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Thread: How I did it: new balsam for a sick RR

  1. #61

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    Re: How I did it: new balsam for a sick RR

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    After about 10 minutes of warming, (ok, it's hot now) the original 125+ year old balsam is melting and the 2 pieces came apart.

  2. #62

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    Re: How I did it: new balsam for a sick RR

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    After cooling in the pan to room temperature, I removed the lenses and put them on a paper towel to dry.

    Next step is to wipe the lenses clean with alcohol.

    More to follow.

  3. #63

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    Re: How I did it: new balsam for a sick RR

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    After cleaning both lenses with alcohol, I placed a small piece of blue tape on each of the "facing out" sides of the lens. Then cleaned again with a mild window cleaner to make sure all the old balsam was gone.

  4. #64

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    Re: How I did it: new balsam for a sick RR

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    Pressing both lens elements together caused the balsam to spread out to the edges of the lens. After double checking the alignment, I used a simple Craftsman brand pressure clamp to hold the lenses together as the balsam dries.

  5. #65

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    Re: How I did it: new balsam for a sick RR

    More to follow when dry.

    Oh, and a huge thank you to Steven for his inspiration.

  6. #66

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    Re: How I did it: new balsam for a sick RR

    Based on old and recent experience, I have found that the occasional devitrification which occurs seems to be associated with:-

    Crown glass used in both Petzval achromats and Rapid Rectilinear (Aplanat) doublets. This is a glass which was used extensively from the start of Photography.

    It is a phenomenum which starts at the surface and can spread into the body of the lens. Both degrees of attack mean a scrap lens. The flint glass is always OK,

    For sometime I thought that use of aqueous solutions used in the separation of cemented lenses might be the cause (microscopic defusion of water molecules into the glass skin) but this is not so. All glass failures have occured during gentle warming. I used to recommend heating as a way of speeding up the slow solvent dissolution of hardened balsam. I now think that the only safe way to harden the new balsam is warming to just over room temperatures in one process. I have examples of repeated warming to just under 100 degree which went OK the first few times, then, suddenly it happened in just a few minutes! Repeated temperature stress is a killer for crown glass.

  7. #67
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    Re: How I did it: new balsam for a sick RR

    Resurrecting a year-and-a-half-old thread as it seems the best reference article about re-cementing with Canadian Balsam on the forum, (thanks, Steven!).

    I just ordered some Balsam from Surplus Shed, and have been reading about using it from many sources around the net. (I'm experienced with UV-cure, but would rather go with Canadian Balsam because it's cheaper, more reversible, and has a very long shelf life (UV cement is only good for 4 months). I also found an old reference that UV cements have a different refractive index and spectral transmission than Canadian Balsam, but I doubt that has any significant effect.

    I did find one source that disagreed with the drying-under-heat technique referenced throughout this thread and wanted some feedback on it. From http://forum.mflenses.com/re-cementi...am-t34467.html

    "Leave your doublet undisturbed in a quiet and warm place for a minimum of 1 week and maybe as long as 1 month. A sunny window is good, but do not let your doublet reach a temperature of higher than about 90 degrees F or the solvent in the solution will bubble (a disaster for you as bubbles were probably the problem you were repairing in the first place) Balsam around the edge will dry rather quickly, however the balsam in the very center will take possibly years to dry...and it is possible that it may never dry completely I suppose."

    Any thoughts on drying/curing Canadian Balsam?
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

  8. #68

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    Re: How I did it: new balsam for a sick RR

    "Drying under heat"
    A belated answer!
    I have progressively reduced the maximum temperature for setting the edge balsam after reassembly! I suppose that room temperature would be good enough if can wait an extra few days.
    I regard all the suggestions of "self healing" through warming the lens without disolving the dude balsam as dangerous heresy!
    Would like to underline that the use of 6 or more rubber bands across the lens, like hour marks on a clockface, is the best way to allow fine adjustments with slippage. I still recommend xylol rather than the more dangerous, acetone!

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