PART I.
MICROSCOPY
Laboratory Exercise no. 1
THE COMPOUND MICROSCOPE
INTRODUCTION
Microscopes were invented at the end of the sixteenth century and put to use during the
second half of the seventeenth century. Those in use for the study are variations of three general
types.
Small objects are magnified by a system of glass lenses and light with widely used light
microscopes, such as those available in our laboratory. Electron microscopes cost more space
than light microscopes, but achieve greater magnification with abeam of electrons controlled
by electromagnets.
Variations of scanning tunnelling microscopes, which came into use in 1980’s use a
minute probe instead of light electrons to scan across the surface, and then reproduce an image
of the scanned area down to the level of their atoms. For manageable classroom laboratory
activity, a simple light microscope is used. They are easy to manipulate and handle by beginners
in Biology classes.
At the end of the exercise, the student should be able to:
1. Know the parts and understand the function of each part of the compound microscope.
2. Calculate the magnification with specific combinations of the lenses of each object
viewed.
3. Determine the differences among resolution, microscopic field and depth of field.
PARTS OF THE COMPOUND MICROSCOPE
Obtain a microscope from the central laboratory. Hold the handle with one hand and
support the base with the other hand. HOLD THE MICROSCOPE IN AN UPRIGHT POSITION.
NEVER CARRY ANYTHING WHILE CARRYING THE MICROSCOPE. Put on top of the table,
one foot away from the edge. Familiarize yourself with the names and functions of the
microscope.
The following are the parts of the microscope:
2 Main Parts of the Microscope
1. Mechanical Parts – These consist of certain precise parts, chiefly of metal to support and
adjust the optical.
2. Magnifying Parts – These consist of a special type carefully grounded and polished
lenses and glasses aligned on an optical axis for the enlargement and focusing of the
image or the object under study.
1. MECHANICAL PARTS:
A. BASE – the heavy solid part on which the microscope stand.
B. PILLAR – a short supporting piece arising from the base to support the upper part parts
of the microscope.
C. ARM/HANDLE – a curved part used in carrying the microscope.
D. BODY TUBE – a short cylindrical piece above the hemispheric prism housing to give the
desired distance (with the draw tube, from the eye to the image).
E. DRAW TUBE – tube attached to the body tube to bear the eyepiece or ocular.
F. HEMISPHERIC PRISM HOUSING – a semi-circular piece that houses the prism that
bends the light6 from the mirror. This part can be rotated.
G. DUST SHIELD – found above the revolving nosepiece, which prevents the dust from
entering into the objectives.
H. REVOLVING NOSEPIECE – a structure to which all the objectives are attached. This
piece allows easy and convenient shifting of the objectives.
I. STAGE – a platform with a central aperture or opening on which the mounted glass slide
is placed for focusing.
J. SLIDE HOLDER – the part that holds and supports the slide and is found on the stage.
K. SLIDE CLIP – this is attached to the slide holder to keep the slide in place.
L. HORIZONTAL BAR – a bar adjacent and is parallel to the slide holder to prevent the slide
from extreme backward movement.
M. HORIZONTAL BAR KNOB- fixes the horizontal bar in place.
N. CENTRAL APERTURE- an opening on the stage through which the light from the mirror
passes to reach the objectives.
O. SLIDE ADJUSTMENT KNOBS
i. FRONT KNOB- moves the slide forward and backward during focusing.
ii. REAR KNOB- moves the slide forward and backward.
P. STAGE ADJUSTMENT KNOBS
i. COARSE ADJUSTMENT KNOB- a large knob found on the pillar for locating the
image of the slide.
ii. FINE ADJUSMENT KNOB- a small knob parallel to the coarse adjustment knob
used for focusing with the high power objectives for detailed or in-depth
examination of the specimen.
Q. SUBSRAGE ADJUSTMENT KNOB- a small knob on the pillar that supports the
condenser, iris diaphragm and the filter.
R. FOCUSING LOCK- a tiny piece on the pillar that is used to keep the mechanical stage in
place.
S. MIRROR RACK OR STAND- supports the mirror and allows it to move multidirectional.
2. MAGNIFYING PARTS
A. EYEPIECE/OCULAR- this part is found inserted in the draw tube which can be rotated.
The lens may enlarge the image 10 to 15 times.
B. PRISM- this is a triangular glass that bends the light from the mirror so that image can
be seen with the eyepiece.
C. OBJECTIVES/NOSEPIECES
i. LOW POWER OBJECTIVE (LPO)- the shortest objective with 10x magnification.
The initial focusing is always done with the LPO.
ii. HIGH POWER OBJECTIVE (HPO)- this objective has a higher magnification that
is 15, 20, 40, 60, or 80. This is used for more detailed examination.
iii. OIL IMMERSION OBJECTIVE (OIO) – this has a magnification of 100x IOI is used
with specimen that requires greater magnification like bacteria. the objective
needs an oil to be mounted in the slide for precise observation of the specimen.
D. CONDENSER- this is supported by the substage apparatus under the stage. The light
rays from the mirror are being concentrated by this part towards the specimen in the
slide.
E. DIAPHRAGM- this controls and regulates the amount of light admitted to the specimen.
there are two types as follows:
i. IRIS- mounted immediately beneath the stage aperture. A lever regulates the
opening and closing of this type of diaphragm.
ii. DISC- mounted similarly as the iris diaphragm; it is a form of plates with several
circular openings of varied diameters.
F. FILTER HOLDER- controls the light concentrated by the condenser. The opening can be
enlarged or reduced. This holds the colored glass to further the intensity of light towards
the object under study.
G. MIRROR- consists of concave and plain glasses for directing the light towards the object
under study.
CARE OF THE MICROSCOPE
Successful microscopy requires skill and proper care of the instrument. With
considerable care, the microscope will certainly last a long time, but a single bit of carelessness
will ruin it. Every student then is responsible for the microscope he signs out, and his cooperation
regarding this matter is very important for his own good.
The following should be observed when using the microscope.
1. Never remove any part of the microscope. Report to your instructor any missing or
damaged parts or if some parts do not work smoothly. You will be held responsible if you
fail to do so.
2. Never let the lenses come in contact with chemicals. Lenses could corrode with acids
present in the fingerprints and other chemicals.
3. Use lens paper or soft tissue to clean the lenses. The glass of the lenses is different from
the window glass. It is relatively soft and scratches easily.
MAGNIFICATION
Laboratory specimens can be classified into two based on their sizes. Macroscopic
specimens are those that can be simply seen by our naked eyes while microscopic specimens are
those that cannot be seen by our naked eyes and need the aid of a microscope. In making a
sketch or a simple line drawing of a specimen, one should indicate its appropriate magnification.
Magnification is defined as the number of times the length and width or the diameter of an
object or a specimen is enlarged or reduced.
Magnification of a macroscopic specimen can be obtained by dividing the size of the
drawing with the size of the specimen:
M = size of the drawing/ actual size of the specimen
On the other hand, magnification of a microscopic specimen is equal to the product of
the separate magnifying powers of the objectives and the eyepiece. The magnifying powers are
stamped on the eyepiece and the objectives. An eyepiece of IOX when working with an objective
of IOX will magnify 100 times. Various degrees of the magnification will be obtained with the
use of THE DIFFERENT COMBINATIONS OF EYEPIECE AND THE OBJECTIVES. Be sure to
understand the magnifying capacity of your microscope assigned to you.
M = magnification of the objective X magnification of the eyepiece
EXERCISE NO.1
THE COMPOUND MICROSCOPE
MATERIALS
Compound Microscope
Prepared slide of letter “e” or “a”
Thread fibers
PROCEDURE
A. Prepared slide of “a” or “e”
1. Position the letter of the prepared slide at the center of the stage.
2. Place the low power objective (LPO) in line with the stage aperture and look through
the eyepiece, adjusting the mirror in such a way that the face of the mirror is directed
towards the light, so s to get the optimum amount of light.
3. Look at the side of the microscope and move the objective downward by turning the
coarse adjustment forwards to about a few millimetres from the cover glass. See to it
that the specimen is at the center of the stage aperture.
4. Look again through the eyepiece and raise the low power objective slowly by turning
backward the coarse adjustment until the outline of the object is clearly seen. Keep the
both eyes open. If you do not see anything with both of your eyes open, cover one eye
with your hand. Avoid closing one eye. Make the specimen clear with the fine
adjustment knob.
5. If the specimen is not centered, move the slide very slowly to bring the object to the
center of the field.
6. Adjust the amount of light reaching your eye by manipulating the diaphragm.
7. This is important. You cannot see detail with light that is too intense or dim for your
particular eye.
8. Once the material is in focus, move the slide slightly to the left, to the right, then
forward and backward. Note which direction the slide goes.
9. Now swing the high power objectives (HPO) into place and refocus with the fine
adjustment knob. You may need to re-center the material after swinging to the high
power objective (HPO). Clean slides, eyepiece, proper focusing and correct light
intensity are all necessary for maximum resolution (the capacity of the microscope to
separate, tiny closely adjacent objectives). Answer the questions on your worksheets.
B. Thread Fibers
1. Place on clean glass slide a few strands of thread and add a drop of water on it.
2. Follow the previous procedure. Locate for bubbles by enlarging and reducing its
opening as you observe the thread.
3. Answer the questions in your worksheet.
UNIVERSITY OF SOUTHERN MINDANAO
College of Mathematics and Sciences
Department of Biological Science
Name ____________________________________ Instructor __________________________
Year & Section ____________________________ Date _______________________________
Laboratory Report No. 1
The Compound Microscope
A. Prepared slide of “a” or “e”
1. Draw the letter s seen with your naked eye, under the LPO and under the HPO.
Compute the total magnification for your LPO and HPO.
The letter as seen with the The letter as seen under LPO The letter as seen under LPO
naked eye Magnification=_____________ Magnification=_____________
2. At which direction did the letter go as you move the slide to the:
Left ______________________________________
Right ______________________________________
Forward ___________________________________
Backward __________________________________
B. Thread Fibers
1. What happens when you close the iris diaphragm? _______________________
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When you open it? __________________________________________________
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Can you see the bubbles clearly? _______________________________________
2. With which of the two lenses is it easier to determine the order of the thread
fibers?
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Why? _____________________________________________________________
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C. Label the parts of a compound microscope
Figure 1. Parts of a Compound Microscope
D. Review Questions
1. Why is it necessary to focus with the fine adjustment in high magnifications?
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2. There are other types of the light microscope. Describe and give the uses of each
variation listed below.
a. Binocular microscope - ___________________________________________
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b. Field Microscope - ______________________________________________
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c. Stereomicroscope - _____________________________________________
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d. Phase Contrast Microscope - ______________________________________
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3. Does the field of view stay bright under the high power objective? Why?
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References:
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