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sophiecentaur
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In this example - as for all optics - the intention is to get diffraction to give you enhancement of all light from one direction and cancellation from all other directions. Your 'main lobe' of directivity is pretty much the same for all reasonable reflectors (optical or radio) or lenses but the higher quality design will provide better and better cancellation of signals arriving off-axis (shaping and spreading 'side lobes' as much as possible to acceptable levels). It's a bit like an air mattress; you squash one part down and another part springs up but the volume of air inside stays the same.hutchphd said:The most recent example is the alignment of the mirrors on the James Webb Space Telescope. In particular the final distance ("piston alignment") for each mirror segment had to be equal to within something like a tenth of a wavelength get the nice coherent center spot. They did okay I guess!