OPERATION
Axioscope 5/7/Vario
Illumination and contrast methods in transmitted light …
ZEISS
03/2018
430035-7344-001
103
4.2.6.3
Measuring path differences
Measuring compensators are required for the accurate measurement of path differences,. These
compensators reset, i.e. compensate the path difference produced by the specimen to zero (first order
black).
While the addition position as well as the subtraction position are of interest for the methods described
above,
only
the subtraction position is relevant for measurements.
Path differences in the specimen can assume very small values (1/50
λ
or 10 nm) and very large values
(greater than 10
λ
or approx. 5500 nm and more) and thus determine the compensator appropriate for
the measurement.
To find the appropriate compensator, proceed as follows:
•
Set the microscope as for transmitted light brightfield microscopy (see also section 4.2.1), taking
particular care to set the inter-pupillary distance correctly on the binocular tube (see also
section 3.1.4).
•
Position the specimen feature to be examined directly above the center of the reticle.
•
Restrict the size of the aperture to a value of about 0.2.
•
Rotate the Pol rotary stage until the specimen is in extinction position, i.e. it appears
entirely dark
. In
this position, activate the 45
°
click stop.
•
Rotate the stage
once
(by 45
°
), so that the specimen is in diagonal position (sample becomes bright).
The intensity of the interference or color produced by the specimen allows the following conclusion to be
drawn:
−
If more or less strong interference colors appear on the object, the path difference ranges
approximately between 1/2
λ
and about 5
λ
.
The suitable compensator is:
Tilting compensator B 0-5
λ
(accessory 000000-1115-700).
−
If the object-side color changes from light gray/white to a strong interference color, when a
λ
compensator (473704-0000-000) is inserted in the compensator slot, the path difference is
(1/4 ... 1/2)
λ
.
NOTE
The occurrence of the color change effect may require the assessment of two specimen
positions lying 90
°
apart. For this purpose, rotate the centered stage (by 2 click stops).
The suitable compensator is:
Tilting compensator B 0-5
λ
(accessory 000000-1115-700).
−
After insertion of the
λ
compensator and rotation of the specimen by 90
°
(2 click stops), the
interference color remains to be white, in this case, however, it is a "higher-order white" and thus
the path difference is > 5
λ
.
The compensator appropriate for this application:
Tilting compensator K 0-30
λ
(accessory 000000-1115-698).