Light Microscope Technical Definition- Engl 202c

7/30/2019 Light Microscope Technical Definition- Engl 202c

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How Does a Compound Light Microscope Work?

By: Spencer Lambert

March 14, 2013

This document will serve to show the different parts of a compound light microscope, and how

they work to magnify specimens. The document will be focused towards high school seniors or

college freshmen who are being introduced to light microscopy. The audience should have a

basic understanding of biology and simple light microscopes. They should also understand the

principles of magnification and illumination. It will serve as a guide to help them understand

the instrument they are using.

The invention of the light microscope is credited to spectacle-makers Hans and Zacharias

Janssen, who first invented the device in the 1590s. The light microscope, however, was

not greatly popular until it was popularized by Anton van Leeuwenhoek in the early 1700s.Van Leeuwenhoek was the first person to view bacteria, yeast, and blood circulation.

Another great achievement in light microscopy was the description of eukaryotic cells by

Robert Hooke, who sectioned plant cork tissue and viewed it under a light microscope.

These early achievements were, however, achieved with relatively primitive single lens

microscopes. Modern compound microscopes use multiple lenses to collect light and a

separate set of lenses to focus the light into the eye. These microscopes feature more


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reliable light sources and lenses of greater magnification and clarity than earlier single lens

microscopes, letting the most complex light microscopes resolve objects up to 0.275

microns in size.

The following section outlines the parts of a modern compound light microscope, and how

they work together to make the device work. They will be presented by following the light

path from light source to eyepiece. Please refer to Image 1 for a visual of the parts

Image 1. Parts of a compound light microscope labeled with light path

a. While many different light sources may be used in a compound light microscope, the

most common light source is a lamp backed by a reflector that reflects light through

the collector lens. Most microscopes will have an intensity knob to adjust the light

emitted from the light source to allow for optimal clarity of the subject.

b.


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The mirror reflects the light emitted by the light source upwards at a 90 degree

angle into the field diaphragm. It allows for a more compact design in modern

compound light microscopes with the light source housed within the base of the

microscope.

c. The field diaphragm controls the diameter of the light beam that is emitted onto the

sample. It allows the user to control how much of the specimen is viewable, and a

fine tune of the intensity of the light

d. The field lens serves to focus light towards the condenser. It is not found on all light

microscopes.

e.

The condenser is a special lens designed to focus light from the field lens ordiaphragm on the sample. The condenser is fully adjustable, which allows the user

to view different layers of thin samples by manipulating the condenser. The

condenser can be moved up or down, but the default position is up.

f. The mechanical stage is the part of the microscope that houses the sample. It will

usually contain a clip or vise to hold the specimen in place, and, in higher end

models, can be moved horizontally by an adjustment knob on the microscope.

When loading a sample onto the stage, the stage should always be completely

down, and the lowest objective should always be used first when raising the stage.

g. The course and fine focusing knobs are used to

focus the light coming from the sample into the

objective. These knobs physically move the stage

up and down. The course adjustment knob, the

wider of the two knobs, should only be used to

bring the sample into view on the lowest objective.

Use of the course knob on higher objectives couldcause collision between the sample and objective

and potential damage to the microscope. The fine

adjustment knob is used to fine tune the focus of

the sample on any magnification.


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h. The revolving nosepiece is a

rotating structure that houses

the microscopes multiple

objective lenses. Lightmicroscopes typically have

between three and four

objective lenses, depending on

whether or not it has an oil

immersion lens. The objectives

are a number of single or multi-

element compound lenses

housed in a cylindrical structure. They focus to collect light from the sample and to

focus it into a real image in the tube of the microscope. It is important to never

touch the actual objectives, but to use the revolving nosepiece to move from

objective to objective. The oil immersion lens should never be used without oil. It

can severely damage the microscope.

i. A microscope with a trinocular head has three potential exits for the light coming

through the objectives. Two exits go to the binocular eyepiece for viewing, and a

third allows the light to exit into a camera adapter at the top of the microscope. The

camera adapter allows for the use of digital photography to photograph samples.

You will most likely not use any digital photography in any entry level courses

requiring light microscopy.

j. The eyepiece houses the ocular lens. In the case of your microscope, the eyepiece

contains two ocular lenses, allowing for viewing of the specimen with both eyes.

The ocular lens bring the real image produced by the objectives into focus for the

human eye. The top piece of the left side of the eyepiece can be turned to allow

users with glasses to focus on samples without wearing their glasses.

k. The stand and arm make up the body of the microscope. When moving the

microscope, you should always grasp it by the arm and stand, in an upright position.

The ocular lenses are not attached to the eyepiece and can fall out of the

microscope is not held properly.


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The light microscope has been a fixture of the biological sciences for over 400 years, and while

compound light microscopes use the same principles as simple microscopes, they are able to

achieve much greater clarity and magnification. Modern compound light microscopes have

features such as the condenser and multiple objectives that allow them to resolve extremely

small objects. These technological breakthroughs have helped students and researchers alike

view wonders that could never be seen by the naked eye.

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Light Microscope Technical Definition- Engl 202c

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