Why a Spinning Propeller Can Look Bent
A camera sensor does not always capture the whole image at one instant. In a rolling-shutter camera, it records narrow horizontal rows in sequence, usually from the top of the frame to the bottom. The gap between rows may be tiny, but a fast-moving object can travel noticeably during the full scan.
Each row therefore shows the propeller at a slightly different moment. A blade that was near one side of the frame when the upper rows were recorded may have swung elsewhere by the time lower rows were captured. The resulting picture combines different positions into one image, making a straight blade look curved, tilted, or even disconnected from the hub.
The Image Is Stretched in Time
The sensor’s scan gives the photo a built-in time gradient: the top represents an earlier instant than the bottom. As the propeller turns, its blades cross the rows at changing positions. The camera has not physically bent the blades; it has assembled a single frame from slices of motion that do not share the same timestamp.
The exact distortion depends on the propeller’s rotation, the camera’s scan direction, and how the camera or object moves. A different scan direction can change the apparent lean or bend. This is why the same propeller may look nearly normal in one frame and dramatically warped in the next.
Why Faster Shutters Can Still Distort
A short exposure can make each individual row sharp by limiting motion blur, but it does not necessarily make all rows record at once. The rolling-shutter effect comes from the timing difference between rows, not simply from a long exposure. Cameras with a global shutter capture the whole frame together, avoiding this particular mismatch; other ways to reduce it include slowing the motion or using a camera that scans the sensor more quickly.
That strange propeller shape is thus a record of time passing across the frame: different parts of one image can show the same object at different moments.
