text: An SADP is acquired under parallel electron illumination. In the case of convergent beam, a convergent beam electron diffraction (CBED) is achieved. The beam used in SAD is broad illuminating a wide sample area. In order to analyze only a specific sample area, the selected area aperture in the image plane is used. This is in contrast with nanodiffraction, where the site-selectivity is achieved using a beam condensed to a narrow probe. SAD is important in direct imaging for instance when orienting the sample for high resolution microscopy or setting up dark-field imaging conditions.
   High-resolution electron microscope images can be transformed into an artificial diffraction pattern using Fourier transform. Then, they can be processed the same way as real diffractograms allowing to determine crystal orientation, measure interplanar angles and distances even with picometric precision. 
  SAD is similar to X-ray diffraction, but unique in that areas as small as several hundred nanometers in size can be examined, whereas X-ray diffraction typically samples areas much larger.