Since this ratio determines the spacing of the individual fringes, it determines the width of the overall diffraction pattern. The diffraction pattern will have a central fringe that is twice as wide as the other fringes. If the wavelength is held constant and the aperture or gap is made smaller, greater diffraction is seen. If different wavelengths enter the same gap, those with a small wavelength will undergo less diffraction than those with longer wavelengths. For example, the use of an aperture of a given width will result in greater diffraction of red light than blue light just as occurred with double-slit diffraction (Figure 11.15). Do not think of diffraction effects as suddenly occurring at a specific wavelength. Although we need λ ≈ w for a good diffraction pattern, diffraction will gradually increase if the values of λ and w are made to gradually approach one another.
Taken from the Heinemann book.