Download Microscope Lab Activity

Laboratory 1: Use and Care of the Microscope
USE OF THE MICROSCOPE
The compound microscope is a precision, highly specialized instrument that is
designed to allow the viewing of objects that are too small to be seen by the unaided eye.
The resolving power of your microscopes is approximately 0.2m (micrometers or
microns), which means it can discriminate objects down to a size of 0.2 (1 micrometer
is 1/1000 of a millimeter). Unfortunately, many users fail to properly adjust the optical
system resulting in unsatisfactory results or resolving power. We will spend one lab
period learning how to properly use a microscope. For some of you this may be a review,
for others, it may be the first time you were properly instructed on the proper use of a
microscope.
MAJOR PARTS AND FUNCTIONS
Optimum clarity of images produced by the microscope cannot be obtained if the
elements of the optical system are dirty. Before using the microscope, always clean the
lenses with lens paper provided for that purpose. Never substitute paper towels of facial
tissues as they contain grit and will scratch the lenses. Dust may be blown from the
lenses with a bulb. Do not touch the surfaces of the glass lenses with your fingers.
The compound microscope is basically a tube with magnifying lenses at each end;
the objective lens at the lower end, and the ocular lens (or eye pieces) at the upper end.
The tube is attached to a supporting frame that is equipped with coarse and fine focusing
screws. There is also usually a stage to support the specimen being examined. In the
case of binocular microscopes, there is an internal image splitting prism and mirror
arrangement to deliver the image to both oculars.
Most microscopes have more than one objective lens attached to a revolving
nosepiece, which allow the selection of objectives of different magnifications. These
objectives are constructed in such a way that they are parfocal; that is, they may be
rotated into position for viewing without danger of touching the specimen slide and
should require only minor adjustment to bring them into sharp focus. The light necessary
for viewing the specimen may be either natural or artificial, and may be directed into the
optical system by either a mirror or be beamed directly through the specimen from below.
When the mirror is used, the flat side is usually utilized with low magnification and the
concave side with higher magnifications. Modern microscopes also have a set of lenses
between the light source and the objective called the condenser. The condenser is
equipped with an adjustment screw so that the light can be focused to provide the most
effective illumination of the study specimen (always use the flat side of the mirror if your
microscope has a condenser). Immediately below the condenser is an iris diaphragm (a
lever on the condenser) which may be opened or closed to control the total light passing
through the optical system. On microscopes with built-in artificial light sources, there is
usually a rheostatic control which regulates the intensity of the light beam illuminating
the specimen.
Parts of the Microscope
Label the microscope with the following terms.
arm - this attaches the eyepiece and body tube to
high-power objective - a large
the base.
base - this supports the microscope.
body tube - the tube that supports the eyepiece.
coarse focus adjustment - a knob that makes
large adjustments to the focus.
diaphragm - an adjustable opening under the
stage, allowing different amounts of light onto the
stage.
eyepiece - where you place your eye.
fine focus adjustment - a knob that makes small
adjustments to the focus (it is often smaller than the
coarse focus knob).
lens with high magnifying power.
inclination joint - an adjustable
joint that lets the arm tilt at various
angles.
low-power objective - a small
lens with low magnifying power.
mirror (or light source) - this
directs light upwards onto the slide.
revolving nosepiece - the
rotating device that holds the
objectives (lenses).
stage - the platform on which a
slide is placed.
stage clips - metal clips that hold
a slide securely onto the stage.
ADJUSTMENT OF THE MICROSCOPE
The following procedures should be performed to adjust your microscope at the
start of each laboratory session:
1. Carefully carry a microscope back to your lab bench. Plug it in. You are responsible
for the care and maintenance of this microscope, so please be careful.
2. Clean all glass surfaced carefully with lens paper.
3. Place the 4X objective in position, turn the lamp on at approximately one-half power.
Obtain a prepared “letter e” slide and place it on the stage with the specimen centered
in the light path. Make sure the slide clips are snuggly against the slide NOT ON
TOP OF IT. While looking at the stage, bring the stage to a position near to the
objective lens.
4. Look through the oculars. Move the oculars farther apart or closer together until the
oculars match your inter-pupillary distance. DON’T LEAN YOUR EYES ON THE
EYEPIECES AND MAKE SURE YOU ARE LOOKING THROUGH BOTH EYES!
What is your inter-pupillary distance? _____________
5. Lower the stage with the coarse adjustment slowly until the specimen comes into
sharp focus. If both oculars are not in sharp focus, follow these procedures. Close
your eye that is over the diopter adjusting ring (usually the left). Use your coarse and
fine focus to bring the image into sharp focus with your other eye (usually the right).
Now close the other eye, and use the diopter adjusting ring to bring the image into
sharp focus. You will probably have to do this every time you use these microscopes,
particularly if other people are using them in the meanwhile.
6. Gently close the iris diaphragm.
7. Raise or lower the substage condenser until the edges of the diaphragm are in sharp
focus when viewed through the oculars.
8. Slowly open the diaphragm until the edges disappear from the field of view.
9. Your microscope is now adjusted and ready to use.
10. Look critically at the prepared slide. Does the specimen appear the same when
looked at with the naked eye as it does when you look at it through the microscope? How
is it different?
ILLUMINATION
Increase or decrease the light intensity of the lamp by turning the variable rheostat
knob on the base of the microscope. Generally, you should avoid moving the substage
condenser to adjust the light intensity. However, for some purposes at lower powers
better contrast can be achieved by lowering the substage condenser.
OBJECTIVE LENSES
1. Magnification of your specimen is a determined by the magnification of your
objective lenses (i.e.4X, 10X, 40X, and 100X) times the magnification of your ocular
lens (ours are 10X). Therefore, fill in the following information:
Objective Lens
4X
10X
40X
100X
Ocular Lens
10X
10X
10X
10X
Total Magnification
2. Always start your study with the lowest power objective. Do not try to focus on a
fresh slide with an objective higher that the 10X. Start with the prepared slide at 4X.
Make sure it is focused and centered in the field of view (the illuminated circle you
see when you look in your microscope). What percentage of the total field of view
does the specimen take up? _______ Now, switch to the 10X objective and use the
fine focus to bring it into focus. What percentage of the total field of view NOW
does the specimen take up? ________. Do it again for the 40X and again notice the
percentage of the total field of view that the specimen takes up.
OIL IMMERSION OBJECTIVE- Think about but do NOT do.
1.
The 100X lens is meant to be used with immersion oil. We won’t be doing this
today as the procedure is messy and it is very easy to break specimen slides.
2. Don’t attempt to look at specimens under 100X as the image will NOT resolve
without the use of immersion oil.
3. However, if you wanted to look at very small specimens such as bacteria, you
would have to use 100X and immersion oil. To do this, place 1 drop of
immersion oil on the specimen in the field of view. Swing the 100X lens into the
oil and carefully use your fine focus to locate the specimen. NEVER GET
IMMERSION OIL ON ANY OTHER LENS EXCEPT 100X. Always wipe ALL
the oil off the 100X lens immediately after use, for if the oil dries on the lens, it
can ruin it.
GENERAL CARE
1. The microscope is a precision instrument. Carry the microscope carefully, avoiding
any bumping or jostling that may knock it out of alignment.
2. Keep the microscope dusted and the optics clean.
3. At the completion of the laboratory or study session, turn the lamp off, place the 4X
objective in position, lower the stage with the coarse adjustment knob, move the
mechanical stage clamp to the extreme left position, and replace the microscope dust
cover.
4. Inform an instructor if your microscope is not working properly. Do not attempt
repairs yourself.
Live Specimens
1.
2.
3.
4.
5.
To make a wet mount, first obtain a clean microscope slide. Using your
disposable Pasteur pipette, obtain a drop of aquarium water from the bottom of
the container. If you get the drop directly off the bottom you have a better chance
of finding live specimens.
Place a drop of water/specimen on your glass slide. Gently place a cover slip over
the water/specimen.
Start at 4X and try and locate a living specimen. Carefully scan the entire slide.
When you find a specimen, draw a picture and label as many parts as possible.
For each organism you find, write what environment (water source you found it
in), some descriptive characteristics, how does it move and anything else you find
interesting.
Repeat for the other water/specimens.
If you find more than 4, you can draw them and describe them on separate paper.
Draw a specimen here: Write descriptions/ water source and locomotion next to the
drawing.
Draw a specimen here: Write descriptions/ water source and locomotion next to the
drawing.
Draw a specimen here: Write descriptions/ water source and locomotion next to the
drawing.
Draw a specimen here: Write descriptions/ water source and locomotion next to the
drawing.