3.4 The eye and the camera
Summary: The iris is the coloured part of your eye. You can see an iris in Figure 1. Everyone’s iris is unique, like a fingerprint. Tags: science oxford-science student-book-7 physics Created: 2026-05-19 Last Updated: 2026-05-19
After this topic, you will be able to:
- describe how the eye works
- compare a simple camera with the eye.
Think back
- What is the Light detector in the human body called?
- What is refraction?
- What does a lens do?
Key idea The eye works like a camera.
Key words lens, optic nerve, cornea, pupil, retina, iris, inverted, photoreceptor, camera, aperture, pixel, charge-coupled device (CCD), real (image)
The iris is the coloured part of your eye. You can see an iris in Figure 1**. Everyone’s iris is unique, like a fingerprint.**
Figure 1No-one has the same pattern in their iris as you.
How do eyes work?
When someone looks at a tree, like in Figure 2, an image of the tree is formed on the retina of their eye.
A Suggest why your pupil gets smaller in bright light.
Figure 2How an image is formed in the eye. Full text alternative to the content
The image is inverted (upside down). However, your brain makes sense of it so that you see an image of the tree that is the right way up. The retina is a light-sensitive material. This means that it reacts quickly to light. This is because it contains Cells that respond to light. These cells are called photoreceptors. When light hits a photoreceptor, Chemical Reactions produce an electrical impulse. This electrical impulse travels up the optic nerve to your brain.
B Name the nerves connecting your eyes and ears to your brain.
How is the eye like a camera?
A camera produces an image, just like your eye. The hole at the front of the camera is the aperture. You can see how a camera works in Figure 3.
Figure 3A lens in a camera focuses light. Full text alternative to the content
Cameras used to contain photographic film (see Figure 4). This film was light-sensitive.
- When light hit the film, a chemical reaction changed the chemicals in the film.
- When you processed the film, you saw the image.
Figure 4Cameras used to use photographic film.
At the back of a digital camera (see Figure 5), there is a grid of light-sensitive picture Elements, or pixels. This is called a charge-coupled device (CCD). When light hits each pixel, it produces a charge. The light produces an electrical, not chemical, effect. When you take a picture, this charge is moved off each of the pixels and stored. This is why there is a slight delay (short wait) before you can take another picture.
C Suggest a value (in centimetres) for the focal length of the camera lens in a smart phone.
Figure 5The digital camera on a smartphone uses pixels instead of film
An image that is formed on a CCD, camera film, or your retina is a real image. Any image that you can make on a screen is a real image. Your image in a mirror cannot be put onto a screen. That is why it is a virtual image.
The pinhole camera in Figure 6 models what happens in a camera.
Figure 6A pinhole camera works in a similar way to your eye. Full text alternative to the content
Light enters the camera through the pinhole, just like it does through your pupil. You see a representation of the object on a screen.
Stretch zone
- Copy and complete the sentences. When someone looks at an apple, light reflects/refracts off the apple into their eye. The light enters the eye through the pupil/retina. The cornea and the lens/retina focus the light onto the lens/retina. A chemical reaction produces an atomic/electrical signal that is sent down the opaque/optic nerve to your brain.
- Describe how the camera in a smart phone is different from a pinhole camera.
Stretch zone
- Compare the eye, a phone camera, and a pinhole camera.