Diopter and magnification relationship Definitions:
Diopter (d): A term used to identify the refractive (light bending) capacity of a lens. In magnifiers, there is a direct correlation between focal length and diopter. To find the diopter of a magnification lens, follow these steps. With the eyes 10″ above the lens, move the object to be viewed to the point the greatest distance below the lens where it remains in sharp focus.

Measure this distance and divide into 1 meter (39.37″). The result is the diopter of the lens – e.g., if the object is at a 13″ distance than it is a 3-diopter lens (39.37/13 = 3d). Each diopter increases the size of the viewed object by 1/4 (25%) when the object is at its full focal length from the lens.

Field of View: The distance across the lens surface to which the viewer brings both his eyes (note: eyes should be 10″ above the lens). It is important to note that as magnification increases, meaning the lenses used are stronger, viewing areas and focal length decrease.

Magnification: The degree to which the viewed object is enlarged. Magnification is usually expressed by a number followed by an “x”, the symbol used to express power or the size of the object in relationship to its actual size.

Diopter indicates the amount of curvature of a lens. The thicker the lens, the bigger the curvature.
To find the approximate magnification level of a lens, divide its diopter by 4, and add 1.
The equation is:
Magnification = Diopter ÷ 4 + 1

Diopter and Magnification for example:
For a 3-diopter lens of a magnifier, its magnification = ¾ + 1 or 0.75 + 1 = 1.75x. Objects viewed under a 3 diopter lens will appear 1.75X larger than normal.
For a 5-diopter lens of a magnifier, its magnification = 5/4 + 1 or 1.25 + 1 = 2.25x. Objects viewed under a 5 diopter lens will appear 2.25X larger than normal.
For a 8-diopter lens of a magnifier, its magnification = 8/4 + 1 or 2 + 1 = 3x. Objects viewed under a 8 diopter lens will appear 3X larger than normal.

Use this chart to convert diopters to magnification simply.

###### Diopter and Magnification

2                  1.5X
3                  1.75X
4                  2X
5                 2.25X
7                 2.75X
8                3X
9                3.25X
11               3.75X
13              4.25X

for magnifying lamp magnification, some time marks 3X or 8D is same, that is the diopter and magnification relationship especially at the field of magnifying lamp

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