USE AND CARE OF THE MICROSCOPE
PURPOSE:
In this laboratory investigation, students will correctly use and identify the parts of a compounds light
microscope.
BACKGROUND INFORMATION:
See attached reading
PRELAB:
1. What is the total magnification of a compound microscope if the ocular lens is 10X and the objective lens is
40X?
2. What is resolving power and how can you improve it?
3. Explain what happens when immersion oil is used with the microscope.
MATERIALS:
Compound Light Microscope
Immersion oil
Lens paper
Prepared slides of algae, protozoa and bacteria
PROCEDURE:
1. Place the microscope on the bench squarely in front of you.
2. Obtain a slide of algae, protozoa or bacteria and place it in the stage clips on the stage.
3. Focus with the 10X objective lens. Diagram some of the cells on the slide under low power.
4. When the image has been brought into focus with low power, rotate the turret to the next lens, and the subject
will remain almost in focus. All of the objectives (with the possible exception of the 4X) are parfocal; that is
when a subject is in focus with one lens, it will be in focus with all of the lenses. Use the fine adjustment.
Only a slight adjustment should be required. More light is usually needed. Again, draw the general size and
shape of some cells.
5. Move the turret to the next lens and slightly adjust to get the cells in focus. Diagram the general size and
shape of some cells.
6. Repeat the steps for the other slides: algae, protozoa and bacteria
7. Oil immersion must be used with only ONE of your slides. With the oil immersion microscope, you need to
start with the 4X objective lens and get to the high-powered lens. Once you have it focused on the high-dry
lens move it out of position and place a drop of immersion oil on the area of the slide you are observing. (See
Figure 1.5 on the back) Carefully click the oil immersion lens into position. It should now be immersed in the
oil. Carefully use the fine-adjustment knob to bring the object into focus. Note the shape and size of the cells.
Diagram what you see.
8. When your observations are complete, move the turret to bring a low power objective into position. DO NOT
rotate the high-dry objective through the immersion oil. Clean the oil off the objective lens with lens paper,
and clean off the slide with a paper towel. Remove the slide.
DATA:
Diagrams and observations of the three different slides: algae, protozoa and bacteria. Next to each diagram make
sure to note the total magnification.
CONCLUSION:
1. Why is it desirable that microscope objectives be parfocal?
2. What controls the amount of light reaching the ocular lens?
3. Assume the diameter of the field of vision in your microscope is 2 mm under low power. If one Bacillus cell
is 2 m, how many Bacillus cells could fit end to end across the field? How many 10 m yeast cells could fit
across the field?
4. What effect does increased magnification have on the field of vision?
5. What would occur if water were accidentally used in place of immersion oil?