Microdensitometry applied to X-ray photographs

A theoretical examination is made of the limitations on microdensitometry of X-ray diffraction photographs by optical means. It is shown that only small ranges of density can be included in the field of view of the microscope at any instant if a satisfactory overall accuracy is to be achieved. A consequence of this is that powder lines and diffraction spots on Weissenberg photographs should be larger than usual. Methods are given for estimating the errors in any given set of experimental conditions. The geometrical conditions which must be satisfied in scanning a diffraction spot along a zigzag path are investigated.