Biology
Topic 2 ­ Magnification, Resolution and Field of View
Student Reference 8: pg. 478 ­ 481
1. What is meant by the word magnification? An increase in the apparent size of an object.
2.
How do you find the total magnification of a microscope?
Multiply the magnifying powers of the objective lens and the eyepiece.
3.
Complete the following table:
Ocular Lens Magnification
Objective Lens Magnification
Total Magnification
10X
4X
40X
10X
10X
100X
40X
10X
400X
20X
40X
800X
10X
4 X
40X
10X
80X
800X
30X
40X
1200X
4. What is resolution? (pg. 255)
The ability to distinguish between two structures that are close together. 5. What is field of view (f.o.v.)? (pg. 478­479)
The area that can be seen through the microscope with a given objective lens.
6. Does field of view vary with different objective lenses, if so, why?
Yes, certain objective lenses magnify more so they are looking at a smaller area.
7. Determine field of view, in micrometers, for each magnification.
f.o.v. = 4000 um
f.o.v. = 2000 um
f.o.v. = 1000 um
8. Why is stain sometimes used when preparing specimens for viewing under magnification? What are names of two common stains?
Stains make it easier to distinguish between different parts of cells. Two common stains are iodine and methylene blue.
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Estimating Specimen Size: (pg. 481)
The sizes of various specimens that you will be looking at in the field of view of a microscope can be estimated quite accurately by following the steps below:
1. Determine the field of view in micrometers. The sizes that we determine will be the same for each of the objective lenses (low, medium, high)
2. Count the number of objects that can fit across the field of view (estimation).
3. Divide the field diameter by the number of objects estimated to fit across the field.
Use this simple formula:
Actual size of object = field diameter (um) . Counted # of objects to fit across field
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