The pinhole camera

Light · The pinhole camera

An empty, closed box. A tiny pinhole in the front face, a screen on the back face. Where do you think light from the TOP of the arrow will land?

Step through the three views, then tap each part of the camera.

Predict, then check

Think about how many rays from ONE point on the object can now get through the hole.

You make the pinhole bigger. What happens to the image?

Tap any cell to reveal it. Tap a column header to read one property down every item.

What you need to know

• A pinhole camera is an empty, closed box with a tiny hole on the front face and a screen on the back face. A translucent screen, such as baking paper or tracing paper, lets you see the image from outside the box.
• For a camera to make an image of an object, light from that object must get into the camera.
• A luminous object emits light in all directions from every point on it. A non-luminous object reflects (scatters) light in all directions from every point on it.
• Light travels in straight lines from the object, through the pinhole, to the screen. The pinhole does not change the direction of the light.
• With no pinhole, every point on a screen gets light from every point on the object, so there is no image. With a tiny pinhole, only one ray from each point gets through, so each point on the object lights a different single point on the screen, and that forms the image.
• The image is dim (only a little light gets through) and inverted: light from the top of the object lands at the bottom of the screen, and light from the bottom lands at the top.
• Moving the camera closer or using a longer box gives a larger image. A shorter box gives a smaller, brighter image. Each extra tiny hole gives one more image.
• A bigger hole gives a brighter but blurred image: more rays from each point get through in more directions, so each point lights a patch of the screen and the patches overlap.

The big picture

A pinhole camera is an empty, closed box with a tiny hole in the front and a translucent screen at the back. Light travels in straight lines, so only one ray from each point on the object gets through the hole, and each point lights its own spot on the screen: that's the image. The top and bottom rays cross at the hole, so the image is inverted, and it's dim because little light gets in. Closer, or a longer box: bigger image. Shorter box: smaller and brighter. More holes: more images. Bigger hole: brighter but blurred.

⚠ Watch out

Bending the rays at the pinhole, or drawing them flipping over as they pass through. The pinhole is just a hole, so draw each ray as one straight line from the object, through the hole, to the screen.

Memory hook

A hole with no lens makes a picture. Straight rays cross at the hole, so the picture's upside down. Make the hole bigger and you get a brighter picture that's worse.

Check yourself

Sketch a pinhole camera pointed at a tree. Draw one ray from the top of the tree and one from the bottom of its trunk, then explain why the tree appears upside down.