Do you know of any manufacturer that makes filters thin enough so that the can stay on the Voigtländer Bessa III even when folded? I would need yellow, red and polarising filter.
It's not really an answer, but if I had a folding Bessa, I wouldn't do it. But if you're feeling lucky, why not to try the low profile (meant to minimize vignetting on wide-angles) Hoyas? Or any other company that makes low profile filters.