Key Concepts: Microscopy

Microscopes are a fundamental piece of equipment in biology. They are used to observe organisms and structures smaller than can be seen with the naked eye.
The two main types of microscopes that you will need to know about are light microscopes and electron microscopes.
Light microscopes transmit light through a slide containing the specimen, and they can magnify objects up to 2000 times.
Electron microscopes use a beam of electrons, rather than light, to produce images with extremely high resolution.
Because they use electrons, electron microscopes have a much higher magnification and resolution than light microscopes. They can magnify sample up to 2 million times.
Magnification is the extent to which the image of a specimen is larger than the specimen itself. It is calculated by multiplying the magnification of the eyepiece lens by the magnification of the objective lens.
Resolution is the ability to clearly see and differentiate two separate points or structures as distinct.
Microscopic organisms such as bacteria, viruses and the components of cells (like chromosomes and mitochondria) cannot be seen with the naked eye but can be observed with a microscope.
Scientists use stains to make certain parts of a cell more visible under a microscope.
Cell theory was developed using the light microscope, which led to the discovery of cells.
The invention of the electron microscope allowed scientists to observe and understand the structure of smaller cellular components and viruses.
It’s important to understand how to properly use and care for a microscope, including knowing how to adjust the focus, change the lenses for different magnifications, and clean the lenses properly to maintain resolution.
When preparing a specimen to view under a microscope, a thin slice (section) is often made so that the light or electrons can penetrate the sample.
Always remember: ‘magnification’ is how much larger the image is than the actual size of the object being looked at, whereas ‘resolution’ is the degree of detail you can see in the image.
In many cases, a balance must be struck between high magnification and good resolution. Increasing the magnification can sometimes result in a loss of resolution due to limitations in the optics of the microscope.