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How To Select
Magnifiers
Precision work routinely requires magnification to increase
the visual size of objects. As the eye comes closer to an object, the apparent size
and detail is increased. However, the ability of the eye to focus correctly
diminishes at distances closer than 10" (254 mm). Use of a magnifier provides
increased focusing power, resulting in the visual effect of a clearer, larger image of the
object.
Four Characteristics Of Magnifiers
1) Power of Magnification - The ability of the
lens to increase the visual size of an object. The symbol X (times) is used to
identify this factor. For example, a 3X magnifier triples the size of an image.
2) Working Distance (Focal Length) - In
addition to power, a magnifier will also be classified for working distance. For
example, 2X at a working distance of 5" (127 mm), means that the magnifier will
provide double magnification and be in clear focus when held at a distance of 5" (127
mm) from the object.
3) Field of View - The size of the area that
is seen through the magnifier; the field of view decreases as the power increases.
4) Depth of Field - The distance that a
magnifier can be moved form an object and still have the object in focus; the higher the
power, the shorter the depth of field.
Corrective Magnifiers - Certain magnifiers
have lens systems which correct optical distortion of aberration that might otherwise be
present as follows:
Common Terms
Achromatic - Lens that
eliminates chromatic aberration.
Aplanatic - Lens that
corrects for spherical aberration and coma.
Chromatic Aberration -
Inability of a lens to focus light of different colors at a point.
Coma - Blurry appearance
around an object viewed through uncorrected lens.
Corrected - Lens system that
corrects for distortions and aberrations to produce a sharp image.
Spherical Aberration - Lens
defect that produces an image that lacks contrast.
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