Hello, my name's Dr.

George, and this lesson is called a pinhole camera.

It's part of the unit making images, and today, you're going to make and experiment with a kind of camera.

The outcome for the lesson is I can explain how light passes through a pinhole to produce an image in a pinhole camera.

So I'll be showing you how to make one and helping you understand how it works.

Here are the key words for the lesson.

I'm not going to read all these definitions now.

I'll introduce them as we go along, but this slide is here in case you want to come back any time and check the meanings for yourself.

The lesson has two parts, investigating a pinhole camera and how the image forms. So let's get started.

First, a reminder of some useful things for you to know.

If an object emits its own light, so it's creating and sending out light, then we say it's luminous.

So for example, a lamp or the sun.

All objects reflect and scatter some of the light that hits them.

So if you look around you now, the objects that you can see that aren't luminous, you can see them because they are scattering light.

Scattering is a kind of reflection, but it's when the reflected rays travel in all directions.

Now, cameras can produce images from the light that objects emit or reflect, and an image is a representation, it's something that looks a lot like the real thing but isn't the real thing.

So to produce an image of an object, light from that object must enter the camera.

So here's a simple picture of the most common kind of camera, a lens camera.

So light comes in, passes through the lens, which affects the direction of the rays, and then that light lands on the back of the camera and makes an image.

And this is very similar to how your eye works.

Light from an object has to enter your eye for you to be able to see it.

If no light from an object enters your eye, then you won't see it, and your eye also has a lens and it also focuses the light to make an image on the back where you have the retina.

Now, some of the earliest cameras created what you could call a live image on a plain screen or on a mirror.

So they didn't make a permanent image that you could keep and make copies of it and put on the wall.

They made an image of something that they were looking at right now.

It was still impressive at the time.

But then we started to use photographic film, which you can use to capture an image.

If the image is still, it's not moving, you can make a sort of permanent record of that image on the film.

And the film changes colour when light hits it, that's how it works.

And that was the most common way to capture an image until about the mid or late 1990s.

And then we started to have digital cameras.

And these cameras use light sensitive electronics at the back of the camera where the the image lands and they record the image.

So the electronics records the amount of light hitting different places at the back of the camera, and it can record the colour too.

And the image can then be recreated on an electronic display screen or it can be printed.

So you can record an image, you can store it as a file on a computer, you can print it later.

Now, which of the following statements explains how a camera can create a photograph? Read the three options carefully, and I'll wait for five seconds, but if you need longer, press pause and press play when you're ready with your answer.

The answer is C.

Light travels into a camera from objects in front of it.

That's what's needed to make a photograph.

It's not B, light doesn't travel out from the camera to the object, it comes the other way.

Now, let's start thinking about this special type of camera called a pinhole camera.

It's a very simple camera, but still quite impressive, and you're going to make one in a little while.

So I'll show you how it works.

First, you make a tiny hole using a pin in the centre of one side of a cardboard box.

So this is why it's called a pinhole camera.

And if there aren't any other holes in the box, then light that travels through the pinhole can actually create an image on a screen at the back of the box.

So this type of camera, it doesn't even have a lens, it's just a box with a hole at one end and a screen at the other end.

So we look at something that light is coming from.

So a light source such as a lamp.

Some of the light goes through the pinhole, and then we see an image on the screen at the back.

To make a screen, you can use a piece of white baking paper, so that's also called grease proof paper.

You can also use tracing paper.

So you attach it to the back of the camera covering the hole in the back of the box.

And the baking paper is a useful thing to use because it's translucent, it lets some light through.

And that means you can actually see the image, the image is made on the inside of the box.

But because you can partly see through the baking paper, you can see the image looking at it from the outside.

But an image will only be visible if enough light hits the screen.

You're going to get a better image if you look at something bright, something luminous that's making its own light, than if you try to look at something that's dim or something that's not luminous.

So a good thing to observe with your pinhole camera will be a bright bulb, a filament lamp type of bulb, or an LED lamp.

Also, if you dim the room lights, that will help make the image on the screen more visible to you because there'll be a bigger contrast between the dim image on the screen and the surroundings.

So it helps for the surroundings to be dark.

Although, if it's a bright day, you may be able to produce an image of what's outside on your camera by pointing it out of the window.

And now, here's a question for you.

What is needed for a clear image to be made by a pinhole camera? Read all of the options carefully and choose any that you think are needed.

Press pause when you're thinking and press play when you're ready.

There are two correct choices here.

You need a screen over a large hole on the back side of the camera.

Without that you won't see an image and you need to be looking at a bright, luminous object and have the room lighting dim so that you get a good contrast between the image and the light that's around.

You don't want a large hole in the centre of the front side.

As I've said, you need a small hole, a pinhole, and you don't want a transparent screen because you won't be able to see an image at all.

So now, it's time for you to make your own pinhole camera and experiment with it.

So to make the camera, you can go back if you need to, to the instructions I gave earlier in the video, and then you're going to make an image of a bright filament bulb, filament lamp on the screen of your camera and describe the size and the brightness of the image compared to the real bulb.

Also, state which way up it is and how clear or blurry it is.

And then describe what happens to the image if you move the camera closer to the bulb.

After that, make a second identical pinhole next to the first one, and describe the new image you see, and compare it to the image that you made with just one pinhole.

And then make one of the two pinholes a little larger and describe how the new image is different from the last one.

So pause the video while you do this investigation, and when you're finished, press play.

Here's an example of what you might see.

Here's a photo of a kind of filament bulb.

And on the right, we see an image of the bulb when it's switched on on the screen of a pinhole camera.

The image is smaller than the bulb itself.

So you could say it's reduced.

It's not larger, it's not magnified.

And the image isn't very bright, but it is fairly clear and focused, and I hope it was for yours too.

And it's a little hard to see here, but the image is upside down compared with the real-life bulb.

Now, what happens when the camera moves closer to the bulb? Well, I hope you noticed the image gets larger and it may even become larger than the bulb itself.

If it's larger than the real thing, we would say it's magnified.

The image is always upside down and the image stays clear.

So as you move the camera, the image doesn't get blurry.

And you can see an example here in the photos of what you might see.

Now, if you have two small pinholes, you should see two images of the bulb on the screen at the same time.

They're the same size as each other, the same brightness, and the same clarity, the same sharpness of the image.

And they should both be upside down.

If you made your pinholes very close together, you might have seen your two images overlapping with each other.

Now, if you make one of the pinholes larger than the other, you should see that the two images are still the same size.

It doesn't make one of them bigger, and they're still both upside down.

But the change is that the image caused by the larger hole is now brighter, but it's less clear.

You should find it became a little bit blurry.

So you can see that in the photos here.

So I hope you enjoyed that.

Now, I'm gonna help you understand how this image is made.

How does such a simple device make an image like this? Now remember, every point on a luminous object emits light in all directions.

It sends out light in all directions from all of its points, and we can represent that here with some light rays representing some of the directions of light from some of the points on this bulb.

But a non-luminous object, it doesn't emit light, but it does reflect light in all directions.

So we get a similar effect, maybe the light is less bright, but it's still coming out in all directions from all of the points.

And if you hold up a pinhole camera to one of these objects, some of the light can enter it and form an image at the back of the camera.

And the more light that enters the camera, the brighter the image will be.

Now, imagine a lamp is shining next to a pinhole camera as shown here at the top, and light is going through the hole into the camera.

Which of these four options best describes how light travels from the lamp? So read these carefully and look at the diagrams. Press pause while you're thinking and press play when you've chosen your answer.

So the best description of how light travels from the lamp is D, in all directions from every point.

And here we just see some of those represented by some light rays.

So it doesn't all travel just towards the hole.

The lamp doesn't somehow know that it wants to send light towards your camera.

And B, it travels outwards from every point.

Well, it travels in all directions from every point, not just straight out as shown here.

So well done if you picked out D.

Now, to explain how a pinhole camera actually works, we can draw diagrams with a few useful light rays drawn in.

So when light goes through a pinhole, it just continues in a straight line as usual.

The pinhole is just a hole, so it doesn't affect the light, it doesn't change its direction, change its colour, it just lets the light through.

And here's another ray that could get through this pinhole in a different direction and another.

So actually, many light rays can pass through the hole at once, although it's small because they can come in from different directions, and when they do, they just pass straight through each other, they don't collide or bounce off each other.

So it works something like this.

Here's a question.

Which are possible ways that laser beams can pass through a pinhole? So in these pictures, A, B, or C.

Which of these could happen? Press pause and press play when you've chosen your answer.

And the correct answer is all of them.

Light beams can come in from any direction and they can pass through each other as well.

Now, imagine we don't have a pinhole, we just have a screen and we hold it up in front of an object like this tree.

Well, light from every point on the object is going to hit every point on the screen.

For example, from this point, at the top of the tree, light is going to hit the whole screen.

Here's an example of three light rays.

Light from this point in the middle of the tree, it's going to hit everywhere on the screen, and here, and here at the bottom as well.

So if you look anywhere on the screen, it's receiving light from every part of the object that's not going to give you an image.

To see an image, you'd want different parts of the object to send light to different parts of the screen.

So if you just hold up a piece of paper to an object, whether it's luminous or not, you will just see a blur of light on the screen.

But if we put a very small pinhole in front of the screen like this, only one ray from each point on the object can pass through the pinhole and hit the screen.

So here's some rays from the top of the tree now and only the one that's going in just the right direction to hit the pinhole is going to make it through to the screen.

So light from that part of the tree only hits that point near the bottom of the screen.

Light from the middle of the tree, only light that's going in just the right direction is going to make it, and it's going to land on the screen there.

Light from the bottom of the leaves, only that ray can make it through.

And from the bottom of the trunk, there's just one ray there that can make it through.

So light from each part of the tree only hits one part of the screen.

And so, we get an image of the object on the screen.

By the way, the way we're showing the camera here, it may look a little strange.

We're not showing the sides of the camera which would be there, but this is just so that you can more easily see where the rays of light are going.

So the only trouble with this is we're not letting very much light through.

Each part of the object only gets one ray through the pinhole, and so, the image can be very dim, very faint.

Which of these four diagrams now correctly shows how light from a lamp passes through a pinhole? Press pause while you're thinking and press play when you're ready.

The correct answer here is D.

What's wrong with A? Well, it does show one of the rays that would get through, but it makes it look as though each point on the lamp only sends out light in one direction and that's not true.

In B, we have one ray getting through, but it's then splitting into different directions.

One ray is splitting into many rays and that doesn't happen.

And C is rather similar to A, except we have several rays coming through all in the same direction.

D is the one that's right.

It may look a bit messy.

What it's showing is light coming from different parts of the object in all directions, and some of those rays make it through.

So well done if you pick that one out.

And if you didn't, I hope you can now see why is the right answer.

Now, the image in a pinhole camera, you would've noticed is upside down, and we can use a scientific word for that, inverted.

Vert, whenever it appears in a word, means turn, as in convert, revert, vertex.

So light from the top of the object that passes through the pinhole ends up at the bottom of the screen.

Have a look at this picture here.

You can see it's happening light from the bottom.

Here we have light from the bottom of the trunk.

It ends up at the top of the screen and that's why the image is inverted.

Now, what if we move the pinhole camera closer to the object as shown here? So in the top image, it's quite far away, we move the whole camera closer.

Look at what happens.

The image is bigger.

Now, it's quite hard to explain why in words, but have a look at the image and see if you can make sense of it.

Can you see why this is happening? We could say that different rays from the object are now the ones that pass through the pinhole.

And these rays are rays that are more spread out when they hit the screen compared with how it was before.

Another change we could make, which you didn't get a chance to do, if we actually make the pinhole camera shorter as shown here, we're going to get a smaller image.

Have a look again and see if you can make sense of why this is happening.

The rays just aren't spreading out as much by the time they hit the screen.

So we have a smaller image, but it will be brighter and it's brighter because the light that's coming through is all concentrated on a smaller area of the screen.

Now, which of the following will increase the size of the image in a pinhole camera? And carefully about each option.

Press pause while you decide and press play when you're ready.

There are two ways you could do this.

You could move the camera closer to the object as I've shown you, or you could use a longer box for the camera, I showed you if the box is shorter, you'll get a smaller image.

So if the box is longer, you'll get a larger image.

So well done if you picked out both of those.

Now, what about adding an extra pinhole? You tried this.

You saw that it creates an identical image on another part of the screen, and this diagram is showing you why.

So as before, only one ray from each point on the object passes through each pinhole as long as your pinholes are very small.

A light from each point on the object, therefore, now hits the screen in two places.

That's why you get two images, one caused by each pinhole.

So which of the images below shows what would happen if there were eight small holes in the front of a pinhole camera? Press pause and press play when you've decided.

And I hope you realised that the only correct answer is A.

If you have eight pinholes, you'll get eight small images on the screen of the camera.

Now, you also then made one of your pinholes slightly larger.

And if you do that, you get a blurred image, as an image that's fuzzy, it's not very clear, but it is brighter.

And this diagram is showing you what's happening.

Light rays from a single point on the object can now pass through a larger hole.

So more rays can get through in several directions.

So rays from one point on the object hit the screen over a larger area.

So for example, rays from that point at the top of the tree are going to hit the screen over a little area rather than just at one point.

And these larger areas of light ray from each point overlap with each other, and that's what makes the image blurred.

But the images brighter because more light rays can pass through the bigger hole.

And the larger the hole, the more light rays from each point on the object can pass through it.

So you might think, well, let's just make a really big hole.

But of course, as the hole gets bigger, the image gets more and more blurred because the area on the screen hit by light rays from a single point on the object gets larger and overlaps more with the light rays from other parts of the object that are hitting the screen.

So the image gets more blurred.

And as the hole gets bigger and bigger, eventually, you can't see a clear image at all.

Here's a question about that.

The hole in a pinhole camera is made larger.

Which of the following statements is correct? And if you need more than five seconds, pause and press play when you've decided.

And the correct answer is the image becomes brighter, the size doesn't change, and it certainly doesn't become more sharply focused, it becomes more blurred.

And now, here's a final task for you to show what you've learned in this lesson.

I'd like you to copy the diagram shown here.

It shows a pinhole camera and an object on the left, which is an arrow made of two colours.

And then I'd like you to draw four rays of light from the object through to the screen of the pinhole camera.

And on the screen, draw how the image of the arrow would appear.

So you might like to think about which rays will be most useful to draw for that.

And then pick out some of these words to describe the image as shown at the bottom here.

So pause the video for as long as you need and press play when you finished.

I'll show you a suitable answer.

Have a look at this diagram.

We have four rays going through the pinhole and hitting the back of the screen.

And notice that they include the ray from the top of the object and the ray from the bottom of the object.

And those are very useful to draw because they show you where the top and bottom of the image will be.

And from this diagram, you can see that the ray from the top of the object ends up at the bottom of the image, which shows why the image is upside down.

The words that describe this image are inverted, upside down, sharply focused, dim, not very bright and smaller than the object.

So well done if you got that right.

And now, we're at the end of the lesson.

So I'll give you a summary of what we've done.

Cameras can produce images from the light that objects emit or reflect.

A pinhole camera is an empty closed box with a tiny hole on the front face and a screen on the back face.

Light moves in straight lines from a light source through the pinhole to the screen at the back of a pinhole camera.

A pinhole camera produces an image because light from each different point on the object falls on a different single point on the screen.

The image produced by a pinhole camera is dim and inverted.

Adding more holes produces multiple images, making the whole larger makes the image brighter but blurred.

So well done for working through the lesson.

I hope you enjoyed it, and I hope to see you again in a future lesson.

Bye for now.