USE OF THE
Students should be able to...
identify the various parts of
the microscope and their function
calculate total magnification
define: field of view,
parfocal, working distance, and depth of field
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:
||Parts of the Microscope:
objective (magnifies 4X)
objective (magnifies 10X)
high power objective
- stage clips
- stage platform
- condenser with iris (disc) diaphragm
- light source/power source
- ocular (magnifies 10X)
- coarse adjustment knob
- fine adjustment knob
- body tube
- mechanical stage knobs
- 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). Letter E low power -
and Letter E higher 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 "thread" slides 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.
Cross threads low power -
and Cross threads higher power -
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
While using the high power
objective, the fine adjustment knob should be utilized for
focusing because the working distance decreases as magnification
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
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
Replace prepared slides in the
properly marked tray and disposed of wet mounts in the glass-disposal box.
Make sketches as necessary to
help you remember what you have seen.
Report any difficulty or
malfunction to the instructor.
V. Useful Website