An electron energy loss spectrometer for electron microscopy is disclosed having an electrically isolated drift tube extending through the bending magnet and through subsequent optics that focus and magnify the spectrum. An electrostatic or magnetic lens is located either before or after or both before and after the drift tube and the lens or lenses are adjusted as a function of the bending magnet drift tube voltage to maintain a constant net focal length and to avoid defocusing. An energy selecting slit is included in certain embodiments to cleanly cut off electrons dispersed outside the energy range incident on the detector, thereby eliminating artifacts caused by unwanted electrons scattering back into the spectrum.