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  1. #1

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    Final call for lens doublet separation.

    I might have entitled this something more specific or eye-catching, but the title line cuts off on long titles. Specifically, I have in my charge the now-ewtracted front doublet from an older-style silver Hasselblad Zeiss Planar 80mm. It belongs to a good buddy, and he has faith in me to get them apart with their coatings intact and use this little bottle of Balsam Fir gum to get them back together again. He refuses to accept that the 3/32 ring of separation around the perimeter is of no concern.
    I've studied hot water, a crazy light-bulb trick, and acetone. These are my final choices, excluding the crazy light-bulb trick. Because I know that the indisputable experts at the big lens re-coating company that shows up high on the google listings say: "be prepared to accept that temperatures above 200 degrees may damage lens" The glass itself can't accept that, not even considering the coating too.
    So that brings us to dropping the doublet into a padded jar of acetone for about a week. I'd REALLY like to know how lenscoating likes that. Because I can't think of any other coating, including porcelain and powder-coating that can stand a long soak in acetone.
    I intend to do the separation in the next few days. Last call for a bright idea. Thanks.

  2. #2

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    Acetone and xylene are the accepted solvents for balsam. But is your lens cemented with balsam or epoxy/UV curing adhesive? You need to find this out and use the correct method of decementing the lens. Someone posted here that boiling the lens in water would free the (non-balsam) cement.
    As for damaging the coatings, acetone shouldn't harm them nor should xylene nor boiling.
    Must not have been porcelain, porcelain is a type of glass and acetone will not dissolve it under any circumstances.

    The best and brightest idea I have is to learn the ins and outs of lens recementing on something a lot less valuable than a Planar off a Hassy, unless you feel able to buy the owner a new one. Learn on some old R-R types.

  3. #3

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    I thought methylene chloride (found in paint remover) was the proper solvent for balsam and lens cement. That is what I use, last time I did it. I had to soak the doublet for more than a week, at room temp.

    Now, if Hasselblad happened to use a more modern UV cured epoxy, then you are stuck (sorry no pun intended). It isn't going to be separated, ever.

    http://www.apug.org/forums/archive/i...p/t-71602.html

    http://www.optical-cement.com/cement...cementing.html

  4. #4

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    Quote Originally Posted by vysk View Post
    I thought methylene chloride (found in paint remover) was the proper solvent for balsam and lens cement. That is what I use, last time I did it. I had to soak the doublet for more than a week, at room temp.

    Now, if Hasselblad happened to use a more modern UV cured epoxy, then you are stuck (sorry no pun intended). It isn't going to be separated, ever.

    http://www.apug.org/forums/archive/i...p/t-71602.html

    http://www.optical-cement.com/cement...cementing.html
    Methylene chloride is hard to find in "straight" form, although it might be the best solvent. It's also rather toxic - more so than xylene and much more so than acetone.
    Acetone and xylene are off-the-shelf hardware items, too. So is toluene, now that I think of it.

    Whatever solvent is used, patience is the key. It might take anything from a week to a month or more.

  5. #5

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    I can get methylene chloride down at the plant.

  6. #6

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    Quote Originally Posted by Tom1956 View Post
    I can get methylene chloride down at the plant.
    If it turns out to be UV cement, try methyl-ethyl-ketone, that usually loosens it after a few days. Or weeks.

  7. #7

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    Well I guess if I try boiling and it doesn't budge, I'll know it's synthetic cement.

  8. #8

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    Quote Originally Posted by Tom1956 View Post
    Well I guess if I try boiling and it doesn't budge, I'll know it's synthetic cement.
    No. The word is that boiling loosens the synthetic cement. I wouldn't boil a lens except as a very, very last resort.

    You want to be as gentle as possible with the lens, start with solvent and patience.

  9. #9

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    I didn't really intend to "boil" it. My idea was to make a double boiler out of 2 cookpots, and not let the inner one actually come to a boil. I'm afraid of removing the coating no matter what I do, but particularly that.

  10. #10

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    Quote Originally Posted by Tom1956 View Post
    I didn't really intend to "boil" it. My idea was to make a double boiler out of 2 cookpots, and not let the inner one actually come to a boil. I'm afraid of removing the coating no matter what I do, but particularly that.
    The double boiler is probably a good idea, you can still raise it to whatever temperature water boils at your altitude without the agitation risking chipping it. You won't remove the coating in boiling water. Some (many modern) coatings are more durable than the glass they are applied to.

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