Elementary chemical microscopy elementarychemi00cham Year: 1921 VERTICAL ILLUMINATORS, METALLURGICAL MICROSCOPES 85 Parallel light should fall upon the lens L. This is obtained by employing a suitable lens between the illuminator and radiant. The Leitz Company supply a very conveniently mounted lens for this purpose. A metal screen A, Fig. 36, is attached to a stand B. Mounted in the screen is a lens in front of which is an iris diaphragm D. The stand and radiant are placed at such distances from L as to project a small beam of approximately parallel light upon L. The milled head a serves
Elementary chemical microscopy elementarychemi00cham Year: 1921 VERTICAL ILLUMINATORS, METALLURGICAL MICROSCOPES 85 Parallel light should fall upon the lens L. This is obtained by employing a suitable lens between the illuminator and radiant. The Leitz Company supply a very conveniently mounted lens for this purpose. A metal screen A, Fig. 36, is attached to a stand B. Mounted in the screen is a lens in front of which is an iris diaphragm D. The stand and radiant are placed at such distances from L as to project a small beam of approximately parallel light upon L. The milled head a serves as a fine adjustment up and down of the lens and diaphragm. When either day- light illumination, direct sunlight, or a radiant at a distance are to be used, the mirrors Ro and Ri are brought into service, the light from the chosen source being received upon R2, reflected upon Ri, and thence through the lens and diaphragm opening. When a radiant close to A is used the mirror R: is raised until it stands in a vertical posi- tion, thus giving an unobstructed passage through the center of A. Correct illumination of the surface of an object m is obtained as described above by trying the lens L at different distances from P and by tipping P or k until the most satisfactory angle of inclination is obtained. It may also be necessary to slide S slightly to the right or left of the indicator t. It is usually best to start with a diaphragm opening yielding a beam of light which will not more than half fill the aperture of the lens L. Tassin Vertical Illuminator. - - One of the greatest annoyances encountered in the work with ordinary vertical illuminators is the necessity of readjusting the height of the radiant whenever a change of objective is made or objects of different thicknesses are studied, since refocusing is essential and this necessarily alters the position of the disk or prism with reference to the axis Fig. 36. Condensing Lens and Iris Diaphragm for Use with Leitz Vertical I
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