Final call for lens doublet separation.

Discussion in 'Camera Building, Repairs & Modification' started by Tom1956, Jul 22, 2013.

  1. Tom1956

    Tom1956 Inactive

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    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. E. von Hoegh

    E. von Hoegh Member

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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. vysk

    vysk Member

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  4. E. von Hoegh

    E. von Hoegh Member

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    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. Tom1956

    Tom1956 Inactive

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    I can get methylene chloride down at the plant.
     
  6. E. von Hoegh

    E. von Hoegh Member

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    If it turns out to be UV cement, try methyl-ethyl-ketone, that usually loosens it after a few days. Or weeks.:laugh:
     
  7. Tom1956

    Tom1956 Inactive

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

    E. von Hoegh Member

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    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. Tom1956

    Tom1956 Inactive

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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. E. von Hoegh

    E. von Hoegh Member

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    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.
     
  11. Tom1956

    Tom1956 Inactive

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    So, boiling it is. As far as the bobbing around, or letting the glass contact the metal of the cookpot, I plan to jam some cheap sponges in the bottom of the pot to pad it. Then, put the glass in the cool water and bring it to a boil in the outer pot. I'll be using my gas range, but I think the water insulating the bottom of the interior pot will keep the bottom of the pot from taking the brunt of the heat of the flame. I've been more worried about ruining the coating than cracking the glass. I'll use some sort of stiff padded tool to "fish around" the glass to dsee if it is actuall separating. If it does, I'll kill the flame and let the water cool down naturally. Avoiding thermal shock is the best policy.
     
  12. E. von Hoegh

    E. von Hoegh Member

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    As I posted earlier I would not boil the lens except as a very, very last resort.
    You're so worried about damaging it, yet you start with the most agressive and fraught-with-potential-catastrophe method of separating it - which I also pointed out was apocryphal information. You have no experience recementing optics, yet you start with an expensive lens that is not your own.

    Good luck, it looks like you'll need it.:whistling:
     
  13. benjiboy

    benjiboy Subscriber

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    What I don't understand is, if you didn't know how to do the job and had no experience of ever doing it before, why did you accept it ?
     
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  15. Tom1956

    Tom1956 Inactive

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    I'll answer that. He's a good buddy, but I believe he is also bipolar. He can be stubborn and has no sense of the value of money. He cannot be made to understand that the 3/32 ring of separation around the perimeter is of no consequence. To try to tell him makes him even more obstinate. To him the lens is already dead and he knows how much I have learned about these kinds of things from you people. Don't try to figure the logic.
     
  16. Tom1956

    Tom1956 Inactive

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    Well, EvH, I caved into your pleas. The doublet is now sitting in a jar of acetone. I saw right off where it seeped into the separated areas around the perimeter. Whether it will continue its penetration of the cement to the center of the lens is something that leaves me in doubt. But we'll see. I suppose after a week and nothing is happening, no point in waiting a month, or a hundred years.
     
  17. Tom1956

    Tom1956 Inactive

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    FYI After 8 hours soaked in Acetone, absolutely no signs of change. Will allow a week, then boil.
     
  18. E. von Hoegh

    E. von Hoegh Member

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    Is that lens cemented with balsam or UV curing cement? Balsam = acetone, xylene. UV/epoxy = methyl-ethyl ketone. It can take several weeks for any solvent to work.
     
  19. Tom1956

    Tom1956 Inactive

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    I have no idea what the glue is. Gut instinct tells me it's probably not gum. Lens is about a 1970 model, I'd say. And as an aside, I'm guessing you don't like hot water on account of possibly of glass cracking from thermal shock.
     
  20. Barry S

    Barry S Member

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    I use xylene for 19th c lenses that I know used balsam cement. It can take a month or more for the solvent to reach the center of a doublet. Heat shock is a good way the shatter the lens and heating may not even be that effective for modern optical cement. Find the correct solvent and give it time.
     
  21. Tom1956

    Tom1956 Inactive

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    I wonder how hot the Zeiss lenses on the moon got. I'd say near 200 degrees is a safe bet. Just talking.
     
  22. Tom1956

    Tom1956 Inactive

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    Thanks to a link that one of you posted (repeated here http://www.optical-cement.com/cements/decementing/decementing.html
    this was for a product made for the purpose. This product is to be used at 340 degrees F. All of a sudden, 212 degrees pales in comparison on the possibility of lens fracture. I had my buddy stop by after work and I explained my options. I have the go-ahead to try the water boiling. If it does not work, our agreed logic is that it might work well enough to go back to the solvent method with better effectiveness. Because right now, 2 days in Acetone has done nothing. Being the stubborn man, he refuses to believe that it could take a whole month in MEK. Hell, I can't get him to believe in the principle of the double-boiler. He refuses to believe that an ordinary metal cookpot can be brought to a boil in a bigger cookpot of boiling water. Of course it can.
     
  23. Tom1956

    Tom1956 Inactive

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    Well, boiling didn't work. Didn't even faze it. Next up--methylene chloride. Will be several days before I can get my hands on some. Can buy MEK tomorrow, but am too cheap.
     
  24. Jim Rice

    Jim Rice Member

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    The more interesting question might be how you plan on re-centering the elements.
     
  25. Tom1956

    Tom1956 Inactive

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    The same way they are now. They're totally flush all the way around. If they're off by a molecule I'm not going to sweat it. My buddy will be happy. It's no-good now, isn't it? If you want a perfect one go on fleabay and pay 4 or 5 hundred dollars for one. Or send it off to somebody and pay the worth of it to have it done on their fancy microscopes. My approach is free, I'm not a boob, and I do careful work, and I won't scratch it. So...
     
  26. John Koehrer

    John Koehrer Subscriber

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    MEK/Acetone won't work. Xylene, maybe, never tried it.
    Methylene Chloride will do the job. It's the only solvent that has separated UV cure cement for me.
    After a week in MEK it took less than two days in the Methylene chloride. It's the main component in some paint strippers. I use is Parks Pro Stripper. 32 oz is a common size from the hardware store. Brand won't make a difference but it HAS to have the MC as the Primary component.

    If you want, send it to me & I'll separate it for you. 32oz is about two lifetime supplies.

    RE: recentering. I use two pieces of 3/4" aluminum angle. Set the glass in place and one angle on each side. Hold 'em together with a rubber band or two.
    It's gonna look like this <O>. I use a UV cure cement and wipe the edges with a paper towel dampened with Acetone. The edges are painted with a glossy black enamel. As long as it's OK for glass, it works on the lens group.
     
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