Yeah, when are we going to do the science?

DIANNA COWERN: This is the science!

Hey, I'm Dianna.

You're watching "Physics Girl."

And we made a camera obscura in the back of a U-Haul.

So last week, I held a meetup in San Diego with donuts and science, which attracted some awesome people, including the star of the show, Lily.

I need everybody to scoot in.

This is a director right here.

The meetup was super fun.

But the purpose was to make a massive camera obscura that you could get inside.

So I got this idea from the guys from the channel, "How To Make Everything," who visited me in San Diego earlier in the summer.

And we had made this U-Haul contraption, which was awesome.

Are you set to see it?

MAN: Whoa, that's so trippy.

Crazy!

DIANNA COWERN: The reason that the channel "How To Make Everything" wanted to make the camera obscura was because they were, in the end, making a camera.

I'll tell you a little bit more about that video at the end of this video.

But you should definitely check it out, and I have a link to it in the description.

So I decided it would be fun to get some reactions.

So again, we covered the back of a U-Haul with cardboard and tape so it was completely dark inside, except for a single hole, and invited people out to experience this massive camera obscura with us.

Are you ready?

WOMAN: She wants to sit by you.

DIANNA COWERN: Oh, OK, I'll come over there.

Lock us in.

WOMAN: All right.

DIANNA COWERN: It's so ominous as it closes.

(WHISPERING) It's very dark.

There we go.

DAN: There you go.

DIANNA COWERN: Oh, that's so-- DAN: Oh, wow, that's really cool.

DIANNA COWERN: I know.

Dan, can you wave your arms?

As your eyes adjust to the dark, the first thing you notice is that the image is upside down.

GIRL: Wow.

DIANNA COWERN: How did he do that?

DAN: It's so cool.

It's on the sides, too.

DIANNA COWERN: Yeah.

Mn, you can see the seam the whole way around.

Look at the trees over there in the corner.

WOMAN: Oh, wow, that's cool.

DAN: Whoa!

WOMAN: What is that?

DIANNA COWERN: That was people shining their phone lights at the back of the U-Haul from the outside, which must have looked hilarious from the outside.

Whoa!

What was the most surprising thing about it?

It was when we saw the image on the right side of it.

That came in really clear.

DIANNA COWERN: Dave, can you turn in a circle?

Yes.

MAN: All this stuff out here is like in there.

DIANNA COWERN: Yeah But like flipped and upside-down and backwards.

It was really just awesome.

MAN: We also pan to different places.

DIANNA COWERN: Oh, yeah.

DAN: Oh, that's cool.

MAN: What's over here.

DAN: That's good.

Take a panorama.

DIANNA COWERN: Quick side note, my friend Dan and I liked this experiment so much that we decided to redo it a third time but this time put the camera in the back of the U-Haul and hang a sheet from the ceiling a few feet in front of the hole, so we could do this.

This is our moving, U-Haul camera obscura.

There.

What did you think?

Good!

DIANNA COWERN: Good?

GIRL: I want to tell some people around the park around us.

DIANNA COWERN: About what?

And a science communicator is born.

So what is a camera obscura?

Well, the name suggests that it's camera-- like chamber-- obscura-- like dark, so like a dark room.

It's kind of what it is.

It's like a projector.

But you're not using a light bulb, you're using ambient light.

And what's projected on the back of the chamber is upside down, backwards, and pretty dim.

It's something often used by intro art classes, so that they can set this up and trace the image.

As you'll see, the camera obscura explains a lot about why our eyes are made like they're made, and how they work.

OK, so how the camera obscura works.

It's kind of like your eye in that there's a hole-- like the hole in the cardboard or the hole in your eyeball, the pupil-- that lets in some light to project on the back of the U-Haul, or the back of your retina.

The key to how this works is figuring out why you need the tiny hole.

Why doesn't an image just project itself nicely on the back of an open box?

It's not a dumb question.

OK, imagine trying to image or project this vertical rainbow poster.

We're first going to shine light on the poster because we need to be able to see it.

And now, if the box were wide open, let's see what we would get projected at the top of the box.

The light we're shining on the poster would bounce off, and then you'd get a green light and red light and yellow light and all the light rays going to the top of the box.

So at the top, you'd see a blur of all the colors.

But if I start to block out some of the rays by making a barrier with a small hole, eventually the only thing getting through to the top of the box is a ray from the bottom of the poster, a purple ray.

So the top of our image will look purple.

Now look at where the rays from all the other colors go, and you'll see they end up projected on the wall in order, but from bottom to top.

So we have a perfect image projected on the wall, upside down.

It's also backwards, because if we did the same process but with the poster sideways, the colors would be flipped horizontally.

But it's not actually a perfect image.

Because if you look really closely, some of the colors bleed together a bit, because our whole has some width.

So that means the smaller we make the hole, the less those colors will bleed together, which translates optically into a sharper image.

But it also translates into a dimmer image, because less light is getting through.

So the hole, in the end keeps the light in order.

Your eyes and most camera lenses do this with the help of a lens, which allows you to let more light in.

But then it has to bend the light, to keep the light in order.

The camera obscura doesn't have a lens, so it doesn't bend light.

Therefore, the opening has to be super small.

Using the same principle, if you're near-sighted and you can't find your glasses, You can use tiny slits in your hands to peer through and focus.

"Minute Physics" has a great video on why this works.

Basically, optics is lit.

Now the whole inner U-Haul was obviously not that small.

It wasn't a pinhole.

And because of that, the image is a little bit blurry.

In fact when we opened the hole up wider, you couldn't make out nearly as much detail, but we sure could see better.

It was amazing how much of the scene we could still see.

Historically, people used camera obscuras to study the sun.

Since you can't look at it directly, you could project it on to something else.

It was pretty awesome to realize the first time we saw that super bright spot that it wasn't light coming in from some crack.

It was the sun projecting sideways through the hole.

The same mechanism also allows people to observe solar eclipses, since you can't look directly at those.

During a solar eclipse, the little spaces between tree leaves will act like little mini camera obscuras and project the crescent shapes onto the ground.

Those crescents are all little tiny images of the sun.

If you had good enough eyes, and you got close enough, and it was projected on something white, you would be able to see the sun spots on those little crescent images.

So cool.

And that's it.

Thank you for watching this video.

I feel like I should recommend a video.

Well obviously, you should check out the video by "How To Make Everything," the YouTube channel that makes everything.

And in this case, after they made the camera obscura with us, they went on to make a camera.

I'll put a link to that in the description and at the end of this video.

It is definitely worth checking out.

Happy physics.