In light microscopy, transparent specimens are usually examined by dark field, phase contrast and interference contrast light microscopy.
In dark field, specimens are illuminated by oblique light beams that come from the periphery of the illuminating apparatus. Therefore, some transparent objects, e.g. unstained
native bacteria, are barely visible and fine structures inside them are oftenly not visible.
In phase contrast, the discernment of fine detail can be reduced by halo artifacts. The intensity of contrast, i.e. the difference in brightness between the background and
specimen, is constant and not variable; it is determined by the specification of the phase ring within the phase contrast lens and dependent on the specific phase differences between the specimen and its
Interference contrast images are free from halo artifacts, but their contrast may be lower than in corresponding phase contrast or dark field images, especially, when
transparent specimens are examined in thin-layer preparations.
Recently, luminance contrast has been developed by the author as a new illumination technique characterized by several advantages in comparison with the usual examination
methods suitable for transparent specimens. With the help of luminance contrast, such specimens can be examined in several variations of contrast effects, which are similar to dark field, phase and
interference contrast. Therefore, these variants have been named luminance dark field, luminance phase contrast and luminance interference contrast. As opposed to common dark field imaging, internal
structures within the specimen are also visible in high contrast. As opposed to common phase and interference contrast, the intensity of contrast is adjustable in tiny steps; and halo artifacts are
either reduced or do not exist. The light path is completely different from common dark field, phase and interference contrast. In all variants of luminance contrast, the specimen appears as a
self-luminous, flourescent object resulting in fundamental improvement in resolving power.
This new method has already been published (8) and applied for a patent.
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Copyright: Joerg Piper, Bad Bertrich, Germany, 2007ight: