This resource provides explanations of the key concepts encountered when exploring Exploring with Microscopes – the ‘basics’ that every student should understand.
1. Optical microscope
An optical microscope (or light microscope) uses visible light (400–700 nm) to illuminate the object being viewed (the sample). In most cases, this is white light, but in confocal laser scanning fluorescence microscopy, samples are illuminated with lasers, which provide coloured light of a single, defined wavelength. Before the 1930s, optical microscopes were the only microscopes in existence.
2. Electron microscope
Electron microscopes use a focused beam of electrons (rather than visible light) to illuminate the object being viewed (the sample). The electron beam is focused by means of electromagnetic coils (rather than the glass lenses found in optical microscopes). The small wavelength of the electron beam means that electron microscopes are capable of visualising samples at very high resolution.
The term ‘lens’ traditionally refers to a piece of glass (or other transparent material) that is curved on at least one side and is used to focus or disperse light. Optical microscopes use biconvex lenses (curved outwards on both sides) to focus light. The electromagnetic coils within electron microscopes are also sometimes referred to as lenses because of their role in focusing the electron beam.
A digital image or photograph that represents the view through a microscope. Many modern microscopes are integrated with computer systems that show the user the microscope image on a screen. ‘Snapshots’ of these digital images are micrographs.
In microscopy and other forms of imaging, resolution is the ability to distinguish two separate points or objects as independent. In practice, resolution is a measure of the degree of detail that can be seen in a sample. Resolution is distinct from magnification, which means making an object bigger, but does not imply any increase in detail.
Artefacts are phenomena that are not naturally present in a sample but have instead been introduced as a result of experimental procedure. Artefacts are commonly introduced during preparation of specimens for microscopy and are a particular issue for electron microscopy because of the complex preparation procedures involved.