What Are Lenses for?

 Lenses are everywhere in the world around us - everything from car headlights and flashlights to the LED lights used in electronic dashboards.

 

Our eyes may contain the most amazing lenses.

Think about what happens when you look at the world around you. One minute you're staring at the ground in front of your feet. A few seconds later you hear a plane whizzing by, turn your head and watch it fly by. Do this trick with a pair of binoculars and you will find that it takes you a long time to adjust your focus from near (looking at the ground) to far (looking at the plane). Try it with the naked eye and you won't even notice what you're doing. That's because your eyes have flexible lenses, controlled by tiny muscles that project outward and change shape instantly to focus on anything from fingerprints on your fingers to the surface of the moon. How amazing is that?

Custom MgF2 Coated Achromatic Lenses

 

A variety of lenses

We all have lenses in our eyes, but many of us balance additional lenses at the end of our noses to correct both distance and near vision: there are more glass and plastic lenses for eyeglasses and contact lenses than for any other purpose. There are a wide variety of eyeglass lenses, including photochromic lenses that darken in sunlight and double as sunglasses.

You can also find lenses in binoculars (using two or three lenses in each cylinder for your eyes) and telescopes, although not all microscopes use them. While ordinary (optical) microscopes use a series of glass lenses to magnify tiny objects, super-intense electron microscopes use electromagnets to bend the electron beam and thus help us see more detail. Movie projectors and projection televisions use lenses to convert a small movie picture into a giant image that many people can see at once. Cameras work in the opposite way, capturing light from a distance and focusing it on a chemically treated plastic film or a photosensitive electronic chip called a CCD. You can even find built-in lenses in magazine and book covers that change the image when you move your head from one side to the other; this tricky technique is called lenticular printing - but it really just means "printing with built-in lenses.