A method of using a Transmission Charged Particle Microscope comprising: A specimen holder, for holding a specimen; A source, for producing a beam of charged particles; An illuminator, for directing said beam so as to irradiate the specimen; An imaging system, for receiving a flux of charged particles transmitted through the specimen and directing it onto a sensing device; A controller, for controlling at least some operational aspects of the microscope, in which method the sensing device is chosen to be an EELS/EFTEM module comprising: An entrance plane; An image plane, where in EELS mode an EELS spectrum is formed and in EFTEM mode an EFTEM image is formed; A slit plane between said entrance plane and image plane, where in EFTEM mode an energy dispersed focus is formed; A dispersing device, between said entrance plane and slit plane, for dispersing an incoming beam into an energy-dispersed beam with an associated dispersion direction; A first series of quadrupoles between said dispersing device and slit plane; A second series of quadrupoles between said slit plane and image plane, which dispersing device and quadrupoles are arranged along an optical axis, whereby, for a Cartesian coordinate system (X,Y,Z) in which said optical axis is disposed along Z, said dispersion direction is defined as being parallel to X, comprising the following steps: In said first quadrupole series, exciting one or more quadrupoles so as to deflect an off-axis non-dispersive YZ ray leaving said dispersing device onto a path paraxial to said optical axis from said slit plane to said image plane; In said second quadrupole series, exciting either: (a) A single quadrupole; or (b) A pair of adjacent quadrupoles, so as to focus said energy-dispersed beam onto said image plane.