A study of heavy-light atom discrimination in bright-field electron microscopy using the computer.

The Z dependence of the phase angle of the complex atomic scattering amplitude can be used to separate the image due to the heavy atoms from that due to the light atoms of the object structure. The linear theory of image formation applied to a focus series of bright-field images leads to Schiske's formula for the calculation of the structure factor. A program system is described which uses this algorithm for computing both images from a set of digitized electron micrographs of a focus series of uranyl-stained DNA on a thin carbon film.