A previous question asked about the origin of the ghost-like image of the fluorescent bulb on this image,
which turns out to be something called a filter flare, of which there are more examples here and here, and which is explained in this page as being caused by a combination of two reflections, one on the camera's sensor and then one on a filter (or any other flat optical element), probably outwards from the lens:
Image source, © Paul van Walree
I am specifically confused about why the 'ghost' image appears inverted (i.e. rotated by 180°); since it has undergone two reflections (with each one causing an inversion), naively, it should appear in the same orientation as the original image. Doing some rough additional ray tracings on the diagram above I can roughly see that the mirror image should indeed be inverted, but I'm struggling to square that with the rough heuristics that each reflection should cause an inversion. So what gives?
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