When you take a photo, it helps to have a pretty accurate idea of what will be inside the frame. It’s something we take for granted now. But early photographers had to guess, because they couldn’t look directly through the lens to see what they were snapping.

There were some cameras at the end of the 19th Century that sort of solved this, using a swinging mirror that reflected the view from the lens to the photographer peering into the top of the camera. But it was rudimentary. Often the mirror had to be raised separately using a piece of string before the camera could be used. And the cameras themselves were huge.

As cameras shrunk in size and became even more portable, the need for this ‘through the lens’ viewer became more pressing.

It took until the 1930s for it to be solved. Almost 80 years ago, a little-known camera appeared in the Soviet Union that contained a simple but ingenious invention.

Technically, the Sport is very influential – Michael Pritchard, Royal Photographic Society

The boxy, lumpy camera called the Sport first appeared in 1937, made by GOMZ in what was then-called Leningrad (now St Petersburg). The Sport’s masterstroke was a big box-like prism that sits above the camera body; it contains mirrors that reflect the view of the lens upwards out of the camera to the photographer. It’s the first camera to have such a prism – a ‘single lens reflex’ or SLR – and would lead to the ‘pentaprisms’ found in modern cameras, which bounce the light out through a rear viewfinder.

“In my opinion, the Sport was a revolutionary milestone in Soviet and world photographic industry, and a stepping stone to later 35mm SLR cameras,” says Vladislav Kern, who runs the Soviet photographic history site USSRPhoto.com.

You could say the Sport is the Betamax of the camera world – Michael Pritchard  

So why is not lauded more today? The Sport became a footnote in photographic history, overtaken by the success of the Kine Exakta – a camera so respected that it’s an Exakta James Stewart is using in the classic Hitchcock film Rear Window.

Michael Pritchard, the director-general of the Royal Photographic Society, says: “Technically, the Sport is very influential, but it never got many sales outside of the Soviet Union.

“The Kine Exakta was much more influential, because it was marketed outside of Germany, and exported widely, and it was seen as a ground-breaking camera at the time. The Exakta evolved into what we call a ‘system camera’, which came with different lenses and all sorts of different accessories.

“That certainly wasn’t the case with the Sport.”

Kern also points out that it isn’t the easiest camera to use. “It's rather awkward to look through the viewfinder – as it's almost like a waist-level finder on old cameras. The angle is very odd.”

The Sport went through several modifications, and as many as 20,000 were made. Production only ended when the invading Germans besieged Leningrad in 1941.

The Sport’s pioneering design became more widely known after the fall of the Berlin Wall, but it’s still seen as a model quickly overtaken by its contemporaries, despite its achievements.

“You could say the Sport is the Betamax of the camera world,” says Pritchard. Like many inventions, the Sport may have failed to beat its commercial rivals, but its creators could claim one thing: it was an ingenious first.

Stephen Dowling is BBC Future’s associate editor. He is @sjdowling on Twitter, and blogs on photography here.

Many thanks to Siim Vahur for proving pictures of the Sport - more of his pictures can be found on Flickr.

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