It was the beginning of photography as we know it. A few months before the outbreak of the First World War, an engineer called Oskar Barnack, who had defected from the rival German optical company of Zeiss to head the experimental department at Leitz, put the finishing touches to a new invention. He called it the Micro Lilliput camera. "Micro Lilliput camera with cine film ready," he noted in his work log in March 1914. The following month he wrote, "Lilliput camera pat. Reg." – the idea was patented, secure from imitation.

Further refinement had to wait for the return of peace, but when the new camera hit the shops in 1925, first and briefly marketed as Barnack before becoming the first Leica (Leitz + camera), it was the beginning of a new age – the age we are still living in today. It was a camera you could carry in your pocket, and pull out to shoot whenever the fancy took you. It was almost silent, so it could be used with maximum discretion. It was so simple any amateur could master it, but its simplicity was the product of great engineering sophistication and ingenuity. In all these ways, it was a small revolution.

Of course there were no semiconductors in the first Leica, but in its conception of what the modern consumer desired, it anticipated every neat, elegant and high-tech product of our own age, up to and including the latest iPhone.

With its simplicity and compactness, it paved the way for all modern photography that benefited from speed, silence and agility: photojournalism, in particular, with war photography as a speciality, but subsequently genres such as fashion, too, when the taboos against less formal photographic styles began to fall.

'Eyes Wide Open: 100 Years of Leica' Show all 9 1 /9 'Eyes Wide Open: 100 Years of Leica' 'Eyes Wide Open: 100 Years of Leica' 100 Years of Leica Laederstraede, Copenhagen, 1935, shot by Heinrich Heidersberger © Institut Heidersberger, www.heidersberger.de 'Eyes Wide Open: 100 Years of Leica' 100 Years of Leica AP 'Eyes Wide Open: 100 Years of Leica' 100 Years of Leica The Broadway Inn, Salford, 1976, shot by John Bulmer John Bulmer 'Eyes Wide Open: 100 Years of Leica' 100 Years of Leica The original Leica from 1914 Leica Camera AG 'Eyes Wide Open: 100 Years of Leica' 100 Years of Leica Horst Faas in the field in Vietnam AP 'Eyes Wide Open: 100 Years of Leica' 100 Years of Leica Wetzlar Eisenmarkt, 1913, shot by Oskar Barnack Leica Camera AG 'Eyes Wide Open: 100 Years of Leica' 100 Years of Leica 'Sidewalk', 1995, shot by Jeff Mermelstein Jeff Mermelstein 'Eyes Wide Open: 100 Years of Leica' 100 Years of Leica Place Blanche, Paris, 1961, shot by Christer Strömholm Christer Strömholm/Strömholm Estate, 2014 'Eyes Wide Open: 100 Years of Leica' 100 Years of Leica 'Go', 2001, shot in Japan by Magnum's Bruce Gilden Bruce Gilden 2014/Magnum Photos

To mark a century since its invention, Leitz has now published a huge book that includes within its covers the work of hundreds of the photographers who have used their Leica as, in the words of Henri Cartier-Bresson, an "optical extension of the eye": from grainy snaps of Barnack himself taken with his primitive prototypes, right up to the harsh and tormented full-colour portraits of Bruce Gilden, by way of Cartier-Bresson, Elliott Erwitt, Sebastiao Salgado, William Eggleston, and dozens of the greatest war photographers.

An early advertising slogan for Leica was "Die Kamera der Zeit" – "The camera of the time" – and when it was first released after the First World War it was, indeed, right in the heart of the zeitgeist. Europe was exhausted and nauseated by war and suffering. The horrors of the conflict contaminated all the culture that had come down through the ages, robbing it of charm and appeal. As one writer in the new book notes, "For the Germans, the past had lost all attraction. They focused their attention on the present and the near-future."

Until the Leica, cameras were clunky great boxes with plates you pushed in and pulled out, black cloths to drape over the head, tripods to keep them steady for the long duration of each exposure. Photography was an art that froze what was already frozen, as the subjects waited patiently for the required time of exposure to elapse; an art that mimicked portrait or still-life or landscape painting in the quest for timelessness, that strove to be taken as seriously as the classical arts by doing the same things as well or better.

US Army helicopters pour machine gun fire into the treeline to cover the advance of South Vietnamese ground troops in an attack on a Viet Cong camp, Vietnam, March 1965, shot by Horst Faas for AP (AP)

But there was a completely different destiny in store for the camera – and it took Oskar Barnack to unlock it.

Miniaturisation was on many inventors' minds. As Hans-Michael Koetzle writes in the book, "Leica… was not the first efficiently functioning compact camera. It was not even the first one to use reeled cine film." After the First World War, there was "a multitude of new designs which… aimed at miniaturisation… [but] the vast majority of the compact cameras brought to market maturity in the 1920s suffered either from combining too many functions" – an example is the Swiss camera Sico, which boasted of recording, copying, enlarging and projecting functions – "or from simply trying to be too small, without coming up with the necessary precision". The Leica, by contrast, was both precise and winningly simple.

Its launch in 1925 coincided with the moment that key modern movements got into gear: modern architecture and design in the creation of the Bauhaus and the work of Walter Gropius; the release of Eisenstein's masterpiece Battleship Potemkin; the flourishing of the Surrealists; the opening of the great Paris design expo of 1925. And it quickly found a central place – persuading the Surrealist Cartier-Bresson, for example, to forsake the easel in favour of the camera.

The original Leica from 1914 (© Leica Camera AG) (Leica Camera AG)

For photographers in the classical tradition, the Leica was a trivial novelty. "Professional photography… accustomed to perfect staging, elaborate light control, large plates, and the option to touch up negatives, saw in the Leica little more than a toy," a German journalist noted in 1929. And 10 years after its launch, its reputation had not improved: Heinrich Kühn, a leading Austrian photographer in the old mould, wrote, "I have now seen a 'Leica' exhibition of 100 pictures. Terrible!"

But amateurs and the people who catered to them saw the camera's point immediately. Leica was "the apogee of clever design", wrote a trade magazine soon after the launch, "a completely new model in the camera's design history". Another writer totted up its advantages. "A Leica with 40 24 x 36 mm shots weighs 500g, a normal 9 x 12 camera with only 20 filled cassettes 4,000g. The 40 Leica shots cost 1¼ marks, an equal number of 9 x 12 plates 12 marks."

'Sidewalk', 1995 (© Jeff Mermelstein) (Jeff Mermelstein)

Ninety years on and the boot is on the other foot. Today it is the Leica that is staggeringly expensive – £5,000-plus, and thousands more for the lenses. Professionals reel off the limitations and drawbacks of some recent models, including flaky electronics, no through-the-lens flash metering and still no autofocus, and although they accept that the company has now mastered digital photography, the costs alone put it out of consideration. "It's jewellery to hang round the neck," they say, "only fit for rock stars and bankers" – even while they grudgingly agree that a Leica is still beautiful to use, that it feels just right, that it is a machine you can trust, that its build quality is second to none.

Let's leave the last word to Cartier-Bresson, who could never be persuaded to betray his first love: "The Leica feels like a big warm kiss, like a shot from a revolver, like the psychoanalyst's couch."