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  • Risley illumination versus koeller illumination in rife microscopes


    ALAN BLOOD alan.blood.research@gmail.com hrife.com

    Rife claimed to achieve images with deep field of focus, which seems unusual for highly magnified images. This article speculates about how deep field was enhanced by various design features including the novel use of Risley prism semi-monochromators.

    During most of the 20th century, nearly all light microscopes have been manufactured with pre-set lamp alignment, and checking and trimming of this alignment by technicians follows a strict routine known as Koeller illumination. Part of the process involves a means to bring the lamp filament into crisp focus while observing through a Bertrand lens. If this is not close to exact, performance will deteriorate.

    Sometimes dominant technical or theoretical paradigms blind us to alternatives. For example, most motor mechanics have been taught that the timing of a single ignition spark should be controlled in specified ways to optimise performance. But then somebody else comes along and in vents a multiple-spark concept which can give even better performance.

    I am not an expert on the subject, but I do know that in the years prior to the Koeller paradigm, Abbe taught methods of oblique illumination that could involve lateral movement of the condenser, and even sometimes involved adjusting the lateral position of the lamp. Abbe’s oblique methods could give interference contrast images, as explained in the Olympus website. The oblique method also allowed the image to contain higher order light diffraction circles associated with increased theoretical resolution. Stated more precisely, one edge of the new circle (or “sideband”) is admitted into the objective at one edge, while the beam center (or zeroeth order) is shifted towards the other edge of the lens aperture. Here we have an old Abbe method that promises better resolution, but ironically it can breach the conditions required for Koeller illumination.

    In 1931, Zernicke developed a low-cost phase-contrast innovation which became popular,and later DIC became available. Abbe’s oblique method became extinct, and the Koeller paradigm became gospel thereafter.

    Now I return to a favorite topic of Rife microscope concepts. In previous articles and Youtube videos, I compared a proposed Rife offset pinhole design to another special “luminance interference contrast” design demonstrated by Joerg Piper. It superimposes a brightfield image onto a special kind of axial darkfield image that shows up internal detail. I interpreted Rife’s long path design as a devise to“project” the objective back focal plane to a convenient distant location to easily allow placement of various arrangements of axial stops or Rheinberg filters or partial masks or neutral density /Hoffman modulator masks etc, including the proposed Rife offset pinhole plate. Optimal fine Z-plane placements and lateral displacements can be investigated. I showed a schematic for a similar long bench microscope prototype to generate so-called “Axial Interference Contrast” or “Zero order Interference Contrast”.The schematic showed simple typical monochromatic light sources,which would be set up for Koeller illumination.

    However the story does not end there. As far back as 1919, Rife developed a unique method to generate color illumination using Risley prisms. Today we use Risleys for beam steering of laser beams but Rife used them in a configuration that split the colors from a broad spectrum lamp, and shone one band of spectrum upwards into the condenser using a prism counter-rotation jig. Let us assume for this analysis that semi-monochromatic light with a bandwidth of 20 nm shines up into the condenser, while other colors are deviated to either side. Let us arbitrarily divide this spectrum window into 20 mini-windows each 1 nm different to its neighbors.

    When we think of the usual process of checking Koeller illumination, we expect to see a single image of the lamp filament in the test. But when the Risley semi-monochromator is used, we now see 20 lamp images each with slight lateral separation, or in practise, perhaps a smudged image.

    I do not as yet have a complete theory of Rife optics, partly because I am still learning,and partly because I lack formal training in optical physics. It maybe that here we have 20 superimposed images all with a different lateral illumination focus, and all with slightly differing incident spectra.

    Rife was reported by other published observers to have produced working images at 5,000 X and 8,000 X. Moreover, Rife made the claim that he achieved deep field images.In some cases, typical microscope images may only allow a very thin slice of the specimen to be in true focus, especially when the condenser aperture is wide open. In other articles I suggested two concepts unrelated to the Risley prisms that might improve image depth. The first was that the superimposed axial darkfield image emulates a very narrow condenser aperture to give deep field.Meanwhile, the widest condenser aperture can be used and this allows maximum theoretical resolution in the brightfield component. The second concept was that where Rife also used the external lamp in a method similar to the modified Rheinberg method of Paul Martin, very high order sidebands can enter the objective, and the extra or third superimposed image has resolution that tends to be enhanced in the vertical direction. In this article I speculate about a third unknown reason for unique optical performance including deep field, that maybe related to Rife’s deployment of the Risley prisms.

    In addition to my comments about 20 illumination focii, it may be that these focii lie along an arc, and the edge focii would lie in a lower Z-plane than the middle focii, in turn giving deeper field images. I would also like to draw readers attention to comments in an interesting article on novel methods of multiple oblique beam illumination, where two or four oblique beams could give a “pseudo-3D” effect and improved image crispness. In the Risley illumination arc scenario, the interaction of the far left focii with the far right focii might constitute a type of multiple oblique beam illumination, albeit with illuminating light in the order of >10 nm apart.

    Unfortunately I am not able offer a proper theoretical analysis here, beyond some hints and speculation. The next best thing to good theory might be good practise, i.e. to construct two prototype long bench microscopes for axial interference, using conventional monochromatic Koeller illumination in the first, and instead using Risley illumination in the second. Because there is only one variable in the comparison, any practical differences in optical quality would become apparent.

    Also, it should be possible to emulate Martin’s Rheinberg method with the pinhole plate removed (two overlaid images), by adding an external “UHOMB”lamp (see earlier articles). The results could be compared to similar images with the pinhole plate installed (three overlaid images).

    See links at hrife.com