When a Hole-Free Phase Plates (HFPP) is prepared, a preferably featureless thin film should be placed with high accuracy in the diffraction plane of the TEM, or a plane conjugate to it. The invention discloses two related embodiments for accurately placing the thin film in said plane. The first embodiment uses a Ronchigram of the thin film while the TEM is in an imaging mode, and the magnification of the Ronchigram should be tuned so that the magnification in the middle of the Ronchigram is infinite. The second embodiment makes use of electrons scattered by the thin film while the TEM is in a diffraction mode. When the thin film does not coincide with the diffraction plane, electrons scattered by the thin film seem to originate from another location than the cross-over of the zero beam. This is observed as a halo. The absence of the halo is proof that the thin film coincides with the diffraction plane. It is noted that the method is best performed without a sample in the sample holder.