Many lay people and beginners believe, somewhat naïvely, that they have a pretty good understanding of microscopes. However, like many scientific instruments, microscopes come in many shapes and forms, with varying levels of intricacy and accuracy. And—much like many of the tools that have been around for centuries—as technology has advanced, so have microscopes. In this buyer’s guide, we’re going to discuss the many iterations of today’s microscopes, and look at the people and professions who rely on these instruments. Along the way, we’ll show each group what they should look for when choosing a microscope for their specific needs.
A Brief History of the Microscope
While the exact origin of the microscope has mostly been clouded by myth and legend, there are some basic facts that are generally accepted today.
In the late 1500s, two Dutch eyeglass makers, father and son Zacharias and Hans Janssen, developed and began experimenting on a crude microscopic device with limited magnifications. In 1609, famed Italian mathematician and scientist Galileo Galilei learned of the Janssen’s work and began refining their system, eventually adding a focusing mechanism.
"As with everything these days, the Digital Age has had an effect on microscopes."
These crude microscopes spread and remained mostly unchanged for the next 50 or 60 years, until the 1670s, when Dutch tradesman and unlikely scientist Anton van Leeuwenhoek began his work. He taught himself how to grind and polish lenses and was able to boost the magnification up to as much as 270x. In 1674, van Leeuwenhoek was the first to observe and describe bacteria, yeast, plants, and life in a drop of water. Because of the design improvements and the microscopy work he did, he’s widely considered the father of the modern microscope.
Fast forward to the mid-1800s: In Europe, Carl Zeiss and his company “Carl Zeiss Jena” began making simple microscopes, leading to the development of the first compound microscope. This design of microscope is what comes to mind when most people think of what a microscope looks like—mostly because the microscopes many of us used in school haven’t changed much since. With the turn of the millennium, advances in digital technology have seen the integration of digital cameras into microscopy and the introduction of imaging software. Even more recently, digital systems are beginning to see wireless connectivity across multiple platforms including computers, smartphones, and tablets.
Starting at the bottom and working our way up is the Base, Light Source, and Diaphragm, followed by the Specimen Stage, then the Objective Lens (or Lenses) which are mounted on the Nosepiece. Above the Nosepiece is the Head that holds the Drawtube and Eyepiece, which is where you observe your specimen. Within easy reach of the observation position will be a Focusing System.
The Light Source
Originally there was a mirror on a pivoting mount beneath a hole in the specimen stage. The user would move the mirror manually to reflect light from an external source, such as a lantern, or light. Later, an incandescent bulb was introduced, and now LEDs are used, although many beginner models are still offered with mirrors. With onboard lights came rheostats to control the brightness. If the specimen blocked the light from below, an external light could be used to illuminate the top surface. Today, some microscopes will have a secondary light or LED that allows users to illuminate their specimen precisely from a variety of angles.
The Specimen Stage
This is where your subject is placed for observation. The size of the tray varies by model, and as a general rule, bigger is better. The larger the stage, the easier it is to place larger specimens. The stage will have a hole in the center through which the light from below is projected. This hole will be directly under the Objective. On higher-end microscopes, the stage will be articulated on one, two, or three axes that allow it to be moved forward and back, left and right, up and down. The ability to move the stage allows the user to view larger specimens without having to reposition them, and can accommodate tall specimens that might not normally fit on a fixed stage. Clips are commonly found on stages to hold slides in place. Specialized stages may be heated for keeping biological specimens alive during observation.
The Aperture Diaphragm
The hole in the center of the stage may have an adjustment mechanism to control the amount of light surrounding the specimen and entering the objective. This is called an Aperture Diaphragm, or just a Diaphragm. The most basic diaphragm is just a disc with different-sized holes, from the same size as the stage hole to a pinpoint. On more expensive microscopes, there may be an Iris Diaphragm. This works much like the human eye or a camera lens, with a continuously variable diameter that gives precise control over the amount of light passing through the Diaphragm.
Objective Lenses and Nosepiece
The Objective Lens is the start of the magnification process. On most microscopes, there will be several different objectives that offer different magnifications—for example 10x, 40x, and 100x. The different lenses are mounted onto the Nosepiece (also called a Turret). The nosepiece rotates to allow the user quick transitions from one power to the next. Typically, there will be a click-stop or some kind of mechanism to lock the objective in the correct orientation directly above the light and below the eyepiece.
The Head and Drawtube
There are a few configurations of the head (which holds the eyepiece). A Monocular will have a single eyepiece, which makes it necessary to hold one eye closed. Binocular heads have two identical eyepieces and are used with both eyes. A binocular head will typically have a diopter adjustment to allow people with different eye prescriptions to be able to use it without their glasses and still be able to achieve precise focus. A more uncommon head type is a “trinocular.” The trinocular has room for a monocular eyepiece for sharing with another person, or with special accessories, a camera may be mounted for photographic purposes.
The eyepiece is attached to the head by the drawtube. It is usually set at an angle to the head for more comfortable viewing—generally between 45 and 35 degrees. In binocular heads, there will be two drawtubes, one for each eyepiece.
The Eyepiece is what you look through to observe your specimen. Depending on the model, the eyepiece may be permanently mounted or removable, with a fixed or a zoom (variable) magnification. This is where the Compound comes in: the magnification of the eyepiece multiplied by the magnification of the objective being used gives you the total magnification at which you’re observing. So, a 10x eyepiece looking through the objectives mentioned above would yield 100x, 400x, and 1,000x respectively. If your model has removable eyepieces, you’ll be able to switch out different magnifications to tailor the total magnifications.
The Focus System
The type of system greatly depends on the individual microscope. In most cases it will be a rack-and-pinion style with a knob that you turn to focus. Certain models will have focusing knobs on either side of the arm for use lefty or righty. Higher-end microscopes will use a dual-speed system, with a large coarse focus to get it close, then a geared smaller knob for precise fine focus.
Remember: this is a precision optical instrument—a bump or drop can cause catastrophic damage.
The body is the framework to which all the different components are attached. The base will be wide to provide a solid footprint, usually with non-slip rubber feet. From the back of the base will be a curved piece called the arm. A third of the way up, the Stage attaches to it with the focusing mechanism. Right above that is the optical system, comprising the Nosepiece and Head. Some higher-end models will have a swivel system that enables the head to swing left and right for easier sharing between viewing partners.
The proper way to pick up and move a microscope is to pick it up by the arm with one hand and immediately place the base on the palm of your other hand.
Bright Field versus Dark Field
There are two basic ways to illuminate and view specimens: Bright Field and Dark Field. Bright Field is the most common and the most basic. A light source shines through a specimen from the bottom through the aperture and stage opening, to the objective and into the eyepiece. Images appear dark against a bright background (hence its name). While it’s popular, there are several drawbacks and limitations: very low contrast of most biological samples, generally low resolution, and most importantly, the sample often has to be stained before viewing. So why use it? The simple answer is that it’s easy to use and set up without special equipment.
In contrast is Dark Field microscopy. It is used to observe unstained samples, causing them to appear brightly lit against a dark, almost purely black, background. A typical problem when viewing cells is that they are hard to distinguish from the background. This is why in Bright Field microscopy, the specimen often needs to be stained. Using the Dark Field method of illumination takes advantage of the different way light is refracted by the different materials within the sample to show detail that can’t normally be seen. The main disadvantage is that it requires some modifications to a conventional microscope. Images appear bright against a dark background showing high contrast and detail with improved resolution.
The Types of Microscopes
If you’ve taken biology or watched television, you’re familiar with the basic Compound Microscope. It can achieve magnification upward of 2000x, with most work being done in the range of 400-500x. With its high-power capabilities, it is mostly widely used in biological and scientific situations. Cellular detail can begin to appear at 40x and, at 400x, significant detail can be seen. You will need at least 100x to study bacteria.
"Microscopes come in many shapes and forms, with varying levels of intricacy and accuracy."
“Compound” refers to the optical system that produces the high magnifications. The Objectives start as low as 4x and typically will go up to 100x. With the right eyepieces, it’s not hard to see how those 2,000x magnifications are possible. The light travels in a single path from the light source to the eyepiece—even if a binocular head is being used—causing images to appear two-dimensional. When looking through the eyepiece, the image is uncorrected, so it will appear upside-down and backward. This means that moving a slide to the right will make the image move left, and moving it forward will make the image go back. Generally, when looking at specimens at the cellular level, this doesn’t cause any confusion or discomfort—it just might take some getting used to when starting out.
These are low-power devices with two eyepieces that are used primarily for inspection purposes. They tend to stay in the 10-40x range and can go up to as much as 100x, to observe details in larger solid specimens like fossils, stamps, coins, or circuit boards. Unlike a Compound Microscope, the Stereo Microscope most commonly uses light from a top-mounted source to illuminate the sample or subject—as opposed to being lit from below and through the sample as with a compound microscope. Two independent, or stereo, light paths produce a true three-dimensional image when you look through the binocular head. This provides a depth to images and gives the user better resolution and perspective over a compound microscope that produces two-dimensional images due to its single-light path system.
The anatomy of the Stereo is virtually identical to the Compound, except for some key differences.
- The stereo microscope will have a pair of objectives of the same power. This is in order to obtain the two independent light paths.
- Because of the typical usage of this type of microscope, the images will be corrected—so moving the specimen left will move the image left, and moving it forward will move the image forward.
- Most will have a built-in or attached light source on the top, since specimens will normally be solid; although some models have a lower light source. Lower-end models might not have a light source and users will have to rely on external lights for illumination.
- Often the entire Nosepiece/Head optical system can be adjusted up and down for proper placement relative to the specimen, with travels up to several inches. Many models will have the stage built into the base for better specimen stability. The part that the optical system is mounted on is called the Pillar and there will be a locking mechanism to hold the optical system at the desired height.
As with everything these days, the digital age has had an effect on microscopes. Beyond the different types of digital microscopes now being offered, there has been a revolution in the ability to view and share microscopic images. As we’ll see below, once images are digitized, the possibilities for sharing between a group of people, a class or lecture hall, or via the Internet become almost infinite. Just a few years ago, schools and institutions were required to purchase dozens of microscopes, and those who couldn’t afford them were forced to have large groups of students huddle around a single instrument, taking turns. These days, a school or institution can greatly reduce its purchasing and simply stream the images to projection screens, computers, smartphones, and tablets. Doctors deployed to a natural disaster area can stream or email images to colleagues on another continent for diagnosis and treatment. The current connectivity we use everyday has improved microscopy and our ability to view and share it.
As discussed above, eyepieces may be removable and changeable. Many manufacturers have come out with digital eyepiece cameras that fit common eyepiece mounts. This enables an analog compound microscope to be converted into a digital one simply by adding a CCD imager in place of the eyepiece. These imagers will often have a lens with a low magnification, such as 10x, to provide an optical magnification before the image hits the camera. The resolution of the camera can be as high as full HD 1080p. These cameras often have digital zoom up to several-hundred power, boosting magnifications beyond what might practically be achieved optically. The usefulness of digital zoom greatly depends on the camera's resolution.
The camera will typically be plugged into a computer’s USB port to stream the image and to give the camera power. Imaging software loaded on the computer will allow the user to adjust the camera settings and performance, capture stills or video, and manipulate the image with stacking, filtering, and color-enhancement options.
Some of the eyepiece cameras feature LCD screens of varying sizes. Generally, the size of the screen will depend on the resolution of the camera. Having a screen provides an easy way to share views among a small group. Often, these units will have an output for USB tethering to a computer, or Wi-Fi capabilities. Since these housings are larger, many offer memory card slots to save images for later review, sharing, or manipulation on a computer.
In the past couple of years, wireless technology has eliminated the USB cable and provides an even greater range of sharing options. Eyepiece cameras can now generate local Wi-Fi networks and can stream images to Wi-Fi-enabled computers, smartphones, and tablets. Where five years ago, students would need to take turns looking through an eyepiece, a professor can now manipulate a specimen and an entire lecture hall of students can stream and capture the images to their computers or mobile devices.
Fully digital microscopes incorporate a lens configuration like traditional microscopes, with the sensor acting as the eyepiece, or relying solely on high-resolution cameras for magnifying images. They may come in desktop models with objectives, like traditional microscopes, or much smaller handheld versions. Since the specimen will still need to be illuminated and held in the proper placement, a traditional-style setup is generally preferred for quality images to be obtained. A digital microscope can be tethered to a computer, be used in stand-alone fashion, with an LCD screen, or wireless, using a Wi-Fi signal.
As mentioned above, the next generation of microscopy instruments will see the integration of Wi-Fi-enabled digital microscopes that will transmit the specimen view to Wi-Fi-enabled devices. These microscopes produce their own local Wi-Fi signal to which you connect your computer, smartphone, or tablet directly without the need for a router. The number of supported connected devices depends on the model, but as the technology becomes more common, the number of simultaneous connected users will increase. Using either manufacture-specific or third-party apps allows you to view the subject on the larger screens found on many tablet devices. This next generation of microscopes is perfect for inspection, forensics, and classroom exploration.
A subset of digital microscopes, USB microscopes are increasing in popularity. They are typically economically priced, with low magnification. As the name implies, they connect to, and are powered by, a computer via a USB cable. Most USB microscopes are handheld models, so they are easy to use. The technology is similar to a standard webcam, but the digital microscope incorporates a lens configuration along with the imaging sensor, to magnify an object. Many models incorporate their own LED illumination, and the LED intensity may be adjustable. Resolution depends on the size and pixel array of the imaging sensor. Magnification ranges will depend on the lens configuration, with some capable of magnifications as high as 500x.
"Today’s hybrid and digital models make it easy to document and share your findings."
While they are typically touted as an economical alternative to conventional microscopes, they do offer significant advantages. They are lightweight and portable, and when connected to a laptop, can be highly effective in the field. They can be used to examine specific areas of large subjects, such as pieces of art or sculptures that cannot be removed from their premises or have specimens taken from them. USB microscopes can be invaluable for ancient manuscript research, on delicate textiles, for document and currency-counterfeiting investigations, coin and stamp valuation, gem and geological research, or industrial inspection. Since they don’t actually affect the specimens, they can be used on animals or for forensic documentation without disturbing a crime scene. Their small sizes also allow them to be inserted into a patient as an endoscope for medical uses.
As mentioned above in the discussion of trinocular heads, there are several adapters to mount cameras to microscopes—and trinocular heads aren’t necessarily required. The most popular method is an adapter that replaces the eyepiece and will generally have a low-magnification lens. A T-ring that is designed specifically for your camera's lens mount will serve as the interface between your camera and the microscope, and will place the camera’s imaging sensor at the objective’s focal plane. In this way, you can use your camera and post-production methods to capture microscope images and manipulate and enhance them for sharing, printing, or publication. The advantage of using a dedicated camera instead of a straight digital or hybrid eyepiece imager is that today’s image sensors are constantly getting upgraded for higher resolutions, generally better image quality, and that the overall capabilities of a camera will generally outperform many specific imagers designed for microscopy.
Similar adapters are also being offered for smartphones. Instead of mounting like a DSLR or mirrorless camera, the smartphone adapters clamp over the onboard camera and are inserted in place of the eyepieces.
As smartphones have grown in popularity and their onboard cameras have gotten more and more powerful, the increase in optical adapters to fit specific models is notable. Now, in lieu of USB microscopes, a user can attach a microscope adapter to his or her smartphone, download one of the hundreds of free or paid-for apps, achieve excellent performance and instantly email the images anywhere. The quality of these adapters ranges greatly, from plastic lenses and low magnifications to high-grade, precision-ground glass. The power of the apps also varies by developer, and often the free “lite” versions will have limited capabilities over the full-version “pay” app.
One of the principal features of this new generation of digital microscopes is the variety of ways and varying degrees to which they interact with computers. Many manufacturers of microscopes, as well as third-party programmers, offer imaging software specifically designed for microscopy. A basic piece of software will display images, offer digital magnifications, and a way of saving images or video clips. As this software gets more intricate and involved, it can offer an incredible array of tools, imaging aides, and sharing options such as:
- Measurement: Using a grid system displayed on the screen, easy measurements can be calculated and documented.
- Camera performance: Users can change resolution, frame-rate, brightness, contrast, color, just to name a few.
- Image comparison: display multiple saved images side-by-side for comparison purposes.
- Filter/Layer: Apply digital filters to enhance and improve sample images and layer multiple images or filtered images to create a single improved image.
- Export to multiple formats for sharing or for publication.
- Image stitching: Create a mosaic-like image from smaller ones to give a view of the “big picture.”
- Focus and color enhancements.
There are also industry-specific software options, which include:
- Basic and advanced research labs;
- Medical and biological;
- Materials and metallurgy;
- Document and textile analysis.
Beyond the basics are microscopes that address the inherent drawbacks to conventional models. These specialty microscopes will differ in the way magnifications are achieved, or how the specimens are illuminated, and sometimes both. Here is a quick list of some of the more popular specialty versions out there.
If you’ve ever seen CSI, NCIS, or Bones, you’re familiar with this style. It’s made up of two connected microscopes used for comparative science or in forensics. It allows for side-by-side comparisons of two slides or material objects—for example, on TV they are often used to compare two DNA samples or metal fragments (like bullets). As with many other microscope types and configurations, digital comparison models are becoming increasingly available.
The main difference between a conventional microscope and a metallurgical one is the method of illumination. Since specimens will mostly be opaque, they need to be lit from above. Usually, the light source will be in the optical tube, and projected down to the specimen through the objective. The light source can be a mirror which reflects an outside light source, but as technology has progressed, LEDs and fiber optics are coming into more common use. These microscopes are generally used for inspection or in research labs for magnified examination or measurement of polished metal, shiny plastic, or other bright materials.
These have a specialized illumination system that projects a specific wavelength of light or a combination of specific wavelengths (meaning different colors as opposed to white light) at a specimen using xenon arc lamps, mercury-vapor lamps and, more recently, LEDs and lasers. The light is absorbed and a different color is reflected back. For this type of microscope to be used, the specimen must be fluorescent—either by using fluorescent stains or samples that are auto-fluorescent. Uses of this type of microscope include DNA testing, or to image-specific features of small specimens, such as microbes. It is also used to visually enhance 3D features at small scales.
These are typically used for viewing details of living cells. Normally, there is little variation when one looks at them using bright field microscopes, since the different parts of the cell are either translucent or are colored the same. A phase contrast model uses the very different refractive properties of different components of a cell to show an incredible amount of detail not revealed using conventional methods. This works on the same principal as the Dark Field method, but instead of modifying a conventional microscope to achieve the effect, this is purpose-built, often with the ability to project different wavelengths using filters or emitters to illuminate a variety of organic matter.
Scanning Electron Microscope
This is a highly specialized variety of microscope. Instead of light, it uses a beam of electrons to create the magnified images. Using this alternative magnification system allows the microscope to achieve resolutions to as little as 5 nanometers, magnifications from as low as 15x to those exceeding 200,000x, with nearly unlimited depth of field. Using an SEM, images are displayed in high contrast and very detailed 3D, but in black and white. Because of the unique way images are magnified, specimens have to be carefully prepared to be able to stand up to the vacuum inside the microscope and they have to be able to conduct electricity. Often, biological specimens need to be coated with a thin layer of metal, such as gold. It should come as no surprise that the overall look and functionality of an SEM is dramatically different from all the other microscopes discussed in this piece, and the price tag would be considered astronomical compared to even the high-end compound or digital models.
Beyond a smartphone adapter and a USB microscope, there is an entire class of handheld microscopes. Their capabilities and uses are as diverse as their quality and price. On the lower end are inexpensive plastic microscopes that will have limited magnifications and will typically have a fixed focal distance, with limited or non-adjustable illumination. They will often come with a fixed stand or clear cup attached to the bottom that will put the subject at the correct distance for it to be in focus. These are considered entry-level microscopes for the young student and are best suited to view some pond water, insects, leaves, or other such specimens.
On the other extreme of the spectrum are high-quality precision instruments. These are medical-grade microscopes with magnifications upward of 1000x, with LED illumination, interchangeable eyepieces, ultra-fine focusing, articulated stages, and can often be adapted to smartphones for instant file sharing. These high-end models are often used by doctors and researchers in developing countries or after natural disasters, where electricity is spotty and facilities are limited. They will usually run on batteries, and can be mounted on tripods to increase their stability.
Uses and Users: Who Needs Microscopes
The Compound Microscope is the standard for students and teachers in the fields of Biology, Chemistry, and Botany (to name just a few). The versatility and high-magnification potential provide the users with the ability to see detail down to the cellular level. LEDs are quickly becoming the illumination standard because of the high-output, reliable variable intensity, and low energy use. Many models are battery powered for use anywhere, using easy-to-acquire AA batteries. For advanced students, look for mid-range models with zoom or changeable eyepieces that can increase the versatility.
Today’s hybrid and digital models make it easy to document and share your findings, and with a changeable eyepiece option, adding an eyepiece camera might be a good option, down the road.
In this new age of education, it’s not hard to see the practicality of the new hybrid and digital models. If buying completely new isn’t exactly in the budget, and your old compound is still in fine order, the addition of one of the eyepiece cameras with screens, USB tethering, or Wi-Fi is an easy solution. Since your work area will usually have an outlet nearby, many models run on AC power for simple and easy long-term use for multiple classes throughout the day. As we’ve already touched on, the ability to stream images wirelessly to mobile devices or to display them on large screens and projectors puts the various forms of digital microscopes and adapters at the top of this list.
For diagnosis, treatment, prevention, or developing treatments and medications, the compound microscope is still the instrument of choice. Consider turrets with more objectives. Many high-end turrets can have as many as five objectives. Changeable eyepieces will increase the usability and versatility, and adding digital eyepiece cameras has obvious advantages for publication and presentation purposes. Since microscopes will often get daily use, stay away from battery-powered models and stick to AC plugs. Ensure the stages are mechanical to make it easier for viewing, and that the base is heavy and wide for maximum stability.
This is the most diverse and therefore the hardest category to give recommendations to. Generally you’ll need both a compound and stereo: the compound for cellular work such as blood samples, and the stereo for hair or fiber. Consider models that have the ability to run on AC power and batteries. It’s possible that you may even require one of the specialty versions, such as comparison or fluorescence. A digital version, either an eyepiece camera/imager or stand-alone digital microscope, can help immeasurably to capture images that can be submitted as evidence, shared, and used in court.
This catch-all category covers everything from jewelers and watchmakers to engravers, electronics, and inspections. As a general rule, the stereo microscope is going to do the most good, or even a metallurgical microscope. The relative low power will magnify the work to manageable levels without being too overpowering. Be mindful of what is going to be happening on the stage and make sure there will be enough clearance to the objectives. Also, make sure the light source is strong enough, and consider variable intensity to add versatility. Depending on the materials that will be under the lens, a USB or handheld may be easier and more practical.
This depends on the hobby. If cellular viewing is necessary, consider a higher-powered compound light microscope or desktop Digital LCD microscope with at least 400x magnification. For coin and stamp collectors, gem or jewelry enthusiasts, or even naturalists, a low power (2x to 100x range) Stereo Microscope or low power digital microscope will do the job. More importantly though, it’s going to be the work space to which you’ll need to pay special attention. The work space is the amount of room between the stage and the objective. If you need to examine large objects, consider a portable handheld digital microscope that is either wirelessly or USB-connected to a laptop. The ease of use, portability and versatility of these types will give the user very competent performance without breaking the bank. It’s important to be mindful of what you’re going to be putting on the stage, and make sure there’s enough clearance. If you’re using it for gems, consider a dual-illumination model with a light source in the stage; for coin collectors, a lower light source would be a waste. As with Industrial applications, a USB or handheld model may be the way to go—or even a simple smartphone microscope adapter.
Despite this age of a camera in every smartphone, microscopes and microscopy are still as relevant today as they were when Anton van Leeuwenhoek first described bacteria, or when Carl Zeiss made his first compound microscope. Medical advances couldn’t have happened without the compound. The electronics that we’ve come to depend on wouldn’t be the size or have the capabilities they have without the stereo microscope. Forensic scientists aid in the capture of criminals, thanks in no small part to microscopes. And with the advances in digital and wireless technology, the importance of microscopy will only continue to grow.