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Magnification-Principles
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As a rough and ready guide
- the larger the physical size of the magnifier, the lower the
magnification.
- the higher the magnification, the smaller the field of view, as
below.
It is generally easiest to use the magnifier that is the weakest
that you can see with, as more words can be seen at one time, and reading is much easier.
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With low magnification there is a large field of view, and many words can be
seen at the same time. The lens tends to be larger.
With more magnification, fewer words
can be be seen at once. The lens tends to be smaller.
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Field of view with high and low
power magnifying glasses
With most magnifiers the field of view, can be made wider
…seeing more letters for instance…. by holding the object or book closer. This
can make your arms or neck ache.
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Holding things close
to read can be awkward and tiring, especially if a magnifying glass is needed, but more
words come into view.
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It is often more
comfortable holding the magnifying glass further away, even if fewer words are seen.
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Contrast is important to aid reading: black print on
white paper maximises contrast to make reading as easy as possible. This is shown below.
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| print not dark enough |
paper too dark |
maximum
contrast |
maximum contrast |
| In the kitchen good lighting and
large labels, black on white or white on black, on jars for instance can make cooking
easier. |
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Reading with a good light helps. the light needs a reflector so the
light shines on the book, not into your eyes.
A strong light on the ceiling is not particularly helpful. A light
with a reflector, angled on to the book is much more helpful.
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Magnifiers, often called magnifying glasses, fall into several
categories. They can be either
1. Spectacle mounted
2. Held in the hand
3. Hung around the neck so the hands are free.
They can have a light inside or on the outside; some are provided
with a stand to keep the magnifier still to help produce a large still image.
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| Use the good eye With
more magnification it becomes impossible to use both eyes together because the nose gets
in the way.
Therefore with more magnification, the lens is put in front of the best eye. When both
eyes are used the object is held in front of the nose. But if you use the right eye only
for instance, hold the the object directly in front of the right eye.
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| Is it tiring? Holding
a book or sewing 5-6" (15cm) away from the eyes becomes extremely tiring. If you use
a "ribbon sling" your hands care supported and it can be more comfortable. This
is a piece of ribbon that is tied in a loop.
The loop of ribbon is then placed around the neck, and each hand is threaded through
the loops. This takes the weight of the arms and and keeps the right working
distance. You need to experiment to find the correct length of ribbon.
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