Leica DM1000 LED manual Measurements with the Microscope Thickness Measurements, Object Marker

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 no of the object and ni of the medium between the coverglass and the objective (air = 1).

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.

n d = d' n0

i

Example:

The upper and lower surfaces of a thin polished specimen have been focused with a dry objective (ni = 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 no = 1.5.

Thickness d = 54 x 1.5 / 1 = 81 μm.

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