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According to an answer to the question Why shutter is not closed by-default on mirrorless cameras as it's closed on film ones? mirrorless cameras have a "default open" shutter.

Mirrorless cameras also, obviously, do not have a mirror.

Thus, when changing the lens, a mirrorless camera has a fully exposed sensor. A DSLR, on the other hand, has a closed shutter and a mirror in front of the sensor.

Do these properties make mirrorless cameras more susceptible to sensor dust?

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The air is full of dust. It's floating around everywhere all the time. When you open the lens in a dusty environment (which is to say "every environment that isn't a clean room"), dust gets into the light-box of the camera.

You didn't ask, but this is why seems silly to advise people to point their cameras down while changing lenses. Observe how dust moves in the air: it falls down gradually, eventually, but mostly it responds to air currents going up, down, left, right, wherever. If you're in an especially dusty situation, the important thing is fast.

The risk isn't really that dust might fall right on the sensor while it's exposed. It's that dust floating around will eventually settle there and stick. As the question you link notes, the shutter itself doesn't protect much against this, since it opens "violently", scattering dust around.

In fact, arguably, the larger mirror box in a DSLR is just more space for dust to drift around in waiting to cause a problem. I don't know if that's a real-world issue, though. In my experience, the automatic dust-removal systems all cameras now include have become very good in the last decade.

The one thing I know for sure is that having the sensor closer to the opening makes it easier to clean once some problematic dust does build up. So, advantage mirrorless for that, at least.

  • On the other hand, the larger mirror box of a DSLR allows more dust to be randomly distributed over its surfaces before having the same average density as the smaller light box of a MILC. The "point down" thing may not be true for dust small enough to be governed by the rules of Brownian motion, but it certainly is true for larger things that are still very small, such as fine grass clippings on an athletic field after it as been mowed. – Michael C Feb 25 at 0:32
  • If you're in an especially dusty situation... Don't remove the lens from the camera. – xiota Mar 3 at 16:50
  • @xiota Zero is the shortest time of all :) – mattdm Mar 3 at 16:55
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YES They are more susceptible to dust Some DO close the shutters when they are off to reduce this. Many are now including ultrasonic sensor cleaners. Lastly IF (internal focus) lenses help a lot whereas zooms suck dust in to float and settle. Newer bodies are weather sealed and this helps too

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