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 then 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. The formula for
calculation Magnification Power is:
| Common diopter/power relationships |
| Diopter |
Power |
% Bigger than object |
Focal Length |
| 3 |
1.75X |
75% |
13" |
| 4 |
2.00X |
100% |
10" |
| 5 |
2.25X |
125% |
8" |
| 7 |
2.75X |
175% |
5.5" |
| 8 |
3.00X |
200% |
5" |
| 9 |
3.25X |
225% |
4.5" |
| 11 |
3.75X |
275% |
3.75" |
| 13 |
4.25X |
325% |
3" |
| 16 |
5.00X |
400% |
2.5" |
| 18 |
5.50X |
450% |
2.25" |
| 20 |
6.00X |
500% |
2" |
 |
If a dime was this small unmagnified ...
3 diopter
5 diopter
10 diopter
15 diopter |
Selecting The Right Magnifier:
1. Determine the desired magnification for your needs. Remember, as you
increase magnification, you decrease both the focal length and the viewing
area.
2. Check to find out the correct diopter you need to achieve that
magnification.
3. Note the focal length and lens diameter that correspond to the
magnification and lens diopter you have chosen, and make sure they are
suitable for your task.
4. As a general rule, because the working distance will be less than 8"
above 5 diopter, stereo microscopes are recommended for rework purposes.
Tips on Proper use of a Magnifier
To take best advantage of the comforts built into
illuminated magnifiers, please keep these points in mind:
1. Use both eyes. Magnifiers are designed as "working tools". They can be
used as comfortably as a pair of glasses.
2. Position the lens so that it is a proper distance from the work area,
yet close enough for your eyes (8" to 10") so that you have the maximum
magnification without distortion. Do not lean back away from the lens to
increase magnification.
3. Chair height and work surface should be positioned so the operator can
maintain good posture while working.