USE OF THE MICROSCOPE
Lab Objectives:
Students should be able to...
1. identify the various parts of the microscope and their function
2. calculate total magnification
3. define: field of view, parfocal, working distance, and depth of field
4. describe and apply the proper use of a microscope
I. Introductory information and care of the microscope:
• The microscopes used in this lab are compound light microscopes. They are
designed to be parfocal; that is, if the microscope is clearly focused on a
specimen with a lower power objective, it will be clearly focused (or very nearly
so) when you swing the next highest objective into place.
II. Checklist of parts of the microscope--please make sure you know the function
and correct procedure for use of these structures:
1. Nosepiece
2. Objectives
3. Stage clips
4. Stage
5. Condenser/Iris diaphragm (not
shown in picture)
6. Light source
7. Base
8. Eyepiece
9. Arm
10. Course adjustment
11. Fine adjustment
12. Body/head
13. Power cord III. Use of the microscope
• Position the microscope so that you can comfortably look through the ocular. Adjust your chair
height if necessary.
•
See that the microscope is plugged into the outlet properly, with very little slack in the cord.
•
Make sure the scanning (4X) power objective is in operating position. The scanning power
objective lens magnifies the image by a factor of 4, for a total of 40X. (Total magnification is the
product of the magnifications of each lens being used, that is, the ocular lens at 10X and, in this
case, the scanning lens at 4X.)
•
Obtain a prepared microscope slide (the newspaper "e" slide is a good one to start with). View the
letter E at low and high power
•
Use of the "e" slide demonstrates the "upside-down, reversed" image: as you move the slide to the
left, the image goes to the right; as you move the slide away from you, the image moves toward
you. Also with the "e" slide you can learn to appreciate the concept of field of view, which
lessens as you advance to higher magnifications.
•
The total magnification achieved with the high power objective in position is ___________.
•
You will examine a "cross threads" slide to observe depth of field. In this preparation, three
different colors of thread were layered across each other. As you attempt to focus, especially with
10X and 40X objectives, notice that you cannot get all threads in focus at the same time. Even
though the specimen on the slide appears thin enough to be two-dimensional, it does have
thickness or depth. It is a three-dimensional object. Magnification emphasizes the thickness of
the specimen. Therefore, you see different levels come into clear focus as you slightly change
focus. This feature will be very important in understanding the position of cell components when
studying tissue slides.
IV. Additional rules to remember
• Always focus with the scanning power objective lens first
• Focus away from the specimen with the coarse adjustment knob while viewing the object on
scanning or low power.
• While using the high power objective, the fine adjustment knob should be utilized for focusing
because the working distance decreases as magnification increases.
• To increase magnification, always center an object of interest using the mechanical stage knobs
before rotating the nosepiece.
• Adjust the light intensity using the iris diaphragm attached to the condensor.
• Do not drag the microscope across the lab table.
• Clean all lenses with lens paper before and after use of a microscope.
• Protect the microscope as you return it to its cabinet by replacing the plastic cover and carrying it
with two hands (one holding it by the arm the other supporting it by the base).
• Replace prepared slides in the properly marked tray and disposed of wet mounts in the glassdisposal box.
• Make sketches as necessary to help you remember what you have seen.
• Report any difficulty or malfunction to the instructor.