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  • Writer's pictureCarolyn Balch

Nature Walk Looking for Pinholes

Updated: Nov 1, 2019

Searching for a new nature walk?

Try looking for pinholes. They’re easier to find than that are to explain but we’ll get to that.

Have you ever noticed circles of light on a sidewalk or driveway?

What could be causing them? Look around. What do you notice? Is it sunny or cloudy? There are shadows in the picture… what are they of?

These circles are pretty easy to find, but you’ll need a few things; foremost, a sunny day. This one is non-negotiable. If it’s cloudy or overcast, you’ll need to wait.

Next, get something smooth and white or light-colored. I’ve used a piece of foam core from a dollar store, a piece of cardboard, a white lid from a plastic storage bin, and even a piece of copier paper. The larger and paler and stiffer the better, but use what you have.

pinholes, nature walk
Sun spots from gaps in leaves. Note the size of these versus the others shown in this post.

When you’re on the walk look for trees and bushes that are casting shadows. Place your screen so the shadows fall on it. Does the way you hold the screen change what you see?

Look for circles. Once you start to find circles, see if you can find a variety in terms of size and brightness and clarity. Are these qualities connected? Are brighter circles sharper or fuzzier? Are larger circles brighter or dimmer or is there no connection?

Now that we’ve found them, consider what’s making them. Study at the gaps between the leaves. Are they round? Probably not. What might they be an image of? What is round and bright and shines in the sky? If you said the sun, you’re right!

nature walk, pinholes
Sun spots seen on a path, notice the leaves for scale

Pinholes (any gap, really) can cast an image of what’s behind them onto a screen. The images are everywhere. The pinhole is simply restricting the light so the image is clear. In this way, they act as lenses. But unlike lenses, they don’t have a focal point so they’re always in focus.

If this gap or pinhole is casting an image of the sky, why can I only see the sun? It’s a question of brightness. The blue sky (and everything else) is reflecting from your screen as well, but likely it’s too dim to see.

If you could build a box around your screen so that only the light from the pinhole entered, you’d see the entire sky pictured on your screen. This is the science behind camera obscura or pinhole cameras.

For a more thorough discussion on this topic, check out the activity available here.

And, as always, all of the labs and units are available inside the membership. Read more here.

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