Further devepolments in VPBC

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Principles of VBDC
Principles of VPDC
Principles of VPBC
Materials and Methods
Results of VBDC
Results of VPDC
Results of VPBC
Further developments
Further developments
Further devepolments
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Both the intensities of illuminating light components producing the phase contrast and bright-field partial images can be regulated by double diaphragms so that the internal and/or the external light outlet can be influenced by iris diaphragms. Some suggestions for construction plans concerning axial and peripheral VPBC are shown in the Figures 56 and 57.

Fig. 56: Construction plans for double diaphragms designed for axial VPBC,
internal (a) and external (b) iris diaphragms and concentric double iris diaphragms (c),
further explanations in the text.

Fig. 57: Construction plans for double diaphragms designed for concentric-peripheral VPBC,
internal (a) and external (b) iris diaphragms and concentric double iris diaphragms (c),
further explanations in the text.

In axial VPBC, the internal perforation associated with brightfield can be regulated by a small internal iris diaphragm whereas the light annulus for phase contrast is designed as a fixed light mask (Fig. 56a). Alternatively, the central perforation for axial brightfield can be fixed, whereas the external light annulus can be regulated with an iris diaphragm (Fig. 56b). In the arrangement shown in Fig. 56c, the external light annulus and the internal perforation can be regulated separately and independent from each other by a couple of concentric iris diaphragms. Corresponding solutions for peripheral VPBC are presented in Fig. 57. In this technique, the internal light annulus producing phase contrast can be regulated by a small internal iris diaphragm whereas the peripheral perforations associated with concentric oblique brightfield can be built up as fixed light outlets (Fig. 57a). Conversely, the light annulus for phase contrast can be fixed and the peripheral perforations can be influenced by an external iris diaphragm (Fig. 57b). Lastly, internal light annulus and peripheral perforations can be separately regulated by concentric iris diaphragms (Fig. 57c).

The intensity of the phase contrast and brightfield partial images can also be modulated by polarization techniques as presented in Fig. 58. A construction plan for axial VPBC is shown in Fig. 58a; a corresponding example for peripheral VPBC is given in Fig. 58b. In order to achieve a maximum variability in brightness and weighting without changing the condenser´s aperture, the coactive internal and external light outlets can be fitted with separate polarizers (P1 and P2) each mounted in crossed position or pivoting so that they are rotatable. In addition to this, a separate rotatable polarizer (P3) has to be mounted beneath the light mask or the condenser. When the internal and external light outlets are each fitted with two concentric polarizers (P1 and P2) in crossed position, the light amplitudes of both zones can be regulated by the additionally inserted rotatable polarizer (P3) in an antagonistic manner. The intensities of both illuminating light components can be regulated still more in higher variance if the concentric polarizers, associated with brightfield and phase contrast, are mounted as rotatable light filters. Of course, polarizers and iris diaphragms can also be combined with each other so that the intensity of the phase contrast and brightfield images and the aperture of the light outlets might be influenced in highest variability and optimally adjusted to the particular properties of the specimen.

Fig. 58: Construction plans for condenser light masks fitted with concentric polarizers (P1 and P2)
and an additional rotatable polarizer (P3) mounted beneath the light mask or the condenser,
design for axial (a) and peripheral (b) VPBC, further explanations in the text.

VPBC can also be integrated in incident light microscopy according to the construction plans shown in Fig. 59 (technical drawings based on and modified from E. Leitz Wetzar, 1969b). In order to achieve this, the objective mounted with the epi-illuminator has to be fitted with a phase ring. Moreover, the vertical illuminator has to be equipped with a light annulus which is congruent and conjugate with the objective´s phase ring so that an epi-phase contrast image can be produced. An epi-brightfield image is simultaneously generated by an additional light outlet according to the principles already described for transmitted light. The light mask within the vertical illuminator can fitted with a small centric perforation for axial VPBC (Fig. 59a), or peripheral perforations can be used for concentric peripheral brightfield illumination (Fig. 59b). As demonstrated in the Figures 59a and b, slides fitted with a pair of two appropriately sized light outlets might be slid into the illuminator so that the illuminating light is separated into two parts leading to the phase contrast and the axial or peripheral brightfield image. In both arrangements, the illuminating light components associated with phase contrast and brightfield are separated from each other, and they should be filtered at different colors – in the same way as already described for VPBC in transmitted light. In the technical variants shown in Fig. 59 , the phase contrast-producing light is colored in blue and the axial or peripheral brightfield light is marked in red. Both partial images, the phase contrast and brightfield image are superimposed in the plane of the intermediate image. Also in this technique, oblique illumination could be obtained in incident light when the illuminating light beams are partially covered within the vertical illuminator. The intensities of both different illuminating light components could be separately regulated when appropriately shaped polarization filters were integrated into the vertical illuminator and combined with a second rotatable polarizer– according to the technical principles suggested for transmitted light. Moreover, the breadth of the respective light outlets could also be regulated with iris diaphragms.

Fig. 59: Vertical illuminators modified for axial (a) and peripheral (b) VPDC in incident light, phase contrast (1) and bright-field (2) producing light, reflected imaging light (3), semipermeable mirror (4), slide with appropriate light masks for VPBC  (5), objective (6), phase plate with phase ring (7), specimen (8).

Last Update: August 10th, 2012
Copyright: Timm Piper, 2012