33
An aperture diaphragm in the objective (Fig. 21)
is normally opened. The reduction in image
brightness caused by stopping down results in:
Greater depth of field
Less coverglass sensitivity (p. 22)
Suitability for darkfield (p. 36)
Change in contrast
2.5x objective*
Condensers CL/PH and CLP/PH: Insert diffusing
screen (like 7.7).
Condensers UCL/UCLP:
first disengage the lens for the 2.5x objective
(9.7) (switch PH or BF position), set Koehler
illumination → p. 30 with 4x or 10x objective.
Engage lens for 2.5x objective with condenser
disc (23.8).
Open the aperture diaphragm (23.7) as far as the
stop.
Narrow the field diaphragm (23.10). In case of
arc-shaped vignetting, center the lens: insert
both centering keys (23.2) into the UCL or UCLP
condenser (9.3) at an angle from the back and
adjust until the asymetrical vignetting disap-
pears. Remove the centering keys and open the
field diaphragm.
The lens can only be used up to an objective
magnification of max. 20x. Exact Koehler
illumination (→ p. 30) can no longer be
obtained! 1.6x objectives can be used if the
condenser is removed.
Immersion objectives*
OIL: only use optical immersion oil of DIN/ISO
standard. Cleaning → p. 46.
W: Water immersion, use distilled water if
possible.
IMM: Universal objective for water, glycerine or
oil. A push-on immersion cap is available for the
10x N PLAN objective.
Locking of objectives
Some immersion objectives (FLUOTAR and
PL APO types) with a knurled grip (Fig. 21) can be
shortened by about 2 mm by pushing in the front
part and rotating slightly. This stops any
remaining drops of immersion liquid from
wetting objects and other objectives when the
nosepiece is turned.
Attention:
This locking device must be released before the
immersion objective is used again, as otherwise
the spring mechanism protecting the specimen
and the objective is inactive and the other
objectives are not parfocal with the immersion
objective.
Colour code rings on objectives
In accordance with DIN/ISO standards the
magnification of each objective is indicated by a
colour ring:
!
1
00x 63x 40x 25x 16x 10x 6.3x 4x 2.5x 1.6x
125x 50x 32x 20x 5x
150x
160x
white dark light dark light yellow orange red brown grey
blue blue green green green
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