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    Using Microscopes—continued

    III. Determining the size of an object under the microscope

    The actual size of an object under the microscope can be determined by the strength of the lens through which the object is being viewed and the fraction of the field of view that the object occupies. This can be expressed with the following formula:

    Actual length
    of object (µm)
    = Fraction of field occupied by object x Diameter of object field (µm)

    Note: As the magnification of an object increases, the diameter of the field of view will proportionately decrease.

    For example, as magnification doubles, diameter of the field of view is halved. Therefore, as magnification increases, the object will occupy a proportionately greater area of the field of view.

    Low Power 40x

    Med. Power 100x

    High Power 400x

    Depth of field

    4500 µm

    1 800 µm

    ____ µm

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