Why do many mirrorless cameras leave the shutter open when powered off?
Asked 5/11/2014
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When changing lenses on a mirrorless camera, the sensor is exposed and can collect dust. Film cameras often sit with the shutter closed, so why don’t mirrorless cameras usually close the shutter automatically when the camera is turned off to help protect the sensor?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
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The shutter is closed by default on film cameras because if it was open it would have exposed the film while the camera is not in use - it's simply this way because there's no other choice.
In mirrorless cameras, the shutter must be open when the camera is on but not taking pictures because otherwise the camera can't show an image on the screen or digital viewfinder (if there is one).
Now, since the mirrorless camera shutter must be designed to be open most of time when the camera is on it makes engineering sense to keep it open also when the camera is off - this way you design the shutter so it's always open and only closes when it needs to - this is simpler (and so, cheaper) than it is to design a shutter that's open-by-default when the camera is on and closed-by-default when the camera is off.
And the shutter is not a good protector against sensor dust anyway, any dust of the closed shutter will be thrown off violently when the shutter opens (it opens really fast) and bounce around inside the camera until it sticks to something, no camera I know off has a mechanism to safely dispose of shutter-dust
Originally by user2481. Source · Licensed CC BY-SA 4.0
user2481
12y ago
0
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Because mirrorless cameras need the shutter open during normal operation so the sensor can provide the live view for the rear screen or EVF. That makes an open-at-rest design practical: the shutter stays open most of the time and only closes briefly to make an exposure. Designing it this way can be simpler and avoids using battery power just to hold the shutter open whenever the camera is on.
Film cameras are different: if the shutter were left open while idle, the film would be exposed, so a closed shutter is effectively required.
There’s also a durability concern. The shutter is a delicate mechanical assembly; using it as a protective door during every lens change could expose it to accidental damage. In many cases, a bit of sensor dust is less serious than damaging the shutter mechanism.
So the main reasons are live-view operation, power/mechanical design, and protecting the shutter itself.
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