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  1. #1
    cooltouch's Avatar
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    Who can re-cement lens elements?

    I have an old Century Precision Optics 650mm f/6.8 preset telephoto lens that takes quite decent photos. Its front (and only?) "element" is a doublet that is beginning to separate around the edges. No fungus, just separation. It's easy enough to remove with a lens spanner, which I own.

    Is there a place in the US that I can send this optic to have it re-cemented? I've found a few how-to links online, but I don't know if I have the proper tools for the recementing procedure.

    Thanks,

    Michael

  2. #2
    Phil's Avatar
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    Here's a place that offers that service:

    http://www.focalpointlens.com/fp_intro.html

  3. #3

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    I too would recommend Focal Point. I have had work done by John VanStelton and he is among the very best.

    Richard Wasserman

  4. #4
    cooltouch's Avatar
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    Thanks guys. Email sent.

    Best,

    Michael

  5. #5

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    I see they also provide anti reflective coating work too, I'll have to book mark them for future work.

  6. #6
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    Quote Originally Posted by cooltouch View Post
    I have an old Century Precision Optics 650mm f/6.8 preset telephoto lens that takes quite decent photos. Its front (and only?) "element" is a doublet that is beginning to separate around the edges. No fungus, just separation. It's easy enough to remove with a lens spanner, which I own.

    Is there a place in the US that I can send this optic to have it re-cemented? I've found a few how-to links online, but I don't know if I have the proper tools for the recementing procedure.

    Thanks,

    Michael
    *******
    Since a lens of that vintage is probably cemented with canada balsam, there is a way to heat the lens, very gradually, in a normal oven; allow it to reach the proper temp (I think it was 350F hold for a time; then gradually reduce to room temp. I did this once with an enlarging anastigmat.
    John, Mount Vernon, Virginia USA

  7. #7

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    I have a pair of Mitchell Baltar primes I sold to a man in China that were returned with separation in the exact same element on each lens. The separation was not there when it left and I have a strong suspicion it was induced by the buyer, who seemed to have buyer's remorse upon winning BOTH lenses in separate auctions!

    In any event, one of the lenses mounts has a big ding in it, but Paypal refused to accept the auction pictures as before and the returned lens pix as evidence. Said I could have manipulated them, so therefore, I couldn't be trusted...

    Now, 3 months later, I am out $700 USD (they issued a payback refund despite my tons of evidence and objections)AND and a pair of Baltar Primes!

    What makes me crazy is the lenses were returned with very well defined and heavy separation that looks suspiciously like someone dipped their finger in a mild solvent and ran it around the elements (middle doublet that is VERY easy to remove).

    I cannot believe the temperature variations between here and China during air mail caused the separations.

    Regardless, I will never use paypal or Ebay again!

    I might try that heating in the oven trick and see if it works; I have little more to loose...

  8. #8
    cooltouch's Avatar
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    Quote Originally Posted by Anscojohn View Post
    *******
    Since a lens of that vintage is probably cemented with canada balsam, there is a way to heat the lens, very gradually, in a normal oven; allow it to reach the proper temp (I think it was 350F hold for a time; then gradually reduce to room temp. I did this once with an enlarging anastigmat.
    So I take it then that if I follow this procedure, the two elements should separate easily? What about re-cementing them? I've bookmarked Summers, so I'll have a source for the cement, at least, but I don't know what sort of clamping procedures, if any, should be used. I do a lot of precision woodworking, so I have clamps out the wazoo, but none of them work very well on curved surfaces. I suppose a padded vise might work. I don't know the interior curvature of this doublet. If it's convex, then the vise will apply pressure at only two points. If it's flat, or even concave, then it will apply even pressure against the back surface, but only at one point at the front element. Is this advisable?

    Best,

    Michael
    Last edited by cooltouch; 02-01-2009 at 11:52 PM. Click to view previous post history.

  9. #9

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    cooltouch,
    I just use acetone as a solvent for the Balsam. Let the elements sit in the acetone for a few hours or overnight & they come right apart. Any glue remaining on the glued surfaces can easily be removed with a Q-tip & Acetone. Alignment is critical when reassembling Use a pair of "V" clamps "<O>" wood with a notch in the ends works to hold the glass while the glue sets.
    I use "Crystal Clear" which is available at Ace hardware, it's around $5 for a lifetime supply. When using it the surface to be glued have to be clean. ONE drop in the center of the concave lens is all it takes. Apply the drop, make sure there are NO bubbles, & gently set the convex lens on the drop of glue. Use the lens to spread the glue evenly by rotating & sliding the two lenses together. The cement will actually hold the glasses together, all you need is the clamping action from the sides. If they're not in alignment, they won't fit back into the barrel. You will need to clean the excess cement from the edges of the elements before they've set. I just use a glossy black spray from the hobby shop to blacken the edges. VERY light coats.
    Heavily sedated for your protection.

  10. #10
    cooltouch's Avatar
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    Thanks for the reply, John. This may be easier than I thought. I take it by "V" clamps, you mean something like this?



    Those should be easy enough to cobble together from some hardwood scrap I have laying around.

    Best,

    Michael

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