Review: Care and Use of the Compound Microscope
Objectives – After completing this review students should be able to:
1. properly clean and carry a microscope.
2. view a specimen using all dry objectives of a compound microscope.
3. identify the major parts of the compound microscope and explain the function of each part.
4. adjust the diopters to fit one's own eyes such that both eyes can be used simultaneously.
5. prepare and view wet mounts using the compound microscope.
Introduction
During this course you will frequently need to view biological structures and organisms too small to
be seen by the unaided eye. Thus, your success in this class requires that you be able to correctly and
efficiently operate a microscope.
Care and Cleaning of the Compound Binocular Microscope
All microscopes are delicate precision instruments. They must be correctly handled and well cared
for to remain functional.
You should always:
1) Use two hands to lift and carry the microscope - one on the arm and one under the base;
2) Set the microscope down gently to avoid knocking it out of alignment;
3) Place the microscope directly in front of you so that you do not have to lean to use it;
3) Clean the lenses with lens paper and lens cleaning fluid ONLY!
4) Replace the dust cover when you are finished.
You must never:
1) Never wrap the electrical cord around any part of the microscope;
2) Never use the Coarse Focus knob with a high magnification lens;
3) Never use Kimwipes, paper towels or other scratchy materials to clean the lenses.
Re-Identify these Parts of the Compound Binocular Microscope
1. The light source. If this has a variable control, it is used to control the brightness of the light. The
ideal brightness for many slides is about 75% of maximum - not 100%! Turning the light intensity to
maximum is usually like looking directly into a light bulb at close range.
2. The iris diaphragm and the delicate arm which controls its aperture. This allows you to control the
resolution by controlling the angle of the cone of light that is reaching the specimen. It is only used to
control brightness when there is no other option. The ideal setting for this is different for each slide and
magnification - get in the habit of adjusting the setting until you can clearly see details of your specimen.
3. The condenser lens. The condenser should be racked up as far as it will go and left there, unless your
instructor tell you otherwise. Learn to distinguish, by feel, the condenser knob and the focusing knobs.
This will ensure that you are not moving the condenser when you should be adjusting the focus.
4. The mechanical stage rests atop the stage. Nothing should ever be forced between the arms and the
1
stage. When inserting a slide, be sure it is tucked into the corner, then slowly lower the curved arm to
avoid chipping the slide.
5. The coarse and fine adjustment knobs are on the arm, behind the stage. The coarse adjustment
knob moves the stage a large distance with a single turn and thus should be used only with 4X and 10X
objectives. It is NEVER used with the 40X and 100X objectives as it can easily damage the objectives
and /or break the slide.
6. The rotating nose piece has four objective lenses. The magnification of each lens is marked on it note that the higher the magnification, the longer the lens. Generally, 4X is referred to as the scanning
lens and 40X as the high power or high-dry lens. The 100X is an oil immersion lens - do not use this
unless instructed to do so.
7. Each ocular can be independently focused. The distance between them can also be adjusted to
precisely suit your eyes. Instructions for this are given below and should be followed at the start of every
session with the microscope.
Calibration of the Binocular Compound Microscope
1. Focus, using the 10X objective, on a specimen.
2. Adjust the eyepieces by looking through the oculars and slide them towards or away from each other
until you see one image. Write that number here:
3. Adjust the focus point of the ocular on the right eyepiece to correspond to the number written in the
above blank by turning the ring at the base of the ocular until the white scale is set to that number. Close
your left eye and look through your right eyepiece. Bring the specimen into crisp focus using the fine
focus knob.
4. Close your right eye and look through the left eyepiece. Do not focus with the fine focus. Instead,
focus the specimen by turning the ring at the base of the left ocular. Once you have it in crisp focus,
double check that each eye is seeing an equally well-focused image and that both eyes can be used
simultaneously. If not, repeat these steps.
Viewing a Specimen
1. Set up the microscope for correct use, making sure to always begin with the 4X scanning lens.
2. Place a slide correctly in the mechanical stage. Use the mechanical stage control knobs to center the
specimen over the condenser lens.
3. Use the coarse focus knob to move the stage and 4X objective lens as close together as possible. Look
through the oculars as you slowly turn the coarse focus knob the opposite direction until the specimen
pops into focus. This should be about a half-turn.
4. Adjust the iris diaphragm aperture until you can see the specimen in maximum detail.
5. Use the mechanical stage to scan the specimen. Then, move an area of interest into the center of the
2
field of view.
6. Increase magnification to 100X by rotating the next objective lens in sequence (10X) into position
over the stage. Be sure that it 'clicks' into position. The portion of the specimen that was in the center of
the field of view will still be in the center - you need only adjust the fine focus and the iris diaphragm
aperture.
7. Use the same techniques to increase magnification to 400X. Remember to adjust the fine focus, light
intensity and iris diaphragm setting to achieve an optimal view of the specimen.
Note 1: The 40X lens should have about 1 mm of clearance between it and the slide when it is rotated
into position. If it appears that it will touch, just move slowly to prevent damage. If it actually does
touch, ask your instructor for assistance.
Note 2: Your microscope is parfocal - this means that if one objective lens is in focus, they all are, or are
quite close to, in focus. Thus, to increase magnification, you need only center the specimen, focus on it,
rotate the next objective lens into position, and touch up the focus with the fine focus knob. It is
unnecessary, counter-productive and very poor technique to lower the stage, increase magnification
and then attempt to re-locate the plane of focus.
Preparing wet mount slides
1. Clean blank slides and cover slips are located in boxes on your lab table. After use, the slide should be
cleaned with tapwater and a paper towel and returned to the box. The cover slip may be carefully cleaned
in the same fashion and re-used, but at the end of the lab period it is to be discarded in the broken glass
container.
2. Place a drop of water on the center of the slide, add a tiny bit of material (if it is not already in the
water) and add the cover slip.
Technique hints:
1) To prevent air bubbles, slant the cover slip as you apply it.
2) Gently press on the cover slip with a non-marking object remove air bubbles.
3) If you are looking for bacteria or other very tiny organisms, be sure you do have an air bubble. It
is quick and easy to focus on the edge of the air bubble and then look in the liquid outside of it for
your organism.
4) If the cover slip falls off when you turn the slide upside down, you used too much water.
5) Be sure the bottom of the slide and top of the cover slip are dry before you place it on the stage.
6) Avoid getting fingerprints on the cover slip or center of the slide. They will interfere with your
view of the organism.
Note: You will occasionally need to use a depression slide. These are thicker than normal and have a
well in the center. They are used with large organisms - those that will be crushed by the cover slip on a
regular flat slide. Your instructor will tell you when use of these slides is required.
3