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The Optical Knowledge Portal
Information – Education – Certification

Microscopy

Microscopy

Microscopy refers to a technology using a microscope (from the Ancient Greek: μικρός, mikrós, "small" and σκοπεῖν, skopeîn, "to look" or "see”). A microscope is a device that significantly enlarges small, close-up objects to make them visible to the eye or to produce an image of them. These objects or object structures are usually so small that they cannot be seen by the naked eye, that is to say their size is below the resolving power of the human eye. In contrast to a magnifying glass, which enlarges images by means of only a single lens, microscopes use two lenses to enlarge small objects viewed at close range. They consist of two collecting systems, the objective lens and the eyepiece or ocular lens. Microscopes can be adapted for specific applications by making many different modifications or additions to their design. Microscopes are used in biology, medicine and materials science.

Some examples of different microscopes:

In microphotography, a microscope is used together with a camera. Electronic analysis of images is suitable as a means of compiling professional documentation in the disciplines of biology, mineralogy and material testing.

Polarisation microscopes are a type of optical microscopes. Two additional polarisation filters create polarised light to show birefringent objects clearly. Crystals or minerals with crystal lattice structures are classed as birefringent objects.

Fluorescence microscopy makes use of the physical phenomenon of fluorescence. Objects containing fluorescent compounds are illuminated with light of a particular wavelength. This causes light of another wavelength to be emitted. Special filters ensure that only the emitted light is observed. Fluorescence microscopy is used particularly for biomedical applications such as, for example, the observation of antibodies or DNA segments.

Phase contrast microscopy is used to examine biological samples which differ only marginally in optical density from the surrounding medium. Phase contrast microscopy makes use of the fact that the phase of light waves shifts as well as their amplitude when they pass through a medium (proportionately with its index of refraction.) This makes it possible to discern structures clearly even when examining specimens of low contrast.

The construction of standard microscopes

Most components of microscopes are fixed to the microscope arm. Microscopes typically utilise two light sources: a mirror, which makes daylight available for microscopy, and an electric light. The condenser or potentiometer positioned above the electric light is used to regulate the light reaching the specimen. The coarse and fine focuses are found on the side of the arm. These adjustment knobs allow the stage (or specimen holder) to be moved up and down to ensure the sharpest image possible is achieved. The stage is height-adjustable; it is not fixed rigidly to the microscope arm. A slide, normally a thin glass rectangle with the specimen being studied, is normally held in place on the stage by means of two stage clips. A revolving turret mounted at the top end of the microscope arm contains several objective lenses with different magnifications (4x, 10x and 40x); rotating the turret allows users to switch between the different objectives. The eyepiece (ocular) lens at the top, where users look into the microscope, enlarges the image of the specimen under the microscope. This ocular magnification (10x–20x) further enlarges an image that has already been enlarged by the objective lens.