Pinhole Designer lets one choose Lord Rayleigh's constant, first Fresnel zone constant, or a user constant. The first two yield pinholes rather larger than optimum for on-axis sharpness. Many of us prefer a 1.5 or 1.4 user constant. The larger constants may sacrifice a little on-axis sharpness for improved off-axis sharpness, and reduce exposure time slightly. This has often been discussed on http://www.f295.org/Pinholeforum/forum/Blah.pl?
Originally Posted by wildbillbugman