Question: does a magnifying glass work in the same way as your eye? (bending light)

Andrew McKinley answered on 20 Nov 2014:

Your eye will “bend” (or, to use the proper word, “refract” – not to be confused with “reflect”) light just like a magnifying glass. These lenses are so called “convex” lenses – they “bend outwards” – or to put it another way, they are thicker in the middle than at the edges.

Light will refract going from one transparent material to another; with a glass block it bends first one way, and then bends back again when it exits the glass. A lens works by having non-parallel edges – when the light bends ‘back’ again, it cannot take the same path it did first time because the glass is no longer ‘pointing’ in the same direction. (think the ‘prism’ sketch, shown in the icon of the Spectroscopy Zone on the top right!)

You can show how the eye works by using a magnifying glass:
1) Stand in a room, preferably with a window
2) Take your magnifying glass over to the wall opposite the window
3) Using the magnifying glass, try to project the light from the window onto the wall
4) Move the magnifying glass forward and back, and eventually you will see an image of the world outside the window focussed onto the wall!

You’ll notice that this image of the world is upside down – exactly how the lens in your eye behaves!

When you put multiple lenses together though, interesting effects start to happen. A telescope is one example – one large convex lens to capture the light, while the second lens at the eyepiece helps to focus this image. A magnifying glass, in combination with the lens in our eyes, helps things to look larger. This is why it looks as though the magnifying glass does something different, but in reality it is the complexity of the optics that results in the ‘magnification’ effect.