Stereomicroscope

Basic characteristics
A stereomicroscope (binocular magnifier - "binocular", dissecting microscope) is a type of light microscope, that is used to observe a sample with different magnification in 3D. Unlike a normal microscope, a stereomicroscope uses lower magnification and longer working distances. It consists of two separate microscopes, one for the right and one for the left eye. Characteristic of this microscope are two separate light beams that lead to the observer's eye, one to each. Each eye creates a separate image of an object, but the brain evaluates these different images as a whole. This microscope is characterized by a long working distance and a large depth of field, while in general the higher the magnification, the shallower the depth of field.



History
One of the first stereomicroscopes was built at the beginning of the 19th century by Charles Wheatstone, who also described the working principle of the microscope. This research created great interest in the world, and in the middle of the 19th century, Francis H. Wenham built the first stereomicroscope with one objective and two eyepieces. However, even that did not achieve a true three-dimensional effect. It wasn't until 1957 that the American inventor Horatio S. Greenough assembled a groundbreaking stereomicroscope, which is the forerunner of today's. The previously used brass was replaced by aluminum and was supplemented with an inverted prism that allowed a direct image. Nowadays, it is mainly characterized by high-contrast images with a minimum of reflections and geometric distortions.

Construction
Stereomicroscopes can be divided into two basic types. Greenough's stereomicroscopic system uses two separate optical paths. It consists of two objectives and two eyepieces. This system is somewhat outdated and is no longer used nowadays. The CMO system uses one large-radius objective and two eyepieces. It creates two independent parallel optical channels passing through one lens. These channels form the optical path through which the light beam (light reflected from the surface of the object) passes. Thanks to this design, both optical axes intersect the plane of the sample exactly at the focal point, so the image is not tilted in the focal plane.

vpravo|180px|náhled|Construction of a modern stereomicroscope. A − objective, B − Galilean telescope, C − zoom control, D − internal objective, E − crystal, F − portable lens, G − reticle, H − eyepiece.

Principle
The human eye and brain work together to create so-called stereoscopic vision, thanks to which we see spatial three-dimensional images. This impression is created by the brain when processing two slightly different images from both retinas. Human eyes are approximately 6.5 cm apart, so each eye sees a given object at a slightly different angle. Only after being transferred to the brain are both images merged to create the resulting three-dimensional image of the object. This feature is ideal for examining the surfaces of solid materials. A stereomicroscope also differs from other microscopes in lighting. It uses an overhead light whose rays are reflected from the surface of the sample. This allows ideal observation of thick or opaque materials..

Use
Thanks to their design, stereomicroscopes are used in biology, botany, entomology and other natural sciences. They are also important in medicine, where they are used, for example, in microsurgery. They enable a precise idea of ​​the three-dimensional appearance of the tissue and surrounding structures. Devices with a longer working distance are used in industry for the assembly and inspection of products, the surface of the material, and further, for example, in goldsmithing and watchmaking. Stereomicroscopes are also used in the study of the surface of solid samples, e.g. in geology.