Actually, that's not true. However, going beyond requires deconvolution of the wavelength-scaling diffraction pattern, so it's only practical if you have narrow

Actually, that's not true. However, going beyond requires deconvolution of the wavelength-scaling diffraction pattern, so it's only practical if you have narrowband radiation (stops working at 10~20% FWHM bandwidth). Suitable sources include monochromatic LEDs, most lasers, and some gas discharge lamps (notably low pressure sodium).