Four causes, cheapest to check first: a filter or step ring in front, a hood meant for another lens, the lens wide open, or a lens whose image circle does not cover the sensor behind it.
Dark corners are common and almost always mechanical or optical rather than a camera fault.
The order worth testing
- Remove any filter or step-up ring. A thick mount sits in the path of the widest angles, and a ring pushes it further forward still. Four titles here print a filter thread in three different diameters, so a ring is often involved.
- Check the hood. One made for a longer focal length cuts into the frame of a wider one, and hoods are their own family here precisely because they are lens-specific.
- Stop down two stops. Optical vignetting is worst wide open and improves quickly.
- Check the image circle. A lens built for the smaller format on a larger body illuminates only part of the frame — six titles here carry the suffix marking the smaller circle, three another.
Which of the four is not a fault
The fourth. A lens covering a smaller circle is doing what it was designed to do, and the maker’s own answer is a crop mode on the body, published per body rather than implied by the mount.
What it is never
The sensor, which records uniformly, and the pixel count. Neither produces a dark corner, and neither fixes one.
What people ask before they commit
How do I tell vignetting from an image circle problem?
Stop the lens down two stops and take the frame again. Optical vignetting lightens markedly; a circle that does not cover the sensor produces corners that stay dark at every aperture, often with a visibly curved edge. The second is a compatibility fact rather than a fault.
Can software remove it?
Corner shading corrects well, because it is smooth and predictable, and many raw converters apply a profile automatically. A hard-edged circle cannot be corrected — there is no information outside it — which is why the two causes are worth telling apart before reaching for a slider.
Last reviewed 12 September 2026