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Background:
The eyepiece (including for the camera) on the digital microscope magnifies objects 10 times. Each lens then further magnifies
the objects: 4X (or 4 times magnification), 10X, and 40X, as marked on the lens used. These magnification numbers combine to
give the actual magnification of the object. For example, using the eyepiece plus the 4X lens, the magnification is 10 x 4 or 40
times or 40X. Any object viewed this way will appear 40 times its actual size.
Also, as the magnification increases, the field of view, or total area that can be seen, decreases. At 40X, the field of view is a circle
about 4.5 mm in diameter. The change in the field of view is inversely proportional to the magnification increase. It's like zooming
in: the closer you go, the less area you see.
4.5 mm x 40 / ___ = ___
For example, the field of view at 100X is:
4.5 mm x 40 / 100 = 1.8 mm
Notes:
In this activity, students make physical models of the salt crystals at the various magnifications. Table salt is approximately
0.3 millimeters on each side, so a 40X salt crystal model would be about 0.3 x 40, or 1.2 cm in each dimension..
Under a microscope, things typically look only two dimensional, but it is important for your students to understand that—
just like the salt crystals look like squares, while they are actually cubes—other items viewed under a microscope are also
(typically) three dimensional.
* Making an actual clay model of this is obviously not practical. Even for the 400X model, you might want to simply have a few
examples available for your class.
Understanding Magnification and Scale (continued)
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Eyepiece Magnification 10X 10X 10X 10X
Lens Magnification 4X 10X 40X 100X
Total Magnification 40X 100X 400X 1000X
Total Magnification 40X 100X 400X 1000X
Field of View 4.5 mm 1.8 mm 0.45 mm 0.18 mm
Actual 40X model 100X model 400X model 1000X model
0.3 mm 1.2 cm 3 cm 12 cm 30 cm*
