Optika Italy B-510 Serie Manual De Instrucciones página 16

Modern substage condensers often have a high degree of correction with numerical aperture values ranging between 1.0
and 1.40. In order to effectively utilize all the benefits of oil immersion, the interface between the substage condenser front
lens and the underside of the microscope slide containing the specimen should be also be immersed in oil.
An ideal system is schematically diagrammed in Fig. 22, where immersion oil has been placed at the interfaces between
the objective front lens and the specimen slide and also between the front lens of the condenser and the underside of the
specimen slide.
This system has been termed a Homogeneous Immersion System and it is the ideal situation to achieve maximum numer-
ical aperture and resolution in an optical microscope.
In this case, the refractive index and dispersion of the objective front lens, immersion oil, substage condenser front lens,
and the mounting medium are equal or very near equal.
In this ideal system, an oblique light ray can
pass through the condenser lens and completely
through the microscope slide, immersion oil, and
mounting medium undeviated by refraction at oil-
glass or mounting medium-glass interfaces.
When using high-power achromat oil immersion
objectives, it is sometimes permissible to omit the
step of oiling the condenser top lens.
This is because the condenser aperture dia-
phragm must often be reduced with lesser-cor-
rected objectives to eliminate artifacts and provide
optimum imaging.
The reduction in diaphragm size reduces the po-
tential increase in numerical aperture (provided
by oiling the condenser lens) so the loss in image
quality under these conditions is usually negligi-
ble.
Darkfield microscopy is a specialized lighting
technique that uses oblique illumination to im-
prove contrast in samples that cannot be well
observed under normal brightfield illumination
conditions.
We are all quite familiar with the appearance and visibility of stars on a dark night, despite their huge distances from the
Earth. Stars can be seen because of the sharp contrast between their weak light and the black sky.
Objective Front lens
Coverslide
Specimen
Condenser
front lens
Homogeneous Immersion System
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Immersion oil
Mounting
media
Immersion oil
F ig. 22 F ig. 22