Thank you everyone for you advice. I got the Noon Pinhole camera last week and shot and deved a roll during the weekend. Here's one of the 6x12 shots I took on Kodak T-Max 100. I calculated exposure time based Joe VanCleave's formula (f/R)^2 x Tm = Tc. Because the exposure times were only around 4-5 seconds, I didn't add any time for reciprocity failure.

The shot (click to view larger version):

The camera: