Which of the following causes the image to get black corners?

"When a lens intended for a larger sensor is used on a smaller sensor camera, the projected image circle does not fully cover the sensor area, causing vignetting or black corners in the image."

— Axis Lens Guide White Paper

"Black corners or vignetting often result from a mismatch between lens and sensor size."

— Axis Communications Academy, Network Video Fundamentals, 2022