Photo 51 Was No Accident: Franklin Planned Her Famous DNA Image After Decoding an Earlier One

One of the most iconic images in the history of science has just been re-examined, and the findings are rewriting a story that has been told for more than seventy years. New research from King’s College London and the Science History Institute, published in the Journal of the History of Biology, shows that the famous X-ray photograph known as ‘Photo 51’ was not a lucky snapshot that Rosalind Franklin failed to appreciate. Instead, it was a carefully planned, high-quality repeat of an earlier image, ‘Photo 49’, that Franklin had already used to calculate key features of DNA’s helical structure. The discovery challenges the long-held belief that Franklin did not recognise the significance of the photograph that became central to the discovery of the double helix.

The story of Photo 51 has long been shadowed by a persistent narrative: that the image was shown, without Franklin’s knowledge, to James Watson in early 1953, and that Watson and Francis Crick then raced ahead to build their double-helical model while Franklin herself supposedly missed what her own photograph meant. Watson later wrote that seeing the photograph helped him and Crick develop their model. Subsequent accounts, however, often portrayed Franklin as having failed to grasp the importance of the image sitting in her own laboratory. The new research argues that this version of events does not hold up against the historical record.

To understand why, it helps to look at the technical details of how the photograph was made. In 1952, Franklin and her graduate student Raymond Gosling took Photo 51 at King’s College London by firing X-rays at DNA and recording the pattern created when the X-rays scattered from the molecules. The resulting X-shaped pattern of dark spots and smears was the signature of a helix: the regular, repeating arrangement of scattering units in a spiral produces exactly that kind of crossed pattern of reflections. The sharper and cleaner the pattern, the more precise the measurements that can be extracted from it, including the dimensions and geometry of the helix.

The crucial new insight concerns Photo 49, the earlier image that preceded Photo 51. Photo 49 contained a blemish caused by a component inside the X-ray camera slipping across the film and obscuring part of the image. Despite this defect, Franklin was able to extract useful information from the photograph and use it to determine key features of the structure of the DNA molecule. At that stage, she had not yet established exactly how many strands made up the DNA molecule, whether it was a single, double or triple helix. But the research shows that she already knew the X-ray pattern could provide important information about DNA’s helical structure, and that a better image would yield better answers.

That is precisely why Photo 51 exists. Rather than being an accidental or routine exposure, it was a deliberate, carefully planned attempt to produce a cleaner version of the pattern Franklin had already begun to interpret. The blemish on Photo 49 had degraded part of the data, so she and Gosling set out to capture a higher-quality repeat. The result was the crisp, striking X-pattern that has since become one of the most reproduced images in science. Seen this way, Photo 51 is not evidence of a missed opportunity but of a scientist methodically refining her experiment to squeeze more information out of her samples.

The researchers reached their conclusions through an unusually thorough reconstruction of the experimental record. They examined laboratory notebooks, manuscripts, photographs and other historical documents held in collections in Philadelphia, Cambridge and London. They also studied Franklin’s original X-ray camera and photographic slides preserved in the archives of King’s College London, allowing them to understand the technical conditions under which the images were produced. By combining the history of the instruments with the history of the ideas, they could piece together why Photo 51 was taken and what Franklin already understood when she took it.

The collaboration itself began with an archival acquisition. Alistair Sponsel, oral historian and curator of life sciences at the Science History Institute, started re-examining Franklin’s DNA research in 2025 after the institute acquired the History of Molecular Biology Collection from the J. Craig Venter Institute. The collection includes Franklin’s own copy of Photo 51, alongside notebooks, correspondence, photographs and other material documenting the history of molecular biology. Sponsel’s research led him to archives in the United Kingdom, including those of King’s College London, where Franklin and Gosling carried out their DNA work. There he joined forces with Brian Sutton, Emeritus Professor of Molecular Biophysics at King’s, who had long been interested in the X-ray crystallographic studies of DNA carried out by his predecessors at the college.

Sutton described how the partnership changed his own view of the famous image. He noted that he had been accompanying visitors to the King’s College Archives over many years, and that the highlight and focus of attention was always the original glass negative of Photograph 51. Just over a year ago, he was introduced to Sponsel, a historian of science visiting the Archive, and they very quickly realised that they looked at Photograph 51 in different ways, and that together they might better understand exactly why she and Gosling took it, and in particular the importance of Photograph 49. He described it as exciting to see Photograph 51 in a different light.

Sponsel, for his part, emphasised how the two researchers, coming from different disciplinary backgrounds, converged on the same questions. He said that he and Sutton were each intrigued by the same features of Photo 51 and wanted a deeper understanding of why the image looked the way it did. After studying so many documents and artifacts together, he said, they were excited to realise they shared a new understanding, not just of how the photograph was made, but of why Franklin had been motivated to take Photo 51 in the first place. He added that they had fun working together and learning to see these original sources through each other’s eyes.

The researchers are careful to say that their findings do not diminish the importance of Watson and Crick’s work in developing the double-helix model. What the study provides instead is a fuller picture of how Franklin’s own experimental work contributed to understanding DNA’s structure, and evidence that she fully appreciated the significance of her work, in particular Photo 51. The study also highlights a broader methodological point: understanding the technical details of how scientific experiments are carried out is essential when reconstructing the history of major discoveries. Without knowing how an X-ray camera worked, how a blemish on film could obscure data, and why a scientist would repeat an exposure, the historical record can be misread in ways that distort who understood what, and when.

The archival dimension of the work is central to its significance. Dr Alexandra Eveleigh, Head of Archives at King’s College London, noted that the King’s Archives preserve photographs, laboratory records, correspondence and other original materials that provide a direct connection to the pioneering scientific research carried out at the university. In this study, she said, archives were used as evidence to re-examine how, when and why the famous Photo 51 came to be produced, revealing the structure of DNA. This, she argued, illustrates the vital role of archives in the history of science: by preserving the original record, they allow established accounts to be revisited and refined, leading to a fuller and more nuanced understanding of how major scientific discoveries are made and of the contributions of the people behind them.

For decades, the story of the double helix has been told as a drama of insight and oversight, with Franklin cast as the brilliant experimentalist who came so close and yet somehow fell short. The new research replaces that drama with something more precise and, in its way, more impressive: a scientist who read a flawed photograph, extracted real structural information from it, recognised what a cleaner image could reveal, and deliberately set out to make one. Photo 51 was not a moment of luck that slipped through her fingers. It was the product of her own understanding, and the historical record, carefully re-read, now says so.

Subject of Research: Historical analysis of Rosalind Franklin's X-ray diffraction photographs of DNA and her role in determining its helical structure

Article Title: Rosalind Franklin deliberately created ‘Photo 51’ after using an earlier image to uncover features of DNA’s helical structure

Article References: Rosalind Franklin deliberately created ‘Photo 51’ after using an earlier image to uncover features of DNA’s helical structure. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Rosalind Franklin, Photo 51, Photo 49, DNA, double helix, X-ray crystallography, history of science, King's College London, Science History Institute, James Watson, Francis Crick, Raymond Gosling