HOW TO DETERMINE
DRAWING MAGNIFICATION
1.
Measure your low power field of view using the mm scale on a clear ruler.
2.
Make note of Low, Medium and High power magnification.
3.
Calculate the field of view for medium and high power.
Example:
4.
Low
Medium
High
4x
10x
40x
FOV = 4.5 mm
FOV = 4.5 mm x (4/10) = 1.8 mm
FOV = 4.5 mm x (4/40) = 0.45 mm
Look at the specimen and estimate how many specimens
will fit across the diameter of the field.
Example: 6.5 specimens (widthwise) fit
across the HIGH power field
5.
Calculate the actual size of the specimen.
Actual Size =
AS = FOV
#cells
field of view
# of specimens across
Actual Size =
0.45 mm
6.5 specimens
= 0.069 mm
6.
Draw your specimen using the drawing rules.
7.
Measure your specimen drawing in mm. Use the same
dimension as used in estimating the number of specimens
across the field of view (i.e. width or length).
8.
Calculate the magnification of your drawing.
Drawing Magnification =
Drawing Measurement (mm)
Actual Size (mm)
DM = DS
AS
= 20mm ÷ 0.069mm
= 290 X
Drawing Magnification Problem Set
Unless stated otherwise, use a low power field of view of 4.2 mm.
1. A cell is observed to stretch half way across the high power field. How long is the cell?
2. Many ponds often have a green scum on the surface. This
scum is a tangled mass of stringy algae filaments. Looking at
a filament under high power shows four cells arranged end to
end across the field of view.
a. What is the diameter of the high power field of view in
millimeters?
b. How long is each cell approximately?
3. 15 cells are observed across the centre of the high power field. How long is each cell?
4. A cell is observed under high power to be about half the field diameter. A student draws the cell
25cm in length. What is the magnification of the drawing?
5. A student draws a cell diagram 24mm long. She writes 400X below the diagram. How large is the
actual cell?
6. A cell is 80 m in length. If drawn 600 times actual size, how long will the drawing be in cm?
7. 5 onion cells are counted across the centre of the high power field. One cell is drawn 18mm
long. Calculate the drawing magnification.
8. 40 potato cells are counted across the centre of the medium field of view. One cell is drawn
2cm long. What is the drawing magnification?
9. The diameter of a hair is estimated to be one tenth of the diameter of the medium power field. It is
drawn 4cm wide by a student. What is the drawing magnification?
10. Copy the chart and complete:
Drawing Size
10mm
Actual Size
100mm
Drawing Magnification
4mm
3X
10cm
25X
150mm
15mm
0.8cm
8mm
Drawing Magnification Problem Set Answers
ALL OF THE FOLLOWING USE A LOW POWER FOV = 4.2 mm
1. high power FOV = 0.42 mm
2. a. high power FOV = 0.42 mm

AS = 0.42 mm ÷ 2 = 0.21 mm
b. AS = 0.42 mm ÷ 4 = 0.105 mm
3. high power FOV = 0.42 mm  AS = 0.42 mm ÷ 15 = 0.028 mm
4. high power FOV = 0.42 mm  AS = 0.42 mm ÷ 2 = 0.21 mm 
DM = 250 mm ÷ 0.21mm = 1190 X
5.
DM = DS ÷ AS
400 X = 24 mm ÷ AS
AS = 24 mm ÷ 400
AS = 0.06 mm
6. AS = 80 micrometres = 80 x 10-6 metres = 80 x 10-4 centimetres = 8 x 10-3 cm
DM = DS ÷ AS
600 X = DS ÷ 8 x 10-3 cm
DS = (600)(8 x 10-3 cm)
DS = 4.8 cm
7. high power FOV = 0.42 mm  AS = 0.42 mm ÷ 5 = 0.084 mm 
DM = DS ÷ AS 
DM = 18 mm ÷ 0.084 mm = 214 X
8. low power FOV = 4.2 mm  medium power FOV = 4.2 mm (4/10) = 1.68 mm
AS = 1.68 mm ÷ 40 = 0.042 mm
DM = DS ÷ AS 
DM = 20 mm ÷ 0.042 mm = 476 X
9. medium power FOV = 4.2 mm (4/10) = 1.68 mm
AS = 1.68 mm ÷ 10 = 0.168 mm
DM = DS ÷ AS 
DM = 40 mm ÷ 0.168 mm = 238 X
10. DM = DS ÷ AS
Drawing Size
Actual Size
Drawing
Magnification
10mm
100mm
0.1X
12 mm
4mm
3X
10cm
0.4 cm
25X
150mm
15mm
10X
0.8cm
8mm
1X