Very few research instruments have as widespread a usage in science as do microscopes. They also are a very useful tool for industries (e.g., failure analysis and monitoring fidelity at a fabrication and production facility), hospitals (e.g., pathology diagnosis, identification of microbial infections, determining hematology status, etc.), minerology, metallurgy, crystallography, etc. In recent years, microscopes have become more available and more utilized for science education in primary and secondary schools. For those of us using microscopes for our work, they additionally provide quite a lot of fun!
In this short series of articles, I will present a very brief and readily understandable description of microscopy and the different types of microscopes. These are not in-depth discussions, but are designed to give an introductory background about microscopy for teachers, technicians, parents, students, and beginning users. I have tried to make everything concise and good for non-experts. Although simplified explanations will be given, some recommended resources for deeper coverage also are provided.
The initial article gives an overview of the most fundamental concepts for microscopes and microscopy. These topics precede actual usage of any microscopes. The following articles will briefly explain the main kinds of microscopes used in 2015. A final article outlines utilization of microscopes for education in primary and secondary schools.
How do microscopes actually work?
Microscopes permit observation of structure, function, and composition that cannot be seen with the naked eye. All the common kinds of microscopes are governed by the branch of physical science known as optics; this describes exactly how microscopes use lenses to form images. A common example of a single lens is the magnifying glass; one need not know anything at all about optics to have fun using one! Compound lenses have multiple single lenses working together to give higher magnification of specimens. As magnification is increased, good compound lenses will reveal smaller and smaller details. Magnifications for typical ordinary uses range from 3 times (3X) to several hundred times (300X) larger than the natural size; for special microscopes, magnifications can go all the way up to a million times their natural size (1,000,000X).
The size of small details that can be visualized with sufficient magnification is limited by the level of resolution. Resolution can range from detection of specimen details that cannot quite be seen with the naked eye (i.e., low resolution), up to visualizing individual atoms (i.e., very high resolution). The resolution level for microscopes is determined by optics, and varies with the kind of lenses and microscope being used.
The functioning of microscopes is generally analogous to the production of images by our eyes. That involves light waves bouncing off some object, passing through our pupils and ocular lenses, and then being detected by our retinas. Most imaging in microscopy uses shining waves onto or through a specimen, then passing them through lenses, and finally registering them on a detector; detectors for microscopy record the waves hitting them via cameras that use either photographic film or digital memory. For microscopy, lenses first focus waves onto the specimen, and then onto the detector. Imaging requires contrast (i.e., relative amount of lighter vs. darker components); this is produced in most microscopes when the specimen causes some portion of the waves to not be transmitted to the detector, due to being absorbed or scattered.
The several compound lens sysytems in microscopes provide enough magnification and sufficient resolution to resolve some small details in specimens. Recorded images give a permanent record of what was observed, and also can be used to make measurements and counts of the small details. Basically, resolution determines the information content of images made with any microscope. In some cases, the smallest details known to be present in a specimen are not able to be imaged because the lenses lack enough resolution even at high magnifications; this is empty magnification.
Information about chemical composition of a specimen also is available from some types of microscopes. Analytical microscopy detects the amount of some element or compound, and/or their location, within the specimen being examined. Resolution here corresponds to the ability to accurately measure amounts for several elements or compounds that differ only slightly. Compositional information is usually displayed as a spectral histogram, with the vertical axis denoting quantity and the horizontal axis showing a scale differentiating the elements or compounds. The compositional data also can be displayed superimposed upon a regular image of the specimen; this mapping shows exactly where some element or chemical component is located.
The different kinds of microscopes.
The most general way of characterizing microscopes is by the type of waves used to view the specimen. Our own eyes produce images using light waves coming from (e.g., stars, neon signs, etc.) or reflected off different specimens (e.g., birds, leaves, other people, etc.). Different portions of the electromagnetic spectrum are used by the 2 main kinds of microscopes: (1) light waves, ranging from ultraviolet, through all the visible colors, and on into infrared, are used in light microscopes, and, (2) electron waves, which are very much smaller than light waves, are used in electron microscopes.
The wavelengths utilized, and the quality of the lenses present, determine the level of resolution given by each microscope. Smaller wavelength and higher quality lenses give higher resolution (i.e., the ability to see and image finer details in a specimen). Bacteria are too small to be observed with the naked eye or with a magnifying glass, but can be seen with a good light microscope; electron microscopes use wavelengths very much smaller than those found in visible light, and so are able to not only easily image bacteria and viruses, but also can show very small details within those objects (i.e., substructure).
There are several other important special types of microscopes, but they will not be included here since this article presents only an introductory coverage.
How is microscopy important for ordinary people?
Microscopes are used for very many different purposes, including usage for research. Images from microscopy show enough details to permit detection, identification, and authentification of many different objects and conditions. The discipline of pathology in clinical medicine uses microscopy extensively for the diagnosis of disease states and the identification of microbes causing infections. Microscopy provides an ideal tool for making size measurements of small objects and smaller details within them; thus, it is fundamental for analysis of all levels of structure. Microscopy often is used to evaluate quality (e.g., perfection of small crystals to be used for x-ray diffraction; status of solid-state semi-conducting components). Developing new high technology directly depends upon microscopy. Dynamic imaging of specimens that are changing with time reveals the course of changes and positions of constituent parts; this capability is a major feature of microscopy at both low and high magnifications. All these capabilities make microscopy very widely used, meaning that microscopes are very important for everyone!
The “simplest microscope” of all is fun and can be useful for science education!
The very simplest microscope often is not recognized as such! A magnifying glass (e.g., a single plastic or glass lens within a holder, provides a magnification of 2-5X) uses white light waves in the visible spectrum to show us some smaller details that cannot be discerned with the naked eye. A magnifying glass is a single lens; light and electron microscopes use compound lenses made from several single lenses working together. Just as you focus images with a magnifying glass by moving either the lens or the specimen along a line towards your eyes, so do light microscopes focus by moving either compound lenses up and down from a specimen, or by moving the specimen relative to stationary lenses.
Teachers should recognize that magnifying glasses are inexpensive, difficult to break, and easy to use by all students. The concepts of a lens, magnification, resolution, and focusing become rapidly understood from hands-on usage, and some unexpected small details often are discovered by young students. Easy specimens for examination with a magnifying glass are table salt or granular sugar, a leaf from a plant, a piece of Kleenex tissue, a cut piece of any fruit, and, skin hairs and scratches on the student’s own forearm.
Kerry Ruef has developed very successful teaching programs for primary school students which use magnifiers extensively ( http://www.the-private-eye.com ). I highly recommend to all teachers presenting science in primary schools Kerry Ruef’s very recent article, “The Private Eye ®– (5X) Looking/Thinking by Analogy”, just published in Microscopy Today (May 2015, volume 23, pages 52-57) . This now is available on the internet as a PDF (see: http://content.yudu.com/web/14lmv/0A3cxwn/MicroscopyTodayV23N3/flash/resources/52.htm?refUrl=http%3A%2F%2Fwww.the-private-eye.com%2Findex.html ). The topic of “Microscopy in Education” is a subject frequently published in this journal coming from the Microscopy Society of America (see: https://www.microscopy.org ).
Even though we have not yet looked at any actual microscope or images, you now should have a good very basic understanding about microscopy, what are the different types of microscopes, and how is microscopy so very important in the modern world. In the next article of this series, we will take a closer look at light microscopy.
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