How Lenses Work – Kid Friendly Activities!

posted in: Learning | 5

Learn About Lenses - Make a Rudimentary Image Projector!This week we’re learning about lenses for my ABCs of Photography series.  And in case you’re wondering, this is really about the concept of lenses, so we’ll be spending time exploring how they work rather than what kind of lens you should get.  We’ll even project an image onto the wall using a magnifying glass!

But first, let’s cover the Dictionary.com definition of a lens:

n. a piece of transparent substance, usually glass, having two opposite surfaces either both curved or one curved and one plane, used in an optical device in changing the convergence of light rays, as for magnification, or in correcting defects of vision.

Your glasses have lenses, your eyes have what’s called “crystalline lenses” …and they all focus light.  As we explored when learning about cameras , you don’t need much to focus light. Even a pinhole can become a lens of sorts.  While not as simple as a pinhole, another simple lens is a magnifying glass.  And that’s what we’re going to use for these activities.

In fact, I originally brainstormed these ideas when we were making our camera obscura, but decided to split the activities into two posts since each set could really stand on their own.  So, don’t mind the fact that these images portray snow on the ground — it really is warmer than that here.  It’s just that this post has been patiently waiting for you!

Now for the fun part.  Activities!

You can do either activity first, or just choose one.  Both will help teach the same concepts, it’s just a matter of which one your kids may find more interesting.

Use a Lens to Make a Picture on Paper

All you need for this activity is a piece of paper, a magnifying glass, and a shaded area next to a window.  Although I suppose you could do it outside too.  Anyways, we put the paper in shade (this is important — your image won’t show up if the paper is in the sun), and then put the magnifying glass between the window and the paper.  As you move the magnifying glass closer to and further away from the paper, the blob of light reflected onto the paper will come in and out of focus.  If your child has enough coordination, you’ll be able to see a somewhat crisp (or fuzzy!) upside down version of what’s outside.

Here’s what it looks like when the paper is in the sun.  You will see the blob of light through the magnifying glass, but not much else, no matter how well you focus it.

Learn About Lenses - Make a Rudimentary Image Projector!

Toby had fun trying to find the focus point of th magnifying glass — you’ll see he was somewhat successful here.  Note the faint pattern of light on the paper.  That’s the view out onto our deck.

Learn About Lenses - Make a Rudimentary Image Projector!

And here’s mommy’s rendition.  See how I was able to get it a little more crisply focused?  It’s all a matter of patience.  Move the magnifying glass slowly back and forth; you’ll find it.

Learn About Lenses - Make a Rudimentary Image Projector!

Want to know what the view actually looked like?  Here’s a snapshot out onto our deck.

Learn About Lenses - Make a Rudimentary Image Projector!

And for those of you who like videos, here’s a video of the whole activity.  Well, a brief shot of the paper, panning to the outside view.  Maybe of interest for your kids, if they like videos as much as mine do. Seriously, we had to search for tornado videos on youtube to learn about how tornados work.  And astronaut videos to learn about rockets. Incidentally, Toby doesn’t want to be an astronaut now that he knows they “have” to wear diapers when in the spacesuits.

But I digress. Here’s the video (under 30 seconds in length):

How cool is that?  Yeah, we were psyched too.

Okay, now for part two.

Use a Lens to Project a Movie onto the Wall

For this activity, you’ll need your magnifying glass, and a smartphone.  We originally projected a picture onto the wall from my smartphone gallery, but a video proved more interesting.  Specifically, a video of our duplo train setup.

In order for this to work, we had to be in complete darkness.  So, we went into our bathroom, closed the door, and played the video.  Toby had fun trying to “find” the picture for a short while, but ultimately he wanted me to hold the magnifying glass so he could watch the “silly” video.  Silly because it projects upside down.  Here’s what it looked like.

Learn About Lenses - Make a Rudimentary Image Projector!

Sorry about the noise in the image.  I had to use my small camera since I was multitasking …it would’ve been crazy to try holding the magnifying glass and my DSLR that could capture this scene more adequately.  Sometimes you have to accept imperfection and go with the flow.  While I don’t settle for less with my clients — when doing activities with my boys, their experience is most important. So the documentary pictures took a place on backburner. Priorities, right?

So, to make up for that, here’s a diagram of this activity.  How you can set up your rudimentary image projection system in under two minutes… or however long it takes you to find your phone and a magnifying glass.

Rudimentary Image Projection simple activity with a Smartphone in a Dark Room!

And since I have them, here are some more pictures of the smartphone image projection activity.

Okay, there you have it!  I love how simple this activity is, and it really is great for helping kids learn about lenses.  The concept of focusing as you move the lens closer to the wall, farther from the wall, etc …all the interaction is fantastic for helping to reinforce what’s being learned.

Make sure to check back next week for the next post, where I’ll share an activity for the letter M. You might also enjoy revisiting last week’s activity where we learned about high key and low key (for the letter K).


The ABCs of Photography - An Educational Series for KidsJoin Betsy as she works through the alphabet in this educational series for kids… The ABCs of Photography!  We’ll cover topics from A to Z, with activity ideas for both younger and older kids

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5 Responses

  1. So neat! I love the way you educate us about photography. Pinned to our Small Victories Sunday linkup board. Thanks as always for hosting with us!

  2. Brandi Clevinger
    | Reply

    That’s so cool! I like the addition of the video. I’m going to try this with my kids when they wake up from their naps. My patio is covered in plants, so they will like the projection!

    • Betsy Finn
      | Reply

      Ooh, that would look cool. Let me know how they like it

  3. Ivan
    | Reply

    Thank you , Betsy! Really inspiring, and your key word “simplified” is very important. I’m putting the abc into practise !

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