Quote Originally Posted by MattKing View Post
Was there a filter on the lens?
No filter, no hood. Essentially all the light is artificial; the room is pretty dim (it was late afternoon on a cloudy day, and there are minimal windows in the upper gallery where this was taken), but off to the right of the frame there are in fact several light sources (the lighting for a photo exhibition).

I do think I see some lightening to the right of the "rainbow", especially at the top of the frame---however, I'm pretty sure that the "map of Africa" shape in that area is actual discolouration on the ceiling, not a light artifact.

Supposing it were a processing issue, is there a plausible mechanism? This frame is in the middle of the roll, for what that's worth. I don't know how Chrome do their E-6 process.