Download Leica TCS SP5 user manual - CALM - Confocal and Advanced Light

1
Out of
focus
2
In focus
3 Pinhole
Figure 49: Creating an optical section using an incident-light process. Light not originating
from the focal plane is cut off by a spatial filter (here, a pinhole). Only information from the
focal plane can reach the detector.
The diaphragm thus acts as a spatial filter, but only when used with the correct, i.e. pointshaped, illumination.
As a rule, the optical section becomes thinner when the size of the pinhole is reduced. This
effect is reduced near the wavelength of the light used, and at a pinhole diameter of zero one
would theoretically receive the thinnest optical section for the wavelength and numerical
aperture used. A range apparently exists at 1 Airy which does not yet offer the thinnest
optical sections, but which is nevertheless very close to the theoretical limit. As the intensity
of the passing light increases roughly in proportion to the square of the pinhole diameter, it is
advisable not to close the pinhole too far to avoid excessive image noise. A value of 1 Airy is
a very good compromise and is selected automatically by the Leica TCS SP5. A dialogue is
available to set smaller or larger diameters if required. Playing with this parameter to study its
effects can be very worthwhile when you have the time.
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