How shutter speed works when recording video
Asked 9/20/2012
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I understand shutter speed for still photos as the time the shutter opens and closes, which is why you can hear the mechanical shutter. But when recording video, I don’t hear that sound. How is exposure controlled in video mode? Is the shutter physically opening and closing for every frame, or is something else happening? For example, at 24 fps, does that mean the shutter would need to operate 24 times per second?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
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The shutter you hear is a mechanical shutter and it cannot on a DSLR move fast enough to shoot at video speeds which is between 24 and 60 FPS. High-end mechanical shutters usually top at 12 FPS.
The shutter used in video and high-speed drive on some cameras is an electronic shutter. There are no moving parts involved and hence no sound. The sensor simply discharges itself at regular intervals.
The issue with electronic shutters is that they cannot make the sensor stop being sensitive to light, so while it is being discharged, some light still gets accumulated. Mechanical shutters are still being used to avoid this happening with stills. For video we just put with the consequences, namely vertical streaking for CCDs (because CCD rows are discharged by shifting into the next ones) and jello-effect for CMOS (because each row is read at a different time).
Things are a little more complicated actually because video has a frame-rate (24 FPS to 30 FPS) and a shutter-speed (which maxes our at 1 over the frame-rate, so 1/24 for 24 FPS). So you may be shooting 24 FPS video in bright light with a 1/1000s shutter-speed, meaning that the frame is read after 1/1000s but the sensor is cleared via the electronic shutter after 1/24s for the start of the next frame.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
13y ago
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In video mode, the sound you normally hear for still photos usually isn’t happening because the camera is typically not using the mechanical shutter for each frame. Mechanical shutters generally aren’t fast enough to cycle continuously at common video rates like 24–60 fps.
Instead, video is usually captured with an electronic shutter: the sensor is read/reset at regular intervals with no moving parts, so there’s no shutter click. The shutter is effectively left open, and each video frame’s exposure is controlled electronically by how long the sensor collects light before being read.
So yes, frame rate and exposure timing are related, but not necessarily through physical shutter movement. At 24 fps, the camera records 24 frames each second, but that does not mean a mechanical shutter opens and closes 24 times per second.
A downside of electronic shutter operation is that the sensor may still collect some light during readout, which can cause artifacts such as rolling-shutter “jello” effects or streaking, depending on the sensor design.
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