It was just a small key, but it could have saved more than 1500 lives if it had been in its proper place on the doomed Titanic.

The key, which was inadvertently taken off the ship before it set sail from Southampton, would have given the crew access to the binocular store.

But it was in the pocket of second officer David Blair, who forgot to hand it to his replacement when he was transferred off the vessel just days before its maiden voyage.

Without access to the crow’s nest binoculars, lookouts had to rely on the naked eye – and the rest, as they say, is history.

Lookout Fred Fleet, who survived the disaster, believed the ship could have been saved if the binoculars had been available.

And while many maritime experts are not so sure, there is still the belief that a simple pair of binoculars could have saved the Titanic from the iceberg. Almost a century after the fateful voyage, the key that some believe could have changed the course of history sold for an incredible £90,000 at auction along with a postcard written by Blair to his sister-in-law expressing his disappointment at being taken off the ship.

The poignant tale of the immense consequences of this twist of fate is outlined in a book – Binoculars and People – described as the most comprehensive ever produced on the history of binoculars.

Author Brin Best says: “Despite not being able to join the Titanic on its first voyage, Blair kept the locker key as a memento and eventually passed it on to his daughter who, in turn, gave it to a society for British and international sailors in the 1980s.

“The key – inscribed with the words ‘Crows Nest Telephone, Titanic’ – and the accompanying postcard sold for £90,000 in a UK auction in 2007. Just how much would the binocular itself be worth should it ever reach the surface again?”

It is a compelling tale, and an example of the important role binoculars can play.

Their importance is something Brin has never doubted. An enthusiast since early childhood, he clearly has a passion for his subject.

The 41-year-old education consultant from Otley said: “Ever since I first looked through a binocular as a tiny child, I have been captivated by how they can change your view of the world, how, as if by magic, they can make the invisible suddenly visible in three dimensions.”

Brin said he came to appreciate “that there was a wonderful story behind binoculars and the way they have shaped people’s lives and memories”.

“The main aim of this book,” he said, “is to tell that story, set against the technological advances in binocular design across the centuries.”

Brin’s own memories hark back to childhood when he used binoculars that were given to his grandfather by a German U- boat officer.

Jack Best, a hairdresser, saw service in the Royal Navy during the Second World War and was given the binoculars after cutting the hair of a captured German officer whose U-boat had been sunk.

In his book he says: “Thirty years on from this incident, Jack still owned the binocular, and used to enjoy telling his grandchildren about his adventures during the war on the high seas.”

“One of his grandsons was captivated by the fascinating story of the binoculars, and used to be allowed to look out of his bedroom window with them when staying with his grandpa. Perhaps it is not surprising that this little boy, whose name is Brin Best, grew up to have a lifelong passion for binoculars.”

Binoculars and People is a four-year labour of love, tracing the optical device’s 400-year history, and looking at its place in warfare, in the observation of nature and for making astronomical discoveries.

“I had the idea for the book about five years ago and decided to try to find some time to do it,” he said. “I realised there was a gap in the market.”

He said he knew there would be lots of interesting stories out there.

“I put out appeals for information and the stories just came flooding in,” he said.

Galileo experimented with binoculars, using them to look at the moon for the very first time. Cosimo III of Medici used a binocular, as did Field Marshall von Hindenburg who gave his name to the infamous airship which caught fire in 1937.

Brin says: “Binoculars have played a more significant part in war than most people realise. Their ability to make the enemy visible, even at a considerable distance, meant that they probably found their niche in conflict zones soon after being invented.”

He adds: “During both World Wars, however, some countries struggled to supply the quantity of binoculars needed by those in conflict zones. This led, on both sides of the Atlantic, for public appeals for binoculars to be loaned to the armed forces. Optimistically, there was sometimes also the offer of the return of the binocular after the end of the war.”

Binoculars have been used to save lives. In one dramatic case in Snowdonia Titch Kavanagh was rescued and saved after falling 140 feet to the bottom of a gully. National Park warden David Williams sparked the alert after seeing the fall through his binoculars.

In the field of astronomy they have allowed mere amateurs to make important discoveries.

“The detection of comets presents an obvious example, with many groundbreaking observations coming first from people gazing up from their back gardens,” he said.

Even professional astronomers would often have a cheap pair of binoculars on their desk, he added.

Brin said: “Many enthusiasts describe the principal joy of binocular astronomy to be the ease with which one can go outside and start observing straight away, without being encumbered with other paraphernalia. It also helps that an impressive view of the night sky can be obtained by using a binocular that costs less than £100, compared to the high price of state-of-the-art telescope.”

Since hitting the shelves just before Christmas the book, which costs £25, has sold more than 120 copies. Published by Biosphere Publications It can be obtained from the Otley bookshop Chevin Books and is available from Brin on 07970 872469.