Luminance contrast, presented as a new illumination technique, has been developed based on hand-made prototypes of objectives and light modulating elements. The conventional lenses, which were equipped with special
light absorbing platelets as well as the Cassegrain-Schwarzschild mirror objectives had been fabricated some decades ago. Nevertheless, the luminance contrast images resulting from these optical components are
characterized by extraordinary contrast, excellent sharpnesss and supramicroscopic resolution. In all objectives, the image quality was visibly improved when compared with conventional illuminating modes carried out
using the same components. Therefore, this new method promises further fundamental improvements of quality when modern objectives are modified for luminance contrast based on up-to-date manufacturing technologies.
Conventional lenses for phase contrast could easily be modified for luminance contrast by replacing their phase rings with a centered beam stop. Alternatively, a beam stop could be mounted instead of a phase ring
according to the construction plan shown in fig. 10 or carried out in variant constructions, e.g. mounted only with one single or two opposite arms.
Mirror objectives might be manufactured with improved precision and quality utilizing modern manufacturing methods. In luminance contrast, mirror systems might be an advantage, because their construction is a priori
based on a centric mirror which can act as a beam stop. The complete absence of chromatic aberration and the planarity of great visual fields may be discussed as additional adventages.
In luminance contrast, the various effects of illumination can be achieved and changed in a simple manner, when the diameter of the aperture diaphragm is appropriately adjusted. Thus, the image can be turned from
luminance dark field to luminance phase contrast, when the aperture diaphragm is opened moderately. In the same way, the intensities of contrast and background illumination can be regulated in tiny steps and halo
artifacts can also be avoided, if necessary. In luminance dark field, marginal blooming effects are less than in the conventional mode. As all illuminating light beams are centered and running in an axial direction,
many more details inside the specimen can be detected. The illumination of specimens is much more homogeneous than in usual dark field; thus, specimens are seen as self luminous or flourescent bodies. Probably
because of this reason, very small structures can be visible in luminance contrast that are smaller than the usual resolving power of the respective optical system. In this respect, luminance contrast might be
comparable to flourescence techniques.
Further improvements can be expected, when the various modes of technical developements are implemented described above. Thus, luminance contrast might also be capable to give new improving impulses for flourescence
Copyright: Joerg Piper, Bad Bertrich, Germany, 2007