Why Are Sheet Magnifiers Called Fresnel Lenses?

Celebrating the life-saving lens invented by Augustin-Jean Fresnel (1788-1827)

Why are sheet magnifiers called Fresnel lenses?

One of the most frequent questions we get asked is: ‘what is the biggest magnifier I can buy?’ We have hand-held magnifying glasses up to 5-inches in diameter but that’s about as big as a normal magnifier can go. If you need something larger, then you will need to go for a fresnel lens, named after the French physicist who invented them – Auguste-Jean Fresnel.

Fresnel lenses are made from flat plastic sheets, comprising of a series of concentric rings, which gather and direct light towards the centre of the lens. They allow magnifier manufacturers to construct lighter-weight lenses over larger viewing areas, though it is fair to say that the optical quality is not as good as on a conventional lens.

They are very popular though, with a number of advantages for uses

• Lightweight magnifying lens – normally made from acrylic or PVC
• Large viewing area
• Inexpensive – cheaper than standard magnifiers
• Different sizes – from credit card to A4 and above
• Flat, easy to store

When you look through one of these seemingly simple credit card or full page magnifying sheets, it seems amazing to think that the real reason for the invention came about from a need to save lives at sea.

A Life-saving Lens for Lighthouses

From around the17th century, maritime traffic increased as a means of carrying goods between nations. Lighthouses were critical for helping ships navigate their way along rocky coastlines. Unfortunately nobody had come up with an adequate way of making the light visible from a distance far enough away from treacherous rocks – often with fatal consequences.

For thousands of years lighthouses had just used open flames to warn sailors but these were ineffective in wind or rain. In the 1690s the glass lantern room was invented and first used with candles at Eddystone Lighthouse off Cornwall, to create brighter, more protected light; whilst mirrors were used elsewhere as crude reflectors to direct the light.

Despite these improvements shipwrecks continued because none of them could retain enough of the light to alert ships adequately of any danger. The number of shipwrecks reached such a level that the French government set up a commission with a financial prizes for anyone who could come up with a solution.

Augustin-Jean Fresnel (1788-1827)

The breakthrough came through the work of Augustin-Jean Fresnel, a 19^th century physicist, born in Broglie, France in 1788. He was brought up in a strict Catholic household, and received his early education from his parents. As a child he was initially regarded as a slow learner, who could barely read by the age of 8, and showed little aptitude for languages or tests of memory.

Despite all this his boyhood friends regarded him as something of a genius, who would spend hours on ways to increase the power of popguns and bows, gradually leading him to an interest in mathematics and a university education studying engineering.

After graduating he worked in various French government departments until finding himself cast out following the return of Napoleon from exile in Elba in 1815.

By this time Fresnel had started conducting his own separate scientific studies into the behaviour of light, calculating different formulas to show how light could change direction, or refract, as it passed through prisms made from glass. Instead of creating one gigantic lens, Fresnel worked with leading glassmakers of the day to produce a thinner, lighter and more efficient lens, made up from multiple panels and prisms to retain and re-direct virtually all the available light.

The first Fresnel lens was installed in 1822 in the Cardovan Tower lighthouse on France’s Gironde River. With a large lamp in the centre, Fresnel’s lighthouse lens could gather, magnify and project the light for more than 20 miles away. In the following years many more European and US lighthouses had fresnel lenses installed, doubtless saving the lives of thousands of sailors.

Thanks to Fresnel, the world gained a greater understanding of the behaviour of light, and his work led to a major breakthrough for lighthouses and maritime safety.

Fresnel’s Lenses – the legacy

Augustin-Jean Fresnel never lived long enough to see how successful his studies proved to be. He did not enjoy good health during much of his lifetime and was only 39 when he died in July 1827. In the century after his death some 10,000 lights with fresnel lenses were installed in lighthouses and other buildings across the world.

He is buried at the famous Pere-Lachaise cemetery in Paris. Once you have taken in the more famous graves of other ‘residents’ – Oscar Wilde, Edith Piaf, Jim Morrison, Frederic Chopin, Yves Montand, Simone Signoret, Camille Pissaro – it’s worth exploring a little further to find Fresnel’s tombstone.

For someone whose invention has made its way to everyday magnifying vision aids, it seems ironic that his grave is somewhat hard to find. It is not well marked and even the original inscription on his tombstone has been eroded. You can just still make out the remaining words ‘To the memory of Augustin Jean Fresnel, member of the Institute of France“.

Where To Buy Fresnel Lenses Today

Magnifico offers the biggest selection of fresnel lenses in the UK. They are very popular, with several variations – card, bookmark, A6, A4, some with frame, some not, flexible sheet magnifiers and rigid page options.

In case you were wondering, ‘fresnel’ being French, has a silent ‘s’ in the middle so the pronunciation is ‘fre-nel’ (actually ‘fray-nel’ if you wish to go for the full French accent).

Cimetière du Père Lachaise, 16 rue du Repos,75020 Paris 
Tel.. +33 (0) 1 55 25 82 10
http://www.paris.fr/cimetieres

Subway – Père Lachaise, Philippe Auguste

Bus – 26, 54, 60, 61, 64, 69, 76, 102, La Traverse de Charonne