Laurence, Lionel · London, School of Optics · leaf 27
When S and B are of equal size (Fig. 10), the umbra does not vary insize with its distance, but the penumbra increases as it is further away,because the penumbral cone diverges. When S is largei than B (Fig. 11), the umbra decreases with distance,since the umbral cone is convergent, while the… … Fig. 11. penumbral cone being divergent; beyond a certain point there is no umbra,as when the screen is at G C or beyond it at E E. The penumbral cone is always divergent, but the umbral cone may bedivergent, cylindrical, or convergent according as the source S is smallerthan, equal to, or larger…
Optics
Internet Archive · Gerstein Library, University of Toronto · Public Domain Mark 1.0. Free to use for anything.
