I would use a 0.15mm diameter pinhole. This was calculated in Pinhole Designer with a user constant of 1.4, derived through research and experimentation. Pinhole photography is not a matter of mathematical precision; personal preferences are important. Different subjects may work best with slightly different diameters. In wide-angle cameras the diameter may be increased for improved off-axis performance with degraded center sharpness. Others may prefer slightly smaller or larger diameters based on other science or actual photography. The magic and mystery of pinhole photography may be frustrating to those who believe in exact answers to any question. To others, a little quirkiness adds pleasure to photography.