New trends in physics teaching, v.4; The ... - unesdoc - Unesco

New Trends in Physics Teaching IV
Images’; really good multiple images can only be obtained if the coherence is very high and are
best demonstrated with a laser source. Figure 8 shows examples.
Figure 7. The lens as a phase adjuster. [23.]
Figure 8. Multiple or Fourier images: the arrangement is as for figure 1, but with a laser source illuminatlng the slide which is
now a piece of gauze in a roughly circular hole in a cardboard screen. a is the image at the normal conjugate position at which
a focused image of an irregular object would be produced. b, c and d are some of the additional ‘images’ that seem to come into
focus successively as the gauze object is moved away from the lens. The lens-to-screen distance remains fixed.
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