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BIO 105
Summer 2012
Name:________________________
Laboratory 5: The Compound Microscope
The microscope is a delicate, precision instrument. It must be treated gently; the slightest bump
or jar may damage the alignment of its lenses. Carry the microscope with care by grasping its
arm with one hand, keeping the instrument close to your body aand
nd supporting its base with the
other hand. Always carry the microscope with two hands. Microscope lenses are to be
cleaned before and after each use with lens paper. Never wipe a lens with paper toweling,
to
handkerchief, Kleenex,, or Kim Wipes
Wipes. If you wear
ar corrective glasses for astigmatism you
must use them with the microscope; if your glasses are for near
near-sightedness
sightedness or far-sightedness,
far
you may use the focus of the microscope rather than your glasses.
Parts of the Compound Microscope
body
y tube. The ocular contains one lens
1. The ocular is located at the upper end of the inclined bod
with a total magnification of 10X.
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2. The body tube and the nosepiece hold the ocular lens and objective lenses at a set distance
from each other. The body stays in place and the stage is raised or lowered during focusing.
3. The three objective lenses are mounted on the rotating nosepiece. The rotating nosepiece may
be turned to either direction, so the objective may be changed while viewing a specimen.
4. Your microscopes have three objective lenses, so called because they are closest to the object
or specimen. These objective lenses vary in length (the shortest is the lowest power or
magnification; the longest is the highest power or magnification) and have individual magnifying
powers of 4X, 10X, and 40X. The 4X objective lens is the lowest power objective, and the 40X
objective lens has the highest magnifying power. When an objective is placed over the specimen,
the objective lens will produce a magnified image which will be viewed through, and further
magnified by, the ocular at the top of the body tube. A combined magnifying action (ocular +
objective lenses) makes this instrument a compound microscope. The total magnification of a
specimen is the magnification of the ocular multiplied by the magnification of the objective, for
example on low power the total magnification is 4 x 10 = 40.
5. The mechanical stage is mounted perpendicularly from the arm and below the nosepiece. This
part supports the specimen slide over an aperture (hole) that admits light for specimen
illumination. The mechanical stage has two clips that hold each specimen in place.
6. The coarse focus adjustment knob is a large, round knob on the side of the microscope used
for focusing the specimen; it adjusts the height of the stage relative to the objectives. You should
only use the coarse focus adjustment knob when you are using the lowest power objective lens.
When you are observing a slide under higher magnification (i.e. using the 40X or 100X
objectives) you should use the fine focus adjustment knob.
7. The fine focus adjustment knob is a smaller, round knob on the side of the microscope used to
fine-tune the focus of your specimen after using the coarse adjustment knob.
8. The arm supports the body tube. The arm is connected to the base and is used to carry the
microscope.
9. The base bears the weight of the microscope.
10. The light source (lamp) is built into the base and illuminates the specimen. The illuminator
has a curved outer lens that directs light through the stage opening. The light switch is located
on the base.
11. The iris diaphragm is located on the underside of the stage. It may be opened or closed to
regulate the amount of light reaching the specimen. Best detail is seen with the lowest light
intensity.
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Focusing
Turn the low power objective lens into position. Put a microscope slide on the stage and secure
with the clips. With the coarse focus adjustment knob slowly move the objective downward until
the image is focused. Note the distance between the point of the objective and the stage. With
the object in focus under low power magnification, turn the 40X objective into position and
adjust the focus with the fine adjustment knob. If a higher magnification is desired, repeat the
above steps. Do not use the coarse focus knob with the higher power objective lenses. Note
how close the high power objective lens is to the slide. There is no "stop" when focusing with
this objective and too great a downward movement may result in the cracking of the slide or the
scratching of the lens.
Objective lens
4X
10X
40X
Total Magnification
Procedure 1: Examining the letter “e”
Step 1: Place a slide of the letter "e" on the stage.
Step 2: Focus the slide first on low power, using the coarse and fine focus, then increase the
power and refocus only using the fine focus knob.
Question 1: Is the position of the letter "e" reversed? ____________
Question 2: Can you see more area of the slide on the low or high power? ____________
Procedure 2: Examining colored threads
Step 1: Obtain a prepared slide of colored threads.
Step 2: Focus this slide as described above.
Question 1: What color is on top? ____________ On the bottom? ____________
Procedure 3: Examining prepared slides
Step 1: Obtain two prepared slides (either human blood, bone, or skeletal/striated muscle).
Step 2: Focus these slides as described above.
Step 3: Sketch the slides at two magnifications using the two lower power objectives.
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Some examples of what you may be looking at:
Compact bone
Skeletal muscle
Blood
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Slide 1:__________________
Slide magnification: ________
Slide 2:__________________
Slide magnification: ________
Slide 1:__________________
Slide magnification: ________
Slide 2:__________________
Slide magnification: ________
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Procedure 4: Examining Human Epithelial Cells
Step 1: Place one drop of methylene blue dye on the microscope slide.
Step 2: Using the broad end of a toothpick, gently scrape the inside of your cheek, mix the
scraping into the drop of dye on the slide.
Step 3: Holding the cover slip at a 45 degree angle, gradually let it fall into place over the
cell/dye mixture. Note: If the cover slip is dropped from too flat an angle, many air
bubbles will form and interfere with accurate observations. Air bubbles are usually
perfectly round with dark black edges.
Step 4: Examine your slide using the compound microscope, using 100X magnification.
What objective will you use to attain a magnification of 100X? _________
Step 5: Sketch the cells that you see under the 400X magnification.
Slide magnification: __100___