45
Operation of phase contrast
Possible errors
Specimen: too thick, too thin, too brightly stained;
identical refractive index of mounting medium
and specimen so that no phase jump occurs.
Attention:
Wedge-shaped coverglass position which
renders the centration of light and phase ring
ineffective.
Wrong light ring, or light ring has been installed
at wrong level.
Aperture diaphragm not opened.
Light ring not centred.
Wrong light ring slide.
IMC modulator in IMC position.
Condenser S 55 and condensor S 90 exchanged.
Phase contrast is used to form high-contrast
images of unstained specimens.
• Adjust the condenser level.
• Place the slide with the required light rings
into the holder (47.1).
• Rotate the objective nosepiece to move the
phase contrast objective (engraving PH) with
the lowest magnification into the light path.
• Open the aperture diaphragm (47.4) marked
“PH”.
• Focus the specimen using coarse and fine
adjustment. If it proves difficult to find the
object plane: Temporarily narrow the aperture
diaphragm or use a stained specimen. Set the
condenser disc to the BF position or pull out
the light ring slide. Reopen the aperture
diaphragm.
• Use the light ring (e.g. 1) that corresponds to
the engraving on the objective (e. g. PH 1).
• Centre the light ring as follows:
• Remove one eyepiece from the tube.
• Insert the focusing telescope.
• Loosen the clamp ring on the focusing
telescope and shift it until the light ring
(bright) and the phase ring (dark) are in
sharp focus.
• If the light and the phase rings are greatly
different in dimension, they need to be
matched by varying the condenser level.
• If the light ring is offset laterally against the
phase ring, centre the light ring. To do so,
rotate the centring key in the centring
screws (47.5) until the phase ring covers the
light ring.
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