How to use a compound light microscope properly
Introduction:
Many things are too small to be detected or seen by the eye alone. They can be seen, however, with the use of an instrument that magnifies, or visually enlarges, the object. One such instrument that is of great importance to biologists and other scientists is the compound light microscope. A compound light microscope consists of a light source to illuminate the object to be observed, an objective lens that magnifies the image of the object, and an eyepiece (ocular lens), that further magnifies the image of the object and projects it into the viewer’s eye.
The microscope is an expensive precision instrument that requires special care and handling. In this investigation, you will learn the parts of the microscope, the functions of those parts, and the proper use and care of a microscope.
Objects or specimens to be observed under a microscope are generally prepared in one of two ways. Prepared or permanent slides are made to last a long time. Temporary or wet mound slides are made to last only a short time- usually for one lab period. In this investigation you will learn the technique for preparing wet mount slides.
Objectives:
Upon completion of this investigation, you will be able to:
Materials:
Compound light microscope, lens paper, prepared slides, glass slides, coverslips, dropper, scissors, newspaper, scissors, water
Procedure: Follow the steps for this lab as the teacher explains the different parts and as you complete the procedure with your lab partner.
Part A: Prelab
1. Obtain a microscope from the cabinet and carry it the proper way: one hand on the arm and one hand under the base
2. Use your diagram with labeled microscope parts to identify all of the parts of the microscope.
3. Notice the numbers etched on the low power objective (4X), high power objective (10X), and eyepiece (10X). The total magnification of the microscope can be determined by multiplying the magnification of the objective (low or high) by the magnification of the eyepiece (10X). Calculate the total magnification for both objectives below:
Total magnification for Low power objective=
Total magnification for High power objective=
4. Before use of the microscope, use lens paper to clean the lens of the objectives and eyepiece.
Part B: Use of a microscope and observation of a prepared slide
5. Turn the coarse adjustment knob of the microscope counterclockwise so that the objective is raised towards the eyepiece.
6. Turn the revolving nosepiece until the low power objective clicks into place.
7. Plug the cord into an electrical socket and turn on the light source. Look through the eyepiece. The white circle you see is called the field of view.
8. Place a prepared slide on the stage so that it is centered over the stage opening. Secure the slide into place with the stage clips.
9. Look at the microscope from the side and turn the coarse adjustment knob until the low power objective is as close to the slide so that it is as close to the slide as possible without touching it.
10. Look through the eyepiece and turn the coarse adjustment knob away from the slide until the object comes into focus. Then turn the fine adjustment knob until the object comes into sharper focus. Sometimes, at this point, you may need to adjust the diaphram to allow more or less light into the field of view.
IMPORTANT: THE ONLY TIME YOU SHOULD USE THE COARSE ADJUSTMENT KNOB IS WHEN FOCUSING ON LOW POWER, NEVER ON HIGH POWER!!!!!!!!
11. Look at the microscope from the side and without moving the adjustment knobs, rotate the nosepiece until the high power objective clicks into place.
12. Look through the eyepiece. Turn the FINE adjustment knob ONLY to bring the object into focus. AGAIN: NEVER USE THE COARSE ADJUSTMENT KNOB IN HIGH POWER!!!
Part C: Preparing a wet mount slide:
13. Obtain a clean glass slide and clean the slide with lens paper. With a pair of scissors, cut out a lowercase "e" from the newspaper. Position the letter "e" on the center of the glass slide. Use a dropper to place a small drop of water over the letter.
14. Hold a clean coverslip by the edges. Slowly lower the coverslip over the letter and place the coverslip on the letter from 45° angle to prevent air bubbles from forming between the coverslip and slide. This is a wet mount slide. You may need to practice making a wet mount slide until you can do so without forming air bubbles.
Why should you hold the coverslip by the edges only? ____________________________
________________________________________________________________________
15. Now, using the same techniques you used to observe the prepared slide, focus the letter "e" on low power and then high power.
16. Rotate the nosepiece back into low power position without moving the adjustment knobs. Move the slide to the right while looking into eyepiece and observe the direction of the movement of the letter "e". Move the slide upwards and observe the direction of movement again. Move the slide left and down also, again noting the movement of the letter.
In what direction does the letter "e" move when the slide is moved to the right? ________
In what direction does the letter "e" move when the slide is moved to the left? _________
In what direction does the letter "e" move when the slide is moved up? ______________
In what direction does the letter "e" move when the slide is moved down? ____________
Part D: Observing Prepared Slides
17. There are two different prepared slides on your desk, all labeled correctly.
18. Focus the first slide correctly, the 2nd and so on.
19. Observe the 1st slide under low and high power. Draw what you see below: Label the picture with the slide name above your drawing.
Low power High power
20. Continue onto the second slide and repeat step 18 and 19.
21. Draw what you see at low and high power below and Label the drawing:
Low Power High Power
Summary:
Directions: Answer the following questions:
Below, draw a SINGLE animal cell from the prepared slide