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- Base, The base is
the foundation on which the
microscope stand is built. It
is important that the base is
relatively large, stable, and
massive. When you are setting
up a microscope for the first
time ensure that the surface
on which it is placed is
level.
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- Condenser, The
condenser under the stage
focuses the light on the
specimen, adjusts the amount
of light on the specimen, and
shapes the cone of light
entering the objective. One
way to think about the
condenser is as a light "pump"
that concentrates light onto
the specimen.
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- The condenser has an
iris diaphragm that
controls the angle of the beam
of light focused onto the
specimen. The iris diaphram is
an adjustable shutter which
allows you to adjust the
amount of light passing
through the condenser. The
angle determines the Numerical
Aperture (NA) of the
condenser. This diaphragm,
generally called the aperture
diaphragm, is one of the most
important controls on the
microscope.
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- Cover slip, Most
objectives are designed for
use with a cover slip between
the objective and the
specimen. The cover slip
becomes part of the optical
system, and its thickness is
critical for optimal
perfomance of the objective.
The cover slip thickness
designation on most objective
lenses is 0.17 mm or 170
microns.
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- Focus (coarse), The
coarse focus knob is
used to bring the specimen
into approximate or near
focus.
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- Focus (fine), Use
the fine focus knob to
sharpen the focus quality of
the image after it has been
brought into focus with the
coarse focus knob.
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- Illuminator, There
is an illuminator built into
the base of most microscopes.
The purpose of the illuminator
is to provide even, high
intensity light at the place
of the field aperture, so that
light can travel through the
condensor to the
specimen.
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- Magnification, The
degree to which the image of
the specimen is enlarged by
the objective. For example, 40
specifies 40 times (40x) the
actual size of the specimen.
As magnification increases,
resolution (NA) must also
increase so that more
information can be obtained.
Magnification without
increased resolution yields no
additional information and is
called "empty
magnification."
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- Numerical Aperture
(NA), The maximum angle
from which it can accept
light. Lenses that accept
light from higher angles have
greater resolving power, thus
NA defines resolving power.
The maximum NA of objectives
is 1.4, and it is limited by
the physics of light and the
refractive index of
glass.
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- Objective Lens, The
objective lens is the single
most important component of
the microscope. Together with
the condenser, it determines
the resolution that the
microscope's capability.
Learning how to use the
correct objective for a
particular application is a
prerequisite for good
microscopy.
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- Important information
describing the objective lens
is engraved on the side of its
barrel. This is the best
performance the objective is
capable of and it will only
yield this performance when
used properly.
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- Ocular Lenses, The
ocular lenses are the lens
closest to the eye and usually
have a 10x magnification.
Since light microscopes use
binocular lenses there is a
lens for each eye. It is
important to adjust the
distance between the
microscope oculars, so that it
matches your interpupillary
distance. This will yield
better image quality and
reduce eye strain.
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- Plan, There are
many different kinds of
objective lenses. Common
designations include "plan"
for flat field, "achromat" for
partially color-corrected, and
"apochromat" for highly color
corrected. These designations
may become combined as in
"plan achromat."
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- Parfocal, The
specimen is focused for all
objectives if it is focused
for one objective. In other
words, once the specimen is
focused under one objective it
will be in approximate focus
under other objectives.
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- Stage, The stage is
the platform that supports the
specimen. It is usually quite
large to minimize vibration
and it attaches to the
microscope stand. The stage
has an opening for the
illuminating beam of light to
pass through.
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- A spring loaded clip holds
the specimen slide in place on
the stage. Other types of
stage clips are designed for
use with petri-dishes,
multiwell plates, or other
specialized chambers.
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- Most stages have a rack
and pinion mechanism that can
move the specimen slide in two
perpendicular (X - Y)
directions. On many
microscopes, stage movement is
controlled using two
concentric knobs located to
the side or below the stage.
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- Stand, The stand is
the basic structure of the
microscope to which everything
is attached. The stand, also
known as the arm, is the part
of the microscope that you
grab to transport the
microscope.
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- Tube, the tube
houses many of the optical
components of the microscope.
The optical tube length of
most biomedical microscopes is
160 millimeters but tube
geometry varies considerably
due to relay lenses and
proprietary design features.
In most modern microscopes the
tube is folded to make the
microscope easier to use.
- Early microscopes had
straight tubes such as this
model built by Robert Hooke in
the mid 17th century.
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- Tube length,
describes the optical tube
length for which the objective
was designed. This is 160 mm
(6.3 inches) for modern
biomedical microscopes.
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- Turret, Most
microscopes have several
objective lenses mounted on
a rotating turret to
facilitate changing lenses.
An audible click identifies
the correct position for
each lens as it swings into
place.
When the turret is
rotated, it should be
grasped by the ring around
its edge, and not by the
objectives. Using the
objectives as handles can
de-center and possibly
damage them.
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