Cleaning and re-cementing lenses

[jgrainger]

I'm considering trying my hand at separating some lens elements and recementing with Canada Balsam.

Realistically I've some Contaflex lenses which are showing some seperation, and a uncommon tessar with some fungus between the elements. I'd like to try on something less great, and have read other forums (and watched some videos). I don't buy into the idea that it's especially impossible - though I can appreciate there are issues, especially with ventilation.

Has anyone here got experience or disassembling groups to clean fungus, and/or recementing?

Jonathan

 

[davidnewtonguitars]

If they were originally cemented with Canada Balsam, denatured alcohol should de-cement them.
But what do I know...

 

[Paul T.]

If they were originally cemented with Canada Balsam, denatured alcohol should de-cement them.
But what do I know...

nice guitars, David.

 

[jgrainger]

I gather there are a few things which will dissolve Canada balsam, and even the early Zeiss post Canada balsam lens cement.

Are there any do's/ don't bits of advice you'd give, and can you (or any other readers) recommend ways of centering elements of differing diameters? - I've seen a vacuum method with an optical display for the concentricity but that's beyond what I can justify.

Jonathan

 

[Livesteamer]

I am no expert but I remember some things from the Focal Point website. Heat was involved and there was some risk of breakage. When John Van Stelten, the owner of Focal Point closed shop earlier this year, I exchanged some e mails with him and he told me the work required great patience and that he had been blessed to start out long ago under the training of an old German technician. I think John also had some specialized tools for ensuring optical centering. Good Luck, Joe

 

[peterm1]

I seem to recall years ago that I had a vintage pair of binoculars (WW1 or earlier) in which elements had decemented and the remnants of the balsam was badly crazed. I removed the remnants I think with methylated spirits which readily dissolved the balsam. (The glasses were more for display so I never tried recementing). It is also possible apparently to remelt balsam by placing the cemented pair in an oven on low heat and when the critical temperature is reached pressing them together. There is an obvious risk of cracking the glass and there is an obvious risk of decentering the elements. I cannot recall the details but I believe that there were some articles on how to do this if you Google it.

 

[x-ray]

Several guys on the Large Format Forum have successfully done this. You might check there. There are quite a few really sharp folks there.

I believe xylene and acetone were used and UV curing cement used to recement.

A couple of these guys were seperating and recementing some rather complex lenses. As I recall it was important to use a pencil and mark the edge of the elements so they could be indexed in exactly the same position. Also, and I can't remember what the name was, but they made metal blocks to wedge against the elements to insure perfect centering when assembling.

Dissolving the balsam by soaking the cell takes time so don't get in a rush. I believe in most cases it too a week or so of soaking.

In theme 70's I had a very nice triple convertible Turner Reich 8x10 lens that had severe balsam crystallization which is very common in these lenses. A friend was an optical designer and builder for the nuclear industry. He designed optical systems to operate in extremely high radiation areas where regular optical glass would turn black in minutes if exposed to that level of radiation. Anyway he offered to recement my lens which was useless due to balsam crystallization. I figured what do I have to lose. My friend used heat to soften the balsam but unfortunately the heat distribution in the glass was uneven and the 4 element cell shattered. I'd definately try solvent first.

 

[bluesun267]

Not nearly as accurate as you need to be with a lens, but I recently had good success re-cementing the rearmost element of a Canon bright-line finder. It had come loose by itself.

A drop of Norland 61 optical cement, pressed the two pieces together, set it in the sun for a couple hours and it seems good as new. I didn't even need to build a jig to hold it in place.

I bought the Norland in a small tube off the bay (no affiliation): https://www.ebay.com/itm/Norland-61-Optical-Adhesive-Glue-UV-Cure-Tritium-Glue-NOA61-1mL/171185267060?hash=item27db6fe174:g:ZmUAAOxyrx5TkM24

 

[jgrainger]

Thank you,
It seems that heat and/or duration of exposure to chemicals are the key methods, I'll have a further look on the large format forum - shall try to find some pictures of centering jigs for the reassembly.

At some point I'll post back here with some good or bad results.

Jonathan

 

[Mr_Flibble]

I've recemented the front group of a petzval (including a large chip of the rear element in the group) where the cement had crystalized.
I split the group by slowly heating it up in an oven, to some 110-120 C.
As the Balsam cement liquified I slid the elements apart (wearing some heat resistant gloves).
After they elements had cooled I removed the balsam residue with acetone.

Then I used Norland Optical Cement and a jig to put it all back together. The cement is great as it made the crack between the broken pieces of the rear element practically invisible.

 

[Gareth Rees]

I believe Zeiss used an experimental epoxy cement on its contaflex pro tessar lenses, and they seem very prone to separation.

Good luck

 

[astro8]

Look here

There are also one or two more articles on re-cementing lenses in the above link.

I think the safest way to separate balsam cemented lens elements is by slowly heating to a boil in a pot of water.

As regards to getting the elements aligned and if they are of the same diameter, some technicians used their tongues to feel even the tiniest misalignment.

If the elements are not of the same diameter, as in the 21 Super Angulon, you can set up something to rotate the elements on a horizontal plane while your 'glue' is setting, but I can't remember what I used. I think it involved plasticine (to have a good grip but be easily adjustable while I got it to run true) to hold the bottom element, maybe on the end of a dowel through a bearing held in a vise. Any misalignment shows up as a wobble and is easily spotted and corrected.

I have used a clear acrylic auto paint as a temporary cement for a test run but 4 years later I haven't bothered to 'permanently' cement the elements. The lens is fine.

 

[Sarcophilus Harrisii]

The Contaflex Pro Tessars were not bonded with Canada Balsam. Some early Contaflex optics such as pentaprisms used in the original model were joined with Canada Balsam. I have a early original model here with a prism that's unquestionably affected by aged balsam. By the time the Pro Tessars arrived, however Zeiss were switching to synthetics. It's why those never go brown or discolour. Other than the blue/white ring that develops around the edge, initially, where the glass is parting, they typically remain crystal clear.

That the new synthetics weren't without teething problems is attested by the high rate of failure with certain lenses, notably the Pro Tessars, but other lenses were certainly affected. The 135mm Sonnar used in the Tele Rolleiflexes is a case in point. Issues with the 80mm Planars fitted to the 2.8 Rolleiflexes are also well known.

I wouldn't bother trying to heat the Pro Tessars up. I doubt it will achieve anything (apart from breaking the glass). A better idea would be to place the affected optics in a container of Milsolve (if you can get it) or acetone, and then forget all about them for a few months. If you're lucky, they will eventually part.

I've posted about the incredible tenacity of the period synthetic cement and the challenges involved in removing it, so additional background is available.
Cheers,
Brett

 

[jgrainger]

Thank you Greg and Brett 🙂

Maybe something along the lines of a watchmakers wax chuck would work.. To heat shellac and centre a fixture on it while rotating and cooling - I'm thinking a turned cylinder, close fitting with only a slight seating shelf to avoid scratching the working part of the lens, with a slit on one side and tightening screw. Fasten the lens in then centre using the exposed outer edge just above the fixture.

I'm also an amateur machinist with some experience doing it where I used to work, but my machines have been moved to temporary storage for the moment.

Jonathan