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Measuring magnification
#1
How to Measure magnification
How can I see how strong a magnifying glass is?


I bought this magnifying glass <!-- m --><a class="postlink" href="http://www.liangdianup.com/inventory/189901.htm">http://www.liangdianup.com/inventory/189901.htm</a><!-- m --> and I want

to know how to test it to see how strong it is. I hear a lot of people talk about

magnifying and how strong the magnification is, but I would like to know the true

magnification of my magnifying glass. I have a few of them and some seem stronger then

others. How can I rate these? How can I pin a correct number on mine? How do the companies

that make these come up with these numbers.
Reply
#2
Dear Green,

Subject: The Power of a lens.

What you show here are "plus" lenses. The best term to use is "Diopters" to describe them.
The "power" is calculated once you know the diopter value of the lens.

If you wish to personally verify the "diopter power" of the lens -- do this.

Take the lens outside in sun light.

Hold the lens above a paper.

Move the lens up or down until the Sun is focused on the paper (smallest image).

Measure the distance between paper an lens.

For example

If the image forms at 20 inches, the power in diopters is 40/20
or 2 diopters.

In cm this would be 50 cm, and the calculation would be 1/0.5 = 2 diopters.

If the image formed at 1 meter (a weak lens), then it would be 1 / 1 = 1 diopter.

The lenses you presented would be in this range.

Best,

Otis
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