Leica DM2500, Manual

Page: 131 / 311

53
8. Operation
8.9 Aperture Diaphragm
The aperture diaphragm (59.3) determines the
resolution, depth of field and contast of the mi-
croscope image. The best resolution is obtained
when the apertures of the objective and the
condenser are roughly the same.
When the aperture diaphragm is stopped down
to be smaller than the objective aperture, re-
solving power is reduced, but the contrast is en-
hanced. A noticeable reduction in the resolving
power is observed when the aperture dia-
phragm is stopped down to less than 0.6x of the
objective aperture and should be avoided where
possible.
In polarization microscopy, stopping down the
aperture diaphragm generally results in more in-
tense colors.
The aperture diaphragm is set according to the
viewer’s subjective impression of the image, the
scale on the dial just serves to allow reproduc-
ible settings and does not represent absolute
aperture values.
Color-coded Condenser
The color markings on the condenser (59.2) cor-
respond to the color rings of the objectives.
When changing objectives, a suitable aperture
diaphragm setting can be found by setting it to
the matching color marking (corresponds to 2/3
of the objective-side aperture).
Attention:
The aperture diaphragm in the illumination light
path is not for setting the image brightness. Only
the rotary brightness adjustment knob or the
neutral density filter should be used for this.
An aperture diaphragm in the objective is nor-
mally fully opened. The reduction in image
brightness caused by stopping down results in:
Greater depth of field
Less coverglass sensitivity
Suitability for darkfield
Change in contrast
Fig. 59 CL/PH condenser
1 Slot for light rings, etc.
2 Color coding
3 Aperture diaphragm
4 Filter holder
5 Field diaphragm
2
3
1
4
5