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  #1  
Old 09-21-2005, 12:38 PM
tiltypig tiltypig is offline
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Pinhole glasses?

On a recent trip to Germany, I saw this cool display at the Munich Deutschesmuseum, in an exhibit about artificial body parts--specifically, those having to do with improving one's vision. It consisted of a piece of cardboard with a pinhole poked into it. You could hold the cardboard up to your eye, look through the pinhole, and voila, no more glasses needed--I am nearsighted, and the blurry, unreadable vision chart across the room suddenly resolved itself into clear letters pretty much all the way down the chart.

Unfortunately, the explanation was in German, so I have no idea why or how this works.

Can someone explain it to me?

Also, why don't people wear glasses with tiny pinholes poked into them instead of glasses? (or why didn't they, in the days before reliable/cheap/accurate glasses?) Or if the answer is because wearing things like that give you a terrible headache, then why didn't people use a piece of paper with a hole in it instead of opera glasses/telescopes/etc.? It seems easy and cheap.

(I haven't experimented with this at all since seeing the museum exhibit, so maybe there are obvious drawbacks that I'm not thinking of.)
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  #2  
Old 09-21-2005, 12:49 PM
JimMacMillan JimMacMillan is offline
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Perhaps this WikiPedia article wil give you some insight . Read the link entitled Circles Of Confusion to get a better understanding. I don't know if this would damage your vision or not. That is for people with more knowledge than I to answer.
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Old 09-21-2005, 12:55 PM
Finagle Finagle is offline
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Most lenses are sharper when "stopped down" because it's harder to focus light the farther you get from the axis of the lens. I believe there's also a pinhole effect in that light rays from a small enough aperture are already pretty much parallel and don't need much focusing (which is how pinhole cameras and camera obscura work).

Unfortunately, the smaller the aperture, the less light is hitting the eye (or film). So in a dark room, you won't be able to see much.
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Old 09-21-2005, 12:58 PM
FatBaldGuy FatBaldGuy is offline
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Quote:
Originally Posted by tiltypig
Also, why don't people wear glasses with tiny pinholes poked into them instead of glasses? (or why didn't they, in the days before reliable/cheap/accurate glasses?)
Think about trying to walk (or drive ) around with all your vision blocked off except for a tiny pinhole over each eye. I don't think I'd like to try it.
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Old 09-21-2005, 01:15 PM
Squink Squink is offline
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Pinhole lenses aren't practical for wearing around town because they block out most of the light. Although they make things clear, they also make them dim.
That said, you can make a functional, if triangular, pinhole with your thumb and two forefingers. It's useful for reading things like LED clocks from across the room.
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Old 09-21-2005, 01:16 PM
CalMeacham CalMeacham is offline
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There are several sites about pinhole glasses, mostly devoted to trying to sell them to you.

It's not a single pinhole -- it's rows and columns of them. The principle does work, but it's not as good as proper eye correction. Each pinhole limits the aperture of your eye, and thus minimizes the aberrations that increase with pupil size. Well-corrected glasses, though, do a better job, and let a lot more light through.

I discovered the effect as a kid when looking through the hole in my wristwatch strap -- distant objects were clearer than they were when I didn't look through the pinhole (although a lot dimmer). You use the same effect when you "squint" to see fine detail -- you're limiting the aperture you're looking through, and eliminating the rays that pass through far from the center of the aperture which, if the lens iasn't perfect, will not pass through the correct focus and would thus contribute to the image blur.



I've wondered whether or not ancient people ever used this principle. Thus far I haven't found any "pinhole glasses" in use in the Graeco-Roman world. They'd be easier to make than quality glass lenses.
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  #7  
Old 09-21-2005, 03:01 PM
xizor xizor is offline
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I asked my eye doctor about these things. His responses:
1). They work just like others have said
2). They will not damage your eyes, nor will they improve vision long term.
3). Who would wanty to walk around looking through pinholes all day?
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  #8  
Old 09-21-2005, 03:02 PM
CookingWithGas CookingWithGas is offline
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Quote:
Originally Posted by CalMeacham
I've wondered whether or not ancient people ever used this principle.
I've seen a photo of Inuit wearing a kind of glasses with a thin horizontal slit, but the purpose was more to be sunglasses than vision correction.
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Old 09-21-2005, 03:26 PM
CalMeacham CalMeacham is offline
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Quote:
I've seen a photo of Inuit wearing a kind of glasses with a thin horizontal slit, but the purpose was more to be sunglasses than vision correction.
Yeah -- in searching for examples I keep coming across these. I've seen examples at the American Museum of Natural History. But their use is different, as you note -- they're meant as glare protection. They perform the other function of apertures -- to limit the amount of light entering, rather than to minimize aberrations associated with large pupil size.
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  #10  
Old 09-21-2005, 09:46 PM
Padeye Padeye is offline
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Pinhole apertures on glasses are often used by shooters with age related presbyopia who have trouble focusing on the front sight.
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