The diffraction limit depends on the pinhole radius, ro. It is defined by the angle Δθ = t0λ/2πro where t0 = 3.832. At the diffraction limit the number of lines equals θS/Δθ. Using this result we can solve for ro in terms of the number of lines which allows us to determine the optimum dimensions for a pinhole camera designed to capture an image of the Sun. For sunlight the wavelength which has the maximum intensity is λ = 555 nanometers.
The results show that the 1 mm pinhole was a little undersized. For 20 lines of resolution the diffraction limit requires ro = 1.5 mm.