Are mirrorless cameras more prone to sensor dust?

Hi,

It seems to me that when you change lenses on a DSLR the mirror is always down and forms a barrier to dust and dirt getting to the sensor (and the focal plain shutter?).

On mirrorless cameras there is no mirror (obviously), so it would seem logical that the sensor is much more open to dust and dirt, especially since the shutter must be open at all times to allow live view off the sensor.

While I'm at it, another question, perhaps dumb. Is the lens always wide open for live view and stops down when I press the shutter release and the shutter first blocks off the light path to the sensor to then open for taking the picture? There doesn't seem a way to stop down the e-mount lenses to see the DOF like you can on most DSLRs.

Thanks for any enlightenment,

Ralph

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