traditional compound microscope
This is a traditional compound light microscope.

Microscopes magnify images that are too small for the naked eye to see. They do this by harnessing the principles of physics, math and biology.

A microscope is basically made of curved pieces of glass, called lenses, inside a tube. The lenses force light waves to bend as they pass through an object. As the light waves bend, they spread out, so the object appears much larger than it really is.

Find out how microscopes use lenses to bend light, and how the Foldscope takes advantage of micro-optics. Having trouble viewing the video? Download or stream it here.

The simplest microscope is a magnifying glass. Made of just one convex lens (thicker in the center than at the edge), it causes rays of light coming in one side of the lens to bend, stretch and converge on a spot on the other side of the lens. Due to principles of geometry, this makes the image appear larger than it is.

diagram of how a convex lens works
A convex lens can bend light and make an object appear larger by creating a larger virtual image that your eye can see.

Common consumer magnifying glasses can enlarge objects about two to five times. The magnification usually depends on how curved the lens is, as well as the distance between the lens and the object and the lens and your eye. More advanced microscopes, using a combination of different types of lenses, can see things as small as an atom.

The microscope is a basic tool of doctors and scientists in every discipline. There are many different types, depending on the need. 

Elijah Martin is a second year graduate student in the Developmental and Stem Cell Biology program at University of California, San Francisco. He uses microscopes to study heart cells. Having trouble viewing this video? Stream or download it here .

A compound light microscope uses multiple lenses to magnify an object in order to achieve greater magnification than a simple magnifying glass or single lens microscope. Compound microscopes are often used to detect a parasite in the blood or other bodily fluids.

A stereo microscope magnifies objects from two different perspectives to create a three-dimensional image. It is used by geologists to identify mineral crystals, botanists to study plant pollen, engineers to reveal flaws in plastics and metals, and crime fighters to detect clues such as hair, dust or blood.

X-ray microscopes use electromagnetic radiation with shorter wavelengths (x-rays) to observe objects like cells. Electron microscopes use electron beams to image objects. They are so powerful that they can magnify an image up to two million times.

tiny lens
The salt-grain sized ball lens is a tiny lens used in the Foldscope.

For his microscope, Prakash selected paper, the cheapest possible material that could build a functioning microscope. The tiny, inexpensive spherical lens attached to the paper looks like a tiny drop of glue rather than the precision-ground, curved glass lens used in a traditional microscope.

“We are making a precise object out of a piece of paper…. It looks like arts and crafts,” says Prakash. “It is very inviting to people.”

close up of Foldscope
Close up of the Foldscope.

In the simplest version of the Foldscope, the lens is press-fit into a small hole in the center of a slide-mounting platform. A sample — a drop of blood, for instance — is mounted on a microscope slide (the same glass slides that are used in regular microscopes, so the preparation of blood and tissue samples is the same), which is wedged between the paper layers of the microscope. With a thumb and forefinger grasping each end of the layered paper strip, the user holds the lens close to one eye. To focus, the user flexes the paper platform or slides it from side to side.

Because of the unique optical physics of a tiny spherical lens held close to the eye, samples can be magnified up to 2,000 times. This helps scientists detect the parasites that cause deadly maladies like malaria, river blindness, African sleeping sickness and tapeworm infections.

Foldscope with LED and battery
This Foldscope has a rechargeable battery and LED light, and can project images on the wall.

Different designs, folding patterns and lens types create different types of microscopes. For example, different Foldscopes can have different levels of magnification. In addition, Foldscopes can be built to do dark field microscopy or fluorescence microscopy. They can even project microscopic images onto a wall.

How tough is the Foldscope? The super tiny lenses are so small they are really hard to damage and break. Prakash has dropped a Foldscope from a third-story balcony. He’s stepped on it. Once he left one in his pocket and it was washed with his clothes — and it still worked!

students with Foldscope
Students in Tanzania are making and using the Foldscope. Courtesy of Prakash Lab/ Stanford University

The microscope makes it possible for health-care workers, laboratory technicians, students and even the world's best scientists to have the imaging power of a fancy, fragile desktop instrument. “It can go anywhere,” says Prakash.