Wavelength average ratio of the two approaches for estimating the image quality at the focal plane of a telescope (i.e., ε_LE(λ)/ε_LE(λ, $\mathcal{D}$ from Eqs. 5 and 6) as a function of the ${ℒ}_0$ of the turbulence for the spectral ranges 3700–9300 Å (top panels); 0.93–2.5 μm (middle panels); and 2.5–5.0 μm (bottom panels) at excellent (left panels), typical (central panels), and fair (right panels) atmosheric turbulence conditions. We considered only those conditions with ${ℒ}_0$/r₀>20, ensuring that errors are within ±1%. The shaded area marks the 1σ of the mean. The colors indicate different telescope diameters as indicated at the right side of each panel.