The image sensor of a mirrorless camera provides a live feed to allow composition, focus, and exposure to happen before the shutter is released. This necessitates the sensor to be uncovered much of the time, so how does the shutter work? There are three different shutter modes found in mirrorless cameras: electronic first curtain, electronic, and mechanical. The majority of models are factory-configured to use electronic first curtain mode. The EOS R3, with a special back-side illuminated high-speed sensor, employs an electronic shutter as its default.
With electronic first curtain shutter, the exposure time is started by electronically switching on the sensor readout and ended by the physical closure of the second shutter curtain. This minimizes the lag between shutter press and the start of the exposure. However it does result in slightly less attractive bokeh when shooting wide open with fast aperture lenses.
