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Koehler Illumination
12
What is the Köhler illumination?
In a microscopic image, only a certain area
of a specimen can be displayed (image
field). Köhler illumination allows for illuminating only this particular area. The technical
background for the illumination of the image
field is described as follows:
If the illuminated area is smaller than the
image field, the luminous cone detected by
the objective lens as well as the numeric
aperture becomes smaller. Since the optic
resolution is directly dependent upon the numeric aperture, a lower illumination also reduces the optic resolution—which is not desired in most cases.
If the illuminated area is larger than the
image field, it leads to increased scattered
light. This, in turn, leads to a reduction of the
image contrast, possibly resulting in the situation where optically dissolved structures
of the microscopic image can no longer be
observed.
Köhler illumination represents a compromise
between maximum contrast and maximum
resolution. The most efficient microscope objectives frequently reach their optimum optic
performance only with exactly adjusted Köhler illumination.
User Manual TCS SP5
V: 02 | Document-ID-No.: 156500002
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