The Best Tool to Carry is a Magnifier
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KEY POINTS:
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Note: This
tip sheet is for general guidance only. Contact your County
Extension agent or land grant university for additional information
on using magnifiers in an IPM program. |
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Why
use a magnifier?
Visually inspecting your plants on a regular basis is
an important component of an effective pest monitoring program.
Careful, systematic inspections will help keep track of the health
of your plants and identify any potential weed or pest problems.
A magnifier is an important part of visual inspection. Magnifiers
let you see small details that are helpful in identification of
weeds and pests.
How do magnifiers work?
Magnifiers work by bending light rays to produce an
image of the object that is larger than life. The more the surface
of the lens is curved, the more the light is bent and the greater
the magnification. The degree of magnification is then determined
by the curvature of the lens surface. Greater curvature limits
the lens size, which means that higher powered magnifiers are
going to be smaller.
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How
is magnification expressed?
Magnification is expressed as "x." A 20x magnifier
shows you an object 20 times larger than life. The lower the magnification,
the greater the "depth of field" and "field of view",
so be sure to choose the lowest magnification needed for your task.
For example, at 2x you may be able to see an entire insect clearly,
from the tips of its antennae down to its tarsi (toes). At 10x,
you'll see either antennae or tarsi in greater detail, but
not both at the same time.
10x or less is a good choice to start with for most pest scouting.
Once a pest is located, a larger power lens may come in handy.
With practice and increasing skill in scouting, you will eventually
want to equip yourself with a wider range of magnifiers to be
able to complete nearly all of your sampling and identification
tasks in the field.
| Magnification |
You
can . . . |
| 2 - 5x |
Scan large areas for insects, eggs, mites,
disease |
| 6 - 10x |
View details on larger insects and plant
parts |
| 11 - 25x |
Identify insects and some eggs and mites |
| 26 - 45x |
Identify small insects, eggs, mites and many
diseases |
| 46x + |
Identify most diseases, nematodes and other
organisms barely visible or invisible to the naked eye |
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| A 10x magnifier is a good starting point for most pest
scouting. As 10x, you'll see either antennae or tarsi in
detail, but you won't see both at the same time. |
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There are many forms of magnifiers; loupes, linen testers, watchmaker's
loupes, aspheric, lighted, folding pocket, etc. One style is
not necessarily better than another. It depends on the style
of magnifier you feel comfortable using.
What are the different
type of lens systems?
When using magnifiers, be aware of distortion, and chromatic
or spherical aberration errors that can occur. Distortion is
a defect in a lens where images of straight lines appear curved.
Chromatic aberration errors are when the lens cannot focus light
of different colors at a single point, causing a blue-red image.
Spherical aberration errors cause rays to focus at different
distances.
Different types of lens systems offer varying levels
of correction for these problems. The simplest type of lens is
the single aspheric lens. This lens is designed for small powered
magnification because it is one lens. The lens has a series of
different curves on the surface for sharper focus over the entire
surface.
Spaced Doublet is two lenses with air space
in between them. This lens system is inexpensive, but does not
offer much distortion or color correction.
Coddington Lens are made of a single lens
with a grooved diaphragm around the circumference. This groove
allows for sharp images at higher magnifications.
Cemented Triplet is the last type of lens,
also called a Hastings. The Hastings lens is three lenses
cemented together, providing the sharpest color-corrected image.
What is the proper way to use a magnifier?
To use a loupe, hold the lens close to your eye and move
the object you are looking at close until it's in focus.
For linen testers, simply place the magnifier on top of the object
and move your head closer to the lens for larger viewing.
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Spaced Doublet
(Double Lens Magnifier)
Achieves limited correction. Consists of 2 plano-convex
lenses with air space in between. |

Coddington
Single lens with a groove diaphragm around it's circumference.
The thickness of the lens aids correction. |

Cemented Triplet
(Hastings magnifier)
Two concave elements cemented to a double convex element.
Two kinds of glass are used. |
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| Dos
and Don'ts of Using Magnifiers |
Do:
- Use the proper technique in using a magnifier.
- Select the proper magnification for the job.
- Know how to select a lens system for your needs.
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Don't
- Think all lenses are the same.
- Only use the largest magnification.
- Forget to visually inspect your plants.
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Have you experienced headaches or eye strain after extensive
monitoring for small insects or plant diseases?
Does the use of a hand lens during scouting make it difficult
to manipulate samples with your hands?
Repetitive sampling and scouting are key components of IPM.
But juggling a hand lens in addition to a sample can be inconvenient
and time consuming. One solution that allows you the freedom
to work with your hands plus reduce eye strain is the OptiVisor® magnifier.
With a magnification power of 3.5x and a focal distance of four
inches, the OptiVisor® is a good tool for scanning large areas
for insects, eggs, mites and plant disease.
The OptiVisor® is mounted to an adjustable headband and can
be tilted up when you're not using it. An optional OptiLoupe,
an attachable lens that adds 2.5x power to one eye, is also available.
This combination creates a powerful monitoring tool. You can
scan large areas with the OptiVisor®, then swing the OptiLoupe
into place to "zoom in" when more detailed examination is necessary.
When selecting a magnifier, keep in mind that:
- Magnification power is described as "x". For example, the
OptiVisor® is rated at 3.5x. That lets you observe an object
3.5 times larger than life.
- Your viewing area decreases in size as magnification power
increases.
For more information on these products, please contact GEMPLER'S
Technical Service Department by phone at 1-800-874-4755, or E-mail
at techserv@gemplers.com.
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The
Opti-Visor® (Item No. R34101), a hands-free magnifier with
3.5x magnification power, is a good tool for scanning large areas
without getting eye strain. |
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