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Thread: Screen Resizing "Lens": Optics question, please help!

  1. #1
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    Screen Resizing "Lens": Optics question, please help!

    Hey guys,

    I was hoping someone here would know the definite answer on whether or not my theory is correct. I have a screen that is slightly taller than the active area on my touch panel and it's not so much that they are unusable as a pair, but I had a theory for correcting the issue.

    If what I know of prisms and optics is correct, I can take a piece of clear acrylic or glass and match the screen area with that. We will call this piece the "lens". Then I can bevel the top and bottom edge to bring the front-side of the lens to match the active area of the touch panel. My theory is that the light coming into the larger side will proportionately be shrunken to fit the slightly smaller side. Does anyone know if this is correct? If not, is there a better way to do this?

    If this works, I hope to make a final version from glass and fill the edges with plastic so the touch panel is evenly supported.

    I just sketched this side-view in MS Paint:

    Name:  lens.JPG
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  2. #2
    Newbie Quaraxkad's Avatar
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    This will not work. Light entering near the edge of your beveled lens will not curve or change direction simply because it's near an angled edge. The lens would need to be a curved surface (or "internally curved" by mating two different density materials).

  3. #3
    Raw Wave
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    The lens has to be carved the other way.

    But it won;t work anyhow, the touchpad will only work for the actual screen underneath it. (Not to mention the difficulty carving the lens...)

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    Quaraxkad, you are saying that creating a prism in this manner will not distort the light at the beveled edges? So this would actually cut off the top and bottom edge of the screen, essentially? Or am I misunderstanding?

    OldSpark, the touchpad works just sitting on the the table. My goal is to slightly distort the screen to squish the vertical size to match the touchscreen better so you will see the full screen under the working area of the touchpad. The x-axis matches up, but the y-axis on the touchpad is smaller, by a few millimeters.

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    Newbie Quaraxkad's Avatar
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    Quote Originally Posted by Ryven View Post
    Quaraxkad, you are saying that creating a prism in this manner will not distort the light at the beveled edges? So this would actually cut off the top and bottom edge of the screen, essentially? Or am I misunderstanding?
    It won't exactly "cut off" the top and bottom edges (you would still see the edge if you looked through at the right angles), but a simple flat lens with a beveled edge like this won't bend the light the way you want it. A better and much easier solution would be to set a custom resolution on your display so that the top and bottom of the screen are not used. This way the "active" display area matches the touch screen perfectly and there are no alignment issues between the two panels.

  6. #6
    Raw Wave
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    It's possible, but realise that whatever is effected by the lens won't align with the touchpad.
    And I doubt that the visual effect will be pleasing unless it's a gradual grind.


    So shrink the lot linearly requires a concave lens, and that assume a straight-on view. (Otherwise correcting concave etc lenses need to be added.)
    Ooops - I meant (at least a) convex correcting lens.
    Last edited by OldSpark; 04-28-2012 at 06:50 PM. Reason: Ooops...

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    Ah, OK. Thank you for the clarification, OldSpark. I was under the impression, that a prism-like shape would scale the image from one side to the opposite side. If it involves curves and such (which will distort the image unevenly) I don't want to bother. I think I can suffer with the slight inaccuracy on the top and bottom edges. We are talking a total difference of maybe 2 mm on each of the two sides, less than 1/10". With my fingertips roughly 0.25 square inches, I think it will be a small enough error that it shouldn't be an issue.

    Heh... I figured this would be simple.

    Also, reducing the viewing angle is only going to create more of a problem. Thank you both for saving me what could have been hours of time & frustration.
    Last edited by Ryven; 04-28-2012 at 03:43 PM.

  8. #8
    Raw Wave
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    A curves lens is required for gradual shaping.

    A prism - like beveled edges (noting that they are bent the wrong way) - has a an edge so no gradual optical "shift".
    Try one on printed text etc and see the 2 superimposed images when viewed from above the edge looking thru both angles sides. (Notice too the the left side gets its image from the RHS, ie, you need a concave lens, not the prism-like convex lens.)


    PS - it would be a lot of work. Probably cheaper to get a new screen...
    Last edited by OldSpark; 04-28-2012 at 06:51 PM. Reason: PS...

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    Quote Originally Posted by OldSpark View Post
    PS - it would be a lot of work. Probably cheaper to get a new screen...
    There is a screen I had my eye on but it uses an LVDS connection and I don't know how I would get a controller board for that. I will have to finish my bezel, see how well it works and then look to replacing the screen if it is a problem. I think I'll work to find one that is multi-touch already, instead of replacing the panel, if it comes to that.

  10. #10
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    Quote Originally Posted by Quaraxkad View Post
    A better and much easier solution would be to set a custom resolution on your display so that the top and bottom of the screen are not used. This way the "active" display area matches the touch screen perfectly and there are no alignment issues between the two panels.
    I'll try this

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