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  1. #1

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    broken len element in an old brass lens

    Mornin'

    I recently bought a 14" projector lens from an old magic lantern cheap off ebay, it was a bit banged up and dirty, anyway...

    I managed to take it apart and clean it up, the brass cleaned nicely and except for a few stubborn marks looks good, the glass (which I expected to be a bit of a horror show) also came out spotless and except for a couple of chips near the edge on the rear elements was usable.

    So I was happy, until, when tightening the ring on the rear elements there was a crack, crack went the element, and in half, broke clean in half.
    Now I have a lens with 2 good elements and a decent body, but one, one that's now 2.

    So is it worth trying to replace it?
    Fix it?
    Sell it?

    Use it as a door stop?

    Dafydd

  2. #2
    Ian Grant's Avatar
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    Give it away to someone who can use the barrel and bits . . . . .

    Ian

  3. #3

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    You did not tell us did you intend to do with it?
    Suggestion:
    Glue the two pieces together. I would do it with UV-curing glue (need sunny day); do not use instant glue. Before you expose to sun, make sure they are precisely aligned, using the match of the crack surface and checking the surfaces and edges match.
    Then:
    - Either use as-is; at least do a first test
    - Or, if you think you see objectionable flare, cover the region of the (glued) crack with a thin line of black paint. All you will suffer is a small loss of effecitve aperture (plus diffraction by the edges of the black region, but this should be negligible wrt te native geometrical aberrations).
    When you finally re-mount the lens, use some foam or other between the ring and the glass; three small pieces in a triangle should be OK. Whatever method you use, make sure you preserve the centering as per the original design.

  4. #4

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    that would be a further option...
    but I'm hoping someone with the bit I need will come along and give theirs away to me

  5. #5

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    Quote Originally Posted by bernard_L View Post
    You did not tell us did you intend to do with it?
    Suggestion:
    Glue the two pieces together. I would do it with UV-curing glue (need sunny day); do not use instant glue. Before you expose to sun, make sure they are precisely aligned, using the match of the crack surface and checking the surfaces and edges match.
    Then:
    - Either use as-is; at least do a first test
    - Or, if you think you see objectionable flare, cover the region of the (glued) crack with a thin line of black paint. All you will suffer is a small loss of effecitve aperture (plus diffraction by the edges of the black region, but this should be negligible wrt te native geometrical aberrations).
    When you finally re-mount the lens, use some foam or other between the ring and the glass; three small pieces in a triangle should be OK. Whatever method you use, make sure you preserve the centering as per the original design.
    I intended to use it on the camera I'm currently building.
    I might give that a go, but would prefer not to glue anything just yet... having said that, I can't make it any worse really.
    Tomorrow I'll rig something up to see how bad it effects the performance.

  6. #6

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    The curvature of the lens can be determined from one of the pieces. However you would have to find someone to grind a replacement for you. The lesson learned here is do not be hamhanded when working with lenses.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  7. #7

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    Quote Originally Posted by Gerald C Koch View Post
    The curvature of the lens can be determined from one of the pieces. However you would have to find someone to grind a replacement for you. The lesson learned here is do not be hamhanded when working with lenses.
    how would I determine the curvature?

    and I think the lesson here is that I'm a stupid boy with stupid hands

  8. #8

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    Sickening as the thought may be, I'm afraid it's finished.

  9. #9

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    tom, tom, tom, tom, tom
    nothing is ever finished until the end... I see what you mean

  10. #10
    Ian Grant's Avatar
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    At the camera fair I go to one stall holder was selling off the spares etc from a retired camera repair shop, about 18 months ago. I had quite a few shutters, there was also a box of lens elements all wrapped in their original wrapping material, some marked indicating what lens.

    Another trader bought the entire box, as far as I know he still has them. I can find his details (I won't see him until July) if you're interested - he may be able to help. Let me know the diameter, he owes me a favour, and I can see if he has anything the right size, and then that matches.

    Ian

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