Optical vignetting is caused by light hitting the lens aperture at a strong angle - an internal physical obstruction. This effect is often noticed in images taken with wide angle and wide aperture lenses used with wide open apertures. Even many of the best lenses have optical vignetting.

What is the purpose of vignetting?

Vignetting is a reduction of an image's clarity at the periphery compared to the center of the image. It may be gradual or abrupt. Usually photographers think of it as a darkening that starts at the corners, and, in some cases, spreads along the edges of the photo to create a rounded off image.

How do you prevent a vignetting wide angle lens?

There are a few things you can do to avoid minimise vignetting. Before you start shooting, avoid stacking filters with your wide-angle lens. If you're shooting with a CPL or ND filter, remove your UV filter. And try to use the correct fixed ND instead of stacking multiple ND filters.