Calculating the magnification of a microscope:
Total magnification = magnification of eyepiece x magnification of objective lens

2) Measuring the microscope field of view on lowest power:
Place a clear plastic ruler with mm markings on top of the stage of your microscope. Looking through the lowest power objective, focus your image. Count how many divisions of the ruler fit across the diameter of the field of view. Multiply the number of divisions by 1000 to obtain the field of view in micrometers (µm).
Record this in µm (1mm = 1000 µm ).
Magnified at 40X, the lines of the ruler are clearly visible. However, in order to accurately measure the field of view, one line should be moved to the edge of the field of view, as shown in the image to the right.
Now that one of the lines has been moved to the extreme left, it is easier to determine the field of view:
2 mm x 1000 = 2000 µm
(image @ 40X)
In this example, the field of view would be calculated:
3 mm x 1000 = 3000 µm
3) Calculating the microscope field of view on other powers: i. Using the above procedure, determine the field of view in micrometers (µm) for the lowest power on your microscope. ii. After you have determined the field of view for low power, use the equation below to mathematically calculate the field of view on higher powers:

Microscope Calculations – Practice Questions
Using the formulas you have just learned, complete each of the following questions. You may return to the lesson, which includes the formulas, by minimizing or closing this browser window at any time.
1. A microscope has an eyepiece lens with a power of 5X. The objective lens being used has a power of 10X.
Total magnification =
2. A microscope has an eyepiece lens with a power of 15X. The objective lens being used has a power of 40X
Total magnification =
3. A microscope has an eyepiece lens with a power of 10X. The objective lens being used has a power of 10X.
Total magnification =
4. Sue observes a clear plastic, millimeter ruler under low power of her microscope. She sees three divisions of the ruler.
What would be the field diameter of Sue’s microscope on low power? (in micrometers ('µm')
5.
Convert each of the following to micrometers ( µ m).
a) 3.5mm
b) 4.0mm
c) 1.5 cm d) 0.5 cm
6.
The following information is for a microscope which has an eyepiece lens (ocular lens) with a power of 10X:
Objective Lens low medium high
Power
4X
10X
40X
Field Diameter
3500 µm
?
?
Using the information provided above, calculate the field diameter for medium and high power.