Name: ______Date: ______Class: ______
Lab: Using a Compound Light Microscope
Objective Lens X Ocular Lens = Total Magnification
4 X (Red) 10 X ______
10 X (Yellow) 10 X ______
40 X (Blue) 10 X ______
100 X (White) 10 X ______
There are 3 or 4 different types of LM’s in this classroom.
List some of the differences you observe between them.
1. ______
2. ______
3. ______
4. ______
5. ______
Slides - Dry mounts - made by placing the specimen directly on a slide and then covering the specimen with a cover-slip. This method is used when adding water would destroy or dissolve a sample.
Slides - Wet mounts - many samples look better when placed in a drop of water on the microscope slide. This is known as a "wet mount." The water helps support the sample and it fills the space between the cover slip and the slide allowing light to pass easily through the slide, the sample, and the cover slip. In many cases, a stain such as Lugol's iodine, methylene blue, or crystal violet may be added to specimens in order to increase contrast.
Making a wet mount.
o Use lens paper to clean a glass slide and coverslip, if necessary.
o Place specimen in the center of the slide.
o Place one drop of water on the specimen.
o Position the coverlip so that it is at the edge of the drop of water and at a 45º angle to the slide.
o Lower coverslip slowly to avoid air bubbles.
Materials: compound LM , glass slides, cover slips, lens paper, water dropper, forceps , prepared slides
Procedure: Circle each # as you complete that step of the lab, √ appropriate boxes, and answer all questions.
1. Carry a microscope to table, holding the arm with one hand and supporting the base with your other.
2. Place it on your lab table away from the edge. Plug it in and turn it on.
3. Identify the type of LM you are using. Check one.
o Non-mechanical LM (with 2 stage clips)
o Mechanical LM (with 1 slide holder)
As you complete this lab, you will find specific instructions for the type of LM you are using.
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4. The ocular lens for each of these microscopes magnifies 10X. Determine which of the following objective lenses your microscope has and check those boxes. Then, fill in the blanks with the total power of magnification when using each lens.
o Obj. lens 4X (red) Total power ______X
o Obj. lens 10X (yellow) Total power ______X
o Obj. lens 40X (blue) Total power ______X
o Obj. lens 100X (white) Total power ______X
5. Adjust the revolving nosepiece so that the lowest power objective is in line with the body tube.
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6. Place the prepared slide on the stage.
o Non-mechanical: Secure slide under stageclips.
o Mechanical: Secure slide in slide holder.
7. Using the coarse adjustment, raise the stage as far up as it will go and stop. Do not over turn knob by forcing it further. You will break the microscope!
8. While observing stage at eyelevel, move the slide, centering the specimen (the place where the threads cross) under the objective lens.
o Non-mechanical: Manually move slide around on the stage. Always keep slide under stage clips.
o Mechanical: Move the stage using 2 knobs on the left side of the microscope. One moves the stage away from/toward you, the other left/right.
9. While looking through the eyepiece, turn the coarse adjustment until the image is in focus. Then, use the fine adjustment to sharply focus.
10. At the same time, you may also need to move the specimen slightly to center it in your field of view (what you see in the circle).
11. Look through the eyepiece, move the diaphragm to adjust the amount of light that passes through the specimen. Readjust when needed to get the best possible contrast of your specimen. Less light often helps you better visualize clear specimens.
o Mechanical: The light dimmer dial on left side of base allows you to control intensity of the light.
o Mechanical: The focusing condenser can be moved up/down to focus the beam of light on the specimen. Small knob under stage on right side.
12. In the following circle, sketch what you see in your field of view and write the total magnification power you are using here. ______
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13. Make sure specimen (where the threads cross) is in the center of your field of view. Adjust the revolving nosepiece to the next higher magnification.
14. Focus the image with the fine adjustment ONLY.
Never use the coarse adjustment after you leave lowest power!
15. In the following circle, sketch what you see in your field of view and write the total magnification power you are using here. ______
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16. Make sure your specimen (where the threads cross) is in the center of your field of view. Adjust the nosepiece to the next higher magnification. (If your 3rd objective lens is 100X, do not uses this one. Skip to # 19.) Focus image with the fine adjustment ONLY!
17. In the following circle, sketch what you see in your field of view and write the total magnification power you are using here. ______
18. Examine your diagrams.
Can you see more of the slide and specimen under
higher or lower powers?
______
19. What happens to the image in the eyepiece as you move the slide:
to the left? ______
to the right? ______
away from you? ______
toward you? ______
20. Using the fine adjustment, can you see all 3 threads in focus at the same time?
______
The term depth-of-field refers to the fact that a microscope is limited to clearly focusing on only one plane or level (depth) at a time.
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21. Remove your slide. Turn off your microscope, secure the cord, and restore all original settings. It should always be left the way you found it. Return all equipment to original locations.
Post-Lab Questions:
1. You hold a microscope by its ______and ______.
2. Which structure (all LM’s) controls the amount of light that passes through the specimen? ______
3. Which structure (Mechanical LM) allows you to control the intensity of light? ______
4. The ocular lens in the eyepiece has a magnification power of ______X.
5. Which color objective lens magnifies 40X? ______
6. Which color objective lens requires oil to view extremely small specimens? ______
7. What is rotated in order to change objective lenses? ______
8. What do you place on top of a specimen with water on a slide? ______
9. When you are turning the coarse or fine focusing knobs, what are you actually moving? ______
10. The amount of the specimen or slide that you can see is called your ______.
11. Do you see more of the specimen at 100X or 400X total magnification? ______X
12. At which power do you see more detail; 100X or 400X total magnification? ______X
13. Which objective lens do you use when initially locating a specimen in your view? ______
14. When you initially search for an object, should you begin by setting your stage all the way up or all the way down? ______
15. What is the total magnification power if you are using the red objective lens? ______X
16. Which type of LM requires you to manually move the specimen? ______
17. When you are ready to move up to a higher power, first make sure you specimen is ______in your field of view. Other wise, the specimen may be outside of you field of view at the next higher power.
18. What term refers to the fact that a microscope is limited to clearly focusing on only one level at a time? ______
19. You should always clean your slide and cover slip with ______.
20. It is OK to move your stage plate down with the coarse focus knob if you think the next lens might hit the slide and specimen. True or False? ______