In addition to the deflection of the charged particles during their passage through an electrostatic deflector, it is proposed to impose a gradual retardation along their path, so that they leave the instrument at lower energy. By means of a new figure of merit involving the usual optical characteristics (dispersion, aberration, and magnification), it is shown that this principle can improve the performances of electron spectrometers, taking the 127° cylindrical electrostatic analyzer as an example. Calculations of energy transmission functions show that, at constant energy resolution, an increase of about 100% in the transmitted intensity may be expected for a retardation factor of 10. Further considerations on the space charge in a monochromator show that, since the charge density is mainly concentrated at the entrance and relatively unaffected by the retardation, the principle could be efficient for electron monochromators, too.