It's not quite as simple as Ken Rockwell states. It depends on the lens focal lenght type of design etc.

LF Tessar's, and similar designs like Xenar's of around 135mm to 150mm etc are generally bests at f22 and in fact give poor edge/corner sharpness until stopped down to f16.

However more modern 6 element designs are far better optimised and will give better results at wider apertures, this is where depth of field tables, calculators etc become more useful.