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Oblique Illumination
The achromatic!aplanatic condenser N.A. 1.40 has
extremely high resolving power and will give the
operator satisfactory results even when used dry.
When using objectives lOOx, the condenser should
be immersed. The condenser can be used with all
objectives from 4x and up. Oblique illumination
will further improve resolving power.
1.
With oblique illumination, the resolving power
can
be doubled. As against the normal (central)
illumination where the light beams are parallel
to the optical axis of the microscope, oblique
illumination provides light bundles at an angle
to the optical ax is.
The illuminating light proceeds from below with
an inclination to the specimen, which will cause
not only the normal transmitted beam but also
more of the refracted light to enter the objective.
This will double the resolving power as compared
with central illumination. The drawing on the
right hand side illustrates the oblique illumina-
tion system.
The cross-hatched area represents the cone of
light.
c
C: Optical axis
Cd: Condenser
Ob:
Objective~
r: Iris diaphragm
CD
Resolving power
increases in this
direction.
®
Resol'Ving power
decreases in this
direction.
~s
•
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2. Procedure
1) Stop down the aperture iris diaphragm.
2) Loosen the clamping screw and pull out the
aperture diaphragm with the slide lever.
The direction of diaphragm displacement
should
be
at right angles to the specimen
detail to be observed.
For example,
jf
it is desired to identify two
parallel details very close to each other as two
separate Jines, the aperture diaphragm is
moved at right angles to the details. If iden·
tification of two points is desired, the
diaphragm is moved parallel to the straight
line. connecting the two points.
3) Adjustment of the diaphragm slide and
diaphragm diameter while looking through
the eyepiece resolves the two lines or points
and permits very detailed observation of tfie
structure.
3. Observation of Overall Area Possible
O
a Article to
be
identified
bl ique illumination is effective only when the
S~
Sliding direction of iris
illuminating light is directed at right angles to
the specimen
In order to identify individual specimen details, therefore, it is necessary
to adapt the direction of diaphragm displacement perpendicl:llar to
the direction of the specimen detail to be observed.
Diaphragm rotation through 150
0
is possible with the achromatic!
aplanatic condenser. Stage rotation provides further possibility of
directional adaptation.
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