Name: ___________________
USING THE MICROSCOPE
Part 1 – Determining Magnification of the Microscope
Magnification = ocular x objective
1. Find the total magnification of your microscope by filling in the chart below.
Magnification
of Ocular
Magnification
of Objective
Total
Magnification
Low Power
Medium Power
High Power
Part 2 – Determining Field of View (fov)
The diameter of the field of view can be used to estimate the actual size of objects seen through the
microscope.
1. Obtain a microscope and place a transparent ruler on the stage.
2. Observe the ruler under low power. Focus on the millimeter marks of the ruler. Move the ruler so
that one of the millimeter marks is on the left edge of the field of view.
3. Measure the diameter of the low power field to the nearest tenth of a millimeter. Record this
information in the chart below.
4. Use the ratio below to calculate the diameter of the high and medium power fields.
high power field diameter
low power field diameter
low power magnification
high power magnification
Record this information in the chart. Also record the field diameter in micrometers (u).
1 mm = 1000 u. Since microscopic organisms are very small, they are usually measured in micrometers.
Objectives
Field
Magnification
Field Diameter
in mm
Field Diameter
in um
Low Power
Medium Power
High Power
5. Compare the brightness of the field of view under low power and high power.
__________________________________________________________________________
__________________________________________________________________________
6. How many times is magnification increased when you change from low to high power?
__________________________________________________________________________
Part 3 – Estimating an Object’s Size
Estimate the size of an object you view under the microscope by comparing it to the diameter of the field of
view. For example, of an organism takes up one-half of a field of view that is 500 um in diameter, then its
size is one-half of 500 um, or 250 um.
1. Prepare a wet mount of a letter e.
2. Secure the slide on the stage with the clips and view under the low power objective. Focus on the
letter e using the coarse adjustment, then the fine adjustment.
3. a) Move the slide to the left, then to the right. Now move it towards you and then away from you.
Notice the direction in which the image moves.
b) How does an object’s image move in relation to the direction the slide is moved?
_____________________________________________
_____________________________
__________________________________________________________________________
c) How is the letter e seen through the microscope compared to the slide?
4. Draw a diagram of the letter e under low power and high power. When you switch to high power
remember to use the fine adjustment only.
Low Power
High Power
Estimate the size (width) of the letter e: _________________ mm; ________________um
5. Calculate the size of the letter e. Dividing the field diameter by the “fit” number (the number of
times the structure appears to fit across the field of view.
Estimate size = field diameter
“fit” number
6. Fit number: ____________; Estimated size of letter e: _________________um
7. Is it easier to locate objects under low or high power? Explain. ________________________
___________________________________________________________________________
___________________________________________________________________________
8. Approximately 400 bacteria fit across the filed of view of a low power lens. What is the estimated
size of one bacterium?
9. Approximately 6 paramecia fit across the high-power field of view. What is the size of one
paramecium?
10. If 16 organisms for across a low-power field of view whose field diameter is 4800 um, what is the
approximate size of each organism?
Part 4: Calculating the Magnification of a Drawing
The drawing you make of an object is usually much larger than the objects actual size.
It is important to indicate the difference on biological drawings.
The magnification of a drawing is calculated as follows:
Magnification = Size of drawing of object
Objects actual size
* Make sure you stay consistent with your units (either mm or um)
The magnification number should appear immediately following the title of the drawing.
E.g. Human Liver Cell (3000X)
1. Use your drawing of the letter e under low power from part 3 to calculate the magnification.
Actual size of letter e: _______________
Size of drawing:
_______________
Magnification:
_______________
2. To further indicate the size of a specimen compared to the drawing a scale bar is often used.
To convert magnification into scale bars, remember what magnification means. If the magnification
is 200X, it means that 200 cm on the picture would really be 1 cm. So if you draw a scale bar of 1
cm, you should label it 1/200 = 50 um.
Drawings of biological specimens should include a scale bar to indicate the actual size of the
specimen.