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This video* (linked at the correct time of 0:26 sec) shows a scene inside a room of a home. Apparently projected on the wall is an imperfect but recognizable image of the outside street scene. The light forming this image has passed through a translucent curtain.

Here's a still which shows the projected image of an outside building onto the wall:

enter image description here

And another with someone's arm adding a shadow:

enter image description here

An opaque fabric material would just cast a shadow. I would have expected a translucent material to totally distort any pattern on the incoming light from the other side. And without any curtain you would of course expect also get no discernable image.

Instead it seems like this fabric is actually behaving like a lens? I am familiar with the concept of a camera-obscura, which is basically just a tiny hole that acts like a lens. Extrapolating from that... maybe the fabric is like thousands of such pinholes. But what is the mechanism that allows them to form a more-or-less focused image?

Note that the projected image covers a large wall area, including a portion of one wall which is perpendicular to the curtain; so the "focal plane distance" (if that's the right analogy) is not consistent.

It doesn't appear that this video is a fake, though I guess I can't rule that out.

(*) Its not a very serious video in total, and could even be NSFW, perhaps

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  • $\begingroup$ "maybe the fabric is like thousands of such pinholes" - exactly $\endgroup$
    – Max
    Dec 2, 2020 at 3:34
  • $\begingroup$ @Max pinholes invert images see en.wikipedia.org/wiki/Pinhole_camera . I would vote for fake. $\endgroup$
    – anna v
    Dec 2, 2020 at 5:00
  • $\begingroup$ @Max I watched the video at 34'' there is an inverted image. so the one shown above is just the view through the curtain, so I take back my vote for fake. $\endgroup$
    – anna v
    Dec 2, 2020 at 5:18
  • $\begingroup$ @UuDdLrLrSs you have posted a snap that is given to show the road, the inverted image is the object to show at 34'' $\endgroup$
    – anna v
    Dec 2, 2020 at 5:19
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    $\begingroup$ It might not be the curtain only see this people.csail.mit.edu/billf/publications/Accidental_Pinhole.pdf $\endgroup$
    – anna v
    Dec 2, 2020 at 6:32

1 Answer 1

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Here is a better video of this Accidental Camera Obscura/Pinhole Camera Effect :
https://www.youtube.com/watch?v=Leuuaie2K4s&pbjreload=101&ab_channel=ViralHog

The thousands of pinholes in the curtain material are not the only source of light in the room. A more obvious and far brighter source is the narrow vertical slit caused by the gap between the two curtains, shown at the start of the video.

Others have posted similar images in which the light source is clearly a narrow gap between the opaque curtain and the window frame. For example :

https://www.youtube.com/watch?v=NZ-VJfgenfw&ab_channel=squeevey
https://www.youtube.com/watch?v=fU5FqvsOXwU&ab_channel=OlivierLance
https://www.youtube.com/watch?v=qU2FAL4hnJY&ab_channel=ZincDaddy
https://www.youtube.com/watch?v=qgRRgq7ijIU&pbjreload=101&ab_channel=W https://www.youtube.com/watch?v=qgRRgq7ijIU&ab_channel=MrMrMike1337MrMrMike1337

The role played by the curtain here is not as a source of light but as a semi-opaque obstacle to reduce the size of the 'pinhole'. Totally opaque curtains would have given a better effect.

If there had been no gap between the curtains then the image from the holes in the material would have been similar to that from a window-sized pinhole! Each point on the window could be regarded as a pinhole. There is no single image from the window or curtain because the thousands of pinhole images are not aligned - they are almost totally blurred out of recognition. Different point objects are imaged at a single point on the wall, causing no clear overall image to be formed.

What is surprising for me is that a single small round hole is not essential. The effect also works (to an extent) for elongated holes - eg a narrow slit or even a series of narrow slits (see below). The impact of longer, wider or multiple slits is the same as for a bigger pinhole - ie it improves brightness but reduces the focus of the image.

enter image description here

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