OPERATION
ZEISS
Illumination and contrast techniques
Axio Observer
148
431004-7244-001
12/2016
5.12.2
Setting up transmitted light phase contrast
5.12.2.1
General operating principle
The phase contrast technique is ideal for examining thin, unstained specimens such as cultured cells. The
human eye is generally unable to perceive phase differences (differences in refractive index and thickness)
between the various components of the cell.
The phase contrast technique uses "phase stop and phase plate" optical modulators and interference
procedures in forming the intermediate image in order to transform small phase differences into
differences in intensity and color which are visible to the human eye.
The high-intensity, direct light components are attenuated and given a constant phase shift by the
annular channel defined optically by the "phase stop and phase plate". By contrast, the indirect light
components, diffracted by various cell components, bypass this optical channel and their phase is
determined by differences in refractive index and thickness of the specimen.
In the intermediate image plane these two beams interfere and are enhanced or attenuated depending
on their phase position. This interference results in images with intensity and color differences which can
be perceived by the human eye.
The use of objectives with two phase plates enables the user to switch rapidly between positive and
negative contrast by changing the aperture using the condenser turret. Positive phase contrast is useful
for thin cell structures (e.g. filopodia), negative contrast for thicker parts of the cell, as fine structures are
also better visualized.
5.12.2.2
Instrument equipment
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Phase contrast objectives with phase plates Ph 0, Ph 1, Ph 2 or Ph 3 for various mid-range numerical
apertures. They can also be used for bright field techniques without any limitations.
−
Condenser with turret containing centerable phase stops Ph 0, Ph 1, Ph 2 and Ph 3 for various mid-
range numerical apertures.
−
The active condenser phase stop must match the designation on the objective, e.g. Ph 1.
Summary of Contents for Axio Observer Series
Page 1: ...Axio Observer Inverted microscope Operating manual...
Page 192: ......
