<div>The classical interpretation of Young’s double slit experiment is that,
<i>before and after</i> passing through the double slit, the light
behaves as waves. It is “the only mystery [of quantum mechanics]
(Feynman). We proposed Postulates of convex lens for utilizing lens in
wave experiments. By applying convex lens, we observed new phenomena of
the double slit experiments, and referred as “new mystery”.</div>


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<div>In this article, we show the focal point related phenomena attribute to
a thin lens, and confirm Postulates of convex lens. The combination of
Postulates of the convex lens and the geometrical theory of the lens may
describe the function of the lens in the wave experiments. The convex
lens is helpful in studying the mystery of the double slit experiment.
It is the challenge to interpret the convex lens related phenomena in
the wave experiments.</div>