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Foldscope Explores… Convex Lenses

Have you ever looked through a magnifying glass to make small print appear larger?

Foldscope LED Light and Magnifier

Figure 1: Foldscope LED Light/magnifier over text. (Photo Credit: Holly A. Stuart)

What about looking through a sphere of glass? If you have done this before, then you know that it makes everything appear upside down and backwards!

Lens ball in front of Foldscope Deluxe Kit Tin

Figure 2: Lens ball (Photo Credit: Holly A. Stuart)

Many of us have held a hand lens, moved it closer to and farther away from a surface, and caused light to spread out and then focus as a small point of light. If you haven’t then please take a moment and try it out!

Flashlight shining through a hand lens creating a large unfocused circle of light on a white background Flashlight shining through a hand lens creating a small focused circle of light on a white background

Figures 3a and 3b: Flashlight with hand lens in and out of focus (Photo Credit: Holly A. Stuart)

What do all of these things have in common? They all happen because of how light interacts with convex lenses.

Light Waves

Light travels through different materials as a wave of energy and, depending on what it is traveling through, will move at different speeds. Light can move fastest through a vacuum, and slows down when it encounters a different material such as air, water, or glass. This slowing down of light causes it to refract, or bend, as it goes from one material to another. 

Light box producing  one red and two white parallel lines of light over a black surface Light box producing  one red and two white parallel lines of light hitting an acrylic block and refracting

Figures 4a and 4b: Red and white light waves traveling in a straight line through air and bending through an acrylic block (Photo Credit: Holly A. Stuart)

Refraction of Light

The shape of the object that light is traveling through can also impact how the light refracts. Convex lenses are special types of lenses that are wider in the middle than they are at the ends.

two convex lenses

Figure 5: Convex Lenses (Photo Credit: Holly A. Stuart)

When light waves hit a convex lens, they will refract in predictable directions that scientists can calculate. In general, the rounder the convex lens is, the more it will refract light. And conversely, the flatter the convex lens is, the less it will refract light. The point where the lines all meet is called the focal point. This is where images will be clear and in focus when looking through the lens. This understanding is useful in the world of optics.

Light box producing  one red and two white parallel lines of light hitting a wide convex lens, refracting, and coming together at the focal point Light box producing  one red and two white parallel lines of light hitting a narrow convex lens, refracting, and then meeting at a focal point

Figure 6a and 6b: Light hitting two different convex lenses - one rounder than the other (Photo Credit: Holly A. Stuart)

Playing with Light

Here are a few activities that you can do to have fun playing with light while learning about refraction of light through convex lenses.

Flipping Objects

Using hand lenses with different magnifications, find an object to look at. Moving yourself and the lens, determine the point at which the object “flips” and goes from being upside down to right side up. Is it the same for every lens? What are some patterns you can discover with this investigation?

A hand lens in front of text showing the text magnified and right side up Hand lens in front of text showing small text that is upside down

Figure 7a and 7b: An object being viewed upside down and right side up through a hand lens (Photo Credit: Holly A. Stuart)

Let’s Focus

Using a hand lens and a large piece of white paper, find a light source (open window or a lightbulb) to use for this activity. Hold the hand lens between the paper and light source. You should see the shadow of the hand lens on the paper. Move the hand lens back and forth until you can make an image appear on the paper. If you are using a window, you should see an image that looks like what is outside your window. If you are using a light bulb, you should see a clear image of the light bulb itself on the paper. Again, try this with hand lenses of different magnifications to see if you can make the clear focused image appear larger or smaller. What can you infer about the shape of the lens and the size of the focused image?

A hand lens producing a small upside down image on a white background

Figure 8: Using a hand lens to make an image appear in focus (Photo Credit: Holly A. Stuart)


Holding a hand lens over a piece of paper that has very small type on it, try to find the point at which the text is in focus. Does the text also look larger in the hand lens? Do the same thing, but now with a microscope. Starting with the lowest objective, look at the paper. What do you notice about the printed text? Move up in magnification by going to the next highest objective lens. Do this for all possible levels of magnification offered by your microscope. What do you notice about the text as it gets more and more magnified?

If you have a Foldscope and the LED light and magnifier (or hand lens), try viewing a slide through the lens as usual, then hold the magnifier in between you and the Foldscope. What do you see when you try to put it in focus? Try this with both the high and low magnification on the LED light. Pretty neat, isn’t it?!

A hand lens in front of a Foldscope A hand lens in front of a Foldscope showing a magnified view of the microscope slide inside the microscope

Figure 9a and 9b: Foldscope and hand lens magnifying what is on the microscope slide (Photo Credit: Holly A. Stuart)

Have fun exploring these activities using light and convex lenses! Be sure to share your discoveries by visiting the Microcosmos and posting your images or tag us on social media - we love to see how Foldscopers around the world are using their Foldscopes in new and innovative ways!

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