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11-25-2015, 05:07 AM   #16
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QuoteOriginally posted by manntax Quote
I don't think you are entitled to any compensation / refund once you have disassembled the lens. As far as I know eBay will not side with the buyer who was tinkering with item and disassembled it. You were entitled for a full cover when lens was in exactly the same condition as you've received it. Now I don;t think it is even possible for you to claim anything . You should have waited for the result of the dispute and approach the lens only when you (or the seller ) commits/confirms that the lens is yours and there are no further doubts about the ownership of the item.
The seller has been ok for a refund, I sent him a photo of dismounted lens, and he lets me the lens and I get my money back All lenses are now crystal clear, but mounting it is going to take a few more hours as I take this opportunity to lubricate the pump/focus mechanism with silicon grease and clean all parts, If I succeed I'll have a good lens with only some internal scratchs on lens locking rings... But this lens should have been sold for parts, not just as 'used'. Just shipping fees not refund. As we say here "don't sell the bear's skin before you killed it" and le lens is still disassembled atm^^

11-25-2015, 12:19 PM   #17
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QuoteOriginally posted by Digitalis Quote
There actually has been considerable research,as fungal activity can affect a number of industries - silicon fabrication, aerospace engineering, nanotechnology, pharmaceutical fabrication etc. I have several papers regarding fungal growth on silicon substrates dating from 1986 to as recent as 2004 - the general consensus is that softer glass (such as common varieties of ED glass) with high amounts of elemental Phosphorus,Magnesium, Zinc were more favorable to fungal growth, and harder glass types with higher concentrations of heavier elements such as Lead,Thorium,Lanthanum were generally more resistant - especially to the fungal enzymes that lead to etching of the glass.
@Digitalis
Thank you.

But one could have assumed most of this without doing serious research work.
Some of the heavier elements may work as catalysts, but life (at least on our planet) does not include heavy metals in its DNS/DNA. But it seems these fungi just love certain kinds of coatings.

I think most of the stuff you could use to prevent growing fungi in lens arrangements would also be poisonous for people. No way to use it in lenses with their permanent exchange of air with the environment (when in use).
11-25-2015, 06:07 PM   #18
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QuoteOriginally posted by RKKS08 Quote
But one could have assumed most of this without doing serious research work.
Running on assumptions is a bad idea when it comes to lens repairs. What I posted was a less technical summarized overview of the papers, if you want copies of the technical publications PM me.
12-19-2015, 02:50 PM   #19
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QuoteOriginally posted by Digitalis Quote
A 1Kw 355nm optically pumped nitrogen UV laser should do the trick. It also might decompose the optical cement and cause it to ignite, which should make for a fun evening.



There is also a chance of the adhesive between the lenses will also respond by separating.
Interesting point re heat causing elements to separate (not just mechanical bits). I've just cleaned out a 400mm SMC lens with fungus issues and needed to heat the barrel to get it apart. There's a bonded pair of lenses right behind the front lens. They didn't separate, nor have I experienced separation in other lenses where heat was used. From my very limited searching, it appears the adhesive is Canada balsam fir gum which, when dry, apparently has properties nearly identical to glass. I didn't see any information on how much heat would be required to soften it 40 years after assembly, but it would be useful to know. Re-glueing lenses isn't a hobby I need to take up.

12-19-2015, 10:20 PM   #20
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QuoteOriginally posted by Elroy Jetson Quote
Canada balsam fir gum which, when dry, apparently has properties nearly identical to glass
Except for one important fundamental characteristic: the balsam is a primitive polymer, glass has a largely crystalline structure. Both materials behave differently outside of common operating ranges.

QuoteOriginally posted by Elroy Jetson Quote
I didn't see any information on how much heat would be required to soften it 40 years after assembly, but it would be useful to know.
You can separate the elements cemented with Canada balsam by softening the adhesive by heating them in an oven at 150C for about an hour*, and after separating the elements cool them down (carefully) and soak the separated lens elements in acetone. This should remove the balm from the lens surfaces and then you can attempt re-cementing them with a modern UV curing optical cement.

Warning
: I do not recommend anyone attempt the following high risk technique: It is also possible to use cryogenic cooling to separate lens elements with liquid nitrogen, which causes the Canada balsam to become extremely brittle** - brittle enough that it is possible to shatter the cement between the elements with a quick tap, right at the point of interface with a finely honed blade, after separation the balm simply flakes off.

* the diameter and thickness of the elements have a profound effect on the amount of time needed, this is just a standard recommendation.
**the glass is still significantly stronger then the frozen basalm, but extreme care should be taken when handling glass at these temperatures.

Last edited by Digitalis; 12-19-2015 at 10:44 PM.
12-20-2015, 10:04 AM   #21
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QuoteOriginally posted by Digitalis Quote
Except for one important fundamental characteristic: the balsam is a primitive polymer, glass has a largely crystalline structure. Both materials behave differently outside of common operating ranges.



You can separate the elements cemented with Canada balsam by softening the adhesive by heating them in an oven at 150C for about an hour*, and after separating the elements cool them down (carefully) and soak the separated lens elements in acetone. This should remove the balm from the lens surfaces and then you can attempt re-cementing them with a modern UV curing optical cement.

Warning
: I do not recommend anyone attempt the following high risk technique: It is also possible to use cryogenic cooling to separate lens elements with liquid nitrogen, which causes the Canada balsam to become extremely brittle** - brittle enough that it is possible to shatter the cement between the elements with a quick tap, right at the point of interface with a finely honed blade, after separation the balm simply flakes off.

* the diameter and thickness of the elements have a profound effect on the amount of time needed, this is just a standard recommendation.
**the glass is still significantly stronger then the frozen basalm, but extreme care should be taken when handling glass at these temperatures.
Thanks for the information, Digitalis. Very helpful. I should have been more specific about the shared properties of balsam and glass being optical, not physical as you point out. My habit has been to heat only the bonded area (usually a retaining ring or collar) with a heat gun rated at 1200 watts maximum but set at a low-medium range. Total heating time is under 4 minutes. Leather gloves protect the hands and give a good grip.

Since you've raised the possibility of softening the bond through 'slow cooking', I now wonder about people who leave lenses in their cars on hot summer days. It must happen somewhere that a lens is left in a vehicle with the windows up on a hot sunny day for possibly several hours where temperatures could range from 130F to nearly 200F. Presumably the fit between glass components is tight enough that even if the balsam were completely liquified it wouldn't drain away. Still, not a very good idea.

I love the notion of cryogenic cooling, but will respect your warning and leave that to more adventurous souls.
01-11-2016, 04:44 PM   #22
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Does anyone have any actual experience with separating the elements of a cemented doublet? I have fungus remnants too in a lens that I would like to get rid of.
01-11-2016, 08:02 PM   #23
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QuoteOriginally posted by zekewhipper Quote
Does anyone have any actual experience with separating the elements of a cemented doublet?
If you read my post #20, I have already given instructions for doing this.

01-11-2016, 10:42 PM   #24
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Thermal separation (heat or cold) of a balsam-cemented doublet is an incredibly foolish thing to do, since differential expansion can lead to fracturing and much faster and more effective non-thermal methods are available. Even good-sizwd doublets cemented with natural balsam can be easily separated by a 15 minute soak in methyl ethyl ketone, followed by a wipe with the same solvent and kimwipe to remove leftover residue.

UV cure epoxy optical cements can be separated the same way, although soak times are substantially longer, on the order of several days. Methylene chloride works much more quickly but is more hazardous to work with. Due to the longer times involved, some techs will use thermal separation on epoxied doublets, but it is highly inadvisable for anything but very small elements, since the likelihood of fracture increases rapidly with size due to increased torsional stresses.
01-11-2016, 11:45 PM   #25
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QuoteOriginally posted by dcshooter Quote
Thermal separation (heat or cold) of a balsam-cemented doublet is an incredibly foolish thing to do, since differential expansion can lead to fracturing
If the process is temperature controlled well enough the expansion will be gradual, rather than sudden. I admit the cryogenic method I employed was needlessly hazardous to myself and the lens in question, but it was a fun experiment.

QuoteOriginally posted by dcshooter Quote
Even good-sizwd doublets cemented with natural balsam can be easily separated by a 15 minute soak in methyl ethyl ketone, followed by a wipe with the same solvent and kimwipe to remove leftover residue.
methyl ethyl ketone which is better known as butanone is a highly flammable skin and respiratory irritant with mild explosive properties, it has been known to strip coatings off lenses.
01-12-2016, 10:58 AM   #26
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The only lenses where I would hesitate even one bit to use MEK would be the very oldest soft-coated lenses. Of course, I wouldn't use any solvent on such coatings other than distilled water, since they are so fragile as to be damaged even by light mechanical pressure with a microfiber.
Nearly anything postwar is going to be vacuum deposited silica compounds or metal fluoride, chloride, and nitride ceramics, neither of which is chemically affected at all by MEK. In fact, MEK is a preferred cleaning agent for high precision coated optical glass in laboratory environments, for which coating integrity is a far more critical concern than on a mere photography lens.

MEK,like all organic solvents, has toxic properties, so standard safety precautions (good ventilation, avoidance of skin contact) are recommended, but it's more than a little disingenuous of you to try to paint it as overly dangerous when you recommend acetone, which is much much more volatile and has much greater than "mild" flammable and explosive properties.

Also, glass is not crystalline at all, as you contended earlier in this thread, but rather an amorphous solid, which is defined by being non-crystalline in structure.

QuoteOriginally posted by Digitalis Quote
If the process is temperature controlled well enough the expansion will be gradual, rather than sudden. I admit the cryogenic method I employed was needlessly hazardous to myself and the lens in question, but it was a fun experiment.



methyl ethyl ketone which is better known as butanone is a highly flammable skin and respiratory irritant with mild explosive properties, it has been known to strip coatings off lenses.
01-13-2016, 03:48 AM   #27
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QuoteOriginally posted by dcshooter Quote
MEK is a preferred cleaning agent for high precision coated optical glass in laboratory environments, for which coating integrity is a far more critical concern than on a mere photography lens.
The coatings used in labs are different from common optical AR coatings, they are commonly highly efficient coatings tuned to specific wavelengths rather than the inefficient wide spectrum coatings on commercial lenses. Also I highly doubt any serious lab technician would be soaking optics in Butanone for quarter of an hour when there are safer solvents easily within reach. And in any case Butanone has basically no effect on fungal/bacterial spores, the only way to eradicate them would be though the use of an Autoclave which is a critical piece of equipment in any laboratory.

QuoteOriginally posted by dcshooter Quote
glass is not crystalline at all, as you contended earlier in this thread, but rather an amorphous solid, which is defined by being non-crystalline in structure.
I said largely crystalline - not completely. The Structure of glass depends on its chemical composition: glass with a high lanthanum content the structure is highly amorphous, however glass with a high zirconium content will have a more rigid near-crystalline ordered structure. Lenses made of Fluorite and Quartz most definitely have a crystalline structure.

Last edited by Digitalis; 01-13-2016 at 03:54 AM.
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