Principles of 
 Phase Contrast
Principles of 
 Relief Phase Contrast
Material and  
Further technical 
Further technical Developements

Manufacturers of microscopes could implement relief phase contrast if existing condenser annuli in conventional phase contrast systems were replaced by crescent- or punctate-shaped masks (similar to the prototype shown in fig. 5b). In this case, relief phase contrast could be achieved without closing the aperture diaphragm. Moreover, manufacturers could create modified turrets equipped with unconventionally pre-aligned annular rings which could overlap the phase rings tangentially when they are rotated into their fixed position. Thus, the aperture diaphragm could be closed to improve focal depth and sharpness.

Alternatively, circular or semicircular shaped masks could be built, which could be shifted excentrically into the light path to overlap phase-rings tangentially. Some prototypes are shown in fig. 5 d and e. Thus, brightfield mode could be used, when the aperture diaphragm is opened, and relief phase contrast could result when the aperture diaphragm is much smaller.

Universal condensers could also be equipped with several removable turrets to achieve all varieties of relief phase conrast as well as conventional phase contrast.

Moreover, special condensers for relief phase contrast could be created, equipped with various technical modifications to achieve small, circumscribed illuminating light beams with a variable position, length, width and shape. Thus, two separate iris diaphragms could be superimposed on each other, eccentrically aligned which could then be shifted and turned eccentrically (see fig. 11). Alternatively, two excentrically rotating disks could be created, one disk-shaped as a transparent light mask, the other disk as a non-transparent overlapping element, eccentrically superimposed on the light mask. Two non-transparent slides could also be used, overlapping marginally and suitably shaped, so that a small light beam could result. In all  cases, small sectoral illuminating light beams could be achieved by variable transparent gaps, resulting from the position of the double iris diaphragm, the double disk or double slide system.




Fig. 11:
Suggestion for a double iris diaphragm
(1 and 2) producing variable apertures (3) within a special condenser for relief phase contrast


For high-end motorized microscopes, motorized condensers for relief phase contrast could be built, equipped with several freely programmable function buttons. In this way, illuminating light beams with optimized allignment could be achieved and reproduced with a high precision according to the existing kit of phase-contrast objectives.

When the microscope is equipped with a rotary stage, the position of the specimens can be changed according to their individual three-dimensional texture and the direction of the illuminating light beams. Thus, in special cases, the effects of 3d imaging could be optimized or intensified. Alternatively, this optimizing effect could also be achieved when the condenser is pivoted, so that it can rotate around the optical axis.

More intensified three-dimensional images could also be achievable when an inverted microscope is used for relief phase conrast combined with phase-contrast objectives for long distances and thick glass slides. In this case, the illuminating beams will first pass through the cover ship instead of the object slide; the surface of the specimen will be illuminated from the top instead of from the bottom and shadow figures might occur on the surface of the object slide comparable with shadow effects obtained by reflexion contrast with oblique illuminating beams (6, 7).

Alternatively, 3D-effects could be intensified when the adjustment of the illuminating apparatus would be moderately modified so that the optical pathway of the illuminating light beams could be more oblique than usual (fig. 12).




Fig. 12:
Suggestion for a modified adjustment of the illuminating apparatus to achieve more three-dimensional effects in relief phase contrast.
1 = light source
2 = modified mask
3 = condenser
4 = specimen
5 = background light
6 = light bent by the specimen
7 = phase ring
8  = eyepiece with intermediate image
9 = eye




Copyright: Joerg Piper, Bad Bertrich, Germany, 2007


[Principles of Phase Contrast]
[Principles of Relief Phase Contrast]
[Material and Methods]
[Further technical developements]