this defect also does not have a linear progression it is difficult to remove it with common image processing software and brightness/contrast.