History of Imaging – Part 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

We previously discussed light and the study of optics. From understanding how rays of light react with different materials and the human eye, the microscope was invented – a groundbreaking discovery for scientific progress. Think about how important the microscope has been to discovery. Science is an empirical venture such that we need to observe nature in order to make sense of it, explain it or make predictions about it. For example, early humans might have looked into a pool of water and observed their reflections. The human eye, however, isn’t powerful enough to make the observations that were needed to further science – looking at the stars requires a telescope to make detailed observations and similarly, looking at smaller things such as bacteria required microscopes. Light, optics, and optical technology are integral to answering questions that start with “how” or “why”, because they first answered the questions “what does this look like?” and “what is this made of?”.

 

The study of optics dates back to around 1200 BCE – there are records from Exodus 38:8 about the “looking-glasses” of women which were basically mirrors. Plenty of videos on the internet are about cute cats/dogs/children being frightened by their own reflection but at some point, intelligent and learned adults were also dazzled by their twins hidden in shiny objects.  Around the time that Leonardo da Vinci was inventing his famous projects, people were beginning to apply their knowledge about rays of light to technology – specifically the technology of lenses. The properties of lenses have been known since ancient Greek times and they had magnifying glasses in the Roman empire –  but the technology only became popular in the 16th century. Lenses are the basic technology that evolved into microscopes.

 

 

 

 

 

 

 

 

These diagrams from the (practically) omniscient Hyperphysics website demonstrate the basic idea of lenses. Using lenses and a method of “ light ray tracing”, it’s possible to see how light focuses or diffuses. The physics of ray tracing comes from the principles in the last blog as well as principle known as Fermat’s law – essentially, that light wants to travel the shortest distance possible.

 

How did we get to microscopes from our concepts about rays and lenses? In this post we’ll get to the technology behind the optical light microscope. We will need to talk about telescopes first though.

It makes sense in a historical way – looking at the ziggurats of the ancient Mayan ruins in Mexico we can see that the ancients were looking to the stars far before the time that society was wondering up what things were made of. People first wanted answers to questions like “where are we?”, “what is controlling us?” and the stars seemed to provide answers to questions of that sort.

This ray diagram shows how a telescope that uses lenses works:

 

 

 

 

 

 

 

 

 

 

 

 

Let’s say were looking at a star. In the diagram the ends of the axis of star are represented by P and Q. The rays go through the objective lens, form an image to the left of the eyepiece (represented by P’Q’) and are then seen by the observer through the eyepiece. The observer will see the final image of P’’Q’’ which is considerably larger than the original PQ length.

The microscope was invented – we’re not sure exactly by whom – in the early 17th century. Antonie van Leeuwenhook made groundbreaking progress using the new microscopic technology when he discovered the red blood cell.

Note that both microscopes and telescopes utilize convex lenses from the first diagram because that type of lens focuses the light rays. So, is the microscope similar to a telescope? Let’s look at the ray diagram. In this ray image from wiki, the image (what the observer would see) is the big red arrow and the little red arrow is the original object (like a red blood cell). Note that both microscopes and telescopes utilize convex lenses from the first diagram because that type of lens focuses the light rays.

 

 

 

 

 

 

 

 

 

 

 

The two ray diagrams look very similar! That’s because telescopes and microscopes perform similar actions – one takes things from far away and makes them visible to the observer, and one takes small things and makes them visible to the observer.  The difference has to do with the “F”s in the diagram for the telescope – the focal lengths. The lenses focus at different lengths so the microscope and telescope can be adjusted for the original object’s distance or size.

Taking a step back, where are we on the way to EyeWire? It seems that we are closer to the aforementioned ziggurats then to computational neuroscience. We have been talking about optical telescopes and microscopes – the ray diagrams show very simple rays of light.  Starting from these optical microscopes which revolutionized science on their own, there have been massive advancements in technology that have led to electron microscope technology. Those will show up in the next blog post!