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Thread: Strange glass seperation / dirt inside lens element / Need help to identify

  1. #1

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    Strange glass seperation / dirt inside lens element / Need help to identify

    Hello guys, I bought a beautiful Kranz Petzval lens at an auction. But the lens has a strange appearing, which I´ve never seen before.

    Maybe you can help me to identify what this is, how or if I "could" fix it and if not if it will get more worse over time.

    It´s inside the glass element, not on top.

    I am thankful for everykind of help or tip

    Click image for larger version. 

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  2. #2
    Tin Can's Avatar
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    Re: Strange glass seperation / dirt inside lens element / Need help to identify

    I tried 105 mm diopters in a similar situation

    ng
    2022

  3. #3

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    Re: Strange glass seperation / dirt inside lens element / Need help to identify

    I bid for this very large Kranz Petzval too! But under 1/4 of the winning bid.
    It was described as having heavy separation, but no image of the glass itself!
    The auctioneer is notorious for a very restricted images in their catalogues. To be honest, ordinary photographic items on eBay have better series of photographs.
    This has a very distressed “glue”. I have not seen anything like it with balsam. In fact, it looks more like a “failed” modern glass UV adhesive.
    I keep well away from these UV glues but I understand that xylol will (eventually!) separate the two halves.

    Of course, it could be another very large Kranz lens sold at auction.

  4. #4

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    Re: Strange glass seperation / dirt inside lens element / Need help to identify

    I know some large Telescope lenses are just air spaced and not bonded... Maybe that, but held together in cel???

    Steve K

  5. #5

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    Re: Strange glass seperation / dirt inside lens element / Need help to identify

    There is a side view of the achromat in another of the OP’s threads about his current challenges. This shows “beads” of leaking balsam which are showing the typical white deposit from drying out balsam.
    I have only ever seen air achromats - with very thin metal spacers at their edges - in telescopes from the pre-photography era.

  6. #6

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    Re: Strange glass seperation / dirt inside lens element / Need help to identify

    Quote Originally Posted by Steven Tribe View Post
    I have only ever seen air achromats - with very thin metal spacers at their edges - in telescopes from the pre-photography era.
    FWIW. I have an 1893 telescope with an uncemented doublet. It happily disassembles and goes back into a simple tubular mount. No sign of metal spacers. Still surprisingly good and I use it daily for watching shipping.

  7. #7
    come to the dark s(l)ide..... Carsten Wolff's Avatar
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    Re: Strange glass seperation / dirt inside lens element / Need help to identify

    If it is not an airspaced lens after all, but a cemented doublet, this could be a classic case of balsam re-cementing and someone painting around the side of the doublet with black paint without applying a clear varnish barrier first. The black paint then got resorbed into the still not fully cured balsam cement. A wild and unlikely guess of course, but I've seen it before. (Don't ask). Lens could well perform ok despite this.
    http://www.jeffbridges.com/perception.html "Whether you think you can, or think you can't, you are right."

  8. #8

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    Re: Strange glass seperation / dirt inside lens element / Need help to identify

    A very naive question...but was carbon black ever used to help mitigate unwanted light ingress into the edges of these older optics? If so - perhaps some of this has migrated away from the edges? Perhaps some kind of static charge might provide some clue - assuming that this might create some movement of such particles? Just grasping here...thinking way outside the box.

  9. #9

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    Re: Strange glass seperation / dirt inside lens element / Need help to identify

    Painting the Ground glass len’s edges Black was very much a UK habit in the 19th Century! Traditional French and most German makers didn’t consider it important and wrote lots of Strange Numbers and Texts to keep us speculating on their meaning in the 21st C!

  10. #10

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    Re: Strange glass seperation / dirt inside lens element / Need help to identify

    Quote Originally Posted by Steven Tribe View Post
    I bid for this very large Kranz Petzval too! But under 1/4 of the winning bid.
    It was described as having heavy separation, but no image of the glass itself!
    The auctioneer is notorious for a very restricted images in their catalogues. To be honest, ordinary photographic items on eBay have better series of photographs.
    This has a very distressed “glue”. I have not seen anything like it with balsam. In fact, it looks more like a “failed” modern glass UV adhesive.
    I keep well away from these UV glues but I understand that xylol will (eventually!) separate the two halves.

    Of course, it could be another very large Kranz lens sold at auction.

    Yey, now I know this... This was my first auction. The auctioneer did a "great" job. But luckily the dirt has no effect on the ground glass. Someone also told me he can fix it in the tradiotional way, if I want to.

    What do you mean with "it could be another very large Kranz lens sold at auction"?

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