The invention relates to a dual beam apparatus equipped with an ion beam column and an electron beam column having an electrostatic immersion lens. When tilting the sample, the electrostatic immersion field is distorted and the symmetry round the electron optical axis is lost. As a consequence tilting introduces detrimental effects such as traverse chromatic aberration and beam displacement. Also in-column detectors, detecting either secondary electrons or backscattered electrons in the non-tilted position of the sample, will, due to the loss of the symmetry of the immersion field, show a mix of these electrons when tilting the sample.The invention shows how, by biasing the stage with respect to the grounded electrodes closest to the sample, these disadvantages are eliminated, or at least reduced.