Here's some info on the differences between S and PS Bronica SQ lenses:
http://www.buonaluce.com/S2PS.pdf
I notice it says the "S" lenses were not multicoated- is that so? Given that the "E" lenses for the ETR series were, and came out earlier, that doesn't seem to make much sense. The PS lenses came out in 1986, awfully late for multicoating, especially considering that according to their website, they stopped calling the ETR lenses MC in the mid-80's because "the multicoating technique was so universal as to not require that notice".
The original SQ came out in 1980, four years after the ETR; by then multicoating was in wide use, so it seems unlikely any of the "S" lenses were not multicoated. It's of course easy to check if anyone has any "S" lenses.
By looking for the multiple colored reflections in multicoated lenses vs. the two or maybe three colors from non-multicoated lenses. The color differences tend to be more distinct, too. The multicoated lenses I have seen all contain a green reflection as one of the colors, and as far as I recall, none of the non-multicoated ones I have seen do.
You could be right about the image circle and focus distance- also, were the f-stops different?
And yes, I've seen this distortion before, commonly on ultrawide angle lenses on 35mm.
Out of curiosity, is this kind of lens distortion familiar to anyone?
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