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Thread: Polishing out a scratch!

  1. #11
    Tin Can's Avatar
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    Re: Polishing out a scratch!

    Everything if you read it

    Quote Originally Posted by Pfsor View Post
    And what has that to do with the polishing technique discussed in this thread?
    Tin Can

  2. #12

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    Re: Polishing out a scratch!

    Nothing at all - I've read it. Not one word about amateur incorrect lens polishing to cure lens scratches.

  3. #13
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    Re: Polishing out a scratch!

    It may cause more harm, aka Doctrine of Double Effect adapted from this essay.
    Tin Can

  4. #14

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    Re: Polishing out a scratch!

    It may rain today too...

  5. #15

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    Re: Polishing out a scratch!

    Look. Firstly, polishing out a scratch works on acrylic domes. Why would it not work on glass domes? Not forgetting jewellers rouge takes so little off that the result is slow and only marginally alters a small area of the front of the dome.

    What do you think the difference in the final image would be between a scratch on the front element and a marginally adjusted radius over a small percentage of the same? More noticeable, or less?

    I hear lots of optical theories but see very few actual experimental checks on most of them. Isn't it worth checking by trying?

  6. #16

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    Re: Polishing out a scratch!

    Quote Originally Posted by pgk View Post
    Look. Firstly, polishing out a scratch works on acrylic domes. Why would it not work on glass domes? Not forgetting jewellers rouge takes so little off that the result is slow and only marginally alters a small area of the front of the dome.

    What do you think the difference in the final image would be between a scratch on the front element and a marginally adjusted radius over a small percentage of the same? More noticeable, or less?

    I hear lots of optical theories but see very few actual experimental checks on most of them. Isn't it worth checking by trying?
    Let's say it in this way - you're right that you can polish an acrylic dome in this way. But a lens is a different thing.
    The dome doesn't have the function of a lens. All it needs to be is just being transparent. A small deviation of its curvature out of the lens field of focus will not deteriorate the image too much.
    Lens, OTOH, must have the correct curvature in order to function properly. A small scratch on a large dome doesn't not equal a larger area of damaged curvature on a lens, in its effects. First, the larger damaged area on the lens takes proportionally more of the visually correct area on a lens than the scratch takes on the dome. But the main difference is that the polished area on the lens is not polished to the correct curvature so the spot, if not blind, is optically impaired. And that more than a scratch itself would do. Not to speak about the fact that polishing glass is not so easy with a piece of felt. Don't know if you have ever polished a lens by hand (I did, from a simple piece of flat glass - hrs and hrs of tedious work on a polishing machine) but you would need a lot of the felt pieces, let me tell you.

    I think you get the points. If you have a useless piece of a lens, give it a go and see for yourself if changing its curvature will let the lens function normally. Cheers!

  7. #17
    Jac@stafford.net's Avatar
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    Re: Polishing out a scratch!

    Quote Originally Posted by pgk View Post
    Look. Firstly, polishing out a scratch works on acrylic domes. Why would it not work on glass domes?
    I have two experiences, one each for a glass filter and acrylic dome. The dome was more of a lens some 22" in diameter and a lot of work, the filter was color and 138mm. For each I used a kit of Novus polishes and Micro-Mesh pads. I will emphasize the pads - nine grades of abrasion from 1,500 to 12,000. I will never use anything else. Finishing with 12,000 removes micro scratches; made them disappear even at close inspection. Highly recommended.

  8. #18

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    Re: Polishing out a scratch!

    Quote Originally Posted by Jac@stafford.net View Post
    Highly recommended.
    Have you never tried with a lens??

  9. #19

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    Re: Polishing out a scratch!

    I'd stop trying to polish it for all the above replies, as heat build up can cause the scratch to turn into a crack... Heat will start separating the material...

    For a chipped condenser in a projector that showed up on the screen, I used cyanoacrylate cement (superglue) to fill the jagged insert, several layers to build up slightly over the height of the glass, then polished this down to the surface... This made the chip dissappear from the screen...

    Yea, I know, different refractive index from the glass etc, but at least the area is now perfectly clear in transmisson, and in some optical applications, there is bending of light from the glass under...

    Worth a try until you order another port, but be aware this port may be comprised due to the heat from polishing you already applied...

    Stay out of deep water with this!!!

    Steve K

  10. #20

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    Re: Polishing out a scratch!

    Quote Originally Posted by LabRat View Post
    I'd stop trying to polish it for all the above replies, as heat build up can cause the scratch to turn into a crack... Heat will start separating the material...
    The scratch compromises the port already. Doing nothing is not much of an option. I'm keeping the 'heat' down to warmth. There is nothing to be lost by trying. I suppose that this is my point. Why not try if there is nothing to be lost by doing so?

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