Cheap lens? Diffraction? Dirt?

Started Sep 11, 2012 | Discussions thread
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forpetessake
forpetessake Senior Member • Posts: 4,892
Forgot to mention

Since not everybody is going to read the articles, here is the bottom line. The light-wave interference is nothing more than superposition of two or more waves. For the phenomena to be visible, the phase relationships must be stable, i.e. coherent waves are required. There is a characteristic of light called coherence time or coherence length. The longer the distances, the longer coherence time/length required. So one may observe interference in very thin films or tiny holes with low coherent light, like sunlight, but in order to see an interference in say a mirrorbox interferometer you need a significantly better coherency of a laser.

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