Objective lens apertures increase the contrast in images recorded using an electron microscope. They do this by altering the mechanism of image formation so that it is even less faithful to the weak phase model of image formation. The Electron Microscopy Center (EMC) offers a better description of this imaging process. The following images show the size of the three OL apertures currently in the JEOL JEM 1010, their effect on the electron diffraction pattern of a waffle grid and their effect on images recorded at several different magnifications.
