Filter
Top Products
48
10. Measurements with the Microscope
10.2 Thickness Measurements
In principle, thickness measurements can be
carried out if both the upper and the lower
surface of the object can be clearly focused.
The difference in stage height setting (fine
focus knob: distance between two divisions =
approx. 3 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 measured in transmitted light is
given by the vertical stage movement (focusing
difference) d’ and the refractive indices n
o
of the
object and n
i
of the medium between the
coverglass and the objective (air = 1).
d = d'
Example:
The upper and lower surfaces of a thin polished
specimen have been focused with a dry
objective (n
i
= 1.0), scale readings of the
mechanical fine drive (division spacing = 3 μm):
9.0 and 27.0.
Therefore d’ = 18 x 3 = 54 μm.
The refractive index of the object detail was
taken to be n
o
= 1.5.
Thickness d = 54 x 1.5 / 1 = 81 μm.
n
0
n
i
Object Marker*
The object marker is screwed instead of an
objective. When rotated, a diamond is lowered
onto the coverglass or object surface, where
circles of variable radii can be scribed to mark
objects.