Surely many have heard of such a subject as a microscope. And some even know him firsthand. However, few people imagine that there are a different number of types of this device, designed for different functions. What is a microscope and microscopy? What types of microscopes exist and what can they do? The answers to these questions can be found in the proposed article.
History of occurrence
A microscope is a device with which you can significantly enlarge the image, study in detail the structure and structures of the object in question, as well as measure its details that are poorly distinguishable or even invisible to the naked eye.
Methods and technologies that allow using this device for practical purposes are called microscopy.
The very first devices invented were optical microscopes. In addition, it is impossible to say with certainty who owns the laurels of such an invention. In 1538, the Venetian physician Girolamo Fracastoro suggested using a combination of two lenses to achieve the greatest magnification. And the earliest references to the microscope date back to 1590 and are rooted in the Dutch city of Middelburg, where two craftsmen John Lippershey and Zachary Jansen worked, who made glasses.
Around 1624, Galileo Galilei, an Italian physicist and astronomer, introduced his first composite device called “occhiolino”, which means “little eye” in Italian. And only a year later, his friend Giovanni Faber suggested calling the resulting invention a microscope.
Types of microscopes
To date, there are many varieties of this device. Microscopes are: optical and electronic, x-ray and scanning probe. There is also a differential interference-contrast microscope.
Optical instruments, in turn, are divided into near-field, confocal and two-photon laser microscopes. Electronic devices are divided into translucent and raster devices. Scanning microscopes are a combination of atomic force and tunneling microscopes, and X-ray devices are laser, reflective and projection.
The natural optical system is the human eye. At the same time, it is characterized by an accurate resolution. The normal resolution for the normal eye is approximately 0,2 mm. This is typical when the object is removed to the optimal vision distance, which is 250 mm. It is worth noting that the sizes of animal and plant cells, various microorganisms, details of the structure of metals and various alloys, as well as small crystals are much less than the normal resolution for the human eye.
Until about the middle of the last century, scientists used only visible optical radiation in their work, ranging from four hundred to seven hundred nanometers. Sometimes devices with near ultraviolet were used. It turns out that optical microscopes are able to distinguish between substances with a distance between elements of up to 0,20 microns, which means that it can achieve a maximum magnification of 2000x.
In electronic devices, a beam of electrons with wave properties is used to magnify. At the same time, electrons can be focused quite easily with the help of electromagnetic lenses, because they are charged particles. In addition, the electronic image is not difficult to translate into a visible one.
In electronic devices, the resolution is several thousand times higher than the resolution of a light optical microscope. And in modern devices, it can even be less than ten nanometers.
Scanning probing microscopes are a class of devices whose operation is based on scanning various surfaces with a probe. These are quite new devices, the image on which is obtained by fixing the contacts between the surface and the probe. At the moment, in such devices, it has been possible to fix the interaction of the probe with some molecules and atoms, which brings the scanning probing microscope to the level of electronic devices. And in some respects, such devices even surpass them.
X-ray microscopes are a device that allows you to examine very small objects, the magnitude of which can be compared with the length of the x-ray wave. The operation of such a device is based on electromagnetic radiation having a wavelength of up to one nanometer. The resolution of X-ray devices is much higher than optical, but lower than electron microscopes.
The structure of the microscope
A standard optical device has the following parts in its structure:
- nozzle;
- eyepiece;
- base and tripod;
- lenses;
- turret head;
- subject and coordinate tables;
- switch and illuminator;
- macrometric and micrometric focusing screws;
- diaphragm condenser.
The optical system of such a device consists of lenses located on the turret, eyepieces and, in some cases, a prism block. With the help of an optical system, the image of the studied sample is formed on the retina of the eye. Moreover, this image will be inverted.
Currently, many children’s microscopes contain a Barlow lens, the use of which allows you to achieve smooth image magnification up to 1000 times and more. However, the image quality suffers significantly, which makes the use of this lens in such devices rather doubtful.
In professional devices, only various combinations of high-quality lenses and eyepieces are used to change the magnification. And of course, in such devices, a lens of such dubious quality will never be used.
The mechanical system of the microscope is a tripod, a tube, a revolving head, focusing mechanisms and an object stage.
Focusing mechanisms are used to focus the image. The macrometer screw is used at low magnifications, and the micrometer is used at high magnifications. Standard school or children’s microscopes are usually equipped with only a macrometric coarse focusing screw. For laboratory research, a fine focusing mechanism is also required. Optical devices can have separate mechanisms for coarse and fine focusing, and also contain coaxial screws for micro and macrometric focus adjustment.
Focusing of the device is carried out by moving the object table or the tube of the device in a vertical plane.
The object table is necessary for placing an object on it. There are several varieties of them:
- stationary;
- mobile;
- coordinate.
More comfortable for work is the coordinate stage, which allows you to move the sample for research in a horizontal plane.
The microscope objectives are located directly on the turret. Its rotation allows you to select any of the lenses, thereby changing the magnification. Professional devices are usually equipped with removable lenses that are screwed into the turret. Cheap versions of microscopes have built-in lenses.
The microscope tube contains an eyepiece. In devices with a trinocular or binocular attachment, it is possible to adjust the distance between the pupils, as well as diopter correction, which allows you to adjust the microscope to the individual characteristics of each observer. In children’s devices, in addition to the eyepiece, there may also be a Barlow lens in the tube.
The lighting system of an optical device is a diaphragm, a condenser and a light source.
The light source can be either external or built-in. A standard microscope usually includes a bottom light. Some children’s devices sometimes use side lighting, but it does not carry any practical effect.
The condenser and diaphragm are used to adjust the illumination of the microscope. Condensers can be single lens, double lens or triple lens. When lowering or raising the condenser, either scattering or condensation of light occurs, which illuminates the sample under study.
The diaphragm is presented in two versions: iris, with a smooth change in diameter, and stepped, consisting of several holes of different diameters. Accordingly, by increasing or decreasing the diameter of the light hole, one can limit or increase the flow of light pouring onto the sample. Some condensers are equipped with a filter holder into which various filters can be inserted.
Conclusions
A microscope is an optical device that allows you to repeatedly magnify the image of the object under study, which allows you to study substances that are invisible to the naked eye. At the moment, there are many different types of modern devices that differ in resolution, which makes it possible to distinguish and study very small objects.