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Fly’s Eye


Get a friend to stand on the other side of the glass and take a look at them. How many of them can you see?

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This is how a common house fly might see the world around them. It almost looks like a mosaic, lots of tiny images that create one large picture of their environment. The eye of a fly has a very different structure from ours so they perceive the world rather differently. What happens when you move towards and away from the window?

Why so many images?


As you stand in front of the screen, light reflects off objects and passes through the screen and into your eyes, allowing you to see the objects on the other side of the exhibit. As you look through the screen you are actually looking through a series of small lenses (Fresnel lenses). These lenses focus and transmit light over large distances. Each Fresnel lens in the screen focuses the image behind it allowing the person looking at the screen to see multiple images of the person on the other side. The effect you see is similar to compound vision. Compound vision provides multiple images of the objects around you, which is how many insects and sea creatures, see.

Try this

Things you can try yourself

For this experiment you just need a large spoon. Look at your reflection on the inside of the spoon (the concave or inward bending side). What do you notice? Now turn the spoon around and look at the outside of the spoon (the convex or outward bending side). What do you notice now? A concave mirror bends light making the reflection look bigger. A convex mirror focuses light making the reflection look smaller.

Compound Eyes

The compound eyes of insects are made up of thousands of tiny receptors called ommatidia. Each one of these cells is a functioning eye but when you put them all together, you get a huge field of vision for our little fly. Our eyes move around in our head thanks to muscles but a fly doesn’t have that luxury, instead their eyes protrude from their head so that can have an almost 360-degree view of their environment. Despite the advantages of having a smaller lens, the Fresnel lens style reduces image quality.

Did you know?

Flies are short sighted. The light entering each lens in the screen is focused inwards, making the object appear smaller, as if they were far way. Their vision is not as clear as ours but they are very good at picking up on movement around them. If an object near them moves suddenly, their ommatidia fire rapidly, this is called ‘the flicker effect’. This acts like a warning and they speed away, even if the object isn’t a threat.

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Look Closer

Welcome to Look Closer, Techniquest's brand new digital tool. We're trialling Look Closer as a way of offering you a closer look at the science demonstrated by many of our exhibits. You'll find visitor sheets, videos, articles on contemporary science as well as fun trails to navigate your way around the exhibition space.

Speak to our Science Communicators to find out more.