A method and apparatus for use in monitoring a sample with a charged particle beam are presented. A mechanical displacement between a plane defined by the sample's surface and an optical axis defined by a beam directing arrangement is provided so as to orient the sample at a certain non-right angle θ1 with respect to the optical axis. A primary charged particle beam propagating towards the sample is deflected so as to affect the trajectory of the primary charged particle beam to provide a certain non-zero angle θ2 between the primary beam propagation axis and said optical axis.