LAB #1H:
#1H: THE MICROSCOPE
OBJECTIVES: Become familiar with the parts and use of a compound
microscope.
Learn to prepare and observe wet mounts.
MATERIALS: Microscope, slides, cover slips, lens paper, paper towels, water,
beaker, medicine dropper, sheet of newspaper, scissors, ruler,
magazine picture in color, thread (various colors), prepeared slides.
PROCEDURES/OBSERVATIONS:
PART A – LEARNING ABOUT THE MICROSCOPE
1. Obtain your microscope. Carry it with one hand holding the arm and the other
supporting the base. Set it down carefully away from the edge of the table.
2. Examine your microscope. Review the function of each of its parts.
3. Adjust the diaphragm to the largest opening so that the most light enters the
microscope. Check by looking through the ocular.
4. Place a slide on the stage and secure it using the stage clips. Put your thumbs on the
corners of the slide nearest you and your forefingers on the corners farthest from you.
Practice moving the slide back and forth on the stage.
5. Carefully rotate the nosepiece. You should be able to feel and hear a click as an
objective snaps into place.
6. Locate the low-power objective.
What is its magnifying power? ___________________
7. Locate the high-power objective.
What is its magnifying power? __________________
8. Examine the ocular lens.
What is its magnifying power? __________________
9. What is the total magnification produced when the low-power objective is used?
Show your calculations. ________________________________________________
10. What is the total magnification produced when the high-power objective is used?
Show your calculations. _______________________________________________
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11. Carefully turn the coarse adjustment knob. Observe the movement it produces.
Which part of your microscope moves when you turn the coarse adjustment?
____________________________________________________________________
12. Turn the fine adjustment knob. Observe the movement it produces. The motion may
be difficult to see.
How do the effects of the fine adjustment and coarse adjustment differ?
______________________________________________________________________________
PART B – MEASURING AND CALCULATING THE DIAMETER OF THE FIELD OF
VIEW
When viewing images under the compound light microscope, the diameter of the field of view
changes with the magnification of the microscope. Like a zoom camera, under lowest
magnification, your field of view is relatively large, but all your objects appear very small. As
you increase the magnification, the field of view becomes smaller, but the objects you are
viewing appear larger as you zoom into a smaller area. The diameter of the field of view is
inversely proportional to magnification of the microscope. This means that as the magnification
increases, the diameter of the field of view decreases.
1m
1,000 mm
1,000,000 um
1,000,000,000 nm
1. Using a transparent centimeter ruler, measure the diameter of the field view in
millimeters while viewing your compound microscope under 40X magnification.
Diameter =
_________mm
2. Since 1 mm = 1000 microns(um), how many microns is your diameter you measured?
Diameter = _______um
3. Using the equation, d1 . m1 = d2 . m2, for magnification and diameter, calculate the field of
view diameter in microns for 100X and 400X magnifications. Record your result in the
table below as well as your results from part two:
m1 = one magnification
d1 = the field of view at that magnification
MICROSCOPE MAGNIFICATION
40X
100X
400X
m2 = another magnification
d2 = the field of view for that magnification
DIAMETER OF FIELD OF VIEW
um
um
um
How does the above chart of magnification and diameter of field of view illustrate an inverse
proportional relationship?
_____________________________________________________________________
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_____________________________________________________________________
PART C – INDIRECTLY MEASURING THE SIZE OF OBJECTS
1. Now that you know the diameter of the field of view under each of your microscope’s
magnifications, you can use that information to estimate the size of objects you examine with
your microscope. For example, if you estimate that 10 cells will fit side by side across a field of
view with a diameter of 2000 um, then each cell will be 1/10th of the diameter or about 200um
each. In the space below, write the equation that can be used to estimate cell size in microns:
Cell size =
_____________________________________________________________________
2. Obtain prepared slides of various organisms and practice estimating their lengths or diameters
using the equation from part 1. Use the magnification that makes it easiest for you to count. In
the chart below, record the name of the cells or object you observe and its estimated length or
diameter in microns.
Name of cell or object
Estimated size in microns
PART D - PREPARING AND EXAMINING A WET MOUNT
1. Locate a small letter “e” in some newsprint. Cut out a 1-cm square with the “e” near
the center.
2. Place the 1-cm square in the middle of a clean slide. Using a medicine dropper, put
1 drop of water on the square. Drop the water from about 1 cm above the slide. Do
not touch the dropper to the paper because it will stick.
3. Cover the mount with a clean cover slip. Hold the cover slip at about a 45 degree
angle to the slide and move it toward the drop. As the water touches the cover slip, it
will spread along the edge. Gently lower the cover slip into place. Do not press on
the cover slip. It should simply rest on the top of the water. If your mount has too
many bubbles, take off the cover slip. Absorb the water with a paper towel and repeat
steps 2 and 3.
4. Make sure your microscope is in an upright position with the stage horizontal. This is
appropriate for viewing a wet mount. The diaphragm should also be at its largest
opening.
5. Click the low-power objective into place.
6. Make sure the bottom of your slide is dry. Place the slide on the microscope stage so
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that the “e” is in reading position and over the hole in the stage. Secure the slide with
the stage clips.
7. Use the coarse adjustment knob to move the stage up until the objective is
about ½ to 1 cm above the slide, or until you feel the automatic stop.
8. Keeping both eyes open, look through the ocular. This can be difficult at first; but it
helps prevent eyestrain. Do not be discouraged if you are “seeing your eyelashes”. It
will truly become easier with practice!
9. Now SLOWLY move the stage down by turning the coarse adjustment knob until the
letters come into focus. Examine the letter “e”.
10. DRAW the letter “e” the same size and in exactly the same position you are seeing it
through the microscope.
11. Move the slide to the right. Which way does the image move?
____________________________________________________________________
12. Move the slide to the left. Which way does the image move?
____________________________________________________________________
13. Move the slide forward. Which way does the image move?
____________________________________________________________________
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14. Move the slide backward. Which way does the image move?
____________________________________________________________________
15. Observe your wet mount as you change the diaphragm to each of its settings. Adjust
the diaphragm to give good illumination and contrast without glare. What does the
diaphragm control?
____________________________________________________________________
16. It is now time to use high power. Be sure that your “e” is in sharp focus in the center
of the low-power field of view. REMEMBER: There is no automatic stop for the
high-power objective. All focusing under high power is done with the fine
adjustment knob. Watching from the side, CAREFULLY switch to the high-power
objective. Make sure the objective does not hit the slide. It will be very close.
17. Focus on the letter “e”. You will only need to turn the fine adjustment knob a tiny
bit.
18. DRAW the letter “e” the same size and in exactly the same position you are seeing it
through the microscope.
19. Is the field of view bigger under low power or high power?
____________________________________________________________________
20. Compare the brightness of the field under low power and high power.
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____________________________________________________________________
____________________________________________________________________
PART E - RESOLVING POWER AND DEPTH OF FIELD
REMEMBER: RESOLVING POWER is the ability to distinguish between two separate
points that are very close together.
DEPTH OF FIELD is the distance above the slide in which the object is
in good focus.
1. Make a wet mount using a 1-cm square of colored magazine print. Make sure the
paper is thin and has both light and dark tones. What colors do you see?
_____________________________________________________________________
_____________________________________________________________________
2. Observe the slide under both low and high power. Examine the light and dark areas of
the square. How is the color distributed?
_____________________________________________________________________
_____________________________________________________________________
3. What colors do you see? ________________________________________________
_____________________________________________________________________
4. Now prepare a wet mount using two threads of different color. Cross them on the
slide, then add a drop of water and the cover slip. View the slide under low power.
Focus directly on the point where the threads cross. Are both threads in focus under
low power?
____________________________________________________________________
5. Switch to high power. Observe the threads. Are both threads in focus under high
power? EXPLAIN.
____________________________________________________________________
____________________________________________________________________
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CONCLUSIONS:
1. Briefly describe the function of each microscope part listed in TABLE 1.
TABLE 1: Parts of the Microscope
PART
FUNCTION
Ocular
Coarse
Adjustment
Nosepiece
Objectives
Stage
Stage Clips
Diaphragm
Fine
Adjustment
2. What did the microscope do to the image of the letter “e”?
_____________________________________________________________________
3. Why is it important to CENTER and focus the specimen in the field of view under low
power before switching to higher power?
_____________________________________________________________________
4. Why should one only use the fine adjustment when under high power?
_____________________________________________________________________
5. Explain why the color of the magazine picture appeared different when looked at
under the microscope?
_____________________________________________________________________.
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6. Using the concept of depth of field, how can you tell which thread was above the
other?
______________________________________________________________________
7. If you were interested in locating a specific area of your slide, which objective should
you use when scanning the slide? EXPLAIN.
_____________________________________________________________________
FURTHER INVESTIGATIONS:
1. Prepare some wet mounts of other things, such as pieces of cloth or an insect’s wing.
Draw the things you observe. Be sure to label each drawing with its name and the
magnification used.
2. Investigate the development of the microscope through history, modern uses of the
microscope, or different kinds of microscopes.
3. “Working distance” is the distance from the top of the cover slip to the microscope
objective. Determine the working distance for both low and high power.
4. Look at prepared slides or make your own slides of things you would like to see in
greater detail.
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