Biomedical Engineering Reference
In-Depth Information
Phase contrast microscope configuration
Image
plane
Diffracted
light
Direct
(surround
light)
Objective
Specimen
Phase
plate
Condenser
Condenser
annulus
1. 5
Optical components and pathways in the modern phase contrast
microscope.
the diffracted light arrive at the back focal plane of the objective they are
one-half of a wavelength out of phase with each other. The diffracted and
undeviated light exhibit destructive interference, allowing the details of the
specimen to appear dark against a lighter background. This is what happens
in the positive phase contrast imaging mode. To produce the proper condi-
tions to achieve phase contrast imaging, both the ring annulus at the front
focal plane of the substage condenser and the phase plate at the back focal
plane of the objective have to be exactly aligned with the help of a phase
telescope inserted in the eyepiece tube or a Bertrand lens located above the
back focal plane of the objective. The optical components of the modern
phase contrast microscope are shown in Fig. 1.5 .
Polarized light microscopy
Polarized light microscopy provides all the benefi ts of bright fi eld micros-
copy. In addition, by using this technique the microscopist can distinguish
between isotropic and anisotropic materials. The defi nitions of isotropy and
anisotropy are as follows:
