Zeiss LSM 880 Operating Manual page 662

Optical axis
12
Let the statements made on the PSF so far be further illus-
trated by the figure on the left. It shows a section through
the resulting diffraction pattern surrounding the focus on
the illumination side (PSF
ill
The lines include areas of equal brightness (isophote pre-
sentation). The center has a normalized intensity of 1. The
real relationships result by rotation of the section about
the vertical (Z) axis. Symmetry exists relative to the focal
plane as well as to the optical axis. Local intensity maxima
and minima are conspicuous. The dashed lines mark the
range covered by the aperture angle of the microscope
objective used.
For the considerations in this chapter, only the area marked
in red color, i.e. the area at half maximum, is of interest.
Fig. 8 Isophote diagram of the intensity distribution
around the illumination-side focus (PSF ill ).
The intensity at the focus is normalized as 1.
(Born & Wolf, Priniples of Optics, 6th edition 1988,
Pergamon Press)
).