For as long as humanity has existed, we’ve wanted to see things that are too small for our eyes to make out properly. When the Romans invented glass almost 2,000 years ago, they realised that it bends light and so experimented with different shapes. One shape in particular – a disc which is thickest in the middle and thinnest on the edges, made objects look larger when viewed through it.
We know this characteristic disc as a lens. The word lens is derived from the Roman word lentil, as these discs are similar in shape. The Roman writer Seneca also described the process of magnifying small letters by viewing them through a glass globe full of water. However, the use of lenses stalled until the end of the 13th century when spectacles became common. By the start of the 17th century, using lenses in combination with each other to magnify small objects and features started.
The first ever microscopes
These early microscopes were basically fancy magnifying glasses and only had one power – generally less than 10X. People used them for amusement more than anything, looking at fleas and other small bugs. Compare these to modern-day microscopes with their image analysis software!
The big breakthrough came in the 1590s when Dutch spectacle-makers Hans and Zacharias Janssen started to try out combinations of lenses and found that by using two – one at each end of a tube – they could achieve greater magnification.
This discovery was developed further by fellow Dutchman Antony Van Leeuwenhoek a century later when he became the first person to make and use a microscope with a power of 270X. This magnification was the best yet – other contemporary models could only achieve 50X. Van Leeuwenhoek put a lot of effort into his lenses and it’s this dedication that gave us our first real scientific microscopes.
Insight into another world
Van Leeuwenhoek’s microscope, which used a single convex lens mounted on a metal holder, allowed him to see blood cells, bacteria, yeast and single-celled animals. This was ground-breaking as before this, the idea of cells and microbes simply didn’t exist.
The compound microscope
To get greater magnification with a single lens, the focal point must be reduced, but this means reducing the diameter of the lens and so beyond a certain point, the lens is too small to look through.
This is where the compound microscope came in in the 17th century. Compound microscopes work by using a second lens to magnify the already-magnified image from the first lens. We still use this system today, although we call the first lens (the one closest to the specimen) the objective lens and the second the eyepiece.
One thing the earliest microscopists had in common was the distortion of images thanks to inconsistent glass quality and imperfections in the shapes of the lenses. Not much was done about this until the mid-19th century when companies like Zeiss in Germany began to produce better quality optics that overcame the common problems of distortion and colour splitting.