The aperture varies from one Noon to another. My Noon 6x12 has an aperture of /207 but Ive seen others with wider and narrow apertures. Most of them appear to be .23.29mm (/207260).

Each Noon comes with a birth certificate. On one side it has details like the aperture and serial number and on the other side it has a reciprocity failure chart for Ilford FP4. If you dont have the certificate for your Noon I can find my copy and share it with you.