0

Let's define a screen as a surface emitting light in all directions.

What I'm trying to find out is if there is an optical method that allows bundling the emitted light to be focused on a single point in space, behind which an inverse image of the screen would be projected much like a camera obscura, while allowing more light than if the principle of a camera obscura would be actually used. I am not trying to just achieve a camera, the fact that the light must be bundled into a singular point in space is of importance.

Camera obscura and lens solution The above shows a less than ideal solution using a camera obscura and an ideal lens.

A normal lens An ideal lens will focus the light, but not in the same point in space.

The screen cannot be placed very far from the focusing solution, so just placing it far enough away to assume parallel light rays, then using a lens to focus is not acceptable.

Thanks for any help in advance.

Markus Appel
  • 156
  • If all points of the screen are emmmiting, then the rays could be almost paralell... then you'd ony need to put it in the focus. – FGSUZ Feb 10 '21 at 10:50
  • Your assumption that a 'screen' of finite size will produce parallel rays is incorrect. That, even in approximation, can only occur when the source is so far away that the optical system cannot resolve it, so it appears to be a point source. – Carl Witthoft Feb 10 '21 at 13:29
  • 1
    Perhaps check out the term "etendue" for more information on why this can't work. Further, @FGSUZ your statement is incorrect. Each point on the screen emits a hemispherical wavefront – Carl Witthoft Feb 10 '21 at 13:30
  • 2
    TLDR consequence of "etendue;" If you have rays emanating in all directions from every point on a continuous surface, then it is impossible for geometric optics to focus all of those rays onto a single point. – Solomon Slow Feb 10 '21 at 13:53
  • A series of telescopes to demagnify your source until you are happy with the result? So, if you have an object with size X and your definition of a single point is "anything smaller than Y" then making an optical system with a magnification <Y/X would work for you? The last image you showed shows 3 points because you have 3 sources. A continuous screen would create a continuous focus. If you demagnify its image, it becomes very small – José Andrade Feb 10 '21 at 17:00
  • If you try to focus all of the light into one spot, have a look at this question: Is it possible to construct a lens which focuses all the light rays from an extended object in one point? If not, the further you go away from the screen the more parallel the rays will be, so the focus will be narrower. But at the same time the image after the focus will blur, because you run into the resolution limit. It's not possible to have both, a sharp focus and a sharp image. – A. P. Feb 10 '21 at 19:57

0 Answers0