Rolling shutter
An artifact of CMOS sensors that read pixels row-by-row from top to bottom. Fast-moving subjects appear sheared; flashes appear as bands. Affects most mirrorless and phone cameras.
In a rolling-shutter sensor, by the time the bottom row is read, the top row's data is milliseconds old. A vertical line panned horizontally appears tilted; a propeller appears curved.
When it matters
- Fast pans (sports, action).
- Subjects moving across the frame quickly.
- Flickering / pulsed lighting (LEDs, monitors in shot).
- Flash photography in high-speed sync.
How it's measured
Readout time, in milliseconds — how long the sensor takes to scan top to bottom. A Sony A1 reads in ~5 ms; a Nikon Z9 stacked sensor in ~4 ms; older mirrorless in 30+ ms.
Stacked sensors
"Stacked CMOS" designs separate the photo layer from the readout circuitry, allowing parallel readout and dramatically faster scan times. The Z9, A1, R3, and R5 II use stacked sensors and effectively eliminate rolling-shutter artifacts in most situations.
Phones
Computational photography stacks reduce visible rolling shutter by aligning frames in post — at the cost of pipeline latency.