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What is a Diopter


Magnifying Lights - Stereo Zoom Microscopes - Video Inspection Stations

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"
Dime 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.

We Guarantee the Lowest Prices!
Find a Better price on anything and we'll beat it. Call Now: 800-394-1984
We do our best to offer you the lowest prices on all of our products. If you find a better price on an identical item, we will beat it by 10% of the difference. Just give us a call. Or, place your order on our site at our existing price, send us an email with a link to the lower priced site and your order number and we'll refund the difference, plus 10%, back to your card! The item must be in-stock at the other location to get this discount!

Howard Electronic Instruments, Inc.
974 SE Pioneer Rd
El Dorado, KS 67042
1-800-394-1984 Toll Free (USA and Canada)
316-321-2800 Local
01-316-321-2800 International Phone
316-223-3111 NEW Fax Number
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Copyright 1996 - 2015 Howard Electronic Instruments, Inc. All rights reserved.
Current date CST: 09/01/2015

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