Lens Separation - Crazy Idea?

[Fotoguy20d]

I have an old Gundlach triple convertible for 8x10 - it's a 12-21-28 rectigraph I believe - brass barrel. One of the lenses has the worst case of separation I've ever seen. The lens housing though is swaged over so the glass can't be easily removed although there was no problem unthreading the lens assembly from the barrel. What would happen if I just immersed the entire lens assembly in acetone for a day or two? Would it get in and disolve the balsam and would it them wash out? How bad would the lens performance be (given that the cell is entirely unusable anyway, except as a 28" lens, anything would be an improvement)?

Thanks,
Dan

 

[Ian Grant]

Steven Tribe on the Large Format Forum is the person to ask. He's fixed quite a few lenses and posted a thread on how to do it.

Ian

 

[bsdunek]

Agree with Ian. Have somebody re-cement it. It's a shame to ruin a good old lens when it can be fixed.

 

[Ian Grant]

I have a Rodenstock early Sironar, pre the MC version, and that's separating, the company had problems with their first non balsam cements. There's lots of good advice on the other forum on getting elements apart etc, seems more people there tinker with these things.

Steven Tribe is very helpful so ask before you do any damage

Ian

 

[Steve Smith]

I don't know much about cementing lenses but would I be right to assume that they are optically linked by an optically clear material filling the space between the two lens surfaces?

We use a UV cured optically clear adhesive at work. I was wondering if something like that could be used.


Steve.

 

[Ian Grant]

That's exactly what the manufacturers use, and also people doing repairs. For older lenses they also still use balsam.

On the other forum a poster describes how to separate de-laminating modern elements, heat is used but he prefers not to use a furnace instead using hot/boiling water.

I'll be looking for some UV cured Optical cement when I'm next in the UK

Ian

 

[Steve Smith]

I'll be looking for some UV cured Optical cement when I'm next in the UK

Let me know when you are here and I will post some to you.


Steve.

 

[Ian Grant]

Let me know when you are here and I will post some to you.
Steve.

Got to get the lens back first, but I'll take you up on that Steve

It's been on a rather extended loan to an Italian APUG member, hopefully I'll we'll meet up in Venice next Saturday. I plan to put the lens elements in one or two of those bag things that come with washing powder tablets in the UK, that way I should be able to heat up the glass in hot water to separate the errant cell without them getting scratched.

What's the optical cement you use called ?

Ian

 

[desertrat]

One thing the OP mentioned was that the lens elements were "burnished" into the cell. All the suggestions on how to fix the problem are only useful if the elements can be removed from the cell. The only way to get them out is to carefully cut away the cell lip with a very thin, sharp cutting tool after chucking the cell into a lathe. I suppose the lip could also be cut away very carefully by hand with a dremel moto tool or similar small electric die grinder using a thin cut-off wheel. After this is done, some other means must be found to get the re-cemented elements to stay in the cell, because the lip isn't there anymore. A few small dabs of cement or torque paint might work.

 

[Ian Grant]

One reason I suggested contacting Steven Tribe is I think he has some experience, and might be able to suggest the best option.

I'll contact him myself before I attempt my own Sironar repair because any advice is invaluable in getting things right.

Ian

 

[John Koehrer]

Although they're burnished in, the burnished section can be straightened. A very fine blade is worked around the edge several times lifting very small sections at a time. On reassembly they are simply burnished down again.
If you cut the burnished section off the group can be epoxied in place, simply running a small bead or a few drops around the edge.
I've always used Acetone to separate elements but am going to try lacquer thinner for those more persistent jobs.
To the OP don't separate the elements in place, You're going to need to remove them to recement them. I use an optical cement available at my local hardware store, I believe the brand is "Crystal Clear" it comes in a small red syringe & is a UV cured glue. Sunlight or florescent both work.

 

[Steve Smith]

What's the optical cement you use called ?

We have three types:

Optimax, Dymax and one other which I can't remember the name of.

Here is the Dymax website: http://www.dymax.com/

I will post the details of the actual products we have when I get back to work on Wednesday.


Steve.

 

[Ian Grant]

No rush Steve my wife's just postponed my Aegean/Mediterranean trip & visit to Venice

Ian

 

[Fotoguy20d]

John (and all),

I decided to try straightening the burnished section. I was able to get a sharp knife point under but couldn't budge it (and was worried about scratching/damaging the glass). So, I took a small (eyeglass) screwdriver and tapped the back with a pair of pliers to try to work it under. The entire burnished ring just popped right off. So, as solid as the burnished section seemed, the bend point must have been pretty thin.

The glass wouldn't come out though. I put a cutoff wheel into my drill press (300 rpm) and tried to remove more metal - although I cut some away, I was afraid of getting too close to the glass with it. That was a mistake because I think it pushed the remaining metal against the glass tighter (it moved even less freely when I was done with this operation).

So, back to working a knife point under the edge a little at a time. This time, though, it worked and after another 15 minutes the glass came out nicely. There's a little chipping around the edges but nothing more than 1/2 mm or less so I don't think it'll matter.

Total time, around an hour and a half.

Next step, removing the balsam. Any thoughts - does it need to be acetone or will mineral spirits, turpentine, lighter fluid or any of the other hazardous materials I already have in my basement work?

Thanks,
Dan

 

[desertrat]

I believe balsam is soluble in all the solvents you mentioned, but some act more rapidly than others. I think the more volatile solvents will work quicker. Let me know how the project goes, because I've got a 13" 1A Raptar with real bad internal separation. Both groups will need to be recemented.

 

[Fotoguy20d]

The Raptar is probably cemented using a synthetic material, not balsam. So, methods/materials will be different. But, I'll follow-up once I've let it soak for a while.

Dan

 

[John Koehrer]

You might check the link for the hot water technique above.
A little dab of black paint goes a long way to solve small chips.

 

[Fotoguy20d]

I suppose this should have occurred to me earlier, but this thing is a rapid retilinear type so it's actually three pieces of glass so I just doubled my work. I guess I should be happy its not a T-R triple (I have one of those with some edge separation but I"m not messing with it)

Dan

 

[Steve Smith]

What's the optical cement you use called ?

Norland 121: http://www.norlandprod.com/adhesives/nea 121.html

Dymax 4-20688: http://www.dymax.com/products/optical/index.php

Novachem Optimax 4008: http://novachem.ie/Brochures Downloads/Optimax UV Adhesives & Sealant Systems pdf.pdf

The Norland 121 hasn't been used for a while so may be a bit old.


Steve.

 

[goamules]

I suppose this should have occurred to me earlier, but this thing is a rapid retilinear type so it's actually three pieces of glass so I just doubled my work. I guess I should be happy its not a T-R triple (I have one of those with some edge separation but I"m not messing with it)

Dan

Actually most RRs are just two pieces of glass in each element. Gundlach had a habit of adding another glass, which didn't do much, to their designs. I believe the Radar was like that for example, and like you say the T-R lenses were.

 

[domaz]

Actually most RRs are just two pieces of glass in each element. Gundlach had a habit of adding another glass, which didn't do much, to their designs. I believe the Radar was like that for example, and like you say the T-R lenses were.

Wasn't the Radar a Heliar clone? In which case you really would need three elements..

 

[desertrat]

I have Kingslake's book, A History of the Photographic Lens. His diagram of the Gundlach Radar is identical to his diagram of the Tessar, except the Radar uses a cemented triplet in the rear group where the Tessar uses a cemented doublet. He uses the Radar as an example of how some lens designers got around existing patents that way.