Using the Compound Light Microscope

Using the Compound Light Microscope

1. Carry your microscope with one hand holding the arm and the other hand holding

the base.

2. The low power objective (one of the lenses closest to the object being examined)

is shorter than the high-power objective.

3. Low power in our lab is 4x and 10x; high-power is 40x.

4. The ocular lens is the lens closest to your eye. The ocular lens in our lab is 10x or 16x.

5. Total magnifying power is the magnifying power of the ocular lens times the magnifying power of the objective lens.

6. The coarse adjustment is the larger of the two adjustment knobs. The fine adjustment is the smaller of the two adjustment knobs.

7. All focusing under high power is done with the fine adjustment knob.

8. In order to obtain the best possible image, adjust the amount of light passing through the specimen by manipulating the light source.

9. When a slide is moved to the left, the image will move to the right. The opposite also holds true.

10. When a slide is moved toward you, the image moves away from you. The opposite also holds true

11. Always begin viewing a specimen by centering it under the low power objective while using the coarse adjustment. Then use the fine adjustment.

12. The field of view is larger and brighter under low power than under high power.

13. If the image is not centered under low power, it will not be in view when the objective is switched to high power.

14. The depth of field is the distance above the slide in which the object is in good focus. High power has a lower depth of field than low power. (Recall that the low power objective is shorter than the high power objective.)

15. The resolving power, or resolution, is the ability to distinguish clearly and in detail between two lines that lie very close to each other.

16. The oil-immersion objective is used with oil to avoid the loss of light at higher magnifications.

17. Wet mounts should have no bubbles because they interfere with viewing of the specimen.

Microscopic Measurement

1/100 meter = 1 centimeter (cm)

1/1000 meter = 1 millimeter (mm)

1/1000 millimeter = 1 micrometer (um) or 1 micron (u) (Bacteria)

1/10,000 millimeter = 1 Angstrom unit (Viruses)

Convert millimeters to micrometers: Move decimal point three places to the right

Estimating the size of a specimen: Place a plastic ruler in the field of your low-power objective. Measure in mm and then convert to micrometers

Example: 4.72 mm = 4720 micrometers

Preparing a Wet Mount Slide

1. Obtain a clean microscope slide and a coverslip.

2. Place the specimen in the middle of the microscope slide. The specimen must be thin enough for the light to pass through it.

3. Using a dropper pipette, place a drop of water on the specimen.

4. Lower one edge of the coverslip so that it touches the side of the drop of water at about a 45° angle. The water will spread evenly along the edge of the coverslip. Using a needle or probe, slowly lower the coverslip over the specimen and water. If air bubbles are present, gently tap the surface of the coverslip with a pencil eraser.

5. Remove any excess water at the edge of the coverslip with a paper towel. If the specimen begins to dry out, add a drop of water at the edge of the coverslip.

Staining Techniques

1. Obtain a clean microscope slide and coverslip.

2. Place the specimen in the middle of the microscope slide. The specimen must be thin enough for the light to pass through it.

3. Using a dropper pipette, place a drop of water on the specimen.

5. Add a drop of stain at the edge of the coverslip. Using forceps, touch a small piece of lens paper or paper towel to the opposite edge of the coverslip. The paper causes the stain to be drawn under the coverslip and to stain the cells in the specimen.