[popo]

Just for some ball park numbers, according to Canon, their coatings can reduce reflections to a fraction of 1%. To put that into photographic terms, let's just round it about 8 stops down. It wont be precise or exact, but I'm just going for a ball park figure here.



For a flat piece of anti-reflection coated glass angled so it is not parallel to the sensor, the main reflection from subject reaching sensor will reflect off the inner then outer surface, so it is about 16 stops down from the original.



In Sony's case, we're dealing with a mirror surface. The direct light loses a little due to the mirror. The 1st unwanted reflection would bounce off the inner surface, then off the mirrored surface and onto the sensor. Let's say the reflected amount is about 2 stops down, so combined with the unmirrored surface that's about 10 stops down from original.



So compared to the unmirrored case, there is a fair difference of perhaps 6 stops. You can argue the figures used are wrong, and that's entirely likely. If the anti-reflection coating isn't so good, there will be more reflections and the difference is reduced. But the bottom line is still a mirror surface will reflect much more than a typical glass surface, and it will be worse.



As for sensor reflections of uncoated lens elements, I think we have a different mechanism here. I think every lens I've seen has a non-flat rear element, typically convex. The curved nature will disperse any reflections and that will help make them less noticeable.