Let us consider the well-known problem of diffraction of an initially plane wave with wave vector k on a round hole of radius a in a thin screen. If the radius of the hole is sufficiently large, so that ka ≫ 1, then the wave remains essentially plane after going through the hole, with a small distortion due to a diffraction on the edges of the hole. Now we start diminishing a. The wave gets more and more distorted after going through the hole. Indeed, the allowed transverse component of the wave vector in it increases in accordance with the uncertainty relation Δk_ta ≳ 1. At last, with a ∼ 1/k (or a ∼ λ, where λ is the wavelength) the outgoing wave becomes spherical, since in this case the transverse component of the wave vector in it k_t ≳ 1/a reaches its maximum allowed value k.