What is a microscope?
The big test of the microscopes 2018: A microscope enlarges the examined object considerably. Even with simpler microscopes, maximum magnifications of a hundred times are not uncommon. This makes it possible to identify details that are difficult or impossible to see without such aids. In particular, biological tissues and microorganisms can also be investigated. However, models with magnification factors of around 1000 and more are already available at comparatively low prices. These are also suitable for the examination of even smaller structures or specific details of larger cells.
How does a microscope work?
The microscope consists of several functional units, a large part of which belongs to the optical system of the instrument. The microscope is adequately illuminated by a light source such as a halogen bulb or an LED. In the transmitted light microscope, this is located below the sample attached to the microscope slide, in the incident light microscope, on the other hand. Ideally, the intensity of the light source should be adjustable. In this way, the lighting conditions can be adapted to the respective object under investigation.
Magnification is achieved in the microscope by means of a lens system which expands the light beam emanating from the object to such an extent that even the human eye can see the details of structures that are only a few micrometers in size. As microscopes are also usually used by spectacle wearers without glasses, the optics can be adjusted to the respective visual acuity by rotating them on different mechanics of the eyepiece or objective.
Here a distinction is made between the coarse focus adjustment and the fine focus adjustment of the instrument. Therefore, glasses do not normally have to be worn when using the microscope. Of course, there are also visual impairments that cannot be compensated for by simply sharpening. These cannot be neutralized by adjusting the microscope accordingly. Here it is recommended either to try microscopy with glasses or to find another solution in consultation with the ophthalmologist.
At particularly high magnification factors, the light microscope encounters the limitation of the wavelength of light: There is a minimum length that can still be sharply imaged by the microscope. All structures that are smaller than this characteristic size appear blurred and therefore cannot be examined under the microscope.
Thus such e.g. optical microscopes are not suitable for carrying out scientific research on the corresponding structures.
This is why other devices are used here: because it is not only possible to microscope with light, other waves, such as electron waves, also offer the possibility of magnifying objects or specimens. The electron microscope in particular provides very good resolution. However, the test object must be prepared for the image with a metal coating.
This means not only an additional effort, but can also conceal fine details. One example is small openings in the armour of insects in which the metal atoms can accumulate: Clog the fine pores. They are then no longer visible on the image. In addition, there are many other different microscopes which cannot be dealt with in the necessary detail here.
Advantages & Applications
Microscopes are always used where the human eye fails to resolve structures due to their small size. Most people can still recognize objects of a size of about 100 micrometers (0.1 millimeters) as small dots, but much smaller objects or living beings usually cannot be resolved by the eye.
These details of the world around us remain hidden to him without the use of magnification methods such as microscopy. In the course of evolution, this has apparently not proved to be sufficiently disadvantageous to lead to a better resolution of the eye. Here, the greatest life-threatening dangers that could be fatal to early man and his ancestors probably occurred on a different scale.
Examples include predators, hostile strains or poisonous berries. But also for the often quoted “hunting and gathering” the natural visual acuity was completely sufficient. However, man has now reached a point in his development where the exploration of the microscopic world also plays an increasingly important role.
With the progressive development of miniaturization in electronics, microscopes are increasingly being used in this field as well. For example, dead pixels can often be examined more closely on a flat monitor with a microscope: Here it becomes clear that each pixel is in reality not a single point, but is usually (depending on the technique used) composed of light sources in three different colors (e.g. red, green and blue).
Of course, the distance between these different coloured light points on monitors is deliberately chosen by the manufacturer to be so small that the eye can no longer distinguish them. The result is an apparently monochrome pixel. A suitable microscope can therefore also be of interest to hobby electronics technicians and hobbyists as an integral part of the workshop equipment.
It often provides fascinating insights into the design or operation of modern or older devices that remain grey theory without such a tool. Experience has shown that one’s own practical experience cannot be completely replaced by textbook knowledge. The diagnosis of certain defects in electronic components or very small conductor tracks is also facilitated by such an instrument.
In addition, handkerchiefs, fabrics or metal foils can reveal interesting details under the microscope even at relatively small magnifications. Here the working patterns of the industrial machines used can be seen more clearly than on the coarser scale.
Materials made in particular from biological starting materials often still contain indications of their origin, which only become visible under the microscope.
Here most manufacturers do not count on the fact that the customer looks at the bought commodity also once strongly increased. Accordingly, the design is limited to the coarser, with the naked eye visible image of the corresponding article. This is completely understandable, but offers the interested party a wide spectrum for microscopic exploration of such materials.
Much of today’s medical research would be unthinkable without microscopes. Microscopic changes in tissues and other biological samples can only be detected and further investigated under the microscope – the name already reveals this. However, they play an important role not only in basic research, but also in diagnostics, e.g. in hospitals.
In the engineering sciences, for example, they can also help to detect material defects before they become visible macroscopically. This allows important components to be replaced before major damage or accidents occur. In addition, afterwards wear mechanisms can be classified on the basis their appearance in the enlarged picture and be determined so the cause e.g. for an engine damage. This can be of criminal law relevance, but it is also important when investigating claims for damages or insurance fraud.
Particularly interesting for prospective criminologists, but also known from film and television, are investigative procedures in which microscopic traces of a crime are examined under the microscope. This makes it possible to classify tiny blood spatter or identify unique characteristics of materials found at the scene of the crime. In this way, the circle of suspects can often be further restricted or meaningfully expanded.
However, many advanced examination procedures do not go by the trained experts as quickly as is shown in many series. A comprehensive DNA analysis within a time frame of a few hours, because otherwise the suspect could go abroad before being arrested, must at least in the foreseeable future remain reserved for the fictitious world of films and series. Further information on forensic applications can be found, for example, in[5].
However, the microscope not only brings the expertise of established experts to life, it also plays an equally important role in education. Often, even for students, a microscope of their own is a very attractive object of employment and motivates them to explore a completely different micro-world. In particular, if the student is interested, he or she can also collect knowledge that goes beyond the biology school lessons, which are often not particularly interesting.
The samples supplied with many models provide interesting impressions and may even provide a lot of scientific conversation. Of course you can also get to know everyday objects, your own hair or parts of plants from a completely new side. Here the structure is to be emphasized above all, which often enlarges a completely different or further face reveals. This is because, for example, plants often consist of different structures, of which only the larger ones are visible to the naked eye.
In addition to these insights, practical experience with the microscope should not be underestimated: This is required, for example, in medical studies at many universities already in the first semester or must be acquired in a very short time. Here it can also make sense for high school graduates to buy their own microscope while they are still at school, so that later scientific work during their studies is easier.
In addition, it is possible to gain experience in the development of a wide variety of biological tissues before this knowledge is deepened later at university or in class. It is often advantageous to be able to gain practical insight into the various small, naturally occurring structures outside class hours.
Over the course of millions of years of evolution, cells have developed an almost unbelievable number of ways to link together and thus form larger cell assemblies, tissues and organs. It is therefore worth exploring these rich structures on different length scales.
What types of microscopes are available?
Light microscopes can be designed as monocular or binocular microscopes. This means that either only one eye or both eyes are guided to the eyepiece to view the magnified image. With the binocular models, the second eye does not have to be closed to view the microscope image. In the hobby area one should distinguish between light microscopes with and without built-in photosensor.
Sometimes these microscopes are also designed as combination devices, i.e. the image can either be viewed with the eye or digitally transmitted or stored. The microscopes with photosensor can usually be easily connected to the USB port of a computer. Caution: Digital microscopes do not always have the possibility to take a look inside the microscope.
In these models, the digitized image or video on the computer screen is often the only thing the user gets to see from the sample. However, this does not necessarily have to be a disadvantage. For models without digitization or USB option, an ocular camera is often a useful addition – especially if the model used is already of relatively high quality (see the “Useful accessories” section).
With the included software, the various preparations can then be enlarged on the monitor. The recordings can usually be saved as image or video files. Even with cheaper microscopes, various ready-to-use objects are often included. Manufacturers of higher quality models for professional use in medicine and life sciences, on the other hand, often trust that the buyers themselves have the necessary know-how to prepare tissue or microorganisms for microscopy.
Here it usually helps to have a look at the exact description of the respective model or to ask the supplier. Of course, there are also models that can be used and make sense in both the private and professional sectors. Of course, there are also toy microscopes that are more suitable for smaller children.
These usually eliminate dangers such as glass splinters after the breaking of lenses, for example by using relatively inexpensive plastic lenses or pouring the glass lenses used firmly into an edge of transparent plastic. Such a microscope is rather not suitable for serious scientific work, but serves above all the introduction and enthusiasm even small children for the microscopic world.
However, many models in this category do not have sufficient resolution to visualize biological cells and other components. Such a microscope often contains only a relatively small selection of objects to be examined.
Caution is also advised when the model is offered in the toy department: It is best to clarify in advance whether the samples under the lens are actually enlarged or only a prepared image (such as a comic figure) is displayed.
Such a construction may be fun for the gifted children for a while, but it has very little scientific value. Although these points of criticism may not be relevant at all, because a pure toy should be deliberately given away, we consider it our duty to point out this difficulty in the selection of a suitable microscope.
In the scientific field, however, there are a large number of other microscopes in addition to the models that work with light, which do not always necessarily work with visible light. For example, the electron microscope makes structures visible that cannot be resolved with normal light microscopes. Scanning tunneling microscopes can even image individual atoms. To scan the surface, a so-called tunnel tip is moved over the surface to be imaged.
The technology behind this is a technical application of the quantum mechanical tunnel effect. Here the distance of the tunnel tip from the surface to be examined is measured via the tunnel current. Due to quantum mechanical effects, this already flows at a small distance without the tip having to touch the surface.
The intensity of the measured tunnel current depends on the distance to the surface, so that the measurement data (i.e. the information about the respective position of the tunnel tip and the tunnel current measured there) can be converted into a relatively detailed image of nanometer-sized structures on the surface using a computer program, for example.
In this way, the electron shells of individual atoms can actually be imaged. In addition, there are many other types of microscopes, such as the atomic force microscope, which, however, cannot all be described here for space reasons. This is a subject that could and does easily fill books.
Microscope video
How we tested the microscopes
The optical quality of a microscope is measured by various factors. The quality of the lenses used is particularly important. The built-in optical elements should also be ideally matched to ensure optimum imaging quality. The lenses should also not unduly distort the subject during imaging.
In modern microscopes or ocular cameras, which can be connected to a computer via a USB cable, the quality of the built-in CCD sensor is also decisive. Thus, even the highest quality optical system is of no use if the sensor brings an excessive amount of noise into the image. In particular, these two parts of the microscope must work well together: The lens system should provide the CCD sensor with a sufficiently sharp, well exposed, largely distortion-free and detailed image for digitization.
In this way, such a microscope is actually more than just the sum of its parts and was of course evaluated accordingly. However, we have ultimately summarized all points in the image quality, since this is probably the most important criterion for the consumer.
Our experts have tested the microscopes and, of course, modern microscopes should also offer the possibility of digitizing the images taken as the most outstanding technical feature. Therefore, we have also positively included in the evaluation a possibility to connect the microscope via USB to a computer to transfer the images. In addition, the quality of the image or video files obtained in this way is of course also important.
However, it should be noted that models with detachable eyepieces often offer the possibility of replacing them with a suitable USB eyepiece camera. If this has to be purchased separately, as still seems to be the case with some professional models, this has a negative effect on the price-performance ratio of the microscope in our test.
This is another important evaluation criterion: Does the consumer think that his money is a device that makes acceptable recordings possible at this price, and how does it compare to the competition? Particularly inexpensive models, which offer a much poorer quality of display than somewhat more expensive devices, sometimes perform worse at this point.
Finally, we also evaluated the workmanship of the respective instrument. Is the instrument secure, does it make a stable impression? Have the components been properly connected, e.g. has the tube been properly designed? Here, well-processed, solid metal microscopes naturally get a better rating than loosely connected plastic constructions.
Another point is the equipment of the microscope. Here, the enclosed useful accessories are positively received, but also, for example, whether it is possible to switch between reflected and transmitted light microscopy.
What do I need to consider when buying a microscope?
When buying a microscope, you should pay particular attention to whether the model is suitable for the intended purpose. Is the device intended more as a toy to spark enthusiasm for the small and smallest building blocks of nature, or should it be used for serious scientific work? In the latter case, the magnification should be in a suitable range.
Here it is particularly important whether only relatively large cells are to be imaged or whether smaller structures are also to be examined.
A magnification of about a hundred times is usually completely sufficient for the representation of onion cells. These have a diameter of about 200 micrometers, which then appears about 20 mm (200 µm x 100) in the enlarged image for the eye. Thus, even at this relatively low magnification, the individual cells are already clearly visible.
However, it should be said that onion cells are so popular in school lessons precisely because of their rather extensive dimensions and the associated easy microcospability. However, if you want to examine finer details or smaller cells, you should pay attention to an even higher magnification when selecting the suitable model. In many light microscopes, the total magnification factor to be achieved consists of the magnification through the eyepiece and through the objective.
This means that if the objective provides a magnification of sixteen times and the eyepiece an eightfold magnification, the total magnification factor when viewing the image through the microscope is 8×16 = 128, i.e. a good hundred times magnification is achieved. This is particularly interesting for models where the two magnifications are only listed separately.
Apart from that, the tripod should give the instrument a stable, secure stand. Nothing is more annoying than when carefully prepared shots blur due to an inferior tripod or when you lose sight of the long sought-after spot. A distortion-free, clear image is also an important prerequisite for scientific work. This can often best be estimated on the basis of recordings published on the Internet with the respective instrument.
In addition, one should of course be aware of the fundamental limitations of a light microscope: It is particularly suitable for the examination of structures in the micrometer range. The dissolution of atomic nuclei or molecules will not succeed with such a microscope.
Although a Nobel Prize has been awarded in recent years for significant progress in optical microscopy, there are more suitable models, such as scanning tunneling microscopes, which also allow the representation of atomic shells in the surfaces of solids, for example. However, you should already be very familiar with the relevant material before you buy such an STM or even build it yourself.
This is particularly interesting for students of physics or related subjects, but not necessarily inexpensive, depending on the design, since very precise control of the environmental properties and fine regulation of the relevant measured variables are necessary here. These instruments are rarely used for biological preparations.
In addition to the optical properties of the microscope, many users today are also interested in the digital connection: Can the images taken be transferred simply and uncomplicatedly to their own computer and further processed there? The easiest way to do this is to connect the microscope to the corresponding counterpart on your own computer using a conventional USB cable.
In this way, the images taken by the objects under investigation can be transferred to the computer’s own hard disk. If you want or have to evaluate the recordings under special technical requirements of the software, you should of course make sure that you have access to the corresponding programs before you buy them. These can either be included with the microscope or downloaded separately or ordered. However, such special software is usually not required for school or hobby applications.
If you expect high-quality images that are suitable for printing in trade journals, for example, you should invest a few more euros in a high-quality microscope. Often the working group or the company takes over this acquisition. Especially with inexpensive microscopes, more and more imaging errors such as a distorted image and color errors due to chromatic aberration can occur.
But attention must also be paid to the type of lighting. Many users still prefer more traditional illumination, e.g. with illumination inserted into the microscope. Even though this type of light source is no longer entirely up-to-date, it does draw attention to the fact that the colouring and quality of the images taken naturally also depends on the colour spectrum of the lighting.
In this case, in case of doubt, one should avoid using LED light sources that are too artificial. This is especially true if you want to work with the purchased model regularly over a longer period of time. The use of a binocular microscope is also recommended.
Internet vs. specialist shops: Where is the best place to buy my microscope?
As a scientific instrument, a microscope must meet high demands on the quality of images from the microscopic world enlarged by the optics or taken via USB cable. But many consumers also want the best possible price-performance ratio and high-quality recordings for use in hobbies, schools and leisure time.
That is why many buyers of a light microscope would like to be advised by a specialist before buying. For this reason, many interested parties seek advice in a shop before deciding on a specific model. However, the essential information on the various models is nowadays also available on the Internet. However, if you really want comprehensive information about microscopes, the consultation with a specialist dealer will not be sufficient anyway due to the limited time available.
However, without such expert knowledge of the lens systems used, it is difficult to make statements about the truth of the statements made. Thus, in our opinion, the consultation does not offer the customer any significant advantage compared to buying on the Internet. Especially when you may want to invest a little more in a microscope, it is perhaps best – of course in your own free will – to familiarize yourself a little bit with the subject matter first.
This allows you to identify any sales tricks or untrustworthy statements in the sales conversation more quickly. Above all, however, this expertise gives you the opportunity to choose the model best suited to your personal needs from the many models available on the Internet.
In addition, a great deal of information about the various microscopes is available on the Internet, which goes beyond the manufacturer’s product description alone. In particular, they are available in the form of critical customer evaluations and objective comparison results. Of course, the most valuable aspects for the consumer must be distinguished from those that are more informative in the manufacturer’s sense.
However, if this is guaranteed, the following applies: As a rule, when selecting a suitable product from this category, the specialist dealer cannot provide better information than it is currently available online on a large scale anyway. On the other hand, however, the individual retailers on the Internet are exposed to ever-increasing competitive pressure, especially in recent years.
This leads to a price development in the consumer’s interest, namely to very favourable prices, with which many local specialist dealers simply cannot or no longer want to keep up. Instead, the costs of what appears to be a free consultation are often added to the purchase price at a later date. This is not surprising on the one hand, since the further training and working time of the corresponding employee naturally costs the dealer money. On the other hand, however, the question is whether the customer should and wants to bear these costs after all.