Axio Imager 2
OPERATION
ZEISS
Illumination and contrast methods
01/2016
430000-7544-001
167
4.12.3
Setting transmitted-light phase contrast
(1)
General principle
The phase contrast technique is ideal for examining thin, unstained specimens, e.g. culture cells. The
human eye is unable to see phase differences (differences in refractive index and thickness) between the
different cell components.
The phase contrast technique uses the optical modulators "phase stop and phase ring" as well as the
interference procedures during formation of the intermediate image in order to change the small phase
differences into intensity and color differences that are visible to the eye.
The high-intensity, direct light components are attenuated with the optically defined ring channel "phase
stop and phase ring" and given a constant phase shift. The indirect light components diffracted at
different cell components, however, bypass this optical channel. The phase is influenced by the different
refractive indexes and thicknesses in the specimen.
In the intermediate image plane, these differently influenced partial beams interfere with each other and
are amplified or attenuated, depending on the phase position. This interference results in differences in
intensity and color in the image which are perceptible to the human eye.
(2)
Instrument equipment
−
Phase-contrast objectives with phase rings Ph 1, Ph 2 or Ph 3 for different average numerical apertures
that can also be used in brightfield without any restriction.
−
Brightfield Universal condenser with turret disk containing centerable phase stops Ph 1, Ph 2 and Ph 3
for different average numerical apertures.
−
The phase stop on the universal condenser swiveled into the light path must match the corresponding
label on the objective, e.g. Ph 1.
(3)
Setting transmitted-light phase contrast
•
Swivel a phase-contrast objective, e.g. Ph 1, into the light path.
•
On the turret disk of the universal condenser, swivel in the phase stop with the same designation as
the phase-contrast objective, e.g. Ph 1.
•
To check the centering and congruence of the bright phase stop (in the condenser) with the dark
phase ring (in the objective), remove one eyepiece from the tube and replace it with the auxiliary
microscope. Use the correction device on the auxiliary microscope to focus on the phase stop and the
phase ring in the exit pupil of the objective.
To check the centering, you can also use the Bertrand lens slider PH. However, this is only
possible if no camera path deflection is installed on the left side of the microscope stand.
