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I Print something to be seen in focus by person w/o glasses?

  1. Nov 19, 2018 #1
    Is it possible to print something with an ordinary laser printer that is blurred in such a way that it can be seen clearly by someone who ordinarily requires a strong prescription to correct their eyesight but would appear a blurred mess to someone with normal eyesight?
     
  2. jcsd
  3. Nov 19, 2018 #2

    phinds

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    "someone who ordinarily requires a strong prescription to correct their eyesight" would see regular print as a blur and blurred print as REALLY blurred
     
  4. Nov 19, 2018 #3

    A.T.

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    Consider the limiting case of blurring where you have a uniformly grey page, instead of black text on white paper. Is there a way a lens can make text out of it?
     
  5. Nov 19, 2018 #4

    DaveC426913

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    No.

    I used to work in photo printing - back in the days of chemicals and negatives and stone axes.
    A lady came in and handed me a print of a blurred subject (it was blurred in the negative). She wanted me re-print it and "correct the blurriness". (After all, my machine can make pictures blurry; why can't I just reverse the process?) No can do. The information from the scene is gone; it's not there to be extracted.

    On the flip-side, consider what would happen if we could do that. If we could turn any blurry image into a sharp one, then cameras would not need to focus at all. We could just take blurry pictures with our lensless cameras and simply extract all the original data from them into a sharp picture!



    Try an experiment to convince yourself. Draw a diagram with a few key points in it, and draw a simplified eye with focusing "lens" and image plane. See if you can draw some out-of-focus points that somehow cohere just right so that they make sharp-edged points on the image plane.

    Keep in mind that you can't select which parts of the image plane only receive certain rays from certain parts of the object.
     
    Last edited: Nov 19, 2018
  6. Nov 19, 2018 #5

    A.T.

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    Unless you have these CSI machines:

    [​IMG]
     
  7. Nov 19, 2018 #6

    Tom.G

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    Times have changed.
    Using current image processing software I have "refocused" an out-of-focus circuit diagram from one of the threads here that I then re-posted, and have (largely) removed motion blur from digital photos, specifically of a moving vehicle taken at night that was too far away to use a flash. It does take a lot of time and patience though, not commercially viable as a consumer service... especially considering that as of a few years ago, the wholesale price for photo touch-up started at $100/hr.

    The original image 'as taken.'
    IMG_0018-Small.jpg
    Motion blur was removed for the trucks. As a side effect, the rest of the image is degraded.
    IMG_0018-NoBlur-Small.jpg

    Cheers,
    Tom
     
  8. Nov 20, 2018 #7

    phinds

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    The OP asked about the use of a lens

    off topic post small.jpg
     
  9. Nov 20, 2018 #8

    sophiecentaur

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    Not a totally valid objection here, I think. If someone wants to discusses putting a screw in a wall with a hammer, it is quite in order to suggest a screwdriver. :smile: But @phinds is quite right that the OP's request for an actual image, printed on paper, is hardly possible. Some fancy glasses, at least, would be required.
    The equivalent process to what a computer can do is probably achievable with an appropriate 'lens' if the aberration is not too great .
    The action of a lens involves a Fourier Transform of an image at the focal plane and phase shifting parts of the spectrum can bring the phases of those parts together again. See this link which describes the basics of Fourier Optics. High and low pass (spatial frequency) filters are described and the detail of a blurred picture can be extracted optically (thereby ruining the picture as something to look at).
    The sort of enhancements that Photoshop (others are available) can do are way beyond what optics can achieve.
     
  10. Nov 20, 2018 #9
    It's hard for me to tell whether I'm not understanding the answers or if my question is not being understood how I intended it. Would it make more sense if I asked could an image be printed with "anti-blur", blurred in such a way that I could read it clearly with my glasses off but most other people (and myself with my glasses on) would not be able to read it? Like, if I know what my prescription is, is it possible to calculate how the image will be deformed by the lens in my eye and apply counter-deformations to counteract those? Then I could print text out and I'd be able to read it relatively easily but most others would not. Sorry if everyone did already understand my question and it just isn't possible.
     
  11. Nov 20, 2018 #10

    davenn

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    No, I think your responders understood :smile:


    anti-blur ?? never heard of it ... do you have a good reference ?


    No, I know of no lens or set of lenses that can turn a blurry image into a sharp or near sharp image
    It's still going to be blurry with or without glasses
     
  12. Nov 20, 2018 #11
    I phrased it this way to make it easier to understand what I'm asking for. I want the antithesis of what my own defective eye lenses do to images I look at.

    My glasses make the blurry image I see without my glasses appear sharp. Is it possible that I'm using the wrong terminology? Perhaps "blur" has some specific definition in physics which does not apply to the case I am attempting to describe.
     
  13. Nov 20, 2018 #12

    davenn

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    then your glasses are the incorrect prescription for you ... either
    1) made incorrectly or
    2) if they used to be OK then your eyes have changed over time and you need retested and a new prescription
    .... I go through that ( as most glasses wearers do) every year


    welcome to the reality of wearing glasses


    Dave
     
  14. Nov 20, 2018 #13
    Negative. Without my glasses, my vision is blurry. With my glasses, my vision is not blurry. This use of the word blurry is layman and may not be correct usage in the field of physics. My glasses make a blurry image sharp.
     
  15. Nov 20, 2018 #14

    davenn

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    I guess if it isn't #2 reason I stated above ...... then WHY are you wearing glasses if you don't need them to get a sharp image ???

    As I aged through my 40's and into my late 50's it was my near vision focussing that started failing first ... I couldn't focus on anything within a metre or less.
    As the years went by, my longer vision focussing slowly got worse till I finally needed glasses to be able to walk around and drive safely
     
  16. Nov 20, 2018 #15

    davenn

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    OK I misunderstood your wording

    so, that is what glasses are supposed to do .... it is your eyes and their poor focussing that is making things blurry
    correcting lenses solve that problem .... so what is the problem ?

    It ISNT the image that is blurry .... It's your view of it without correcting lenses that make it appear blurry to you
     
  17. Nov 20, 2018 #16
    You said:

    but my glasses turn a blurry image into a sharp image for everything I look at (in concert with my own internal eye lenses). Thus I reason that there must be a way to calculate how an image should be displayed to a person with deformed eye lenses.
     
  18. Nov 20, 2018 #17

    davenn

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    you are not reading what I am saying !! :frown:

    It is ONLY BLURRY to you and anyone else with eyesight focussing problems
    If the image is sharp to good eyesight viewers and blurry to you, then it is YOUR eyes that have the problem
    That is what your glasses are designed to do, restore the original sharpness of the image
    as seen by everyone else with normal eyesight
     
  19. Nov 20, 2018 #18

    phinds

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    I can only suggest you reread post #2. I see no ambiguity.
     
  20. Nov 20, 2018 #19

    davenn

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    @seanspotatobusiness

    there is .......

    correcting for near sightedness ... when far things are out of focus
    https://www.physicsclassroom.com/class/refrn/Lesson-6/Nearsightedness-and-its-Correction


    correcting for far sightedness ... when nearthings are out of focus
    https://www.physicsclassroom.com/class/refrn/Lesson-6/Farsightedness-and-its-Correction


    Note closely why the 2 conditions occur because of where the eye lens focal point is
     
    Last edited: Nov 20, 2018
  21. Nov 20, 2018 #20
    Okay, thanks everyone.
     
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