There is supposed to be a chart that comes with the camera showing how to translate a f22 exposure reading to a correct exposure for the pinhole size. The chart would seem to indicate a stop size of around f190. Don’t forget that reciprocity has to be added to the transposed reading. I have a 6x6 Zero 2000 that has an aperture of f138, the advice given by them is to meter at f8 then reduce the reading by 8 stops finally adding reciprocity to that number.