The Measurement Shop's Guide to Microscope Types

Microscopes have long been considered one of the most revolutionary inventions in modern science. How we see objects is fundamental to our understanding of the world around us, and the creation of optical devices such as telescopes, mirrors, magnifiers, glasses and microscopes have become an undeniable part of our everyday lives. The Measurement Shop's comprehensive guide to microscope types will examine the history of microscopes, what they are, how they are used and made, varieties of microscope, and how to choose a microscope.

Part 1: Introduction to microscope types

What is a microscope?

A microscope is an optical instrument or device used to view objects that are too small to be seen by eye. Coined after the invention of the microscope, microscopy is the science and study of small objects using this instrument.

Who invented the microscope?

An early history of Optics

Optics and optical devices have an exceptionally long history that stretches back as far as the Assyrian kingdom of Mesopotamia (now consisting of modern day Syria, Iraq and Iran) and the Greeks. From around the 5^th century BC, Greek accounts have noted the optical properties of water and how filled glass vessels can magnify or distort the naked eye.

Whilst early cultures had an awareness of optics, a recognisable optical device wasn’t commodified until around the 13^th century where eyeglasses and magnifying glasses were popularised.

The first microscopes

The earliest records of a clearly defined microscope-like device is estimated to have appeared in the late 16^th or early 17^th century. The invention of the microscope has been attributed to several individuals and spectacle makers in the Netherlands and Europe around this time, including Zacharias Janssen, Hans Lippershey, Cornelis Drebbel and Galileo Galilei.

This device was a variant of the compound microscope which would combine 2 lenses (an optical lens and an eye piece) near an object in order to view a magnified image of the object. However it wasn’t until around 1625 that Giovanni Faber coined the name ‘microscope’ to describe this device.

The invention of the modern microscope types

From the late 17^th century onwards, more advanced microscopes were used in biology to study organisms and tissue samples with significant contributions coming from Antonie van Leeuwenhoek who helped to re-discover red blood cells.

The late 19^th and early 20^th centuries saw light microscopes used to further illuminate samples and provide better quality images of specimens. In 1893 the Kohler illumination principle offered a major breakthrough for light microscope technology, involving illumination that produces even lighting beyond the limited contrast of earlier sample illumination techniques. Light microscope techniques have expanded to include phase contrast, fluorescence and differential interference contrast (polarising) amongst others.

How do microscopes work?

The most common types of microscope work by passing light through a sample in order to produce an image. However, the way in which a microscope works is ultimately determined by its type. Some variations may send a beam of light to a sample through the microscope’s optical path optical path, whilst others may scan across a sample from a short distance using a sample probe.

What are objectives?

Objectives are small optical cylindrical parts of a microscope that gather light from the object being observed and focus this to produce a real image. Most compound microscopes include a rotary component above the stage for attaching objectives of different magnifications.

Which microscope has the highest magnification?

Standard light microscopes can achieve up to 1000x magnification. However, the most advanced scanning electron microscopes have managed to achieve up to 10,000,000x.

How to use a microscope

This will vary depending on the type of microscope you are using, however these quick and simple steps will show you how to set up most standard compound microscope models:

1. Turn the revolving turret to set the lowest objective.
2.  Place a microscope slide onto the stage and secure.
3. Whilst focusing on the objective lens and looking from the side, turn the focus dial so the stage moves upwards. Carry on turning this until the stage is close enough to the objective without touching.
4. Look through the eyepiece/ funnel and turn the focus dial until the image comes into focus.
5. You will then need to adjust the condenser and light setting to allow adequate light from the light source. (Modern light microscopes are likely to have a built-in lighting element for illumination, however some microscopes may include a bulb or mirror beneath the stage).
6. Add a sample to the slide and move this around on the stage until the sample appears centred (as seen through the eye piece).
7. Once you have correctly positioned the sample, fix into place. You will then need to turn the focus dial and adjust the condenser until you gain the clearest image possible.
8. Once you are satisfied with the image clarity, you are then free to set the objectives for higher magnifications as appropriate.
9. Once you have finished your observation, turn off the power using the on/off switch and lower the stage using the focus dial.

How are microscopes made?

Microscopes are complex optical instruments consisting of specialist hardware components, optical glass and lenses. Metal hardware components are typically constructed using steel or steel and zinc alloys whilst the casing requires tough, ABS (acrylonitrile-butadiene-styrene) plastic housing.

Metal hardware requires top-quality metalworking equipment with a high-level of precision, whilst the outer plastic casing is cast by applying pressure and heat into to a mould until the plastic has cooled into shape.

The optical glass is formed by mixing the appropriate raw materials and proportions of each with waste glass of the same type. This is then heated in a glass furnace until reaching a liquid state (typically around 1400 degrees). The temperature is then raised until air bubbles rise to the surface of the mixture, it is then slowly cooled and stirred until it becomes an extremely thick liquid that can be poured into a mould. Once the mixture has cooled to around (300 degrees), it is reheated to remove internal stresses which can form and weaken the glass during the cooling period.

The lens is produced by cutting the finished optical glass into a curve (blank) with a rotating cylindrical cutter with a diamond blade. From here, a cast iron grinding surface is placed and moves across the lens, along with a continuous flow of water, abrasive liquid and coolant (slurry). Once complete, the lenses are moved to a polishing machine that uses a polishing substance similar to a slurry without the abrasive material. The lenses are finished with a coating of magnesium fluoride.

This introduction to microscopes from Made How provides further details on how microscopes are manufactured today.

Part 2: Using a Microscope

Who uses a microscope?

Microscopes are typically used in any situation requiring highly detailed images of an object that cannot be seen by the naked eye. They are commonly used in science laboratories, medical research, food testing and in schools.

Science laboratories and research centres use microscopes to closely examine chemicals, compounds and particles. Scientists frequently use microscopes as a means of discovery, with more advanced electron microscopes being used to analyse the ultrastructure of microorganisms, molecules, crystals and metals. Researchers and Palaeontologists may also use high-powered digital microscopes for examining the fossils of plants, dinosaurs and mammals.

Medical institutions use microscopes to provide closer examination of specimens such as bacteria, parasites and intricate cell structures. By using a microscope, medical professionals can detect anomalies in cells, including red and white blood cells caused by viruses, diseases and bacteria. Once identified, medical scientists can develop and test new vaccinations and treatments to alleviate sickness and prevent harmful symptoms.

Microscopes are commonly used in food testing facilities for monitoring the rate of bacteria growth on food products. By placing small food samples under a microscope lens, food testing scientists can precisely analyse the individual elements within a given sample, including additives, genetically modified organisms (GMO’s), traces of pesticides, or food bacteria such as salmonella.

Basic-level microscopes are frequently found in schools, universities and colleges in order to conduct science experiments. Amateur microscopes are used in school science experiments to examine small liquid and food samples as part of the education curriculum. More advanced microscopes are confined to university level students and hobbyists for use in many of the fields detailed above.

Microscope Types

Compound microscopes

The most common microscope type. Compound microscopes consist of two optical lens: the eyepiece (also called ocular) which has a long focal length and low magnification, and the objective lens, which is placed close to the object and has a short focal distance.

Inverted microscopes

Inverted microscopes provide an alternative design to standard compound microscopes. These instruments have a light source and condenser on the top pointing down to the stage, whilst the objectives and turret are located below the stage pointing up.

Light microscope types (phase contrast, fluorescence and polarising)

Light microscopes have a lighting element that employs visible light and magnifying lenses in order to closely examine tiny specimens not visible to the naked eye. Many varieties of microscope fall within this category however the most popular types of light microscope include phase contrast, fluorescence and polarising microscopes.

Phase contrast microscopes employ the phase contrast optical technique that coverts phase shifts in light to brightness changes in the image when passing through a transparent specimen.

Fluorescence microscopes use fluorescence or phosphorescence in order to generate an image of a sample. These instruments require intense illumination found in xenon arc lamps or lasers that typical halogen lamps cannot provide.

Polarising microscope types employ polarised light as a contrast enhancing technique in order to examine the three-dimensional structure of specimens. The difference between regular un-polarised and polarised light is that polarised light shows light waves that vibrate in one direction only (which cannot normally be seen). Un-polarised light found in other types of light microscopes have light waves vibrating in multiple, random directions. Consequently, polarised light can improve the image quality of microscopes when viewing direction-dependent (anisotropic) specimens.

Electron microscopes

Electron microscopes are highly-advanced microscopes that uses a beam of electrons in order to create images of a given specimen. These microscopes provide much higher magnifications and resolutions than a standard light microscope. This instrument allows you to view specimens to an exceptionally high level of detail.

Stereo microscopes

Another variation of a light microscope, stereo microscopes (also known as a dissecting microscope) are designed for low magnification examinations. They are typically used to reflect light from the surface of an object rather than transmitting through it.

Metallurgical microscopes

Metallurgical microscopes are heavy-duty, industrial microscopes with a reflected light source and large specimen stages. These instruments are commonly used for analysing opaque objects and can be used for inspecting the coating or layer thickness of metals and electrical components.

Part 3: Choosing between microscope types

How to choose a microscope type

Choosing the right microscope for your needs can be difficult as you will need to have an idea of your magnification requirements, the necessary applications and your budget before making your decision. We have put together a brief checklist of things to consider when buying a microscope:

What do I need a microscope for?

Simple, yet often overlooked. When starting out, you should first take note of the objects you want to examine. If you are analysing opaque surfaces rather than translucent specimens then you are likely to need to metallurgical microscope, whilst if you intend on examining tiny particles, then you are going to need a more advanced model such as an electron microscope.

How often would I use the microscope?

This may be important for hobbyists or individuals. If you only intend to use this recreationally or as a one-off, then you should probably ask yourself whether buying a microscope is the right option for you. It is sometimes possible to borrow microscopes or for companies to lend out more expensive scientific instruments.

How much am I willing to spend?

Microscopes are quite expensive instruments, therefore you should know your budget before investing.

What level of magnification do I need?

Specimens come in all shapes and sizes. The level of detail you require is going to differ depending on the object, sample size, required depth and priority.

Microscopes Types offered by The Measurement Shop UK

Kern OBS Compound microscope

The OBS microscope is a low-cost, solid and simple microscope suitable for schools, colleges and general training on how to use a microscope. This model can examine translucent, thin and other less complex samples including plant tissues and coloured cells.

Kern OBL Phase contrast microscopes

The OBL employs phase contact microscopy techniques suitable for a wide range of applications, including haematology, microbiology, oncology and similar. This model is exceptionally useful for extremely translucent, thin, low-contrast and challenging samples such as bacteria and mammal cells.

Kern OBN Fluorescence microscopes

The Kern OBN fluorescence microscope is a superb, premium laboratory microscope for examining extremely translucent and challenging samples such as immunofluorescence, fish and DAPI staining. The OBN is frequently used for medical based microscopy, as well as in sewage treatment plants, vets, breweries and for water analysis.

Kern OCL Inverted microscope

The OCL is a robust, easy-to-use microscope for producing high-quality images for common routine applications. This particular microscope is perfect for research and monitoring the breeding of cells and tissue cultures; especially useful for viewing samples in culture vessels, petri dishes and flasks.

Kern OKM Metallurgical microscope

Kern’s OKM metallurgical microscope is a stable, industrial digital microscope which uses reflected light for metallurgy, material testing and quality assurance. This model is suitable opaque and thick samples such as work piece surfaces, fold lines and coatings.

Kern OPE Polarising microscope

The OPE polarising light microscope is ideal for examining translucent, isotropic materials such as crystals or minerals. The OPE is a mid-range microscope commonly used in mineralogy and crystal observation, texture observations and material testing.

Kern OSE Stereo microscope

Kern’s OSE stereo microscope is a basic-level, cheap microscope relied upon for conventional applications in schools, workshops and laboratory training. This model focuses on three-dimensional impression of samples such as insects, seeds, circuit boards and other components. Perfect for vitro-fertilisation, the detection of parasites, zoology and botany.

Taking care of your microscope

Taking care of your microscope is essential in order to keep the instrument in good working order. Here are our top tips on taking care of your microscope:

1. Careful handling - Improper handling is one of the most common causes of damage to microscopes. Before moving the microscope, ensure that all loose components are removed and that power cables are safely tucked away. When carrying the microscope, it is recommend that you use both hands and support the instrument from below, holding the instrument from the stage or the funnel can cause misalignment.
2. Keep your microscope clean - It is recommended that oil immersion is used to carefully clean your microscope. It is crucial that lenses are touched as little as possible as they are notoriously difficult to clean. Do not use damaging solvents.
3. Cover and store safely - Microscope protective covers can prevent the build-up of dust and protect the instrument from liquids and chemicals. Ensure that your microscope is stored in a dry, well-ventilated area.
4. Refer to the user manual - Following correct operation outlined by the microscope’s user manual is necessary for ensuring that your balance continues to work as it should.

Summary

• A microscope is an optical instrument or device used to view objects that are too small to be seen by eye.
• This microscope works by passing light through a sample in order to produce an image.
• The first defined compound microscope was invented in the early 17^th century.
• Microscopes are commonly used in science, food, medical and education to examine bacteria, cell structures and other tiny specimens.
• There are a wide variety of microscope types available including compound, inverted, stereo and light microscopes.
• Microscopes can be expensive pieces of equipment if looking to buy.
• Ensure that you are following correct procedure when taking care of your microscope to prevent damage over time.