In 1975, a young engineer in the company that made Kodak film took the first picture on a handheld digital camera. Photography would never be the same again.

When Steve Sasson started working at Eastman Kodak, the American photographic film manufacturer was a vibrant symbol of American industrial ingenuity.

Set up by George Eastman in the 1870s, the company became synonymous with film photography thanks to their Kodak brand. People bought Kodak films and loaded them into Kodak-branded cameras. Their films were processed using Kodak development chemicals and they thumbed through the resulting prints on Kodak photographic paper.

The company had even come up with a snappy slogan at the end of the 19th Century about this nose-to-tail process: "You push the button, we do the rest."

But when a 23-year-old Sasson joined Kodak in 1973, he felt out of place. He wasn't a research chemist who would work on new films, nor was he a mechanical engineer ready to design new cameras that would work with Kodak films. Instead, he was an electrical engineer, and something about the whole photographic process didn't sit well with him.

"When you first came to Kodak, you have to take photography lessons," Sasson, now 75, says over a video call with the BBC from his home office in the US. "You had to develop film. You had to go out and take pictures and study film and all that. And to be honest with you, I found it really annoying. You take your picture, you have to wait a long time, you have to fiddle with these chemicals.

"Well, you know, I was raised on Star Trek, and all the good ideas come from Star Trek. So I said what if we could just do it all electronically? What if I could store an image electronically, capture an image electronically, and I don't require any film at all?"

The buildings blocks of a camera that didn't need film had already been taking shape, even if no-one had set out to invent one. For decades, scientists had known that when certain metals were bombarded with strong enough wavelengths of light, they would generate weak electrical currents. The first exposure meters – showing a photographer what settings to make on their camera for a correct exposure – used this principle with a cell made of selenium.

Rudimentary digital images were also already being taken by Nasa satellites such as Landsat using a kind of digital sensor based on vacuum tube technology. Astronomers were also using computers to turn light detection from large telescopes into images, but they were enormously expensive and bulky. They were not something that a person would be able to use to take their holiday snaps.

Researchers at Bell Labs in the US had, in 1969, created a type of integrated circuit called a charge-coupled device (CCD). An electric charge could be stored on a metal-oxide semiconductor (MOS), and could be passed from one MOS to another. Its creators believed one of its applications might one day be used as part of an imaging device – though they hadn't worked out how that might happen.

The CCD, nevertheless, was quickly developed. By 1974, the US microchip company Fairchild Semiconductors had built the first commercial CCD, measuring just 100 x 100 pixels – the tiny electronic samples taken of an original image. The new device's ability to capture an image was only theoretical – no-one had, as yet, tried to take an image and display it. (Nasa, it turned out, was also looking at this technology, but not for consumer cameras.)

"I wasn't aware of it until it was brought to my attention by my supervisor, Gareth Lloyd," Sasson says. In 1974, he was working then in Eastman Kodak's Applied Research Laboratory, a tinkerer's paradise. "We would do product ideas, solve problems. It wasn't futuristic research. Gareth came to me one day – I remember it because the conversation was less than a minute, I remember him leaning against my file cabinet – and he said, 'I've got two jobs for you, filler jobs until we have something really useful for you.'"

One of the jobs Sasson was given was to model some exposure controls for one of the company's consumer movie cameras. The other? Take a look at a new type of integrated circuit called the CCD.

"I just loved the idea of how light could affect electronics and control them," Sasson says. "I did a master's thesis in that." He had even built a small device with a semiconductor that could be controlled by pulses of light.

Sasson believed the technology to make a film-less camera was already there, it just needed to be assembled into the right form. "The only thing I need is a few joules of energy to store a charge pattern, an optical pattern. And I thought that was just clean. I thought it was neat. I thought it was modern.

"I wanted to build a camera with no moving parts. Now that was just to annoy the mechanical engineers. Most cameras at the time were mechanical marvels, and I couldn't build a mechanical camera to save my life. So I thought, since these guys are the cream of the crop, I'll just make one with no moving parts, and that'll annoy the hell out of them."

Lloyd had told him to buy one of these new circuits. "I ended up buying two. I said, 'in case I blow one up', which I probably would have done."

When they arrived, Sasson set to work. "These were very, very strange devices. You had to supply about 12 different voltages to it. When the device comes there's a piece of paper folded on top of it that tells you the 12 voltages that this particular device worked on when it left the factory, and then on the bottom it said, 'Good luck.' If any one of these voltages was not right, you just didn't get an output, and it was up to you to figure out which one it was."

Sasson's investigations showed that the new circuit had promise, but also downfalls. "It was a great imaging device, but it was a terrible storage device. You if you had an image that was exposed on it for 100 milliseconds or so, you know, it would start to degrade right away." The problem was something called "dark current", a small electronic current generated from thermal heat that interfered with the circuit. It's a major generator of the interference we know now as "noise".

The CCD........

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