A device for providing an energy filtered charged particle image particularly an electron image in the form of an electron energy analyzer which acts as a band-pass filter whilst maintaining the spatial integrity of the electron image in a uniform magnetic field. It embodies new electron optical properties wherein image electrons injected parallel to the magnetic field are guided, using crossed electrostatic and magnetic fields, to a low-pass electron mirror and then through a high-pass retardation filter. Non-uniform electrostatic deflection fields are used to compensate for the energy-dependent dispersion of the crossed fields whereby it is possible to correct for image distortion resulting from such dispersion.