Variation of the residual energy (dE_p/dx) in the residual optical aberrations as a function of the number of Zernike polynomials used (nz – without the piston term) and the power spectral density 1/n^pw. The figure shows two diaphragm values: when the gain is maximum and when it is equal to zero. The figure in 1/n presents strong residual oscillations owing to low-order aberrations.