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On a clear morning, light comes through this window (viewed from the inside)

It then hits the door on the opposite side (so viewing from the outside the door straight on the other side)

There is nothing particularly special going on.

However, if I go through the door and turn around to face the door, I see this

Light seems to be dispersing into the color spectrum solely because of the hole in the wooden door. Some days it's even clearer than it is today.

What gives? I know light can do this through prisms, but how come it's happening with only a hole in a door?

Edit

As per Floris' instruction, I did a little more experimenting. Here are the results (extra hint/spoiler):


It's far from perfect because I made the hole using a black gym bag and some masking tape, and used a handheld mirror to reflect it onto the door, but I think it shows his explanation to be correct pretty well!

Zach Saucier
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  • Can you place a mirror at the point where blurry image was formed? If possible click a photo and upload it. – Sensebe Sep 30 '14 at 13:58
  • @Godparticle I'll have to wait until tomorrow (hopefully it'll be sunny) because I won't be home until tonight – Zach Saucier Sep 30 '14 at 13:59
  • OK. I will be waiting.. – Sensebe Sep 30 '14 at 14:00
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    A natural pin-hole camera, beautiful. – Adsy Sep 30 '14 at 14:55
  • A friend linked me to a related article on light that is pretty interesting – Zach Saucier Sep 30 '14 at 16:00
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    If you are going to do some follow-up photography, you could cover the hole with a black piece of paper with a smaller hole in it; you will see the image resolved more clearly (although it will be darker, so you may need to put your camera on a tripod). With a piece of white paper to project onto things will be even clearer. Would be an awesome update to the question (and nice confirmation of the answer...) – Floris Sep 30 '14 at 16:13
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    @Floris I updated to show the results of a little more experimenting :) – Zach Saucier Sep 30 '14 at 20:41
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    That's great - you can even see the red and white cars! – Floris Sep 30 '14 at 20:49
  • Not often one to make a plug, I highly recommend anyone who finds this accidental pinhole camera interesting to check out the documentary "Tim's Vwrmeer" which explores in a very hands-on way what might have been the secret behind Vermeer's astonishingly life-like (almost photographic- spoiler alert) paintings. http://m.imdb.com/title/tt3089388/ – Floris Oct 01 '14 at 10:40
  • @Floris: Although being able to examine scenes as two-dimensional projections may help an artist develop an understanding of perspective, and artists were no doubt aware of the camera obscura as well as photography, many good nineteenth-century painters such as William Bouguereau much preferred painting live subjects to painting from photographs. My personal hunch is that the role of the camera obscura in the development of painting may be similar to the role of motion reference films in the development of animation. A good animator won't copy the movements from a live-action reference, but... – supercat Oct 01 '14 at 15:25
  • ...studying a live-action reference may help an animator to understand how things move in general. Tracing live-action footage (rotoscoping) results in dull and lifeless animation. Likewise with tracing photographic projections. A camera captures everything things from one focal point, but that's not how people see them. People's eyes change focus as they look at different parts of a real-world scene; a good artist can capture that in a way that a camera cannot. – supercat Oct 01 '14 at 15:31
  • @supercat - the documentary I refer to goes far beyond just accurate perspective, and demonstrates how exact reproduction of lighting and coloring could be achieved using an optical apparatus; remember that Vermeer lived in the 17th century, well before photography. And one of Vermeer's most famous paintings (the piano lesson) shows optical effects (foreground detail out of focus; chromatic aberration; spherical distortion) that could be explained by postulating the use of a lens-based imaging system. – Floris Oct 01 '14 at 15:31
  • @Floris: Some people can produce very realistic paintings entirely free-hand. It's also possible to use a compass and straightedge to work out perspective projections; I think even the ancient Greeks figured out such things. I've seen one of the oft-cited paintings at the Memphis Brooks museum; photographs don't really do it (nor many other paintings) justice, and for all I know it might have been done via camera obscura, but at most the CO would have been a tool for getting an understanding of the world, and artists since have certainly learned to paint without the CO. – supercat Oct 01 '14 at 15:43
  • @supercat - I agree with everything you say; but while it is possible to produce life-like paintings without aids, there is substantial evidence that Vermeer and other "old masters" did use optical tools; it's a fascinating story captured in several books and the documentary linked above. See also http://www.vermeerscamera.co.uk/home.htm and http://en.wikipedia.org/wiki/Hockney%E2%80%93Falco_thesis which has both pros and cons of the theory. – Floris Oct 01 '14 at 16:28
  • @Floris: Have you seen artrenewal.org? That site has a paper which discusses Hockney. My own view is a bit more tempered than that of the authors on that site; I think it's entirely plausible that some artists used a CO to understand how things should be depicted on canvas, but consider ridiculous the notion some people have that use of a CO negated the need for genuine artistic talent. – supercat Oct 01 '14 at 18:03
  • I don't understand the latest edit (v7) -- it's extremely annoying and degrades the usefulness of the post. – Emilio Pisanty May 12 '20 at 14:58
  • @EmilioPisanty I didn't want people to get an extra hint at what could be causing it if they didn't want to, so I hid it by default. I won't be upset if someone reverts the edit, though I would disagree with the revert. – Zach Saucier May 12 '20 at 15:11
  • @ZachSaucier This is a science venue, not a puzzles site. If you want that type of structure, then I would suggest moving the added photographs to the accepted answer instead. – Emilio Pisanty May 12 '20 at 15:14
  • @EmilioPisanty Adding my content to the answer felt wrong given it's not my answer. Feel free to bring it up on meta if you'd like. – Zach Saucier May 12 '20 at 15:21

1 Answers1

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You have created a rather poor pinhole camera (camera obscura). You can see an "image" of the sky, a green space (trees) and even a reddish brown blur that is your driveway.

This is not diffraction or refraction - it's geometrical (classical) optics. Because the hole is pretty big, you see a very blurry image. But basically, the light from the sky falling through the hole hits one part of the door; the light from the trees hits a slightly different part; and the light from the driveway (the lowest object on the outside) hits the highest part on the inside, after coming through the hole.

enter image description here

Incidentally - if you took a picture from the perspective of the hole in the door, I am guessing you would see more of the sky - in your photo of the view, the sky is barely visible, but in the doorhole image it's much more prominent; and conversely, one sees less of the driveway. This is consistent with the photo being taken from a different vantage point.

Community
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Floris
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  • You are right. Diffraction only occurs at a width not possibly obtained by the manipulation of the wooden door. – t.c Sep 30 '14 at 13:47
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    @t.c indeed - the hole is much too big for diffraction. – Floris Sep 30 '14 at 13:49
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    I suppose I was thinking about my physics lectures on light diffraction too much, preventing me from thinking of a more simple principle. Thanks for the help! – Zach Saucier Sep 30 '14 at 13:52
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    @ZachSaucier - this happens all the time: ideas we use a lot (or have recently been exposed to) seem to show up in all kinds of places. The doctor that learns about a new disease suddenly "realizes" that lots of his patients have it... etc. This is normal. For me these puzzles are fun. You're welcome. – Floris Sep 30 '14 at 13:56
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    Good explanation. One can read more on pinhole cameras and camera obscuras on Wikipedia and elsewhere. – Jeppe Stig Nielsen Sep 30 '14 at 15:18
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    +1 Though instead of OP having created a poor pinhole camera, I'd say rather that his house has created a pretty good one, as far as pinhole cameras accidentally created by houses go. – Reinstate Monica -- notmaynard Sep 30 '14 at 15:58