Eye vs. Camera

Your eyes and your brain work together to allow you to see. In fact, human eyes and brains have been coevolving for millions of years.
Your eyes are a bit like something else that captures images of the world: a camera. Let’s look at the similarities and differences between an eye and a camera.

How are an eye and a camera similar?

An eye and a camera both have lenses and light-sensitive surfaces.

Your iris controls how much light enters your eye. Your lens helps focus the light. The retina is a light-sensitive surface at the back of your eye. It captures an image of what you’re looking at. Then, the retina sends impulses to your brain along the optic nerve. Finally, the brain interprets what you’re seeing.

Did you know? 

The most common eye colour in the world is brown.

This is similar to what happens when a camera captures an image. First, light hits the surface of the camera’s lens. The aperture controls how much light enters the camera. Then, the light makes its way to a light-sensitive surface. For a long time, this surface was the camera’s film. In today’s digital cameras, this surface is an imaging sensor chip. 

Retinas, film, and imaging sensor chips all have one other thing in common. They all receive an inverted (upside-down) version of the image. Why? The lens in both an eye and a camera is convex, or curved outwards. When light hits a convex object, it refracts. This flips the image upside-down.

But you don’t see images upside-down. And the movies you watch aren’t upside-down either. Why not?

This is because your brain steps in to help your eyes. It knows the world is supposed to be right side up. So it flips the image over again. Digital cameras are programmed to make the correction on their own. Non-digital cameras contain a prism or mirror that flips the image so it appears right side up. Film is transparent so you can view the images on it the right way around.

How are an eye and a camera different?

There are two major differences between the human eye and a camera. The first relates to how they focus an image. The second relates to how they process colour.

How does an eye focus differently than a camera?

The lenses in your eyes change shape to stay focused on a moving object. The thickness of the lens also changes to accommodate the image being viewed. It is able to do this because the lens is attached to small muscles that contract and relax.
A camera lens can’t do this. That’s why photographers change lenses, depending on how far away they are from an object. Mechanical parts in the camera lens also adjust to stay focused on a moving object.

How does an eye process colour differently from a camera?

Your retinas contain two types of photoreceptors: rods and cones. Rods allow you to see in low light. They aren’t useful for colour vision.
Cones let you see in colour. There are three types of cones. Each type responds to different wavelengths of light. Red cones respond to long wavelengths. Blue cones respond to short wavelengths. Green cones respond to medium wavelengths.

When your brain activates different combinations of cones, you can see the world in colour. 

Did you know? 

Colour vision deficiency is often called colour blindness. Colour blindness affects people whose retinal cones don’t work properly. 

Cameras also have photoreceptors. But they only have one type. Cameras respond to red, blue and green light using filters placed on top of their photoreceptors. The photoreceptors in a camera are evenly distributed across the lens. In the human eye, however, the cones are concentrated at the centre of the retina. There are no rods at all at the centre of the retina. 

How else are your eyes different from a camera? 

Because a camera has photoreceptors all over its lens, it always sees a “full” picture. Your eyes, on the other hand, have a blind spot. That’s the point where the optic nerve connects to the retina. It has no photoreceptors at all. 
Most of the time, you don’t notice your blind spot. This is because when light hits this area of one eye, your brain uses information from your other eye to fill in the gap. 
If you want to test your blind spot, you can with a simple experiment.

Finally, your eyes actually stop seeing clearly whenever you spin or turn quickly. It’s why dancers learn the technique of spotting. They focus on one spot and turn their head quickly to refocus on that spot with each turn. This helps maintain their balance and orientation. It can also keep them from getting dizzy. Now a camera can’t do that!