How to choose a microscope

The microscope is the most important device that you cannot do without in scientific research. Modern microscopy is rich in various types of microscopes, each of which has its own purpose, structure and features of work. This guide will not only tell you about the basic elements of a microscope, but also help you make the right choice.

Eyepiece
An eyepiece is a system consisting of several lenses (usually 2-3) through which the researcher will view the object under study. The lenses are built into a metal case (tube) and can be of either fixed or focal magnification. The lowest lens is for focusing on the subject, and the top one is for observing it. All eyepieces provide a certain magnification factor – 10x, 20x, 25x, etc.

Lenses
The most important part of the microscope, thanks to which a microscopic image of the object under study is built with accurate reproduction of the smallest details, color, structure. In other words, the user will be able to see the object in front of him in detail, even if it is not visible to the human eye. The lens has a rather complex optical-mechanical device, which includes several lenses and other components. The quality and quantity of lenses depends on the tasks for which the device is created and can be up to 14 pieces. These include complex and expensive plan-apochromatic objectives, which are most often used in biology and medicine. For the study of plants, substances, tissues, achromatic objectives are suitable, in which there can be only 2-3 lenses.

The turret has 4 objectives, one of which (far right) gives 100x magnification.

Modern technologies make it possible to create and produce many types of lenses, depending on the intended purpose, device and principle of operation. There are devices with small (10x), medium (up to 50x) and large (more than 50x) magnifications, as well as extra-large lenses with a magnification of over 100x. A microscope can be equipped with one objective, but most often it has two or three with different magnification.

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Most often, a microscope has three objectives. Closest to the viewer gives 40x magnification.

The total magnification of the microscope is calculated by adding the magnification of the eyepieces and objectives. For example, if the eyepiece is 10x and the objective is 90x, the total magnification will be 900x.

Backlight
This is an equally important part of the microscope, allowing you to illuminate the object of study. Most often it consists of two parts: a collector and a condenser. The condenser has several built-in lenses and is designed to increase the amount of light coming from the illuminator. The collector is located between the object of study and the condenser and helps to regulate the light intensity.

A brief diagram of the operation of the optics of the microscope

The source of illumination in the backlight is halogen lamps, LEDs, mirrors or incandescent lamps. In the design of the microscope, the illumination can have an upper, lower location, or be combined (upper and lower). The upper one is located above the stage and is needed in order to view opaque or translucent objects. The lower one is located under the table and is needed to study transparent objects to which a beam of light is directed. The backlight needs mains power, USB or batteries.

Condenser, top illumination, combination illumination (top and bottom):

Visual attachment type
There are monocular, binocular and even trinocular attachments. Monocular has one eyepiece, binocular two. Two eyepieces are preferable to one, however they require some skill. In the trinocular attachment, in addition to two eyepieces, there will be an additional tube on which you can install a camera and transmit an image to a computer monitor.

Example of a binocular attachment

Minimum and maximum optical zoom
The minimum optical magnification is calculated by adding the magnification of the eyepieces and objectives. For example, if the minimum magnification for both the eyepiece and the objective is 10x, then the minimum optical magnification will be 100x. This gives a not very clear picture, but with a wide field of view.

The maximum optical magnification is calculated in the same way as the minimum. Example: a 10x eyepiece and a 90x objective lens together give a 900x magnification. This allows you to consider the subject of study in the most detailed way, however, if the magnification is chosen much higher than the allowable one for a particular subject, then this will not reveal any additional details, but the quality and clarity of the image may deteriorate. Accordingly, the field of view will also be much narrower. For example, grains of normal sand can be viewed at 400x magnification, so higher values ​​would be redundant. At high values ​​of magnification (800x and more), you can study the detailed structure of objects, pollen, minerals and much more.

Onion peel at 150x magnification

Digital camera and maximum digital zoom
Some models of light microscopes are equipped with a digital camera for photo and video shooting. The camera can be built into the microscope body along with the objectives, but most often it is a device with a trinocular attachment, in which the third eyepiece is intended for a special video eyepiece. It should be noted that the video eyepiece can also be installed on a device with a monocular attachment. There are also special digital microscopes in which the lens as such is absent and is replaced by a digital camera. The image is transmitted immediately to the computer, and the camera resolution is measured in megapixels and can be from 0.3 to 5 megapixels. The maximum digital zoom in this case will relate specifically to the capabilities of the camera, although other factors should not be swept aside: how high-quality the monitor is for viewing, etc. The magnification in digital models can be 300x, 1600x, etc.

Digital table microscope

Digital microscope image of a butterfly’s wing

Focusing
Typically, focusing in microscopes is rough and accurate.

Rough is performed with a special screw (macroscrew), which allows you to change the distance between the objective and the object of study.
Fine focusing (microscrew) will help focus on the subject up to a hundredths of a magnification, sharpen it and examine it in the smallest detail.
Turret
A revolving device into which lenses are built. There may be only one lens, but more often heads have two, three and four lenses. The user, if necessary, simply turns the head, choosing the lens he needs.

One of the options for the turret

Interpupillary distance
The distance between the pupils is measured in millimeters. This characteristic applies to microscopes with a binocular attachment. To create a stereo picture or a single field in which both eyes will see the subject of study, you need to make simple settings. To do this, you first need to adjust the sharpness of the eyepieces, and then bring the image together by turning the tubes into which the eyepieces are built. If everything is done correctly, then both eyes should see a single field, without darkening the center or edges of the image.

Selection Tips
Amateur or professional

For amateur, children’s research, an inexpensive device with 10x or 20x eyepieces and lenses up to 40x is suitable. Devices with a magnification of up to 200x or 400x will be optimal .

For serious research, a more powerful device with a maximum magnification of several hundred ( more than 400x ) or more than 1000 times is needed . It is also worth paying attention to digital microscopes that do not require special settings and work skills. In them, the image is transmitted immediately to the monitor.

Visual attachment – which one is better?

Even if you are purchasing a microscope for simple experiments, amateur research or for a child, the binocular attachment is best suited , since it is it that gives a good stereo image. If there is a need to obtain a photo or video, then it is better to take a device with a trinocular attachment .

Lenses – the bigger the better

Even if you are not going to become a microbiologist, it is advisable to purchase an instrument with two or three lenses, 4x, 10x and 40x . The most optimal option would be a device with a lens in 40x. Focusing on an object should be carried out starting with a lens with a small magnification (for example, with 4x).

Lenses – the higher the magnification, the more professional

If you have to choose a microscope for professional research, then you need to pay attention to devices that give a maximum magnification of at least 400x. This is the lower boundary necessary for effective work. The upper limit is not set, and you can choose a device with a magnification of several thousand times, for example, in 2000x . For serious research, a 100x objective is required in the turret.

Backlight – better combined

As you already know, it can be lower, upper and combined. A device with a combined illumination is best suited, since with its help it is possible to study both transparent and opaque objects (coins, insects, minerals, etc.). It is also advisable to purchase a device with a halogen or LED backlight .

Focusing – rough but accurate

Don’t forget that focusing can be rough and precise . For amateur research, a device with only coarse focusing is quite suitable , although a combined version (with both coarse and precise) will be more preferable. But for professional research, fine focusing is a must.

Tripod

There are no special requirements for the tripod, but you should take a closer look at the device, the tripod of which is made of metal or has metal inserts.

conclusions

Modern industry offers many options for fruitful exploration of the world around you. For beginners and schoolchildren, for small amateur studies, microscopes with a maximum magnification of up to 400-640x are perfect. If serious scientific research is planned, then a device from 640x and higher will be needed, and the upper limit, in principle, does not exist. It is also worth paying attention to the combined illumination, binocular attachment and the ability to record photos and videos.