HOW TO DETERMINE MICROSCOPE FIELD DIAMETER
Teacher Directed Class Notes
Abbreviated Terms:
Low Power Magnification = LPM
Higher Power Magnification = HPM
Low Power Field Diameter = LPFD
Higher Power Field Diameter = HPFD
Formula to determine HPFD:
1. Determine the diameter in millimeters of the low-power field using a metric ruler.
2. Convert the diameter from millimeters to microns [1000 microns (µm) = 1 mm].
3. Use the equation below to determine the field diameter of higher magnifications.
High Power Field Diameter =
LPM x LPFD
HPM
Example: If a metric ruler placed under a 40X magnification shows a field diameter of 4 mm
or 4000 µm, then what is the field diameter for a magnification of 400X?
HPFD
=
HPFD
=
40X x 4000 µm
400X
400 µm
The graph below demonstrates the inverse relationship between field diameter and
magnification. The diagram on the right shows how an object viewed under a microscope
should be drawn in a lab write-up. The scale drawn is typically 1/4 the diameter of the field.
400X
Microscope Field Diameter as a Function of
Total Magnification
Field Diameter (microns)
4500
4000
3500
3000
2500
2000
1500
1000
500
100µm
0
0
100
200
300
400
500
600
700
800
Artemia
(brine shrimp)
Total Magnification
cm
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15