Today’s Question: For cameras that have an electronic shutter mode available wouldn’t you get the same benefit as from a “global shutter”? I would think in this mode the sensor would not be read row by row, or if it is that it would be so fast as to not be relevant.
Tim’s Quick Answer: An electronic shutter would not provide the benefits of a global shutter, and in fact in many cases an electronic shutter represents a disadvantage compared to a mechanical shutter.
More Detail: In a previous answer I addressed the concept of a global shutter, which is an image sensor that can read the data from the entire sensor at once, rather than reading that data line by line. The line-by-line readout can result in a rolling shutter distortion effect when photographing fast-moving subjects.
An electronic shutter is a feature of some cameras where you can shoot silently because the mechanical shutter doesn’t need to be activated. Instead of using the mechanical shutter to control how long the sensor is exposed to the light passing through the lens, the image sensor controls exposure by turning the photosites on and off.
With an electronic shutter the speed at which the camera can read data from the sensor determines the limitations of the electronic shutter. By contrast, with a mechanical shutter the sensor can activate photosites on the sensor before the shutter starts moving and can deactivate the photosites after the shutter has closed, because the shutter itself controls the flow of light to the sensor.
When a mechanical shutter isn’t in use the electronic shutter can therefore result in a greater rolling shutter effect than would have been present when using the mechanical shutter. Therefore, when photographing particularly fast-moving subjects it is generally better to use the mechanical shutter rather than the electronic shutter option.
Of course, as cameras continue to get faster and faster the risk of the rolling shutter effect is reduced. But as noted previously, the only way to eliminate the risk of a rolling shutter effect is to use a camera that features a global shutter, such as the new Sony a9 III (https://bhpho.to/3FP2f3B).