Optical adhesive used in mamiya RB67 C/ KL lenses

Discussion in 'Medium Format' started by markruskikh, Mar 2, 2021.

  1. Dear community,

    I own a mamiya 127mm K/L lens. The lens has a “foggy” rare lens doublet. Which I recently learned is quite common on this particular lens. Most listing on eBay rated at near mint/exc5 or even mint have this problem (which is for another discussion as rating of lenses especially by Japanese sellers over the years have degraded significantly.)

    many people use this lenses with that condition as is, which is doable, and somewhat gives you a soft focus 127mm lens if you watch out for high contrast scenes, or during long exposure night photography you will get results somewhat similar to the look of cinestil 800t. Which I do not like (for my style the more sharp the image is the better, even for portraiture.)

    after consulting with photo repair stores, optics labs, and even some of my scientist friends who work in the field of optics I learned that no one will take my oldy MF mamiya glass and take apart the doublet re-align and recement it. I was told that the price for the job is just many times higher than the price of the lens.

    so here comes the fun part. I decided to do it myself. As I really have no use for a soft 127mm. Now the doublet is being soaked In methylene chloride and soon will be ready for re-cementing.

    the question is does anyone know what kind of optical adhesive was used in mamiya k/l glass? I assume it’s a synthetic cement or UV cured epoxy adhesive as it did not look like Canadian balsam or something of older types adhesives. The most important question is does anyone know the refractive index of the used adhesive? So I can chose a replacement accordingly.

    best regards,

  2. I suspect there's a good reason that Mamiya used a weird adhesive. None of their other lenses show the same cement degradation, do they?

    I know there's no sign of it with my M645 lenses.

    It probably has little to do with refractive index, but more with compatibility with the lens material. Doublets always use disparate refractive indices - otherwise there would be no need for a doublet - meaning that the RI of the cement should ideally fall between the RIs of the two glasses. In practise, the thinness of cement makes its RI pretty irrelevant, as long as it's close to that of one of the glass types.

    So. If the cement has been chosen for compatibility with one of the glasses; you have to ask why? Is it a fluorite glass that's attacked by water? A plastic or resin that's attacked by acrylic cements? Who knows.

    Maybe a search of Mamiya's registered lens patents might throw some light on it.
    markruskikh likes this.
  3. You are not getting a lot of responses because there are not that many people here that cement lenses, so I'll give you my opinion. I've only cemented a hand full, and I'm no expert in the process or cement, so take that as you may.

    Canadian balsam has been in use for over 100 years. It works well, is optically clear and has an index of refraction ~1.5 (close to glass). It was used in photographic lenses right into this millennium, and is still used in labs and optics today.

    As far as I know, optical epoxy's were first widely used by Zeiss for it's UV lenses (because balsam was opaque at that frequency) and that has progress to UV cured optical cement (polymer). It comes in indices from 1.3~1.5

    Canadian balsam is dissolved in Xylene, a drop is sandwiched between 2 lenses, and then it's left to dry - about a month, depending on size.

    UV cured optical cement comes in a bottle, you put a drop between 2 lenses, and expose it to a UV light for 30 sec. I've used the Sun for an hour.

    I used Canadian Balsam for the first double I re-cemented. Not really interested in doing that again, UV cured optical cement is much easier.

    I'm not aware of haze and fungus appearing in the bond of UV cured optical cemented lenses, at most you get separation, usually at the edges, which appears clear. This happened to a lot of early Zeiss lenses when they started using synthetic cements. Fungus and haze only show up in the bonds if balsam is used - it is an organic material. My rule of thumb is - (haze and/or fungus) = (Canadian Balsam); (clear separation) = (synthetic optical cement)

    The last doublet I re-cemented was from a Bronica GS-1 50mm f/4.5 lens, the rear group doublet was hazy in the bond. It used Canadian Balsam, so I separated it with boiled water, cleaned and re-assembled without any cement (the Newton's rings pattern between the 2 element indicated that they were properly aligned). I then used the lens for a few years because - 1) it's good to wait and see if the fungus comes back - which means you did not clean the rear group properly, and - 2) I did not have any UV cured optical cement handy, and did not want to mix Balsam and Xylene. However, last year I bought some UV cured optical cement to fix a stone chip in a windshield, and I used a drop for that to re-cement the doublet.

    I don't think it matters which you use. People have been using UV cured optical cement to fix old lenses that used Canadian balsam for as long as ... UV cured optical cement has been around. Also, it does not keep, so unless you cement a enough of lenses, it's not worth buying a bottle. Canadian Balsam keeps forever, but you have to dissolve it in Xylene.
  4. Tom , I'm curious about your answer , you mention using Xylene to separate the lens bonded with Canadian balsam ,
    and then later you mentioned using boiling water . Are they both effective at freeing up Canadian balsam bonded lens ?
  5. Rather than waiting on the sun, a cheap source of 'hard' UV is a sterilising cabinet bulb. These are used by hairdressers and beauticians to sterilise scissors and combs, etc.

    The cabinets use a simple quartz envelope filament bulb with a drop of mercury enclosed. When the filament lights the mercury is vapourised and a mercury arc strikes up between the element supports. This shorts the filament out and you have a miniature arc-lamp. The bulbs need a resistive ballast in series to limit the current.

    Not to be stared at once the arc has struck!
  6. Xylene is used to dissolve the raw Canadian Balsam (which is solid) to make it liquid so you can cement the lenses. Canadian Balsam in solid form keeps a long time, the cement in liquid form does not (although you can probably keep a bottle of Canadian Balsam dissolved in Xylene for as long as an opened bottle of UV cured optical cement).

    You can use it to separate lenses too, but all you need is some heat, and boiled water worked fine for me.
  7. A former partner had a UV-B lamp for treating psoriasis and eczema, I used that for a few lenses. But I don't do enough to buy an optical source (or more correctly, I don't do enough to make me look for an optical source...). And the sun is free. And on that last lens, it did take me a few years from separating the lens, to re-cementing it!
  8. Tom, thank you for sharing your experience . I have few questions. Did you use that non cemsnted lens? If so did you notice any degradation of the image quality? Olso what brand of UV cured cement did you use? I have three Mamiya lenses with foggy rear doublet and I want to re-cemet them
  9. I've only done a couple lenses and I've used Norland #61 optical cement- seem to work fine. Not cheap and has a short shelf life. LED UV sources are common now. There are good clear epoxies for this, but the minimum orders are high. 40 0005 Industrial Fiber Optics | Tapes, Adhesives, Materials | DigiKey might be a good choice but I'd do a junk lens first.
  10. I used it for a few years that way, it was fine - there may have been a 1%~2% drop in transmission, but I did not notice and difference in the pictures prior and after cementing with UV cured optical cement. There certainly were differences when the bond was hazy.

    On that last one, it was Permatex. It came from an automotive windshield stone chip repair kit - I needed it for a windshield...

    Prior lenses were Norland (either 61 or 81), we had some in a lab, so I borrowed it. As Conrad said, it's not inexpensive and has a shelf life, I was not planning to buy any until I had a few lenses to cement. You can order it from Edmund Optics for ~$50. The windshield repair kit was $15 - and it repaired a windshield!
  11. I'll be interested to know how successful the OP was in getting the doublet apart.

    Methylene chloride will soften an acrylate, but I'm not sure about Canada balsalm. Risky stuff to use on any synthetic lens element too, I would imagine.

    Anyway, some feedback would be good.
  12. Today I was trying to separate a doublet from Mamiya KL 150mm f 3.5 lens.

    I used three methods without a success:

    1. Put a doublet in the oven and hit it up for 15 min at the temperature 225F

    2. Boiled it in the water for approximately 15 min

    3. Put a doublet in the oven and hit it up for 15 min at the temperature 350F

    The elements did not move at all.
  13. That then must have been an epoxy or UV cure adhesive. Most epoxies will fail at 400F or so, but I'd be scared to do that to a lens. It would have to be done slowly to avoid cracking and it still might crack. The solvents that will attack epoxy like methylene chloride and NMP have been or are being banned for consumer use, so I don't know what to recommend.
  14. Hi Mark. Were you able to separate a doublet? If so, how long did it take? Any side effect on the elements coating?

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