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My plan at the moment was to remove the roll over, remove the lens spacer ring, and then the lens VERY carefully. I have heard that alcohol will dissolve the old canadian balsam, but I certainly would like some advice on what / how to dissolve the old balsam.
I have some other old lens assemblies I can practice on with regards to dis-assembly and re-gluing for practice.
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The best I have found to dissolve Balsam is MEK (methyl ethyl ketone). You might be able to get a small amount from your local chemical supply house, otherwise you are stuck getting a 4 litre container. Nail polish remover (Boots Brand if in the UK) has sufficient amount of ketone that will also do the job, but it just takes longer. DON'T get in a hurry when soaking the lens couplet. It might take a week or longer, but longer soaking will save the lens from chipping if pried apart when not completely loose. The big problem is getting Canadian Balsam. It is now a hazardous product and my supplier cannot ship over one ounce (he now removes 1 ml from the bottle to make it under the ounce, and will now ship to me).
There are other products available to glue lenses but they are epoxy's and if you miss most are permanent so be warned.
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"Canada balsam is soluble in benzene, chloroform, xylene, ether and ethanol." Also see Re-cementing doublet elements with Canadian balsam. However, I would seriously suggest try my non-destructive tip a few posts above. Terry Lee is the fortunate individual who stumbled upon this phenomenon, serindipitously.
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I have separated about a million lenses over a bunsen flame. That's the way we used to separate microscope slides at school and optical lenses while I was an apprentice and out in the real world. Mark the edge with a pencil or a v shaped file mark then place on a gauze tray allowing just sufficient heat to allow the flint and crown to slide apart. Allow to cool. The balsam can be cleaned off in clean industrial methylated spirit. You're not so much interested in dissolving the old balsam as just cleaning it off!
I have only ever had one lens crack and that was a Scout Reg scope OG doublet that someone had re-cemented with UV-light cured non refractive index cement not realising that it SHOULD be separate but thinking that the cement had come apart. When I tried the heat, thinking that it was Canada Balsam, it wouldn't budge so I tried a bit more heat and it cracked internally. Luckily I had a load of them
In the Army, if lenses are UV cured, we write UV on the edges although I don't think that anyone re-cements lenses now. Maybe they ought to go back to the days of the No5 binos with a lens doublet cemented to a prism assembly! Phew........ that'd bring on the pains....
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Thanks for all the information! The article that RobD mentioned is very informative. Seems this gentleman uses a light bulb to separate the lens!
RobD: Do you have any idea what solvent Terry Lee was using? Always worth a shot before moving to more dramatic steps.
Thanks everyone.
Richard
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Richard, I've sent you a PM.
Rob
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Is it just me - Does anyone else here feel a sense of foreboding about how Richards valuable lens assembly is going to end up........... Sorry Richard. I think it's time to let a local pro loose on your predicament.. The forum is only so good......
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Peter: I have sent the scope off to several people here in the US that rebuild antique scopes - mostly Winchester A5's and Unertl's. They have all returned it saying that they do not wish to work on it. This is why I am now down to trying to repair the scope myself.
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Here is Sunday's Update - I have the lens soaking in Xylene at the moment. I have made a detailed record by time with photos. So if anything good happens it will be fully documented. If Xylene does not work then Acetone will be tried as the next solvent.
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On the other hand Richard, just do what lens makers and Instrument technicians have been doing since Canada Balsam was invented and gently heat it over a bunsen or gas flame. Sit it on a fork, about 6" above the flame and it WILL just slide apart, believe me. Or just boil it up in a pan - starting from cool. That's all the temperature that you need.
Or just send the thing here and I'll have it apart, cleaned, polished and re-cemented in 5 minutes flat!
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2 Attachment(s)
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Peter:
I freely admit I have no idea what I am doing. If you are willing to repair the scope I am more than happy to send it to you.
I have started the Xylene experiement, and here are the initial before and current time results. Watching it since last night I did not believe that anything was really happening - just wishful thinking. Here are the startup and 0500 photos after soaking for about 8 and 1/2 hours.
Richard
