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I was chewing gum when I took the Trident gum wrapper and rolled it into an open cylinder with a diameter of about 1.5mm (give or take 0.15mm). When I look through the gum wrapper (I have to put it right up against my eye and position it just right to be able to see all the way through), images seem about 10% smaller (extremely back of the napkin assumption) than without the gum wrapper.

This is hard to measure empirically, so I tried to take a photo showing this effect, but the camera showed no difference between the two (the one through the wrapper is brighter, but I think that's just the iPhone camera trying to adjust to the surrounding dark and thus trivial). Just to confirm, I asked 6 people if they see any differences between viewing items through the gum wrapper and without the gum wrapper, and all of them said that the images through the gum wrapper looked smaller than without the wrapper. [EDIT: Asked 4 more people and 3 of the 4 said the image was 5-10% larger than normal]

[EDIT 2: The images also get larger (smaller for the people who said the image was larger) as the wrapper moves away from the eye and towards the object, eventually reaching true size when the wrapper is at the object.]

The only reason I could think of this happening is based on another observation I made. As I brought the gum wrapper into position, objects seemed to bend as they passed over the wrapper in my vision. The only thing I could think of is that the diameter of the cylinder is small enough that this "bend" doesn't have time to even out, and thus collides with the "bend" on the other side of the wrapper and creates a smaller image. However, this assumes that the distortion is causing images to be smaller when viewed through the wrapper. The "bend" distortion could also just be a byproduct of the actual cause of this phenomenon and just a symptom of the image getting smaller.

Why is this occurring?

Qmechanic
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d1600552
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    had to upvote after reading just the first line. – dlatikay Jan 31 '20 at 14:45
  • Actually, after having re-read your question, I now think my answer might be wrong. There's an effect I've recalled discussed here: How does light bend around my finger tip?. Although in the answer there the occluder isn't a hole, the background does distort in a way that might change apparent size of the object. Could you try re-taking the photo, making sure that both the object and the wrapper's inner edge are out of focus? I suppose you might capture the effect with the camera then. In that case you might want to un-accept my answer. – Ruslan Jan 31 '20 at 15:48
  • When I make a little hole with my hand and look at the title of the movie I'm looking at I can see no difference, so I guess the first answer is right. This isn't a physics phenomenon, though. – Deschele Schilder Jan 31 '20 at 16:02
  • @Ruslan ran out of gum. will buy more and update in a bit – d1600552 Jan 31 '20 at 23:46
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    I'm voting to close this question as off-topic because it belongs to the psychology SE-site – Deschele Schilder Feb 01 '20 at 00:05
  • @dlatikay Upvoting after reading the first line? Why? I know you have to be nice to new contributors but basing an upvote on a first line... – Deschele Schilder Feb 01 '20 at 00:30
  • You have failed to provide evidence that there is any consistent effect at all, either real or imaginary. It is pointless to try to speculate about an effect which has not been corroborated and might not exist at all. – sammy gerbil Feb 04 '20 at 03:28
  • @sammygerbil It's difficult to provide said evidence. I did the best I could (asking multiple people and using a camera) with the data I could think of. I can try any other methods you suggest to give better data. – d1600552 Feb 04 '20 at 07:23
  • @Ruslan Managed to get more photos. It looks like you're right. The last image is out of focus in both places and looks a little larger in the camera. I wonder why it looks smaller through my eyes then. – d1600552 Feb 04 '20 at 07:39
  • Could you try to tame the exposure settings? Overexposure makes it hard to compare the images. – Ruslan Feb 04 '20 at 07:51
  • @d1600552 Yes I appreciate the difficulty. I am not blaming you for lack of effort. – sammy gerbil Feb 06 '20 at 22:34

5 Answers5

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Given that your camera failed to notice the difference, what you describe sounds like the Moon illusion. Namely, when you see an object in some confined context, the object seems larger, although actual size of its image on the retina remains the same.

Ruslan
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  • That makes sense, but then why does it become smaller for some people and larger for others? – d1600552 Jan 31 '20 at 06:01
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    @d1600552 that's a hard question (at least to me), because it's beyond the scope of physics, and instead is in the scope of cognitive science. – Ruslan Jan 31 '20 at 06:02
  • I see. That wouldn't make the moon illusion answer to this invalid then? – d1600552 Jan 31 '20 at 06:13
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    @d1600552 I don't think it would make this invalid, since the reason remains the same: contextual perception distorting attempts at measurements. The variability of results between the people only underlines the fact that this is not a physical (geometrical) effect, but cognitive. – Ruslan Jan 31 '20 at 06:16
  • Rusian I wanted to make the same comment. But I don't understand why you have written "confined". Moon is smaller when confined as seen through a pinhole not in sky. I want to add that moon illusion has even two scenarios . Larger than it is up in the sky. Even larger down at horizon. One point here is brightness. We tend to perceive as bigger the object that are brighter. If this is cognitive or related to the optics of the eye I don't know. Plus one although now I am curious about the mechanism proposed below, too. – Alchimista Jan 31 '20 at 09:03
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    @Alchimista I won't make any hypotheses here about how this cognitive effect works, because it isn't my area of expertise. The main point of this answer is that, if an instrument doesn't see the difference, and there shouldn't be any when you think of it, and when different human observers report different perception, most likely the effect is subjective and not physical. – Ruslan Jan 31 '20 at 09:10
  • That is sure, wasn't my point. – Alchimista Jan 31 '20 at 09:12
  • The camera may fail to notice the difference, first, because it is way smaller than a human eye and has a lot shorter focus. – fraxinus Jan 31 '20 at 15:26
  • @fraxinus this doesn't change anything. Size of the camera and its DOF might mean something if the effect were related to an out-of-focus (partially or completely) scene or something like that. But the scene is supposed to be in focus, so that is irrelevant. – Ruslan Jan 31 '20 at 15:34
  • When I initially did the experiment, I thought it had to do with the human eye lens vs a camera's digital input, as the first 6 people all said it was smaller for them too. It was only once the 3 people said it was larger for them that I am more inclined towards this being a cognitive effect. – d1600552 Jan 31 '20 at 23:34
  • @Alchimista This would make sense given the initial findings, but the brightness and largeness correlation doesn't explain why some people perceive it as larger and others as smaller. – d1600552 Jan 31 '20 at 23:35
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    @d1600552 surely our brain is involved, no doubt about that. I also wanted to mention the moon paradox, indeed. – Alchimista Feb 01 '20 at 08:04
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This is a matter of perception, rather than actually bending or focusing the light. This is why different people can perceive the effect differently, and the camera does not. When you see things out of their normal context, you may orient their perception differently.

Adrian Howard
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It's because your vision processing wetware evaluates the image as being closer than it really is. So naturally it appears smaller, given that its angular diameter remains unchanged.

There are two factors at work here: firstly, you lose binocular vision; secondly, the image is always in focus because of the narrow viewing aperture, so you lose the ability to estimate the distance from the blur. Possibly these factors work against each other in some people, so results may differ.

But you say you performed the experiment twice, with opposite results; so perhaps conditions were different? Maybe the first experiment was performed indoors, and the second experiment in bright sunlight?

TonyK
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  • Nope, it was in the exact same conditions (from my desk). Any modifications between the 2 experiments are listed there. – d1600552 Jan 31 '20 at 23:31
  • Listed where? In any case, this is clearly a question of perception rather than physics. You can't change the size of the image with just a gum wrapper. – TonyK Jan 31 '20 at 23:43
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With a hole diameter small against the iris, the lens becomes superfluous, you have a pinhole camera, that maps points outside to points on the retina regardless of distance.

The image scale fo a pinhole camera is identical for all distances, objects of equal diameter simply scale linearly by distance on the retina.

The aspect ratio is simply given by the distance from the retina to the diaphragma, i.e. to the point of the smallest diameter of the light ray bundle. The effective focal lenght in your experiment is 10% longer than than the distance iris-retina.

Imaging by lens and by a pinhole in front of the eye

I tried the experiment with two holes, a tiny on and a biger one side by side in an aluminium foil.

Fast changing the diaphragm before the eye only changes sharpness, the object seems to be reduced by image dilation.

But this an effect strongly dependent on the individual lens quality, of course.

Roland F
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The fact you are looking through a small (1.5 mm) hole causes diffraction, i.e. the paths of the photons start diverging after they go through the hole.

This has two effects:

  1. The object looks smaller, because it is like seeing it through a diverging lens.
  2. If you are so lucky to be myopic, i.e. short-sighted, you can see the object slightly more in focus.
Pietro
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  • Diffraction is not operating to a meaningful degree on this scale. Nanometer-wavelength light does not diffract around millimeter-scale objects very much at all. Nearsighted people can improve their vision by squinting, but the entire world does not appear to shrink or grow as you close your eyes. – Nuclear Hoagie Feb 16 '24 at 17:01
  • @NuclearHoagie - Diffraction is detectable with the naked eye. If you are moderately short-sighted and you squint, you can realize you see red lights better than blue ones, because of their longer wavelength, causing more diffraction. And an in-focus world looks a bit smaller than an out-of-focus one (as any myopic can see putting their glasses on and off). The same phenomenon can be noticed reading with a piece of paper covering half of your field of view. – Pietro Feb 16 '24 at 17:40
  • All that is true, but the everyday experience of a normally sighted person confirms that squinting definitely does not change the apparent size of objects to a meaningful degree. As you point out, diffraction depends on wavelength, and the OP described no prismatic effect. – Nuclear Hoagie Feb 16 '24 at 17:46
  • @NuclearHoagie - Also consider that even if the wavelength of red light is 700 nm, this is not the distance you have to perceive, but the angle its path deviates from. – Pietro Feb 16 '24 at 17:46
  • @NuclearHoagie - That is the only good side of being myopic: you can witness optical phenomena with the naked eye that normally sighted people can only dream about. – Pietro Feb 16 '24 at 17:51