Pinhole glasses

Discussion in 'General Science & Technology' started by SoLiDUS, Jan 4, 2003.

  1. Leland Registered Member

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    17
    hey cool i too was reading about these pinhole glasses so let me get this right they work by differing contrast that makes the rod cells in your eyes detect light better? and the muscle tissue in the eye to react and change shape better when wearing them?
     
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  3. exchemist Valued Senior Member

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    No. Chroot explained it all well in 2 posts at the top of the thread. This was a decade ago, by the way. Pinhole glasses do not seem to have taken the world by storm during the intervening years......

    .....must be a conspiracy [puts on bobble hat].....

    ..... by multinational corporations [repeat and fade].......

    ....zzzzzz.....
     
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  5. Leland Registered Member

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    They still make a fashionable accessory though pinhole glasses do... albeit you walk into lamp posts when wearing them
     
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  7. tritus Registered Member

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    Chroot gives a very clear and logic explanation. There is just one thing I still don't get fully. I have read about camera obscura and I understand that the image is reversed on the screen. I wonder why pinhole glasses do not reverse the image since it is the same principle.

    Does anyone know?
     
  8. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    As I understand it, pinhole cameras work on the same principle, and the image is reversed. The puple of the eye is like that too, the image is reversed on the retina, and the brain simply corrects for it.
     
  9. Dinosaur Rational Skeptic Valued Senior Member

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    From FedR808 Post #18
    Why not turn the photo upside down?

    BTW: They do not tend, They always turn it upside down.
     
  10. exchemist Valued Senior Member

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    In the case of pinhole glasses, you are not relying on the pinhole of the glasses to form the image. That is done on the retina by the lens of the eye as normal. The pinhole eliminates rays that would pass through those portions of the lens of the eye that do not have the right curvature to contribute to a sharp image on the retina. As Chroot said, all those years ago when the thread was started, the pinhole "stops down" the aperture, reducing aberration. So no need to worry about inverted images.
     
  11. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    I thought they were interesting, so I checked on eBay. Believe it or not, $1.14 each, so I bought a pair. I'll post when I get them, and give a critique.
     
  12. sculptor Valued Senior Member

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    4,528
    simple really
    poke a pinhole in a 3x5 note card and hold it up to the eye
    Normally, the analogue wall clock 12 feet away is a vague smudge----through the pinhole, I can see the time. The image is up side up.

    I used to form rough pinholes 2 fingers and 2 thumbs ---also improved focus(as does crossing my eyes---curiously enough).

    I'll keep wearing the prescription lenses, thanx.
     
  13. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    I have used the pinhole technique to view an eclipse of the sun. You put a pinhole in one side of the box, and the image is projected on the opposite side, upside down and backward. But I didn't know that with the naked eye you would see the face of a clock reversed; interesting.
     
  14. sculptor Valued Senior Member

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    4,528
    small correction?
    not reversed
     
  15. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    It does, like you say, make things look sharper. I just made a pinhole in a card and took off my glasses, and the resolution is very much improved through the pinhole. Of course, I can only see a tiny field of view. I am curious what the effect of the glasses will have. They said about two weeks for delivery.
     
  16. DaveC426913 Valued Senior Member

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    Do not mix up the order of these instructions!
     
  17. DaveC426913 Valued Senior Member

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    Years ago, when the bedroom TV was on, I would make a pinhole from the my hand so that I could watch a news item without putting my glasses on.

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    Eventually, I made a pair of "emergency eyeglasses" out of cardboard - with a pinhole for each eye. You have to ensure the distance between the two pinholes is adjustable, so you can see with both eyes. These ones don't adjust.

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    I fancied one day, I'd distribute them in 3rd world countries where they couldn't afford expensive glasses.

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  18. Xelasnave.1947 Valued Senior Member

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    3,351
    About 25 years ago I purchased a pair made of plastic. They were excellent for working where you were looking up to the job (in my case a boat on the slip) and water was splashing on your face, whereas conventional glasses required constant cleaning.
    If you get caught without glasses put a hole in a business card to enable reading something.
    Alex
     
  19. Xelasnave.1947 Valued Senior Member

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    I think the Chinese used them over 1000 years ago.
    Alex
     
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  20. exchemist Valued Senior Member

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    You do not see the image reversed. That is not what he said. I repeat, you are not using the pinhole to form an image. You are using it to exclude rays that your defective eye is unable to bring to a sharp focus, that's all.

    So you get an image that is sharp, but dim, due to the reduced amount of light that is let through.
     
  21. Yazata Valued Senior Member

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    I'm near-sighted. When I'm not wearing glasses, I occasionally do that in order to read the menus at fast food restaurants, distant signs or whatever. I make a small aperture with my fingers and look through it.
     
  22. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    https://en.m.wikipedia.org/wiki/Pinhole_camera

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    Last edited: Jul 9, 2016
  23. exchemist Valued Senior Member

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    Yes but the lens of your eye does this too. Did you not realise that the image on your retina is always inverted? An inverted image is what your brain considers to be "the right way up". So the pinhole changes nothing.

    To see an inverted image, you would need the pinhole to form an image in front of the lens of your eye, which your eye would then see as inverted. I repeat, pinhole glasses do not form such an image, as there is no screen for it to be projected onto. They simply exclude the off-axis light rays, which are the ones that your lens fails to focus properly if you have imperfect eyesight.
     

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