A method of operating a Post Column Filter (PCF) in a Scanning/Transmission Electron Microscope, and a Post Column Filter configured to operate according to the method. In an embodiment, the method includes receiving, at an entrance plane, an incoming beam of electrons; dispersing, by an energy dispersive element, the incoming beam of electrons into an energy dispersed beam of electrons; disposing a first plurality of quadrupoles between the entrance plane and a slit plane; operating the PCF in an EELS mode; and operating the PCF in an EFTEM mode. Operating the PCF in an EELS mode includes exciting one or more quadrupoles of the first plurality of quadrupoles at a first excitation level, wherein the first excitation level does not enlarge the energy dispersion of the energy dispersed beam of electrons; and forming an image of the energy dispersed beam of electrons on the image plane, the image being an EELS spectrum. Operating the PCF in the EFTEM mode includes including a slit at the slit plane in an optical path; exciting one or more quadrupoles of the first plurality of quadrupoles at a second excitation level, the second excitation level different from the first excitation level; forming an energy dispersed focus of the energy dispersed beam of electrons on the slit at the slit plane; and enlarging the energy dispersion of the energy dispersed beam of electrons caused by the energy dispersive element based on the one or more first plurality quadrupoles excited at the second excitation level.