. The microscope; an introduction to microscopic methods and to histology. Microscopes. Fig. 12.—Double Convex Lens, Showing Chromatic Aberration. The ray of white light (w) is represented as dividing into the short waved, bine [b) and the long waved, red (r) light. The blue (b) ray comes to a focus nearer the lens and the red ray (r) farther from the lens than the principal focus (_/). Principal focus ( /') for rays very near the axis ; f and f", foci of blue and red light coming from near the edge of the lens. The intermediate wave lengths would have foci all the way between f and f&quo
. The microscope; an introduction to microscopic methods and to histology. Microscopes. Fig. 12.—Double Convex Lens, Showing Chromatic Aberration. The ray of white light (w) is represented as dividing into the short waved, bine [b) and the long waved, red (r) light. The blue (b) ray comes to a focus nearer the lens and the red ray (r) farther from the lens than the principal focus (_/). Principal focus ( /') for rays very near the axis ; f and f", foci of blue and red light coming from near the edge of the lens. The intermediate wave lengths would have foci all the way between f and f". '£ 7. Chromatic Aberration —This is due to the fact that ordinary light con- sists of waves of varying length, and as the effect of a lens is to change the direc- tion of the waves, it changes the direction of the short waves more markedly than the long waves. Therefore, the short waved, blue light will cross the axis sooner than the long waved, red light, and there will result a superposition of colored images, none of which are perfectly distinct (Fig. 12). Fig. 13. The ray (0) near the edge of the lens is brought to a focus nearer the lens than the ray (/). Both are brought to a focus sooner than rays very near the axis, (f) Principal focus for rays very near the axis; (f) Focus for the ray (*'), and [f") Focus for the ray (o). Intermediate rays would cross the axis all the "way from if" tof). 'i S. Spherical Aberration—This is due to the unequal turning of the light in different zones of a lens. The edge of the lens refracts proportionally too much and hence the light will cross the axis or come to a focus nearer the lens than a ray which is nearer the middle of the lens. Thus, in Fig. 13, if the focus. Fig. 13. Double Convex Lens, showing Spherical Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfect
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