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How To Select A Magnifier
Working with precision such as with jewelry routinely requires magnification for the best results. Maginification increases the visual size of the objects being studied. Magnification becomes critical because the ability for the eye to focus correctly diminishes at distances closer than 10" (254 mm.) Your selection of a good magnifier should provide increased focusing power and should result in the visual effect of a clearer, larger image of the object.
Look for the Four Characteristics Of a Good Magnifier
- The Power of Magnification
The ability of the lens should increase your visual size of an object. The symbol X (times) is used in identifying this factor. For example, a 2X magnifier will double the size of an image.
The light rays of a magnifier are bent by the curved lens surface. This results in an image that looks larger than the actual object.
- The Working Distance or Focal Length
As well as with power, a magnifier will be classified for working distance. For example, 2X at a working distance of 5" (127 mm.) The magnifier will provide double magnification and be in clear focus if held at a distance of 5" (127 mm) from the object.
In the amount of space between the object and the magnifier, the shorter the working distance, the higher the power will be.
- The Field of View
This is the size of the area that is seen through the magnifier. The field of view will decrease just as the power increases.
- The Depth of Field
This is the distance that a magnifier can be moved from an object yet still have the object in focus. The higher the power, the shorter the depth of field will be.
The Corrective Magnifiers
Some magnifiers will have lens systems which correct optical distortion of aberration that could otherwise be present as follows:
- Distortion
Uncorrected lens - "straight lines" will curve toward the center.
- Chromatic and Spherical Aberration
With uncorrected lens-size and shape differences there will be a pattern consisting of on size dot.
Common Terms When Selecting a Magnifier
Achromatic - Lens that will eliminate chromatic aberration.
Aplanatic - Lens that will correct for spherical aberration and coma.
Chromatic Aberration - The inability of a lens to focus light of different colors at a point.
Coma - A blurry appearance around an object viewed through uncorrected lens.
Corrected - A lens system that corrects for distortions and aberrations. Produces a
sharper image.
Spherical Aberration - A lens defect that produces an image that lacks contrast.
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