The conditions for being in the far field and exhibiting an Airy pattern are: the incoming light illuminating the aperture is a plane wave (no phase variation across the aperture), the intensity is constant over the area of the aperture, and the distance formula_11 from the aperture where the diffracted light is observed (the screen distance) is large compared to the aperture size, and the radius formula_12 of the aperture is not too much larger than the wavelength formula_13 of the light. The last two conditions can be formally written as formula_14 .