Microscope Anatomy & Function

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Base, The base is the foundation on which the microscope stand is built. It is important that the base is relatively large, stable, and massive. When you are setting up a microscope for the first time ensure that the surface on which it is placed is level.


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Condenser, The condenser under the stage focuses the light on the specimen, adjusts the amount of light on the specimen, and shapes the cone of light entering the objective. One way to think about the condenser is as a light "pump" that concentrates light onto the specimen.

The condenser has an iris diaphragm that controls the angle of the beam of light focused onto the specimen. The iris diaphram is an adjustable shutter which allows you to adjust the amount of light passing through the condenser. The angle determines the Numerical Aperture (NA) of the condenser. This diaphragm, generally called the aperture diaphragm, is one of the most important controls on the microscope.

Cover slip, Most objectives are designed for use with a cover slip between the objective and the specimen. The cover slip becomes part of the optical system, and its thickness is critical for optimal perfomance of the objective. The cover slip thickness designation on most objective lenses is 0.17 mm or 170 microns.

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Focus (coarse), The coarse focus knob is used to bring the specimen into approximate or near focus.
Focus (fine), Use the fine focus knob to sharpen the focus quality of the image after it has been brought into focus with the coarse focus knob.

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Illuminator, There is an illuminator built into the base of most microscopes. The purpose of the illuminator is to provide even, high intensity light at the place of the field aperture, so that light can travel through the condensor to the specimen.

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Magnification, The degree to which the image of the specimen is enlarged by the objective. For example, 40 specifies 40 times (40x) the actual size of the specimen. As magnification increases, resolution (NA) must also increase so that more information can be obtained. Magnification without increased resolution yields no additional information and is called "empty magnification."

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Numerical Aperture (NA), The maximum angle from which it can accept light. Lenses that accept light from higher angles have greater resolving power, thus NA defines resolving power. The maximum NA of objectives is 1.4, and it is limited by the physics of light and the refractive index of glass.

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Objective Lens, The objective lens is the single most important component of the microscope. Together with the condenser, it determines the resolution that the microscope's capability. Learning how to use the correct objective for a particular application is a prerequisite for good microscopy.
Important information describing the objective lens is engraved on the side of its barrel. This is the best performance the objective is capable of and it will only yield this performance when used properly.

Ocular Lenses, The ocular lenses are the lens closest to the eye and usually have a 10x magnification. Since light microscopes use binocular lenses there is a lens for each eye. It is important to adjust the distance between the microscope oculars, so that it matches your interpupillary distance. This will yield better image quality and reduce eye strain.

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Plan, There are many different kinds of objective lenses. Common designations include "plan" for flat field, "achromat" for partially color-corrected, and "apochromat" for highly color corrected. These designations may become combined as in "plan achromat."

Parfocal, The specimen is focused for all objectives if it is focused for one objective. In other words, once the specimen is focused under one objective it will be in approximate focus under other objectives.

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Stage, The stage is the platform that supports the specimen. It is usually quite large to minimize vibration and it attaches to the microscope stand. The stage has an opening for the illuminating beam of light to pass through.
A spring loaded clip holds the specimen slide in place on the stage. Other types of stage clips are designed for use with petri-dishes, multiwell plates, or other specialized chambers.
Most stages have a rack and pinion mechanism that can move the specimen slide in two perpendicular (X - Y) directions. On many microscopes, stage movement is controlled using two concentric knobs located to the side or below the stage.  

Stand, The stand is the basic structure of the microscope to which everything is attached. The stand, also known as the arm, is the part of the microscope that you grab to transport the microscope.

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Tube, the tube houses many of the optical components of the microscope. The optical tube length of most biomedical microscopes is 160 millimeters but tube geometry varies considerably due to relay lenses and proprietary design features. In most modern microscopes the tube is folded to make the microscope easier to use.  
Early microscopes had straight tubes such as this model built by Robert Hooke in the mid 17th century.

Tube length, describes the optical tube length for which the objective was designed. This is 160 mm (6.3 inches) for modern biomedical microscopes.

Turret, Most microscopes have several objective lenses mounted on a rotating turret to facilitate changing lenses. An audible click identifies the correct position for each lens as it swings into place.

When the turret is rotated, it should be grasped by the ring around its edge, and not by the objectives. Using the objectives as handles can de-center and possibly damage them.

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