CYTOLOGY LAB ACTIVITY
PART I
THE LIGHT MICROSCOPE
PURPOSE
To acquaint with the features and procedures to ensure proper care of the microscope.
PRE-LAB
Microscopes are precision instruments and expensive. As such, they demand proper use and care from
students so that they can be utilized for many years.
WHAT WE NEED TO DO.





Always carry the microscope with two hands; one holding the arm and the other under the base.
When preparing to view specimens under the microscope, set it on the bench with the arm
closest to you.
If the eyepiece needs cleaning, use lens paper and not a paper towel.
Whenever you are viewing with the medium or high-power objective lens, NEVER use the
coarse adjustment knob while focusing.
When you are finished with the microscope:
o Make sure that the lowest objective lens is in place
o Remove the slide from the stage and clean stage if necessary
o Wrap cord around base of microscope (if it has a cord).
o Properly return microscope to its storage area
MATERIALS



Light microscope
Microscope slide
Cover slip
PROCEDURE
A. Obtain a microscope from your teacher. Carry it to your desk properly. Label the parts of the
microscope using the diagram on the next page.
The Compound Light Microscope
B. Clearly indicate the location of the following microscope parts as well as their functions.
Microscope Part
Location
Function
Ocular lens
Revolving Nosepiece
Objective Lens
Arm
Diaphragm
Coarse Adjustment Knob
Condenser Lens
Fine Adjustment Knob
The total magnification obtained by the microscope is the product of the ocular power and the objective lens
power. The total magnification is recorded as a number followed by the magnification symbol (I.e. 150X).
C. Calculate the total magnification for each of your objective lenses in the chart below:
Ocular Power
Objective Lens Power
Total Magnification
D. One of the safety rules is to always store microscopes with the lower power objective lens in position over
the stage. Why would this be considered to be good practice?
CYTOLOGY LAB ACITIVITY
PART II
THE MICROSCOPE AS AN INSTRUMENT
PURPOSE
To acquaint you with the capabilities of the microscope as an instrument.
MATERIALS



Light microscope
Microscope slide
Cover slips
Acetate ruler
Scissors
Coloured hairs
Coloured photograph
Coloured pencils
PROCEDURES
Part 1:
Depth of field

Obtain a slide and cover slip and prepare a dry microscope mount by making an X from two different
coloured hairs about 1 or 2 cm in length. Note the colour of the hair on the top.

Place the dry mount on the stage with the low-power objective lens in position and the hairs directly over
the hole in the stage.

Use the course-adjustment knob to raise the stage until it is about 0.5cm from the objective lens.

Look through the ocular with one eye. Keep the other eye open as well and eventually you should see a
circular “field of view” while looking through the ocular, slowly rotate the course-adjustment knob until
the hairs come into focus. Use the fine-focusing knob to focus on the upper hair.

Rotate the revolving nosepiece so that the medium-power objective lens is in position. Use only the finefocusing knob to clarify the image. Centre the slide and adjust the diaphragm for proper light intensity.

Slowly rotate the high-power objective lens into position. It should not strike the slide if you were
focused under medium-power. Use only the fine-focusing knob, centre and focus the image.
1.
What happened to the diameter of the field of view as you switched from low to medium to highpower?
2.
In terms of the field of view, why is it better to start the focusing procedure with the low-power?
3.
Why did you only use the fine-focusing knob to focus the image when the high-power objective lens was
in place?
While under high-power, use the fine focusing knob to move the focus on the upper hair and then the lower hair at
their crossing point. Switch to the other two objective lenses, focus back and forth between the hairs in the same
manner.
DEPTH- OF- FIELD is a term used to describe what lies in focus. If the top hair is in focus, while the lower hair
is out of focus then we have a shallow depth of field. If both hairs are in focus at the same time then we have lots
of depth of field.
4.
Which of the objective lenses exhibits the most depth of field? The least?
Thus, when you view a three dimensional object such as a cell under the microscope, you have the capability to
focus anywhere down through the cell to observe the different levels.
Part 2: Resolution
Prepare a dry mount of a piece of coloured photograph from a magazine. Do not use a primary colour. Observe
the photograph under the three powers of the microscope.
5.
With coloured pencils sketch what you observe under each power:
Low-power
Medium-power
High-power
You should have observed that the magnification increases, you were able to distinguish more and more detail.
This phenomenon is called resolution, the ability to distinguish two points as being separated. Resolution is
determined by the wavelength of the illuminating light. The shorter the wavelength the better the resolution.
6.
Some microscopes are equipped with filters on their light source. What colour is this filter?
7.
Predict whether blue or red light (opposite ends of visible spectrum) has the shorter wavelength.
Part 3:
Diameter of Field of View
The circular area that you see when you look through the ocular is the field of view. Under low- power, view an
acetate ruler on a clean slide or use the inbuilt ruler.
8.
Measure the diameter of the low-power field of view to the nearest tenth of a millimeter and determine its
equivalent in micrometers.
Diameter of low-power field of view ______________________ mm
1 mm = 1000 µm (micrometers)
Diameter of low-power field of view ______________________ µm
9.
Use the same procedure to measure the diameter of the high-power field of view.
10.
Do you feel confident in your measurement of the high-power field of view? Why or why not?
11.
If you know the diameter of the low-power field of view you can calculate the diameter of the high-power
field of view mathematically. This will give you more accuracy than trying to measure the diameter of the
high power field of view with a ruler.
Diameter of low-power field of view
_______________________ µm
Magnification number of low-power objective lens
Magnification number of high-power objective lens
Magnification number of high-power objective lens
Ratio quotient = -------------------------------------------------------------Magnification number of low-power objective lens
Low-power field diameter
Diameter of high-power field of view = -------------------------------Ratio quotient
________________ =
___________________ µm
Part 4:
12.
Estimating Size Under the Microscope
Determine the diameter of the medium-power field of view in both micrometers (µm) and millimeters
(mm) without using the acetate ruler. (Hint: you need to know the measurement of the diameter of the
low-power field of view. (Show your work).
Prepare a dry mount of a human hair and focus it under medium-power of your microscope.
13.
Sketch the field-of-view and the relative size of the hair in the space below.
14.
Estimate the number of times the width of the hair will fit across the diameter of the field-of-view. (This
is called the “fit” number).
If the diameter of the medium-power field-of-view (determined in # 12) is divided by the “fit” number then this
will give you the approximate size of the width of the hair.
15.
What is the estimated width of the hair in micrometers? (Show your work).
Now, use the high-power and repeat the procedure outlined in # 12 – 14.
16.
What is the estimated width of the hair in micrometers under the high-power? (Show your work).
17.
The hair is the same. How do the value of the width of hair compare when determined under different
objective lenses?
Objective Lens
Hair Width (µm)
Medium
High
18.
Which estimate value (medium or high power) do you feel is more accurate? Why?