The invention relates to a filter which is formed by twelve poles that extend in parallel to the optical axis, each of said poles comprising a magnetic conducting material. According to the invention, a potential is applied to the aforementioned material and said material is magnetised with a current, said potential and current being configured to produce a configuration of fields such that the magnetic and electric dipolar components satisfy the Wien condition. At each pole, adequate potentials and currents are excited in order to create quadrupolar magnetic and electric fields which, combined with the above-mentioned fields, can be used to control the total force acting on the charges and, in this way, to correct the aberrations inherent in the system. The radius of the diagonal poles can also be modified in order to obtain another control factor. For a parallel beam, when the excitations and radius are adjusted simultaneously, the energy resolution is improved by a factor of greater than two thousand in relation to standard Wien filters. As a result, the beam dispersion is reduced to nanospot size, such that the resulting filter is essentially corrected for second-order aberrations. The invention improves the most-characteristic parameters of Wien filters, namely: energy resolution and spatial dispersion.