Can you have an anti focal point of a lens?

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The discussion explores the concept of an "anti" focal point in a lens, where light paths could cancel out at the focal point, resulting in no photon detection. It suggests that creating concentric rings within the lens, made of materials with varying refractive indices, might allow light to arrive out of phase, achieving this cancellation effect. The implications of such a lens are examined, particularly regarding the behavior of light when an absorbing sheet is placed at the anti-focal point. The idea raises questions about whether light could "tunnel" through the sheet, given that photons would have a zero probability of detection at that point. Overall, the conversation delves into theoretical optics and the potential for innovative lens designs.
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Can you have an "anti" focal point of a lens?

Hi,

Imagine putting a convergent lens in the path of a laser beam. I put a small light meter at the focal point of the lens.

If I move the lens along the beam will there be positions of the lens where the light paths through it completely cancel at the focal point so that no photons are detected there?

John
 
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Hi,

I've been thinking...

In order to get the effect of light cancellation at a focal point maybe one needs to implant concentric rings inside the lens made of glass with a different refractive index. Adjacent rings could then be designed to cause the light to arrive at the focal point precisely out of phase.

Maybe that would do it?
 
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If you could make a lens that focussed light to an "anti" focal point what happens if you place a thin absorbing sheet at that point?

Would light somehow "tunnel" through the sheet as photons cannot be absorbed at the anti-focal point (zero probability for them to be detected there)?
 
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