36
10. Measurements with the Microscope
10.2 Thickness Measurements
In principle, thickness measurements can be car-
ried out if both the upper and the lower surface
of the object can be clearly focused. The differ-
ence in stage height setting (fine focus knob: dis-
tance between two divisions = ca. 1 μm) gives a
value for transmitted light objects that is falsified
by the refractive index of the object (which has
been „transfocused“) and perhaps immersion
oil. The true thickness of the object detail mea-
sured in transmitted light is given by the vertical
stage movement (focusing difference) d’ and the
refractive indices no of the object and ni of the
medium between the cover glass and the objec-
tive (air = 1).
d = d‘
n
0
n
i
Example:
The upper and lower surfaces of a thin polished
specimen have been focused with a dry objec-
tive (n
i
= 1.0), scale readings of the mechanical
fine drive (division spacing = 1 μm):
9.0 and 27.0.
Therefore d’ = 18 x 1 = 18 μm.
The refractive index of the object detail was tak-
en to be n
0
= 1.5.
Thickness d = 18 x 1 x 1.5 = 27 μm.
Fig. 28
Scale division of the graticule in the eyepiece (left) and
image of the stage micrometer (right)
Object Marker
The object marker is screwed in instead of an ob-
jective. When rotated, a diamond is lowered onto
the cover glass or object surface, where circles
of variable radii can be scribed to mark objects.
