Olympus VANOX Gebrauchsanweisung - Seite 23
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G.
Use of lris Diaphragms
Aperture iris diaphragm
as
well
as
field iris diaphragm are provided
on
the microscope.
The aperture iris diaphragm
is
part of t h e condenser and the field irk diaphragm is built
into the auxiliary lens system.
When ultra low magnification objectives are used, the
function of the diaphragms is reversed.
Aperture lris Diaphragm
Condenser Diaphragm
An aperture diaphragm opened too wide impairs
image
contrast due t o internal
Auxiliary Lens
System Diaphragm
reflections and related factors. On
the
other hand,
if the
diaphragm is stopped down
excessively,
resolution
is unduly
reduced.
It
is
therefore
suggested
to
match
the
opening of the aperture iris diaphragm t o the numerical aperture of the objecrive
Ultra Cow Power
(
U L l
Low Power
(
L)
High
Power
(H}
in use, in order t o achieve maximum objective performance.
For that
purpose
simply set the numerical
aperture scale
on
t h e condenser
t o the
numerical aperture
(N.
A,)
of
the
objective in use.
However, since microscopic specimens generally are low in contrast, their image lacks
Field Iris Diaphragms
Aperture Iris Diaphragm
Aperture Iris Diaphragm
contrast if the objective is used with
i t s
full numerical aperture.
Therefore,
it
is
Aperture Iris Diaphragm
Field Iris Diaphragm
Field Iris Diaphragm
occasionally preferable
ro
stop down the aperture diaphragm slightly
more
than
indicated
by
the objective N. A. This will result in increased image contrast, larger
depth of focus and a flatter field.
On the other hand, stopping down too much
impairs r ~ o l u t i o n . An aperture setting of 0.7 X t h e N. A. of the objective is recom-
mended.
If the numerical aperture of the objective is 1, for instance,
you
can set the scale to
0.7.
2. Fielcl lris Diaphragm
The field iris diaphragm controls the diameter
of the ray bundle impinging on the
specimen surface and thus increases image definition.
Stop down the field diaphragm while looking through
the
eyepiece.
An image of an
iris diaphragm will appear within the field. Now open the filed diaphragm until its
diameter is just slightly larger than the diameter of the field of view.