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 (QI, QII) between said dispersing device and slit plane; - A second series of quadrupoles (Q1, Q2, Q3, Q4) 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, characterized by the following steps in EELS mode: - In said first quadrupole series (QI, QII), 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 (Q1, Q2, Q3, Q4), 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; - wherein, for a beam energy E and detected spectral energy spread ΔE, an energy parameter ΔE r /E r has a value > 0.0125, where: ΔE r E r = 1 + E mc 2 1 + E 2 mc 2 ΔE E with m the electron mass and c the speed of light. - 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, - 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 (QI, QII) between said dispersing device and slit plane; - A second series of quadrupoles (Q1, Q2, Q3, Q4) 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, characterized by the following steps in EELS mode: - In said first quadrupole series (QI, QII), 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 (Q1, Q2, Q3, Q4), 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; - wherein, for a beam energy E and detected spectral energy spread ΔE, an energy parameter ΔE r /E r has a value > 0.0125, where: ΔE r E r = 1 + E mc 2 1 + E 2 mc 2 ΔE E with m the electron mass and c the speed of light. - In said first quadrupole series (QI, QII), 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 (Q1, Q2, Q3, Q4), 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; (a) A single quadrupole; or (b) A pair of adjacent quadrupoles, so as to focus said energy-dispersed beam onto said image plane; - wherein, for a beam energy E and detected spectral energy spread ΔE, an energy parameter ΔE r /E r has a value > 0.0125, where: ΔE r E r = 1 + E mc 2 1 + E 2 mc 2 ΔE E with m the electron mass and c the speed of light.