### Calculating the Diameter of the Field of
View

One part of our exercise involves the direct measurement
of the diameter of the field of view using a clear ruler at 40x and 100x.
Because the working distance of the 40x objective is shorter than the thickness
of that ruler, the diameter at 400x cannot be directly measured. To determine
this value an equation is given in the manual that requires the use of the
measured value of the diameter at one of the other magnifications.

While memorizing this equation is not important, understanding
how it is derived is easy and will reinforce your understanding of the relationship
between the diameter of the field of view and the total magnification.

The relationship between the diameter of the field of view
and the magnification is **inversely** proportional: mathmatically it
can be expressed as

Now by simply multiplying both side of the equation by
the diameter of magnification "A" we arrive at the equation given
in your lab manual

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