If we now consider the situation where L ≫ ≫ ( x + a / 2 ) , the path length becomes S ≈ ≈ ( L + ( x + a / 2 ) 2 2 L ) = L + x 2 2 L + x a 2 L + a 2 8 L This is the Fresnel approximation. To further simplify things: If the diffracting object is much smaller than the distance L , the last term will contribute much less than a wavelength to the path length, and will then not change the phase appreciably. That is a 2 L ≪ ≪ λ λ . The result is the Fraunhofer approximation, which is only valid very far away from the object S ≈ ≈ L + x 2 2 L + x a 2 L Depending on the size of the diffraction object, the distance to the object and the wavelength of the wave, the Fresnel approximation, the Fraunhofer approximation or neither approximation may be valid. As the distance between the measured point of diffraction and the obstruction point increases, the diffraction patterns or results predicted converge towards those of Fraunhofer diffraction, which is more often observed in nature due to the extremely small wavelength of visible light.