Figure 7.

Characterization of distortions. (a) Array of illumination spots made by stepping the beam in small increments through a two-dimensional lattice. The microscope was set to 245 kV, the decelerator to 200 kV. (b) Representation of displacements of the spots from ideal lattice positions as determined by program QUADSERCH (Ref. ¹⁹). Line segments correspond to ten times the actual displacement. (c) Image after correction for displacements using program CCUNBEND. (d) Fourier transform of the original image; diffraction spots are spread over many pixels, even at low spatial frequencies. (e) Fourier transform after correction; diffraction spots are concentrated essentially to a single pixel and extend to the edge of the transform.