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  • Writer's pictureTruc Le

The Many Lenses on Ben

Today is Benjamin Franklin’s birthday! He is now 318 years old but, he’s not really alive. In the colonial era, 1784, Ben was getting tired of switching his glass whenever he looked up or down. He suffered from presbyopia, a condition that happens to most people as they get older when their eyes lose the ability to see things up close.

Essentially, he was farsighted.

a picture of Ben Franklin's bifocals

Through struggle, he created the bifocals. He split two different lenses apart and glued them together to create a double lens! The top half of his glasses were normal, while the bottom of his glasses helped him see things up close whenever he was reading.

How do Glasses work:

Glasses are made out of a glass material, shaped in a specific way to help "bend" light in a way that helps your eyes "catch up". There are many lenses for different purposes, which is why Ben had the idea of combining both for them in his glasses. The most basic lenses are convex and concaves.

Convex lenses are thick in the center and thin near the edges, kind of bulbous. They are used to help with farsightedness and help reduce focal length. These lenses help patients "zoom in" and fix help them see things up close.

Concave lenses are the exact opposite of convex lenses. Concave lenses are shaped like a thin hourglass, thin in the center, and thick by the edges, which help patients with nearsightedness see things from far away. This shape affects light refractions in a way that helps your eyes expand their focal length and see farther away.

An easy way to remember this lens is by remembering that it "caves in".

a picture showing the difference between concave and convex lenses. Concave lenses go into themselves. Convex lenses bulge out.

New Technology:

Thanks to technology and advancements, we now have cool lenses like the transition lens or the trifocal and quadrifocal lens! But it's thanks to Ben Franklin that we have these innovative "granny-glasses."

Transition lenses help protect you from the sun and they aren't sunglasses! These lenses use a specific dye that reacts with the sun UV rays to turn your normal vision correcting glasses into "sunglasses"! After entering a building, the effects would slowly wear off and you would be able to see normally again, without the shades.

a portrait of Ben Franklin wearing his bifocals

Back in 1784, when Ben Franklin invented the bifocals, technology wasn't advanced enough to meld lenses together so he had to glue them. Now, in 2021, we can meld multiple lenses together for multiple purposes! Trifocals and quadrifocal lenses are made to help patients from switching their glasses whenever they change activities throughout their day. From reading to driving, different people need different lenses for different things. Yay for advancements in technology! Thank you Ben for being old and needing glasses, happy birthday!

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