When the paper was close to the texts , the texts were pretty clearly visible (however I couldn't take a nice pic of that )

But when the distance between the paper and the text was increased (by just a little amount) , the texts disappeared (as in this picture)

I think it is happening because after lifting the paper l , the reflected light coming from the text (beneath the paper ) get scattered after striking the surface of the paper and could not transmit .

However I am not sure what is happening here .

1 : Can someone give a proper reason for this ?

2 : Also can this be used as an invisible cloak ?

3 : What's so special in this paper causing this effect ?

Note : I don't know which paper is this but a chocolate was wrapped in it.


1 Answer 1


Congrats! (joke) You have discovered what's known in Astronomy & adaptive optics circles as "The shower-curtain effect."

What you're observing is that the paper is a diffuse transmitter, meaning the light from the object beneath (your textbook) is transmitted but with some angle-scattering. Now, consider this as part of an optical system. Each point on the object is emitting(reflecting) light into a wide cone. If there were no diffuser present, your eyeball, i.e. the focussing lens, collects all those light rays and focusses them back to a point on the image plane (retina).

When the diffuser is very close to the object, the emitted cone of rays from each point is still small (diameter), so the diffused output is close to a "clean" cone, and thus can be focussed.

When the diffuser is farther from the object, the emitted ray-cone is large, and as it gets diffused the wavefront is now created from a multitude of points within the circle of incidence, and thus the best your eye (lens) can do is focus that 'blob' .

(Note: the "shower-curtain" name most likely stems from the scenes in "Psycho" where the killer can reasonably clearly make out the form of the woman showering, but from her point of view the murderer, several feet from the shower curtain, is not discernable)


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