How can an intervening lens correct an out-of-focus projected image?

Thread starter Loren Booda
Start date Dec 3, 2008
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An out-of-focus image from a projector can be corrected by an intervening lens because the lens can adjust the light rays before they reach the screen. Once the light hits the screen, the direction of the rays is altered due to specular reflection, making it impossible for a lens to refocus the image. In contrast, using a mirror instead of a screen allows the light rays to be redirected back, enabling refocusing. This difference highlights the importance of preserving the light's direction for effective image correction. Ultimately, the medium that the light interacts with determines the possibility of refocusing the image.

Dec 3, 2008

Loren Booda

Why can an out-of-focus picture on a screen from a projector be corrected by an
intervening lens, while a lens cannot correct the out-of-focus image once
impinged on the screen?

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Dec 3, 2008

russ_watters

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When the light hits the screen, the direction the rays travel is not preserved due to the specular reflection. Replace the screen with a mirror and you can re-focus the light.

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