Today’s Question: With the advent of the new products (ie: Canon’s R5/R6 today) rolling out almost monthly, I see photos of cameras without a lens attached and the sensor seems to be in a very vulnerable position. Is there a much higher risk of sensor dust given that there isn’t a mirror in front the sensor when changing lenses??
Tim’s Quick Answer: I would contend that the mirror of a digital SLR provides a very slight degree of protection against blemishes on the image sensor. I do not, however, think this is a reason to avoid a mirrorless camera.
More Detail: Needless to say, I have not conducted any testing that would even remotely qualify as a scientific study of this issue. I also don’t know of any other such studies that would provide a definitive answer.
The primary benefit of a mirror in the context of contaminants getting on the image sensor is the fact that the mirror physically blocks the sensor to some extent. Similarly, the shutter mechanism (in cameras that include a physical shutter mechanism) blocks the sensor.
However, physically blocking the sensor when changing lenses won’t protect the sensor from all contaminants. For example, a water droplet that strikes the mirror on a digital SLR might evaporate and never cause any problem for the image sensor. Dust, on the other hand, can linger inside the camera and eventually get attached to the image sensor.
Keep in mind that the image sensor in a camera creates static electricity that can act like a magnet for dust. So, while a mirror or shutter mechanism may protect the image sensor from certain sources of contamination, any dust that gets into the camera could eventually find its way onto the image sensor.
In my mind, much of this is theoretical, and only reflects the potential statistical chances of a particular contaminant getting on the image sensor. To me it is more important that you exercise caution when changing lenses, regardless of what type of camera you’re using. And I also think the many other features of a given camera model are more important to consider when it comes to making a purchase decision, rather than whether or not the camera happens to have a mirror.