An inspection system comprising: a stage for mounting an object to be inspected; at least one charged-particle source for generating at least one beam of charged particles, at least one multi-aperture plate having a plurality of apertures formed in the plate, wherein the plurality of apertures are arranged in a pattern, wherein the system is configured to form an array of charged-particle beamlets from the at least one beam of charged particles downstream of the multi aperture plate; a first voltage supply for supplying predetermined first voltages to the plurality of apertures; a first single-aperture plate (367 3) arranged at a distance upstream or downstream of the multi-aperture plate, the first single-aperture plate (367 3) having a single aperture for allowing the beam of charged particles or the plurality of charged-particle beamlets to pass therethrough; and a second voltage supply for supplying a predetermined second voltage to the first single-aperture plate (367 3), an objective lens for focusing the array of charged particle beamlets on the object to be inspected; and a detector arrangement for detecting secondary electrons from the object generated by the array of charged particle beamlets, to produce an array of signals corresponding to the secondary electrons generated by substantially a single charged particle beamlet in the array of charged particle beamlets; characterized in that at least one of the following conditions is fulfilled: the distance between the multi-aperture plate and the first single-aperture plate (367 3) is selected such that it is less than one half of an average focal length of the apertures of the multi aperture plate, and the distance between the multi-aperture plate and the first single-aperture plate (367 3) is selected such that an average electrical field on a surface of the multi aperture plate at a center thereof is higher than 100 V/mm. a stage for mounting an object to be inspected; at least one charged-particle source for generating at least one beam of charged particles, at least one multi-aperture plate having a plurality of apertures formed in the plate, wherein the plurality of apertures are arranged in a pattern, wherein the system is configured to form an array of charged-particle beamlets from the at least one beam of charged particles downstream of the multi aperture plate; a first voltage supply for supplying predetermined first voltages to the plurality of apertures; a first single-aperture plate (367 3) arranged at a distance upstream or downstream of the multi-aperture plate, the first single-aperture plate (367 3) having a single aperture for allowing the beam of charged particles or the plurality of charged-particle beamlets to pass therethrough; and a second voltage supply for supplying a predetermined second voltage to the first single-aperture plate (367 3), an objective lens for focusing the array of charged particle beamlets on the object to be inspected; and a detector arrangement for detecting secondary electrons from the object generated by the array of charged particle beamlets, to produce an array of signals corresponding to the secondary electrons generated by substantially a single charged particle beamlet in the array of charged particle beamlets; characterized in that at least one of the following conditions is fulfilled: the distance between the multi-aperture plate and the first single-aperture plate (367 3) is selected such that it is less than one half of an average focal length of the apertures of the multi aperture plate, and the distance between the multi-aperture plate and the first single-aperture plate (367 3) is selected such that an average electrical field on a surface of the multi aperture plate at a center thereof is higher than 100 V/mm. the distance between the multi-aperture plate and the first single-aperture plate (367 3) is selected such that it is less than one half of an average focal length of the apertures of the multi aperture plate, and the distance between the multi-aperture plate and the first single-aperture plate (367 3) is selected such that an average electrical field on a surface of the multi aperture plate at a center thereof is higher than 100 V/mm.