34
Immersion objectives have a second coloured
ring (Fig. 21) further down:
black Oil or Imm (= universal objective oil,
water, glycerine)
white water
orange glycerine
Immersion condenser
The condensers CL/PH 0.90/1.25 OIL and UCL
0.90/1.25 OIL (Fig. 7) are usually used dry. The
maximum illumination aperture is then 0.90. Both
condensers can also be used with immersion oil
(25.4). 1 – 3 drops of immersion oil are applied to
the front lens, the specimen is put on the stage,
avoiding air bubbles, and Koehler illumination is
set as usual, → p. 30. The optical coupling
medium then allows apertures of up to max. 1.25,
i. e. an improvement of the resolving power of
high-aperture oil objectives (e. g. 100x/1.25 OIL),
but only for brightfield. See p. 46 on how to
remove the oil.
You can also use glycerine instead of oil. The Pol
condensers CL P/PH 0.85 and UCL P 0.85 can
only be used dry.
Brightfield
Illumination techniques which display the empty
areas of the specimen as the brightest parts of
the image are called brightfield. Light-absorbing
object structures are required for this type of
imaging, i. e. it usually makes sense to stain the
specimen first. Optical contrasting techniques
offer an alternative (PH, DF, POL, etc.).
Possible errors
Wrong coverglass thickness (→ p. 22) or wrong
objective. Specimen has been placed on stage
with coverglass downwards instead of upwards.
Aperture diaphragm (23.7) opened too wide or
closed.
Condenser at wrong height or wrongly centered.
Lamp not inserted straight (→ p. 16). Dirty optics.
Phase contrast
Similar to transmitted light darkfield (→ p. 36),
phase contrast is used to form high contrast
images of unstained specimens.
Turn the phase contrast objective (engraving
PH, Fig. 21) with the lowest magnification
(usually 10x) into the light path and focus the
specimen. If you have difficulty in finding the
object plane: Temporarily narrow the aperture
diaphragm (23.7) or use a stained specimen. Set
the condenser disc in the BF position (23.8) or
pull out light ring slide (8.7).
Set Koehler illumination (→ p. 30): Focus the
field diaphragm together with the object by x, y
and z adjustment of the condenser.
Set the light ring (e. g. 1) corresponding to the
objective engraving (e. g. PH
1
) on the condenser
disc (23.8) or use the light ring slide (8.7).
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