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LEITZ DIALUX 20 - Centring the Condenser; Use of the Field Diaphragm; Use of the Aperture Diaphragm

LEITZ DIALUX 20
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Centring the condenser
Fig
.
32
Fig.
33
. .
'
--
-r
•J
u,
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~
22958-512 A
20
Focus the specimen
with
the coarse
and fine adjustment.
Adjust
the field
diaphragm
so that the
white
ring (Fig.
32,
arrow) is completely
covered
.
1. Close the field
diaphragm.
2. By rotating the
condenser
stop screw
lower
the
condenser
so
that
the edge
of
the field
diaphragm
appears shar
p.
3. Centre the image
of
the field dia-
phragm
with
the
two
centring
screw
s.
4. Open the field
diaphragm
so that it
just
disappears
beyond the edge of
the
field
of
view
.
After
objective
change,
carry
out fi ne
centration
only
by
adjusting
the fi eld
diaphragm
.
[
t
use
of
the field diaphragm
The field
diaphragm
protects
the spe-
cimen from heat and prevents the
light
not required
for
image
formation
from
entering the
object.
The
diaphragm
is
therefore opened
just
far
enough
for
the observable field
of
view
to
be fully
visible.
A change
of
magnification
there-
fore
always calls
for
an
adjustment
of
the field
diaphragm
.
Use
of
the aperture diaphragm
The setting of the
aperture
diaphragm
is
one
of
the
factors
determining
the
resolution and the
contrast
of
the
mi-
croscopic
image.
Optimum
optical
per-
formance is reached when the
aper-
tures
of
the
objective
and
of
the
con-
denser are identical. When the
aperture
diaphragm
of
the
condenser
is
closed
beyond the
aperture
of
the
objective
the resolving
power
of
the
objective
de-
creases but image
contrast
increases.
A visually
appreciable
reduction
of
the
resolving
power
occurs
when the
aper-
ture
diaphragm
is
closed
beyond
lj
3
of
the aperture
of
the
objective
and
should
therefore be avoided if possible.
Remove the eyepiece from the eyepiece
tube
. Close the
aperture
diaphragm
so
that
its image
just
appears on the rear
lens
of
the
objective.
This is regarded
as
the
normal
position
. Replace the
eyepiece.
If the
specimen
lacks
con-
trast
the
aperture
diaphragm
can be
further
closed
so
that
the less
contrasty
structural
elements
,
too
,
become
clearly
visible.
Settings
of
the
aperture
diaphragm,
once
determined
, can be
reproduced
with
the aid
of
the
scale
.
Attention:
Image
brightness
must never be re-
gulated
with
the
aperture
diaphragm
,
but
only
with
the
transformer
or
with
neutral-density
filters.
Turn
out
the
condenser
top
when using
objectives
of
apertures
< 0.25. The
condenser
remains in the same
position
as
for
objectives
of
aperture
> 0.25.
The
aperture
diaphragm
always re-
mains
fully
open.
Set the lamp
condenser
on the Lamp
Housing
102 Z so
that
the field
of
view
is
uniformly
illuminated
.
This
setting
remains unchanged
for
all
magnific-
ations
.
21

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