What the Photograph Reveals
Scattered light encodes structure
Each spot on the film corresponds to a single reflection — its position and intensity map directly onto atomic coordinates within the crystal lattice.
The X-pattern is the helix, seen sideways
The characteristic diagonal cross on Photo 51 arises because the molecule is a coiled spring — diffraction from a helix produces layer lines spaced at 3.4 angstrom intervals.
Symmetry constrains the possible
Crystallographic symmetry operations — rotation axes, mirror planes, glide reflections — reduce the number of independent atoms you must determine by an order of magnitude.
Density maps make atoms visible
Fourier synthesis transforms measured intensities into an electron density map — contours that reveal where atoms sit, down to sub-angstrom precision when data is complete.