![]() ![]() The center of the annular filter can be cut with the same cork-borer used to prepare the central filter. This die can quickly stamp very smooth circles from sheets of acetate or gelatin colored filters. In our laboratory, the support machinists have constructed a brass die that cuts annular filter circles that are the same diameter as our Rheinberg filter holder. Gelatin filters can be prepared by cutting the central filter with a cork-borer of the proper diameter, and the annular rings can be prepared by carefully drawing a circle on the filter paper and cutting it out with a pair of scissors. These filters can also be readily fabricated in the laboratory using either Kodak Wratten filters or colored filters that are widely available at scientific supply houses and optical component distributors. The annular rings had outside diameters of 31-35 millimeters and central filters usually had a diameter of 15-18 millimeters for use with a 10x - 0.25 NA objective. ![]() For example, a clear ring with a red central filter will produce white or colorless images on a red background.įor years, some microscope manufacturers sold Rheinberg filters in colored gels (similar to Kodak Wratten filters) that were precut to fit the substage filter ring of their microscopes. Other visually effective images are produced by using a clear uncolored ring with a colored central filter. These combinations can be explored using our Rheinberg Illumination Java Tutorial to adjust both the annular ring and central filter colors. Effective combinations include: red ring, violet central filter yellow-orange ring, blue central filter, and so forth. The diameter of the central filter can be varied (to modulate background illumination intensity) by increasing the size of the narrow black rings that separate the filter from the outer ring (Figure 4(a-c)). ![]() In commercial versions of these filters, an accompanying set of transparent colored spots or "central filters" is made to fit snugly into the openings of the annular rings (Figure 4). The Rheinberg filters are prepared, or manufactured, in the form of transparent, annular colored rings with a circular opening in the center as depicted in Figure 3. ![]()
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