In today’s modern era, it’s almost impossible to imagine a time when we didn’t know about microscopic particles and structures; magnification is a fundamental part of everyday life, from a pair of reading glasses to the side mirrors on a car. With the birth of the optical microscope in the 17th century, scientists were able to meticulously document, research, and discover a world of things normally invisible to the naked eye. It seemed as though the wonders of the microscopic was infinite – until the 1930s, when it became clear that optical microscopy wasn’t telling the entire story. There were forces at work that were far too small for even the most powerful lenses to see; at some point, the image simply couldn’t resolve clearly. It seemed as though optical microscopes had been pushed to their furthest possible limits. But how could something be too small for light to see, and how could you possibly examine it?

This set of problems was the catalyst for scientists to begin branching out from light-based microscopy. The theoretical framework explaining the limits of light-based magnification were already in place. The issue lay in understanding how light worked, and why it failed at certain magnifications. Visible light is electromagnetic radiation, part of a wide spectrum of rays that stretches from radio waves to X-rays, microwaves, gamma rays, and more. All EM Radiation is made of particles called photons, which travel in a wavelength; the speed and frequency of that wave will determine what sort of radiation it is, and how it interacts with various objects. X-rays, for instance, have a wavelength that is too short to bounce off of human flesh, but does reflect dense material like bone, allowing the doctor to clearly see your broken wrist. UV radiation can penetrate the skin enough to cause a sunburn, but we can’t see the rays with our eyes.

We are able to see objects because visible light bounces off of them and returns to our eyes. When that wavelength encounters an object, like a sample on a slide or the magnifying lenses of a microscope, the interference will cause the wave to spread out and weaken. As the light passes through a smaller and smaller space, it will scatter more and more. This phenomenon is called diffraction, and it is the major limit of optical microscopy: at a certain point, the photons are just too big and clunky to accurately bounce off of the sample and resolve clearly.

All of this was proven in 1873, when physicists Hermann von Helmholtz and Ernst Abbe demonstrated that optical resolution was dependent on the wavelength of the light source. They posed the crucial question: what if you could somehow use an illumination source that had a smaller wavelength than light? It was purely theoretical; the existence of electrons wasn’t proven until 1896. But the idea stayed around in various scientific circles; the theory that electrons could travel in a wave was proposed in a 1924 paper, and in 1926 German scientist Hans Busch showed that magnets could be used to direct a stream of electrons in a specific direction. The problems were in place and the theories were quickly being proven: it wouldn’t be long before scientists broke through the limits of light and found a way to see the invisible all over again.

electron microscopy

We’re surrounded by an abundance of technology, nowadays so it can sometimes be hard to imagine what it was like to look through a microscope for the very first time in the 1600s. Before the invention of the compound (multi-lensed) microscope, people believed that the world was comprised solely of what could be seen with the naked eye; it must have been overwhelming to realize what humanity had been missing! Once optical microscopy took off, scientists could finally get a detailed look at everything from well-known insects to completely new bacteria and understand how the tiny structures of a material affected its behavior.

Scientists are well-known for conducting experiments and documenting every detail of their actions. So it’s not surprising that the great analytical minds of the day began to sketch out the details of what they saw under the microscope  in order to preserve the images for future reference. These images came to be known as micrographs, and they have evolved alongside the microscope in terms of their level of detail and use of technology.

Initially, micrographs were hand-drawn sketches detailing what the observer saw on the slide. One of the first known images made with a microscope was drawn by Francesco Stelluti, who published a sheet of bee anatomy in 1630. Thirty-five years later, scientist Robert Hooke wrote and published Micrographia, the first major book about microscopy. The tome detailed his observations: the eyeball of a fly, a plant cell, insect wings, and a huge fold-out engraving of a louse. Micrographia was a monumental best-seller that also coined the biological term ‘cell’ after Hooke’s famous inspection of a piece of cork.

Basic sketches remained an easy method for documenting microscopic images for many years. When photography technology caught up, people would often simply hold a standard camera up to a microscope eyepiece and take a picture; after all, the camera was designed to resemble the viewpoint of a human eye, so it made sense to try to capture the slide permanently by exposing it to film. This technique is called the afocal method’. A typical optical microscope emits parallel light rays from its source up into the ocular, so an image can be created using a camera that is made for capturing very distant objects; those lenses are designed to work with parallel light as well. The eyepieces of both the ocular and the camera must be carefully chosen to work together to capture a clear image.

The direct imaging method is far more straightforward: both the eyepiece of the microscope and the lens of the camera are removed, and the camera is placed on the microscope tube so that its shutter surface matches the primary image plane projected by the microscope. You can also purchase mechanical adapters, which attach the camera to the microscope tube directly and allow for a much clearer method of focusing. Digital photography has made micrographs much easier to produce. Modern microscopes may contain a built-in camera and USB connection, which will allow you to plug them into a computer and record images directly onto the hard drive. However, a more flexible approach is to buy a standard microscope and add an external microscope camera. That way, you can use different cameras on the same microscope and vice versa. As important, you do not need to buy an entirely new unit if the camera software fails. Whatever your method, microscope imaging, or photomicrography, has grown and changed alongside microscopy, recording humanity’s findings for future research and posterity.

No tags

During my quest to find microscope-related news and content on the Web (it’s a tough challenge sometimes), I came across this blog by way of Boing Boing Gadgets: BibliOdyssey: Early Microscopes. This particular entry shows illustrations of early microscopes dating back to the 1600s culled from various books, including Robert Hooke’s famous Micrographia (1665),  Le Microscope à la Portée de Tout le Monde, or The Microscope Made Easy, (Henry Baker, 1742) and Phisicalisch Mikroskopische (Martin Frobenius Ledermüller, 1760s).

There are excerpts from the books, too, including this quote by Antonie van Leeuwenhoek about his discovery of bacteria:

“They were incredibly small, nay so small, in my sight,
that I judged that even if 100 of these very wee animals
lay stretched out one against another, they could
not reach to the length of a grain of coarse Sand.”

Continue reading through the entry and there’s a short history of the microscope, which includes some interesting facts. The first scientific paper relying on microscopy studies was published in 1661. Robert Hook’s Micrographia was a hit four years later because it showed a mesmerized public the very first illustrations of everyday items as they appeared under a microscope, turning experimental science on its head.

Pretty neat stuff, actually. Oh, and the pictures are cool, too.

No tags