1X Total Mag.
40X Total Mag.
4X Objective
2

x
x
1X Total Mag.
400X Total Mag.
40X Objective
3

Working distance is the distance between the tip of the objective and the specimen.
4
]
Working Distance [

Resolution is the ability to distinguish between two points that are close together.
Good resolution depends on both magnification and lens quality.
Low Magnification
High Magnification
Higher Resolution of individual legs
5

40X Magnification
Poor Quality Lens
40X Magnification
High Quality Lens
Better Resolution
6



The field of view is the circular area that is visible when you look through the microscope.
Because the size of objects is different at each magnification, you have to calculate the diameters of the fields of view at each magnification
 this is also called “calibrating your microscope”
40x
100x
400x

 As you change from the low power objective to the high power objective, the field of view changes.
 As the magnification increases, the area that you are viewing decreases. Magnification is inversely proportional to field of view
 In order to determine the size of the object that you are viewing, you need to understand the scale that corresponds to the magnification you are using.

 Copy the table in your science notebook.
Eyepiece
Magnification
Objective
Magnification
Total
Magnification
Field of
View width
–diameter
(mm)
Field of
View width
- diameter
(µm)
10x
10x
10x
 You will need this table to estimate the size of the cells that you will be viewing in the next activities.

Measuring Field of View width for the low power objective (4X)


Using the low power objective (4x), focus on a clear millimeter ruler

Count the number of lines that you see in the field of view. (The distance from the center of one line to the center of the next line is 1mm.)

This is the diameter of the field of view for the scanning objective.

Field of
View

Low Magnification
Large FOV
High Magnification
Small FOV
As you increase magnification, you see less but in more detail.

Measure field of view with low magnification.
Field of View is about 2.5 mm diameter at 40X total magnification.
14

FOV low mag.
X Mag. low
= FOV high mag.
X Mag. high
2.5 mm X 4X = FOV high mag.
X 100X
0.1 mm = FOV high mag.
For example, if the FOV diameter is 2.5 mm at 4X, then at 100X the FOV diameter is 0.1 mm.
15

Calculating the Field of View Width – Low Power decreases

Calculating Field of View Width – High Power
 decreases

 Finally, fill in the table you created earlier today.
Eyepiece
Magnification
10x
10x
10x
Objective
Magnification
4x
10x
40x
Total Magnification
Field of View width
–diameter (mm)
Field of view width diameter (µm
40 x
100x
400x
1.8 mm
0.45 mm
2.2 mm
0.9 mm
0.2225 mm
 In your notebook, answer the following: How can you use this table to estimate the size of cells that you view?

 ocular power = 10x low power objective = 20x high power objective = 50x a) What is the highest magnification you could get using this microscope ? b) If the diameter of the low power field is 2 mm, what is the diameter of the high power field of view in mm? in micrometers ? c) If 10 cells can fit end to end in the low power field of view, how many of those cells would you see under high power ?

 ocular power = 10x low power objective = 20x high power objective = 50x a) What is the highest magnification you could get using this microscope ? 500x
Ocular x high power = 10 x 50 = 500. (We can only use 2 lenses at a time, not all three.) b) If the diameter of the low power field is 2 mm, what is the diameter of the high power field of view in mm ? .8 mm
The ratio of low to high power is 20/50. So at high power you will see 2/5 of the low power field of view (2 mm). 2/5 x 2 = 4/5 = .8 mm in micrometers ? 800 micrometers
To convert mm to micrometers, move the decimal 3 places to the right (multiply by
1000). .8 mm x 1000 = 800 micrometers c) If 10 cells can fit end to end in the low power field of view, how many of those cells would you see under high power ? 4 cells.
We can answer this question the same way we go about "b" above. At high power we would see 2/5 of the low field. 2/5 x 10 cells = 4 cells would be seen under high power.