Talk:Speckle pattern
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I understand that the speckle pattern one sees moves as you move your head in different ways depending on how near or far sighted you are. Could more information be added about this? —Ben FrantzDale 00:29, 27 June 2006 (UTC)
- I talked with Laura Scudder at Wikimania yesterday. We hypothesized about this effect including what would cause bigger and smaller speckles and why the image of the speckles would appear to move differently for near- and far-sighted people. But that's original research, so should be avoided. Here's a fragment, though. Maybe someone can find a citation:
- Consider an atomically-smooth surface with a step on it of λ/4, like so:
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- Now consider a plane wave aligned with the surface bouncing off it. The reflected surface will have peaks 180° out of faze on opposite sides of the step. If you had perfect optics, an image of the step would give you full intensity. However, if you were slightly out of focus, the circle of confusion sorrounding the step would contain light from both sides of the step which would destructively interfere creating a black spot in the image.
- Another factor would be that different rays will follow different paths through an optical system, so the image of a point might interfere with itself.
- Does anyone know a reference for this. —Ben FrantzDale 13:54, 7 August 2006 (UTC)
- The idea that perfect vision eliminates speckle is mentioned in this article, which even talks about sunlight speckle. — Laura Scudder ☎ 17:56, 10 April 2007 (UTC)
I've always understood that the speckle interference happens *on your retina* (or imaging plane for film or optical sensors). This explains why speckle changes when you move your head around a stationary illuminated object, as well as differences due to optics in the path (including near- or far-sightedness). I like to point out that even if you are extremely nearsighted, the speckle pattern will be crisp (in "focus") even if the object is blurry without correction. Once again, I can't find a reference. -- Jonathan Foote, rotorbrain.com
- Yes, it's certainly interference at the imaging plane of your retina that creates the speckle. Unfortunately my library doesn't have the Goodman book, but I did stumble on this interesting article. — Laura Scudder ☎ 17:56, 10 April 2007 (UTC)
Hi I am new, so this might not be the way that things are done. But if you need a reference I recomend the new book by Goodman - Speckle Phenomena in Optics.
There is a article called eye testing using speckle which gives a reference explaining in detail how eyesight can be tested using speckle. Epzcaw (talk) 13:59, 11 May 2008 (UTC)
[edit] Correction
The recent alteration by an anonymous contributor is incorrect;
"If light of low coherence (i.e. made up of many wavelengths) is used, a speckle pattern will not normally be observed, since the speckle pattern varies over time and for light with a large bandwidth the speckle pattern will shift fast enough for the eye or detector to average out to give a uniform field of view"
The lack of speckle in non-coherent light has got nothing to do with speckle patterns shifting in time, but is due to the fact that each wavelength produces its own stationary speckle pattern; the dimensions of the speckle patterns vary with wavelength, and the individual speckle patterns will therefore normally cancel one another out. Speckles may still be observed if the bandwidth is narrow enough, or the the surface is only slightly rough (speckle in your fingernail in sunlight).Epzcaw (talk) 07:54, 5 June 2008 (UTC)
