"The word vignetting is
used to indicate an unintended darkening of the image corners in a photographic image.
There are three different mechanisms which may be responsible. Natural
and optical vignetting are inherent to each lens design, while
mechanical vignetting is due to the use of improper attachments to the
Natural and optical vignetting lead to a gradual transition from a
brighter image center to darker corners. At large apertures both
phenomena are present and the combined effect is often designated by
the term ‘illumination falloff’.
Mechanical vignetting can also give rise to gradual falloff, although
the usual connotation is one where it causes an abrupt transition with
entirely black image corners.
The Vignetting Reducer will …(hold your breath)… reduce vignetting to a
minimum by performing some computer magic. Interested?