Optical vignetting is a phenomenon where the corners of an image appear darker than the center. This effect occurs due to the lens design and the way light enters the camera. It can be more pronounced when using wide apertures or certain types of lenses, such as wide-angle lenses. Photographers often encounter optical vignetting when shooting with filters or at extreme angles. While some may find it undesirable, others use it creatively to draw attention to the subject in the center of the frame. Understanding optical vignetting can help photographers make informed choices about their equipment and settings.