A multi-axis magnetic lens, comprising: a pair of parallel magnetic conductor plates (40, 41) having a plurality of through holes (4, 6, 8, 5, 7, 9) for allowing a plurality of charged particle beams to pass, the pair of parallel magnetic conductor plates (40, 41) comprising an upper magnetic conductor plate having a plurality of upper holes (4, 6, 8), and a lower magnetic conductor plate having a plurality of lower holes (5, 7, 9) aligned with respective upper holes (4, 6, 8) constituting a plurality of sub-lens modules; and a common excitation coil for providing magnetic flux to the plurality of sub-lens modules; wherein each sub-lens module further comprises: an upper magnetic insert ring arranged inside the upper hole; and a lower magnetic insert ring arranged inside the lower hole; characterized in that: either the upper magnetic insert ring and the lower magnetic insert ring have a much higher magnetic permeability than, and are in contact with, their respective magnetic conductor plates (40, 41), or an upper gap is present between the upper magnetic insert ring and the upper magnetic conductor plate and a lower gap is present between the lower magnetic insert ring and the lower magnetic conductor plate, with both the upper gap and the lower gap having at least one vacuum layer or being filled with one non-magnetic material layer, such that each pair of upper magnetic insert ring and corresponding lower magnetic insert ring function as a pair of magnetic pole pieces of the respective sub-lens module. a pair of parallel magnetic conductor plates (40, 41) having a plurality of through holes (4, 6, 8, 5, 7, 9) for allowing a plurality of charged particle beams to pass, the pair of parallel magnetic conductor plates (40, 41) comprising an upper magnetic conductor plate having a plurality of upper holes (4, 6, 8), and a lower magnetic conductor plate having a plurality of lower holes (5, 7, 9) aligned with respective upper holes (4, 6, 8) constituting a plurality of sub-lens modules; and a common excitation coil for providing magnetic flux to the plurality of sub-lens modules; wherein each sub-lens module further comprises: an upper magnetic insert ring arranged inside the upper hole; and a lower magnetic insert ring arranged inside the lower hole; characterized in that: either the upper magnetic insert ring and the lower magnetic insert ring have a much higher magnetic permeability than, and are in contact with, their respective magnetic conductor plates (40, 41), or an upper gap is present between the upper magnetic insert ring and the upper magnetic conductor plate and a lower gap is present between the lower magnetic insert ring and the lower magnetic conductor plate, with both the upper gap and the lower gap having at least one vacuum layer or being filled with one non-magnetic material layer, such that each pair of upper magnetic insert ring and corresponding lower magnetic insert ring function as a pair of magnetic pole pieces of the respective sub-lens module. an upper magnetic insert ring arranged inside the upper hole; and a lower magnetic insert ring arranged inside the lower hole; characterized in that: either the upper magnetic insert ring and the lower magnetic insert ring have a much higher magnetic permeability than, and are in contact with, their respective magnetic conductor plates (40, 41), or an upper gap is present between the upper magnetic insert ring and the upper magnetic conductor plate and a lower gap is present between the lower magnetic insert ring and the lower magnetic conductor plate, with both the upper gap and the lower gap having at least one vacuum layer or being filled with one non-magnetic material layer, such that each pair of upper magnetic insert ring and corresponding lower magnetic insert ring function as a pair of magnetic pole pieces of the respective sub-lens module. either the upper magnetic insert ring and the lower magnetic insert ring have a much higher magnetic permeability than, and are in contact with, their respective magnetic conductor plates (40, 41), or an upper gap is present between the upper magnetic insert ring and the upper magnetic conductor plate and a lower gap is present between the lower magnetic insert ring and the lower magnetic conductor plate, with both the upper gap and the lower gap having at least one vacuum layer or being filled with one non-magnetic material layer, such that each pair of upper magnetic insert ring and corresponding lower magnetic insert ring function as a pair of magnetic pole pieces of the respective sub-lens module.