What technique did Rosalind Franklin use to obtain key DNA images?

Rosalind Franklin used X-ray crystallography, more precisely X-ray fiber diffraction, to obtain key images of DNA. Her experiments produced diffraction patterns that revealed important clues about the molecule’s shape and dimensions.

The best-known image is Photo 51, a 1952 diffraction photograph of DNA’s B form. Its distinctive X-shaped pattern indicated a helical structure. Franklin and her student Raymond Gosling produced the image at King’s College London, where Franklin also studied how DNA’s structure changed with humidity.

Franklin’s work showed that DNA’s phosphate groups were on the outside and helped establish measurements for the helix. The famous photograph was later shown to James Watson by Maurice Wilkins, contributing to Watson and Francis Crick’s 1953 model. X-ray crystallography is not the same as electron microscopy, nuclear magnetic resonance, or chromatography: it infers molecular structure from how X-rays diffract through an ordered sample.