Further Mysteries from the Optical World
Jason Kuznicki on Sep 3rd 2006 12:28 am |
Last night Scott showed me a trick he discovered as a child: It’s a remarkably simple way, within certain limits, to improve your eyesight — using only your hand. Scott stumbled onto it back when he was still in the single digits, during that time of life when everything seems mysterious and inexplicable. So he kind of just accepted it, as part of the manifold mysteries of life. No one taught him; so far as he remembers, he simply found it.
But it seems really — really – weird to me. Almost magically weird. It seems to bring his vision — and mine — back from the nearly blind myopia that we both suffer without our contacts. And we can’t explain the mechanism behind it.
The basic method is to create, in whatever way is easiest on your hand, a very small aperture. The thumb, index finger, and middle finger work well for this; squeeze the tips of these fingers together until they make a tiny triangle. Then look through it without your glasses. Do not press the aperture to your eye; look through it at a distance of perhaps two to five centimeters.
If you do it right, you will find yourself seeing things you could never have seen before. I get similar results by simply curling the index finger upon itself, but I could imagine different hand shapes and levels of flexibility that might make this impossible.
That’s really all there is to it. I was able to objectively confirm the benefit, too: While using this method, I could accurately read a digital clock across the room without my glasses. Usually it’s just an indistinct greenish blur from that distance, but there it was, right in front of me, as sharp as anything: 10:58. Only a moment before, I’d had no more than a vague idea of what time it was.
Then we started talking about how this phenomenon actually works. And we were mystified: A NASA engineer and your humble narrator — with all his, uh, savoir-faire — were unable to advance beyond a few improbable hypotheses in our quest to explain the Mysterious Seeing Fingers Trick. Here are some observations and possibilities:
–It seems unrelated to camera obscura effects; the image is neither upside down nor backwards. Letters and words read exactly as they should.
–There is a noticeable darkening of the entire visual field. This was especially pronounced in a dark room where the only visible object was the aforementioned digital clock. To my perception, the light of the clock itself was dimmed.
–It works even when the aperture is quite shallow; the effect is fully present when using a tiny hole in a piece of ordinary paper. Whereas when using the fingers the aperture is perhaps half a centimeter in depth, with the paper its depth is well under half a milimeter. There is no subjectively apparent change.
–It may have something to do with diffractional bending of light. Yet it seems an awfully big coincidence that any tiny aperture seems to work well, and that this tiny aperture restores excellent vision to each of our four myopic eyes.
–Distance between the aperture and the eye seems not to matter. Although to be perfectly sure of this one, I would want to conduct some experiments with an eye chart.
–A similar though much attenuated effect can (perhaps?) be had simply by squinting. Scott thinks he remembers that he hit upon the aperture method as a child while trying to figure out why squinting helps your vision. But squinting seems to help vision for an unrelated reason. You need not squint to obtain the effects of the aperture method, and for me at least, this effect is vastly stronger than the one to be had by squinting.
–Bizarrely, looking through an aperture with my glasses also yields perfectly sharp long-distance vision. If the aperture were somehow doing the work of a lens (through diffraction, for instance), we would expect the image to be blurry — exactly as my vision becomes blurred when I wear my contacts and my glasses simultaneously. It’s almost as if I had summoned Maxwell’s Demon, and he now sits frantically refocusing light waves so that they always form beautifully sharp images on my retinas. Were I inclined to detect consciousness in nature, I’d almost be tempted to start right here. (But to infer consciousness requires more evidence than this, I know…)
–We have no data on farsighted people using the aperture method. Scott and I both have slight astigmatisms, but we were not able to verify whether these were corrected, as they are so minor as to be unnoticeable.
–”Aperture glasses” work; stereo vision is possible with the technique. I verified this by using my left and right hands simultaneously, one on each eye. I also made myself look very silly at work. But wow, I sure could see well.
–One hypothesis would hold that the light hits only a small amount of the cornea. Because the ratio of thicknesses in the cornea determines the lensing properties of the eye, the “curvy” parts of the cornea — that is, the bad ones — are excluded. But this hypothesis seems untenable: If it were true, then we would expect the very center of the eye to have near perfect vision in all cases. But it certainly doesn’t.
–A second — and stranger — hypothesis is that the aperture does nothing in particular to the light. The effect, then — I’m sure this sounds pretty weird to optometrists — is entirely psychological. And so is myopia itself: Nearsightedness has nothing to do with the shape of the eye, and everything to do with unconscious bad habits. I mean, if it takes effort and practice to use all our other physical faculties, and if these may all be done well or badly, then why should we expect differently of sight? By focusing not the light but our attention upon a target, the aperture momentarily corrects our bad habits. According to this hypothesis, if we could train ourselves, perhaps with aperture glasses of increasing size, we could eventually correct myopia, which is after all a bad habit and not a physical characteristic.
–Another hypothesis — and this probably sounds really, really weird to anyone who knows optometry — would be that it’s somehow less work to focus a smaller image. The eye doesn’t have to change its curvature so much. I don’t see how this makes any sense at all, but I offered it up since I don’t have anything better right now.
–Googling doesn’t seem to help. I’ve tried and tried, and I can’t seem to find a search string that yields what I’m talking about. Instead I get information about high-tech cameras, yogic vision techniques, and enigmatic notes to physics classes. Just add a few tentacles and you’d have an H. P. Lovecraft story. But no explanation of the Mysterious Seeing Fingers Trick.
What say you, readers?
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I have been using that technique every say for thirty years. When I wake up at night, I make the small triangle to read the clock.
Wow, what a neat trick! My right eye has always been fine, but my left is mildly myopic. I, too, can now read that clock across the room with just my left eye. Youth and vigor return.
Myopia occurs when an image focuses (i.e., the light rays composing the image meet) in front of the retina rather than on the retina. The only light rays involved in myopia, therefore, are those that reach the retina by diffraction, in other words those that do not hit the pupil dead-on. The direct rays have nothing to do with myopia. The aperture method limits the light rays to the direct ones, and removes much of the light that reaches your retina by being diffracted. It doesn’t matter how non-spherical your eye becomes with age; the direct rays don’t contribute to myopia. This would tend to support your “diffractional bending of light” hypothesis. Another observation: It seems that the aperture must be smaller than your pupil to work.
Of course, now that I know this trick, people will think that I’m trying to crush their heads, or communicate that some part of their anatomy is very, very small, when all I really want to do is see them clearly.
I also discovered this trick at a young age. I have had to wear glasses since I was five years old so there was ample opportunity for me to experiment with various techniques.
Much later in life I was taught that a small camera aperture would tend to bring more of a photo into focus at a time. Maybe it’s part of the same phenomenon.
You’ve rediscovered the aperture stop. Your artificial aperture, whether it is made with your fingers, or a hole in a piece of paper, is “stopping down” your eye, like raising the f-stop on a camera lens.
This has the effect of increasing the depth of focus of any lens–as the light from any point in the scene enters your eye from a more and more restricted angle, the consequences of misfocus become less and less important.
There’s a reasonably good explanation, as well as pictures of the same scene taken with a lens both wide-open (low-f/number) and at small aperture (high f/number) at: http://en.wikipedia.org/wiki/Aperture
You were too quick to dismiss the camera obscura–the reason this trick doesn’t seem to invert the scene is that the image on your retina is already inverted. Your brain processes the signal so as to report to you that the world is right side up.
There’s more on the psychological foundation of myopia here. The short: it’s provocative, but research is lacking.
I remember hearing about a study of pilots who failed vision tests under control conditions, but passed them when told their careers were on the line. Can’t find a direct reference (yet), though.
A little further research, as Sam Paris pointed out, would have shown that it is a well-known effect in optics. Many photographers could tell you that you are just increasing depth-of-field. Because the aperture is small, you are also blocking more light, which is why the scene seems darker.
Of course, if you were a proponent of so-called intelligent design, your answer could have been this is just another proof of G-d, since it could not have arisen out of a random collection of physical and optical properties. No need to investigate further.
Sam –
I think you were too quick to dismiss my dismissal. You wrote,
You were too quick to dismiss the camera obscura-the reason this trick doesn’t seem to invert the scene is that the image on your retina is already inverted. Your brain processes the signal so as to report to you that the world is right side up.
But this can’t be correct: I am well aware that the eye acts as a camera obscura, and that it turns the image upside down and backwards on the retina. We don’t “notice” this because we are wired to receive our information this way. But if the aperture were also inverting and reversing the image, then the end result would be an image right side up and not reversed on our retinas. And this, since we are not wired for it, would look wrong. It does not, however, look wrong: It looks like it always does. So unless I misread you, this isn’t what’s going on.
Nitpicker —
You’re right. And that’s just what I had in mind when I wrote what I did.
Jason sez:
” But if the aperture were also inverting and reversing the image, then the end result would be an image right side up and not reversed on our retinas.”
Erm, no. You only get the one inversion. You would get two inversions if you formed a real image with the “pinhole” you create with your fingers, then looked at that image with your eye. As you’re doing it, though, your pinhole is simply a part of the image forming system of your eye, little different from your iris. You wouldn’t expect your view of the world to suddenly invert just because you walked from a dark room into bright sunlight, would you?
Look at it this way: The lens of your eye, like any image forming lens, takes all of the light from any given point on the scene, and redirects it to a corresponding point on your retina; that is, light from a point that hits the top of your lens, the middle of your lens, and the bottom of your lens, all goes to the same place on your retina–or it’s supposed to, anyway.
Often, it does not, either because your eye is focused on something else, or because you are nearsighted, or have some other aberration in your vision. The aperture restricts the set of angles through which the light from any given point hits your eye, and the area of the lens that the light hits, making the job of forming an image easier, and the consequences of imperfect focus less severe, since the rays all leave the lens traveling in nearly the same direction, and end up in nearly the same spot, even if the lens is not capable of perfect focus.
This effect is most striking in a pihole camera (which is often, but not always, the image-forming element in a camera obscura), where the aperture is stopped down so severly that even with no light bending, no “focusing”, at all, the rays from a point on the scene that manage to get through the pinhole will all end up on nearly the same spot on the screen or the film.
A related feature:
I’m now over fifty and getting to the stage of not having arms that are long enough :-). And, as others have noted as their eyes age, I really prefer a strong light to be able to read in. It struck me about a year ago what was going on, and it’s the same f-stop solution that Sam Paris mentioned.
Under a strong light, the pupil contracts, which is like a higher f-stop and which has a much greater depth of focus. So things that are outside of the focus range in dim light are within focus in bright light.
Very interesting, am myopic as well (in more ways than one!) and believe, if I’m doing what you described right, that it seems to work. Since this is the ‘net maybe you can post a pic or how you form the aperture :)
Nice tangents provided by your commenters too, am off to go follow them now…
http://en.wikipedia.org/wiki/Pinhole_camera
Thanks to everyone who contributed to the discussion, and especially to Sam, who made it all clear as of his last post. I think I’ve got it now. I should stress that I have no training in this area at all, so it really was puzzling to me. And I’m sorry to have sounded like such a crank there about it all.
Another fun trick I’ve found that does this same optical effect: shine a really bright light into your eyes. After you stop being dazzled, turn off the light & look around. For a couple seconds, your vision will be much sharper, although (as with the finger trick) everything will seem a bit dark … In this case, your pupil is acting as the tiny aperature. It dilates in response to the bright light, to prevent damage to your retina. When the bright light is removed, it takes some time for the pupil to relax & open up to let in more light. Until it does, you’ll get a marked improvement in visual acuity.
Nice. Blogged it to the site in about one nanosecond. Thanks.
My brother figured this one out when he was young too. I thought he was nuts–me being the only member of my family who has never needed glasses (I’m pushing 40 now, and still waiting for my vision to start blurring.)
As a person with normal vision, I’ll offer this: when I do this to my right eye, and then at the same time open my left–so that I see both the pin-hole image, and a normal one–the two images meet up exactly and are the same size. They meld together just like they would if the pin-hole weren’t there. I also checked to see if my brain was just processing my dominant eye–I intentionally focused with my left and then my right. Still the images were the same size. I switched the pin-hole to the other eye, again to check the dominance issue, and the sizes still came out the same.
In other words, with my good eyes I don’t get this effect.
I remember a TV comercial quite a few years ago about glasses made like that . a piece of something with alot of tiny holes in it replaced the lens.
I got my first eye exam and pair of glasses about thirty years ago. I clearly remember the doctor telling me at the time to do this if I lost my glasses. He demonstrated it with the curled index finger method.
While in the eye doctor’s office the other day, I picked up what looked like a pair of dark glasses. In fact, it was literally “full of holes.” I am somewhat far sighted and was shocked to discover that the glasses worked to “correct” my vision! I could read with them! It turns out that multiple holes work as well as one, if they’re small enough.
The conundrum, of course, is light. Because the glasses block large amounts of light, everything is darker. If the room is dark, they pin-holed glasses are no good.
Also, that is why you can generally see better by bright light. The strong light narrows your iris, which has roughly the same effect–improving your depth of field/focus.
There is another useful thing you can do if you’re shortsighted and find yourself without glasses. Put your index fingers at the outer corners of both eyes, narrow your eyes to slits, and then pull back with your fingers so that there is a bit of pressure on your eyeballs. (It looks like you’re pretending to be Oriental.) This slightly shortens the distance between the lens and the retina, which is a way of correcting for myopia. (At the same time it will increase the depth-of-field as discussed above, if your eye-slits are narrower than your pupils.) Focusing on distant objects can be greatly improved this way.
The iris does not dilate in bright light; it contracts.
Rooming with optometry students in college, I learned that pinhole glasses would work for everybody…if there were enough light. Pinholes also restrict the field of view, but that’s why they work. And pinholes are not lenses, any more than the iris of the eye is a lens. Which is why there is no image inversion with pinholes.
It’s all a matter of depth of field and what photographers call “the circle of confusion.” Light rays that are more parallel allow the retina (or the film in a camera) to create a smaller circle of confusion on the light-sensitive surface; when the circle of confusion grows larger, points in the image are perceived as large blobs of light. That is why the image is blurry, or “confusing.” A small aperture (f-stop) militates against that by making the light hit the film/retina at an angle closer to the perpendicular. But there is a limit: light passing through a very tiny aperture bounces around as it hits the edges of the aperture, messing up the smooth advance of the waves/particles, and a blurring of the image occurs. It’s called diffraction distortion, and that’s why photographers do not take photos at very tiny apertures (f-stops numerically higher than 32 begin to cause serious problems for 35 mm photographers, and yes, the point at which such problems arise is a matter of opinion, depending on the results the photographer is willing to accept).
If I could edit my comment, I’d change “depth of field” to “depth of focus.” Everything else in the comment is still correct, because if you limit the incoming light so that the rays are all close to parallel, you get great depth of field and great depth of focus. Sorry for the slip in technical terminology!
pretty well known phenomenon , however the physics has to do with both aperture and size of pupil. the post about diffraction being a limiting factor is correct. the post about why image not inverted is a good way to explain this to a non professional. we were given full explanation at med school however i remeber little bits of the physics only.
I really enjoyed reading this article and comments cause it reminded me of my childhood days when i became myopic but did not know that and kept thinking the teacher had horrible handwriting. then almost instinctively i curled my index finger with thumb and WOW i could see again. i felt i discovered something major. i played around with this for a while and ended up piercing rubber erasers with a freshly sharpened lead pencil to create a non fatiguable pinhole that helped me see the blackboard until the teacher figured from my requests to enlarge her writing that my vision was screwed and wrote a note to my parents to visit the doc. at discovery i had more than two diopters of loss already.
this article felt cool to read as it returned me to a tiny schoolday adventure