The word lens comes from the Latin for lentil
A lens bulging on both sides looks a lot like a lentil, and that is exactly where the name comes from: lens was the Latin word for the legume. The object itself may be far older than the word, with a polished rock crystal from 7th-century BCE Assyria still debated as a possible magnifier.
Scholars disagree about ancient lenses. Some see archaeological evidence of widespread use over thousands of years; others think most were ornaments, apart from burning glasses used to start fires. The first certain mention of a burning glass comes in Aristophanes' comedy The Clouds of 424 BCE, and Pliny the Elder confirms Romans knew them. Pliny also reports that Nero watched gladiatorial games through an emerald, which some read as an early correction for nearsightedness, though that interpretation is disputed. Seneca noticed that small letters look larger and clearer through a water-filled glass sphere.
Ptolemy's second-century book on optics survived only through a poor Arabic translation, later rendered into Latin, but it fed a rich tradition in the Islamic world, where Ibn Sahl and then Alhazen advanced the subject. In Europe, between the 11th and 13th centuries, readers used reading stones made by slicing a glass sphere in half. Spectacles followed in northern Italy in the late 13th century, founding an industry in Venice and Florence that spread to the Netherlands and Germany. Dutch spectacle makers, relying on trial and error rather than theory, produced the compound microscope around 1595 and the refracting telescope in 1608.
Early telescopes blurred colours, and opticians wrongly blamed imperfect curves. In fact no single piece of glass can bring every colour to one focus. Chester Moore Hall solved this in 1733 by combining lenses into an achromatic doublet, although John Dollond also claimed the invention in a 1758 patent.
Growing ocean trade demanded brighter lighthouses, but a conventional lens large enough would have been hugely heavy and costly. The Fresnel lens cut the curve into concentric rings, using far less glass, and first equipped a lighthouse in 1823. The same name now covers devices that bend microwaves, electrons or sound.
Source: Lens
