Allan Mitchell (Microscopy Otago) talks about the meaning of the term ‘resolution’ in microscopy. Using real-world examples, Allan explains that resolution is the ability to distinguish two points as separate structures rather a single fuzzy dot. In practice, resolution is a measure of the level of detail that can be seen using a microscope.
Resolution is the ability to see two structures as two separate structures rather than as one fuzzy dot. A good example of this is when you look at the Moon with your naked eyes – you see a bright spot with patterns on it. However, if you look at it through the telescope, you can start to make out detail on the surface. Another example of resolution is at night-time when you have headlights coming towards you. In the distance, you may see one bright spot, but as they get closer and closer to you, you see two bright spots, which are the headlights. You’ve been able to resolve that there are actually two sources of light.
Another example of resolution is flying over a forest. When you look out the window of an aeroplane, you see lot and lots of trees but you can’t make out the fine detail within the forest. If you get close to the forest, you start to see more and more resolution, you start to see the leaves, the branches, the bark.
And the resolution comes from the wavelength of the illumination source that we’re using. There is a physics formula that tells us that any structure that is smaller than half the size of the wavelength of the illumination source will become invisible. With white light, for example, the wavelength is 400–700 nanometres, so what we’re saying is anything smaller than 200 nanometres will not be visible. The wavelength of electrons, however, is in picometres, which is trillionths of a metre, so theoretically you should be able to see things down to picometres in size.
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Moon surface, courtesy of NASA
Kahunapule Michael Johnson