Vignetting
Vignetting is a darkening toward the corners of a frame relative to the center, most commonly caused by a lens's optical design allowing less light to reach the sensor's edges than its middle. It's typically most pronounced at a lens's widest aperture and diminishes, often disappearing entirely, as the lens is stopped down a stop or two.
Separate from optical vignetting, mechanical vignetting can occur when a lens hood, filter stack or adapter physically blocks light at the frame's edges, and this type doesn't improve with aperture the way optical vignetting does. Most photo-editing software includes vignette correction profiles matched to specific lens and camera combinations, and some photographers add vignetting deliberately as a stylistic choice to draw attention toward the frame's center.
Frequently Asked Questions
Does vignetting mean my lens is defective?
No — some degree of optical vignetting, especially wide open, is a normal characteristic of most lens designs, not a flaw specific to one copy, and it's easily corrected in post-processing if unwanted.
Why would a photographer add vignetting deliberately?
A subtle darkened edge naturally draws a viewer's eye toward the center of the frame, which some photographers use as a compositional tool independent of whatever vignetting the lens itself produced naturally.