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Is DIY splitting cemented lens elements possible?
Old 07-29-2019   #1
Puggie
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Is DIY splitting cemented lens elements possible?

I have a Canon 50mm f1.8 ltm here bought cheap and what I thought was cleaning marks at a glance is actually fungus between two of the rear cemented elements (I will drop a pic up if it helps). I have cleaned up the rest of the lens and its not bad at all. I just wondered if there was a relatively DIY (I work in a university so I have more 'tools' available than most for DIY) method for splitting cemented elements to clean and reassemble. The lens is IMHO too good to junk, but not valuable enough to warrant sending out for repair, so I may as well try a DIY job on it if possible.

I assume the elements can be separated by careful heating to break the bond, then clean and 're-cement' with some optical UV curing adhesive?

Sounds like a fun way to spend an evening!
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Old 07-29-2019   #2
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It is feasible but risky. Slow, controlled heating - it’s the rate at which you heat it that’s important - is the key. There are general instructions at several astronomy sites, such as: https://www.cloudynights.com/topic/3...-re-cementing/

Don’t be surprised, however, if you destroy the doublet.

My father was an optical engineer before he retired and showed me how to do this, but emphasized it simply does not always work, and can be unpredictable depending on the age of the doublet, the type of cement used, the heat conduction properties of the elements and the oven used to heat the doublet.

Marty
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Old 07-29-2019   #3
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I seem to remember reading, probably on photrio, that some people preferred prolonged soaking in nasty solvents for separating elements bonded with modern cements. No risk of physical damage that way.
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Old 07-29-2019   #4
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Quote:
Originally Posted by retinax View Post
I seem to remember reading, probably on photrio, that some people preferred prolonged soaking in nasty solvents for separating elements bonded with modern cements. No risk of physical damage that way.
I have done something of this sort. Years ago a pair of very old (1890 'ish) binoculars (French manufacture if my memory serves me correct) came into my hands. When I looked through them, is was very apparent that the old balsam had perished badly and had cracked up and dried into flakes.

I opened up the binoculars (Front elements only I think and removed a bonded doublet from each side which I soaked most likely in methylated spirits (methyl alcohol) I do not recall which solvent specifically but "metho" is so ubiquitous it seems the most likely option). And it is pretty save - in fact I would go so far as to say it is very safe unless taken internally where it causes blindness, kidney failure and death. Just don't plan on drinking any of the stuff. In any event it dissolved and allowed me to remove the remnants of the old balsam. It was too long ago for me now to recall the details but the operation was a success, the patient did not die and in fact I still have them somewhere though long unused. However I can say that even though I never recemented these elements the binocs still function pretty well.

EDIT: I recalled that I had seen an advert for balsam on eBay so I checked it out. I figured that you may need some of this stuff. One eBay ad came up for "Canadian Balsam Fir Gum".

The ad contained a list of virtues and uses: "Helps eliminate toxins, immunostimulant, helps eliminate mucous from the respiratory tract, antiscorbutic....... etc." and is used for "Sleep disorders, stress, anxiety, constipation, abdominal or stomach pain, rheumatism and kidney pain" and so on.

I thought for a moment I had wandered into a cowboy movie set where there was some snake oil merchant selling bottles of his patent remedy for grandpappy's rheumatism from off the back of his covered wagon in the town square. Yer darn tootin' I did!

Until right at the end the ad it also stated: "Canadian balsam is used as a glue" and listed a further use as including: "High precision optical lens assembly" (They did not seem to specific what form of assembly - However I don't think balsam is used to actually glue lenses together other than in optical elements so I had to figure it's most likely the right stuff.

And if it's not, well at least you can cure your rheumatism and kidney pain. Oh and of course your constipation should you have it.

https://www.ebay.com/itm/Canada-Bals...oAAOxycmBS3Yut
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Old 07-29-2019   #5
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Quote:
Originally Posted by peterm1 View Post
I have done something of this sort. Years ago a pair of very old (1890 'ish) binoculars (French manufacture if my memory serves me correct) came into my hands. When I looked through them, is was very apparent that the old balsam had perished badly and had cracked up and dried into flakes.

I opened up the binoculars (Front elements only I think and removed a bonded doublet from each side which I soaked most likely in methylated spirits (methyl alcohol) I do not recall which solvent specifically but "metho" is so ubiquitous it seems the most likely option). In any event it softened and allowed me to remove the remnants of the old balsam. It was too long ago for me now to recall the details but the operation was a success, the patient did not die and in fact I still have them somewhere though long unused. However I can say that even though I never recemented these elements the binocs still function pretty well.

Great success story! Canada balsam does dissolve in alcohols, but modern cements need nasty stuff.
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Old 07-29-2019   #6
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Quote:
Originally Posted by retinax View Post
I seem to remember reading, probably on photrio, that some people preferred prolonged soaking in nasty solvents for separating elements bonded with modern cements. No risk of physical damage that way.
Indeed. I'd suggest chemical attempts before resorting to heat. You have nothing to lose but a bit of time. If unsuccessful, you can, after all always try heating it up subsequently. But if it does work, you have neatly side-stepped the risk of breakage.

Acetone is a reasonably effective, cheap and safe solvent to try. Milsolve, if you can find it easily enough and at an affordable price is efficient. But much depends on what the pieces were bonded with. Canada Balsam will yield much more easily to chemicals than synthetic UV cure cements that began to appear around the 1950s. These might conceivably need weeks of soaking in solvent to penetrate their tenacious grip on the glass.

But before even attempting to split the pieces, do you have a plan for accurately aligning the newly cleaned glasses before re-joining them? Because there's little point in trying to split the affected doublet, unless you can accurately re-set the pieces—unless perhaps you want to turn the lens into a lomo facsimile.
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Old 07-29-2019   #7
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Canada Balsam is one means of cementing the pieces again. If using pure Balsam it's usual to dilute it with xylene before applying to the glass. It's not the fastest curing method however so you will need to keep the glass both accurately aligned, and stable, until it has cured.

You can source UV cure cements which have the advantage of speed. These work well in a manufacturing environment where the facilities and tooling needed to quickly and accurately align the pieces to be joined are sophisticated and efficient. But get the alignment off in a home repair scenario and you're right back to square one, should you need to split and re-attempt. Hence, whilst I might use alternatives for more easily assembled items such as Eg finder optics, for lens glass I'd be inclined to stay with Balsam simply because it is so much more forgiving should you subsequently need to fine tune or revisit the work. If you have laboratory facilities perhaps you may feel more confident using the fast curing cements instead.
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Old 07-29-2019   #8
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You're right in thinking it's too much money for a CLA, as it's not an inexpensive fix.

It's not really a DIY repair. The simplest solution would be to sell your lens as-is and invest the money in a clean one. You could also try putting a yellow filter on your current lens to boost contrast (if you mainly shoot B&W). I would get rid of it and get a clean one.
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Old 07-29-2019   #9
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The balsam you'll get online is not optical grade and will be yellower than you'd like from the outset. Buy some optical cement if you can, but get one that can be released if you need to.

What Brett wrote about recollimating once you have separated the doublet and are reassembling it is very important. If you just add a drop of cement and place them back together you'll almost certainly get some very, very interesting decentering.

Marty
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Old 07-29-2019   #10
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And to add something to this discussion , I tried using acetone on a fujica lens a couple of years ago ( submersed for 4 days and ) and it was still as good as welded together . So be prepared to WAIT . Peter
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Old 07-29-2019   #11
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I'm pretty sure I recall a thread about this by ex RFFer Brian Sweeny many years ago ... and I think he did it from memory. He was remarkably resourceful and quite a loss to this place when he left.
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Old 07-29-2019   #12
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I wonder if you couldn’t air space it afterwards?

Most objective lenses (on telescopes) are either air spaced or oil spaced.

Without knowing how the doublet mounts in... could be a stupid idea.
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Old 07-29-2019   #13
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Quote:
Originally Posted by Freakscene View Post
The balsam you'll get online is not optical grade and will be yellower than you'd like from the outset. Buy some optical cement if you can, but get one that can be released if you need to.

What Brett wrote about recollimating once you have separated the doublet and are reassembling it is very important. If you just add a drop of cement and place them back together you'll almost certainly get some very, very interesting decentering.

Marty
This one says it is "microscopy grade" - which I believe means it is used for mounting specimens on microscope slides not gluing the optical elements in a microscope's optical system. But I would anticipate that even for specimen mounting the balsam must be absolutely clear and have the right refractive index. The ad says it is "neutral and clear". It may not be absolutely Kosher but sounds like it could work.

https://www.ebay.com/itm/Canada-bals....c100005.m1851

PS I note the reference in a post below to collimating the elements when glueing them. I was going to say something of this sort but felt I could add little as I do not know exactly what the process is - only that it is necessary (I do however recall a lens tech I once knew who showed me a tool he made for collimating lenses he repaired but that was long ago and I cannot recall details). I should add that this was a factor in me suggesting using balsam for the purpose - having split the glued element once you would know how to do it again if needed - e.g. if the collimating was not a success first time around.
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Old 07-29-2019   #14
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Quote:
Originally Posted by B-9 View Post
I wonder if you couldn’t air space it afterwards?

Most objective lenses (on telescopes) are either air spaced or oil spaced.

Without knowing how the doublet mounts in... could be a stupid idea.
Multiple unit optical groups are designed to not have an airspace, to utilize the glass to glass change in refractive index. Putting an airspace in there would render the lens useless.

Marty
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Old 07-29-2019   #15
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Quote:
Originally Posted by peterm1 View Post
This one says it is "microscopy grade" - which I believe means it is used for mounting specimens on microscope slides not gluing the optical elements in a microscope's optical system. But I would anticipate that even for specimen mounting the balsam must be absolutely clear and have the right refractive index. The ad says it is "neutral and clear". It may not be absolutely Kosher but sounds like it could work.

https://www.ebay.com/itm/Canada-bals....c100005.m1851

PS I note the reference in a post below to collimating the elements when glueing them. I was going to say something of this sort but felt I could add little as I do not know exactly what the process is - only that it is necessary (I do however recall a lens tech I once knew who showed me a tool he made for collimating lenses he repaired but that was long ago and I cannot recall details). I should add that this was a factor in me suggesting using balsam for the purpose - having split the glued element once you would know how to do it again if needed - e.g. if the collimating was not a success first time around.
I use bucket loads of microscopy grade canada balsam at work to mount the small marine animals we work on. It is always yellow. Good optical cement is properly clear, with no tint, has a reliable even refractive index and is formulated to heat release reliably. The problem with balsam is you never know the grade or homogeneity of the product and the refractive index varies between batches and in the product.

Marty
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Old 07-29-2019   #16
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Quote:
Originally Posted by Keith View Post
I'm pretty sure I recall a thread about this by ex RFFer Brian Sweeny many years ago ... and I think he did it from memory. He was remarkably resourceful and quite a loss to this place when he left.
https://rangefinderforum.com/forums/...ad.php?t=89797

https://www.rangefinderforum.com/for...ad.php?t=10834

Marty
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Bubbles
Old 07-29-2019   #17
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Bubbles

I used the "microscopy" grade balsam years ago in college to make slides for microscopy. Generally slightly yellow in color, but such a tiny amount remains between the elements that were being glued that it appeared clear. That said, bubbles were the bain of our student existence. It was almost impossible to slide, place, push the elements together without getting some bubbles between the elements. That, I think, may be the limitation here.
The other problem with balsam is that it takes a while to dry. A week or two later, it was not unheard of to have the cover glass slide off the slide if it was tilted.
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Old 07-29-2019   #18
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I have a list of links stored on re-cementing and I am happy I did not need to do it myself yet.

If you can use chemical way to dissolve things, it is probably better as heating. Just make sure you follow all warning labels on chemical agents and use protective gear and ventilated rooms as needed.

More info you get, the better picture you can make yourself, so I add some those links for ya:

http://jimshomeplanet.com/lensglue.html

http://skgrimes.com/library/old-news...y-re-cementing

https://www.optical-cement.com/cemen...al/manual.html

https://www.edmundoptics.com/c/adhesives/644/
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Old 07-30-2019   #19
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xylene and alcohol works on older lenses
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Old 07-30-2019   #20
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Wow thanks for all the advice, so my thoughts and plan of attack:

1) Strip the lens and upload a pic of the offending element
2) Make some form of Jig to re-centre the elements for re-assembly (I can turn something up on a lathe or laser cut something probably from PTFE sheet if I'm bonding near it)
3) Soak the thing in a range of organic solvents (its a late 50s lens, I'm assuming it is a Balsam that can be dissolved chemically here) I have some awesome petrochem based degreaser that may work well, I think carb cleaner is predominantly xylene and I have DCM and trich in the 'old solvent' collection.
4) Give it all a good clean
5) acquire some releasable optical adhesive from somewhere (any specific recommendations in the UK)
6) Re-mount the 2 elements together and re-assemble the lens
7) Test and grin like a Cheshire cat or grumble into beer.

Does that sound like a reasonable way to go about this?
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Old 07-30-2019   #21
Sarcophilus Harrisii
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Quote:
Originally Posted by Freakscene View Post
I use bucket loads of microscopy grade canada balsam at work to mount the small marine animals we work on. It is always yellow. Good optical cement is properly clear, with no tint, has a reliable even refractive index and is formulated to heat release reliably. The problem with balsam is you never know the grade or homogeneity of the product and the refractive index varies between batches and in the product.

Marty
That's very useful information, Marty, thank you.
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Old 07-30-2019   #22
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Quote:
Originally Posted by Puggie View Post
acquire some releasable optical adhesive from somewhere (any specific recommendations in the UK)
https://www.edmundoptics.co.uk/f/nor...dhesives/11818 or search the web for optical adhesive UK. The Norland 60 and 61 will release in methylene chloride even when fully cured. If you plan to go to the arctic the 61 is meant to be better, but plenty of great photos have been taken all sorts of very cold places with lenses cemented with balsam, which is theoretically a terrible very cold weather adhesive.

I had some Zeiss optical adhesive I’d donate, but some time between when it was given to me and now it turned into, well, for want of a better description, a very aspherical element.

Quote:
Originally Posted by Puggie View Post
Does that sound like a reasonable way to go about this?
Yes, entirely. Good work for planning it at all, actually.

Marty
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Old 07-30-2019   #23
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I have a sacrificial Canon 1.8 50mm here which was originally on a LTM. The rear cluster is OK but the front is not. Postage down to you.
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Old 08-01-2019   #24
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So I have uploaded a couple of pic of the offending element. The fungus is between the two bonded surfaces. This lens group is the second and third pieces of glass from the focal plane (best description I can think of) just before the iris. they are accessed by removing the rear most ring, then the whole lens block drops out of the barrel. then if you unscrew the rear most section of the block, you have the rear three lenses. Then this bonded pair unscrews from the front of that set of three (confused yet)!

Murray has kindly offered me a better copy of this lens group, I still intend to try and rectify this one, just to see what can be done.
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File Type: jpg Canon ltm.jpg (21.2 KB, 17 views)
File Type: jpg canon ltm2.jpg (24.9 KB, 23 views)
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Old 08-01-2019   #25
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That’s not fungus.

Marty
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Old 08-01-2019   #26
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That’s not fungus.

Marty
OK then... its between the lens elements, so what is it?
Admittedly I thought someone had had a quick go at cleaning it (assuming being a canon ltm, it may fog like my 1.2 does) and done a poor job, this being some residue on the surface of a lens element. but its not, its between two cemented pieces of glass. Its not the spidery web looking residue normally associate with fungus, neither does it look like the 'bubble' I've seen of balsam separation I have on an old schneider 90mm f8 LF lens. I thought is was a fungus,but just a different propagation through the lens balsam as it was between layers of glass not just on the surface as I had seen before. Pics are crops from an old phone cam too so apologies they are not the clearest.

So please enlighten me, what issue do I have here?
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Old 08-01-2019   #27
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These are the rear pair from the lens I have for donors. I''s quite hard to tell exactly if they are the same. I leave it to you.
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Old 08-01-2019   #28
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I believe the one on the right is the one I have uploaded, might have to take another couple of pics and measure the diameter and height this evening to check. My lens is the Canon 50mm f1.8 III (like this link https://global.canon/en/c-museum/product/s48.html). I believe the previous version II of this lens with 11 blade diaphragm (mine is the 8 blade) is of identical optics.

I will measure up the element diameters and heights this evening and post, so you can confirm your element is the same physical size.
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Old 08-01-2019   #29
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Quote:
Originally Posted by Puggie View Post
OK then... its between the lens elements, so what is it?
Admittedly I thought someone had had a quick go at cleaning it (assuming being a canon ltm, it may fog like my 1.2 does) and done a poor job, this being some residue on the surface of a lens element. but its not, its between two cemented pieces of glass. Its not the spidery web looking residue normally associate with fungus, neither does it look like the 'bubble' I've seen of balsam separation I have on an old schneider 90mm f8 LF lens. I thought is was a fungus,but just a different propagation through the lens balsam as it was between layers of glass not just on the surface as I had seen before. Pics are crops from an old phone cam too so apologies they are not the clearest.

So please enlighten me, what issue do I have here?
It’s separation, but from balsam autdegradation rather than from a breakage or bubble. Balsam gets hard over time unevenly which creates internal shear forces that pull it apart. When this happens inside rather than from the edges this is what it looks like. It’s also possible that when the cleaning was attempted a very small channel formed from the edge inwards and the solvents made the separation worse. All this, further, is good reason not to use balsam to fix it.

You won’t get fungus growing from inside cemented multi unit groups. There is no way for fungal spores to get in, and when fungus does grow it has very distinctive mycelia with a branched structure, rather than the irregular pattern you can see here.

Irrespective of the problem, the fix is to separate the elements, clean away the old adhesive, clean and polish the surfaces and re-glue the cleaned elements.

Marty
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Old 08-01-2019   #30
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I need to find my sheet of 6mm PTFE and cut some jigs then

thanks for the school lesson
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Old 08-01-2019   #31
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I need to find my sheet of 6mm PTFE and cut some jigs then

thanks for the school lesson
Sorry if it sounded like a lecture.

Just let us know how you go when you attempt the repair!

Marty
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Old 08-01-2019   #32
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Sorry if it sounded like a lecture.

Just let us know how you go when you attempt the repair!

Marty
No it was meant in all seriousness, I've learnt something new, I'm grateful for that. I sometimes come across as a bit blunt and abrasive, especially with written communication which misses out the wry smile and cheeky grin that end the statement... maybe I need to use more smilies
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Old 08-01-2019   #33
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I have done it a few times on Petzval lenses and prisms that had become unglued.

In one case I used heat on a Petzval front group to melt the yellowed and cracked balsam. It had nearly turned opaque.
Luckily balsam becomes soft at slightly over 100C.
Seperated the elements by sliding them apart and breaking the cohesion of the balsam, then cleaned them off with thinner. Reglued the elements using Norland Optical cement.

In case of prisms I seperated them all by soaking them in thinner overnight.
They were already clean when they came out of the tray.
Again using Norland Optical Cement to reglue them.

Using a jig is a must.
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Old 08-01-2019   #34
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FYI
At one of the sites previously mentioned, there are a couple of specialist solvents for dissolving lens cement and the smaller sizes may be transported by air apparently. Instructions for the general one still recommend heat. Fair enough I suppose. The maker knows best. Myself, if I was doing a lens that was valuable enough to me to be worth the effort in the first place—except as a learning exercise, perhaps, and there's much to be said for practicing on an inexpensive optic first—then, I think that if it was a Balsam-cemented lens, I would probably still give it the benefit of the doubt and leave it to soak for a couple of days in a clean container, first. This might do the trick possibly and even if not I reckon it would have to give the heating stage a head start.
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https://www.optical-cement.com/cemen....html#decement
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Old 08-05-2019   #35
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I've separated many cemented doublet. I get never lucky with solvent (either with canadian balsam glue, but was a very large doublet) also waiting for 10 days. I've used acetone and paint remover as norland instruction says.
I use low ramp heat soaking them in water or better in (olive) oil to reach more high temperature than water.
After separation i remove the glue with paint remover and i bond them again with norland 61 and a uv led lamp for nail paint.
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Old 10-23-2019   #36
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Puggie, did that lens ever turn up in the post?
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Old 3 Weeks Ago   #37
Freakscene
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And if you’re looking to work out what cement to use:
https://www.edmundoptics.com/resourc...e-should-i-use

Marty
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