Elementary chemical microscopy elementarychemi00cham Year: 1921 Fig. 14. Types of Dark-field Illuminators. A. Nachet et Fils. B. Reichert. C. Bausch & Lomb. D. E. Leitz. The Beck illuminator is unique in that it permits adjustment for different thicknesses of object slides, an impossiblity with other forms of paraboloid illuminators. This adjustment for slide thickness is accomplished by changing the distance between the focusing lens L and the para- boloid P. As seen in the diagram, the illuminator consists of two parts, the paraboloid mounting screwing into that which holds the lens; there
Elementary chemical microscopy elementarychemi00cham Year: 1921 Fig. 14. Types of Dark-field Illuminators. A. Nachet et Fils. B. Reichert. C. Bausch & Lomb. D. E. Leitz. The Beck illuminator is unique in that it permits adjustment for different thicknesses of object slides, an impossiblity with other forms of paraboloid illuminators. This adjustment for slide thickness is accomplished by changing the distance between the focusing lens L and the para- boloid P. As seen in the diagram, the illuminator consists of two parts, the paraboloid mounting screwing into that which holds the lens; therefore raising or lowering the paraboloid will displace the focal point / and bring about an accom- modation for different thicknesses of slides. In practice it is rarely possible to have such accurate grinding that all the rays are properly deflected and none enter the objec- Fig. 15. Beck Adjustable Dark-ground Illuminator.
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