Using the Microscope
The microscope is an essential tool for exploring small structures such as cells.
Before looking at differences between animal and plant cells, it is important to
understand microscope care and operation.
Objectives:
1.
2.
3.
4.
5.
6.
To demonstrate the correct way to care for and use a compound light microscope.
To locate the parts of a microscope and describe the function of each part.
To calculate the total magnification.
To prepare a temporary wet mount of a specimen.
To understand the following concepts: magnification, resolution, and working distance.
To describe how the microscope alters the orientation of images.
Materials:
1.
2.
3.
4.
5.
6.
Compound Microscope
lens paper
microscope slides
cover slips
medicine droppers, fine forceps, and scissors
Newsprint
Procedure:
Care of Microscopes
The microscope is a finely crafted optical instrument (not to mention an
expensive one!). Please treat it as if you own it. Microscopes should be handled
carefully according to the guidelines in Table 1.1.
Table 1.1. Guidelines for Microscope Care.
1. Obtain the microscope from back table or closet.
2. Carry microscope with two hands – hold the arm with one hand and the bottom of the base
with the other hand. NEVER carry 2 microscopes at once.
3. Keep your microscope clean. Use only lens paper to clean the microscope lens. DO NOT
USE PAPER TOWELS OR TISSUES because they may scratch the lenses.
4. Never take the microscope apart. Never remove the eye piece or any objective lens.
5. Do not loosen the setscrew for the eyepiece tube.
6. Never place any solution, crystal, or other chemical in contact with the microscope.
7. Always put slides into the mechanical stage, and take slides off the stage when the
microscope is in low power (10x objective) – never high power objective (40x).
8. Do not let the electric cord become covered with books or lab supplies. The microscope
could accidentally be pulled from the table.
9. Place the microscope flat on the lab table at least 4 inches from the edge of the table.
The Parts of the Compound Light Microscope
Table 1.2. Parts of the microscope and their functions
Microscope Part
Ocular (eye piece)
Arm
Revolving nosepiece
Objectives
Head piece
Stage
Mechanical Stage
Condenser
Diaphragm
Coarse Adjustment knob
Fine Adjustment knob
Base
Lamp
Light level control
Power cord
Power switch
Function
Uppermost lens through which specimen is observed; magnifies image 10x.
Used to carry the microscope.
Movable plate which holds objective lens.
3 lenses which magnify the image:
Scanning objective – 4x
Low power objective – 10x
High (dry) power objective – 40x
Conducts light from objective lens to ocular.
Platform containing a central opening.
Device that holds the microscope slide in place and moves it along the
stage.
Group of lenses below the stage which directs and concentrates the light
beam from the lamp to the specimen.
Adjusts the amount of light passing through the condenser: controls
brightness.
Focuses image by raises and lowering the stage. Turning the knob
clockwise (away from you) raises the stage; counter-clockwise lowers the
stage. Use only with the scanning (4x) and low power (10x) objectives.
Never use it to focus at high power (40x).
Small knob in center of coarse adjustment knob used for final focusing.
Bottom support; house lamp
Light source
Controls intensity of light from lamp.
Plugs into receptacle on the microscope base
Switch on front which turns on lamp; indicator shines when light is on.
Principles of Microscopy
1. Magnification
The compound light microscope is used to enlarge the image of the specimen.
The microscope is called compound because it requires two lenses for
magnification, the ocular lens and the objective lens. The total magnification of
any specimen is equal to the power of the ocular lens multiplied by the power
of the objective lens used. For example, if the ocular lens magnifies 10x and the
objective being used magnifies 40x, the total magnification is 400x.
CALCULATE the total magnification that may be achieved with each of the
objectives on your microscope, record your results.
2. Resolution or resolving power
The usefulness of the compound light microscope is limited by a factor called
resolution or resolving power. Resolution is the ability to distinguish between two
points that are close together. For example, the resolution of the human eye is
100 micrometers. If they are closer together than 100 micrometers, they appear
to merge together and we see only one point. The compound light microscope has a
resolution of 0.2 micrometers. Therefore, we can see objects that are much
closer together as distinct points. This permits us to observe fine details. The
compound light microscope not only makes objects bigger, but it allows us to see
the living world in more detail.
Using the compound light microscope to observe specimens
1. Preparation of wet mounts
Wet mounts are useful preparations for viewing specimens for short periods of
time. You will prepare a wet mount of the letter “e” for microscopic examination.
Directions for Letter “e” preparation.
a. Obtain a clean microscope slide and cover slip.
b. Use a medicine dropper to place a drop of water in the center of the slide.
c. Cut a row of letters from the newsprint. Be sure to include at least one
lowercase “e”.
d. Place your row of letters in the drop of water.
e. Gently apply the cover slip.
2. Using the microscope
a.
b.
c.
d.
e.
Plug in microscope
Turn on microscope, adjust light intensity
Place specimen on the stage
Move specimen into position
Observe letter “e” at low power
a. How does the orientation of the letter e compare?
f. Sketch the letter “e”
a. Sketch letter “e”
b. Calculate total magnification
c. Record total magnification by your sketch
d. Why is it important to indicate magnifications when drawing
specimens?
g. Move the slide
a. Move the stage left, right, forward, backward
b. Record the direction the image moves
c. What is the general relationship between slide movement and image
movement?
h. Increase the magnification
a. Rotate the high power objective (40x) into place
b. Focus with the fine adjustment knob
c. What new details can you see?
d. Sketch the letter “e” at high power magnification
e. What is the total magnification now?
f. Is the “e” larger or smaller?
g. Can you see more or less of the letter “e”?
h. Is the field of view larger or smaller at the higher magnification?
i. Why should you center the object you are examining before increasing
magnification?
j. Should you increase or decrease the light when increasing
magnification? Why?
i. REVIEW!
a. What generalizations can you draw from your experience examining
the letter “e”
Parts of the microscope and their functions. Fill ‘er up!
Microscope Part
Ocular (eye piece)
Function
Controls brightness
Fine adjustment knob
Bottom support; houses lamp
Group of lenses that concentrate and direct the light beam
from the lamp to the specimen.
Revolving nosepiece
Coarse
knob
adjustment