What limits the fastest shutter speed with an electronic shutter, and can it freeze fast-moving paper?
Asked 5/17/2015
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I understand how mechanical and electronic shutters work, but I’m confused about what determines the maximum shutter speed for an electronic shutter. Camera specs often list frame rate, but not a clear “max shutter speed” for electronic shutter operation.
For a CMOS sensor, is the limit set by how quickly the sensor can be read out? If so, does that mean the sensor’s readout time also limits electronic shutter use and causes rolling-shutter effects?
I need to photograph paper moving at about 17 m/s and want sharp images. How can I tell from a sensor’s specifications whether an electronic shutter will be fast enough, especially for a global-shutter sensor?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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The electronic shutter speed is limited by the rate at which the camera reads the image data from the sensor.
For most CMOS sensors, and therefore most regular DSLRs, the camera reads image data from it progressively, rather than reading all the image data instantaneously. As it reads, it resets the data held by those pixels.
If this process takes, for example, about 1/120 of a second to read the whole frame, this is the hard limit on the speed it can use as an "electronic shutter". For exactly the same reason, this also governs the maximum frame rate that it is able to shoot in video or in live view mode. If a camera is capable of recording video at 60fps, for example, then you know that the image data takes less than 1/60s to read.
A mechanical shutter is able to reach much higher speeds. When using the mechanical shutter, the shutter is closed for the duration it takes for the sensor to undergo a reset, then the shutter will open for a short time and expose the frame (one shutter curtain following the other), then the shutter will end up in a closed state. The data is then read from the sensor while the shutter is in the closed state after exposing. Therefore, the read rate of the sensor has no limitation on the shutter speed.
Mechanical shutters are able to reach high speeds because they involve two independent shutter curtains, and one curtain is able to closely follow the other such that one is opening while the other is closing at the same time. An electronic shutter is unable to do this: it's not possible to be progressively reading and resetting data from the sensor in two places at once.
Originally by user3422. Source · Licensed CC BY-SA 4.0
user3422
11y ago
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Generated from our catalog & community — verify before relying on it.
For most CMOS cameras, the practical limit of an electronic shutter is the sensor readout speed. The sensor is usually read progressively rather than all at once, so the full-frame readout time sets the limit for electronic shutter operation and also relates to max video/live-view frame rate.
So yes: if a full frame takes about 1/120 s to read, that’s effectively the limit for that type of electronic shutter, and fast motion can show rolling-shutter distortion.
That does not mean moving paper is automatically impossible to photograph sharply. What matters is how much the subject moves across the image during the exposure, which depends on magnification/distance as well as subject speed.
If you need to avoid rolling shutter and freeze motion, a mechanical shutter can help, and another common solution is to use flash as the effective exposure. If the ambient light is low and the flash provides most of the illumination, the very short flash duration can freeze the motion much better than the shutter timing alone.
For sensor specs, look for readout time / frame rate information, and whether the sensor is global shutter or rolling shutter.
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