Can you have an anti focal point of a lens?

In summary, the conversation is about the possibility of creating an "anti" focal point in a lens by using concentric rings of different refractive indices, which could result in light cancellation at the focal point. The discussion also touches on the concept of light tunneling through an absorbing sheet placed at the anti-focal point.
  • #1
johne1618
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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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  • #2


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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  • #3


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)?
 

FAQ: Can you have an anti focal point of a lens?

Can you explain what an anti-focal point is in terms of a lens?

An anti-focal point, also known as a virtual focal point, is a point on the opposite side of a lens from the focal point where parallel rays of light appear to converge. It is created by diverging lenses and does not actually exist physically.

How is an anti-focal point different from a focal point?

A focal point is the point on a lens where parallel rays of light converge after passing through the lens. An anti-focal point is the point where these same rays appear to converge when looking at the lens from the opposite side. The main difference is that a focal point is a physical point where light actually meets, while an anti-focal point is a virtual point where light appears to meet.

Can an anti-focal point be used to create an image?

No, an anti-focal point cannot be used to create an image since it is a virtual point and does not actually exist. It is only a visual effect created by the lens.

How is an anti-focal point related to the focal length of a lens?

The focal length of a lens is the distance between the lens and its focal point. The distance between the lens and the anti-focal point is also equal to the focal length, but in the opposite direction.

Is an anti-focal point important in lens design?

Yes, an anti-focal point is an important consideration in lens design as it affects the overall performance and quality of the lens. It is especially important in correcting for spherical aberration and creating a clear and sharp image.

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