[popo]

I just played about with some calculations. Of course there are a lot of unknown variables.



If we assume the mirror is 45 degrees from vertical with the silvered surface on the outside, and it has a refractive index of 1.5, then an unwanted reflected image would be formed at a spacings multiples of about 1.07x the thickness of the mirror.



For the mirrored surface reflecting at 30% and the glass surface at 1%, each additional reflected image is about 7.2 stops down from the previous. If you assume the coating is even better at 0.1% reflection then the figure becomes 10.5 stops. With such huge losses, the reflection of the reflection is going to be so far down it is unlikely to be significant short of pointing the camera at a very bright point source.



So looking back at the sample image earlier, or more precisely the original of it, the spacing of the secondary image is about 12 pixels offset from the original, working out to be about 0.06mm. That's pretty small! Even if they used a high refractive index material and a more vertical angle the mirror would still have to be pretty thin, a fraction of a mm.



I can refine the above if anyone has more precise values for any of the variables.