The microscope is the most important piece of equipment in the clinic laboratory. The microscope is used to review fecal, urine, blood, and cytology samples on a daily basis (see Figure). Understanding how the microscope functions, how it operates, and how to care for it will improve the reliability of your results and prolong the life of this valuable piece of equipment.
Parts and functions of a compound microscope
Used to carry the microscope.
Supports the microscope and houses the light source.
(C) Oculars (or eyepieces)
The lens of the microscope you look through. The ocular also magnifies the image. The total magnification can be calculated by multiplying the objective power by the ocular power. Oculars come in different magnifications, but 10× magnification is common.
(D) Diopter adjustment
The purpose of the diopter adjustment is to correct the differences in vision an individual may have between their left and right eyes.
(E) Interpupillary adjustment
This allows the oculars to move closer or further away from one another to match the width of an individual’s eyes. When looking through the microscope, one should see only a single field of view. When viewing a sample, always use both eyes. Using one eye can cause eye strain over a period of time.
The nosepiece holds the objective lenses. The objectives are mounted on a rotating turret so they can be moved into place as needed. Most nosepieces can hold up to five objectives.
(G) Objective lenses
The objective lens is the lens closest to the object being viewed, and its function is to magnify it. Objective lenses are available in many powers, but 4×, 10×, 40×, and 100× are standard. 4× objective is used mainly for scanning. 10× objective is considered “low power,” 40× is “high power” and 100× objective is referred to as “oil immersion.” Once magnified by the objective lens, the image is viewed through the oculars, which magnify it further. Total magnification can be calculated by multiplying the objective power by the ocular lens power.
For example: 100× objective lens with 10× oculars = 1000× total magnification.
The platform on which the slide or object is placed for viewing.
(I) Stage brackets
Spring-loaded brackets, or clips, hold the slide or specimen in place on the stage.
(J) Stage control knobs
Located just below the stage are the stage control knobs. These knobs move the slide or specimen either horizontally (x-axis) or vertically (y-axis) when it is being viewed.
The condenser is located under the stage. As light travels from the illuminator, it passes through the condenser, where it is focused and directed at the specimen.
(L) Condenser control knob
Allows the condenser to be raised or lowered.
(M) Condenser centering screws:
These crews center the condenser, and therefore the beam of light. Generally, they do not need much adjustment unless the microscope is moved or transported frequently.
(N) Iris diaphragm
This structure controls the amount of light that reaches the specimen. Opening and closing the iris diaphragm adjusts the diameter of the light beam.
(O) Coarse and fine focus adjustment knobs
These knobs bring the object into focus by raising and lowering the stage. Care should be taken when adjusting the stage height. When a higher power objective is in place (100× objective for example), there is a risk of raising the stage and slide and hitting the objective lens. This can break the slide and scratch the lens surface. Coarse adjustment is used for finding focus under low power and adjusting the stage height. Fine adjustment is used for more delicate, high power adjustment that would require fine tuning.
The illuminator is the light source for the microscope, usually situated in the base. The brightness of the light from the illuminator can be adjusted to suit your preference and the object you are viewing.