Which Canada balsam to restore a Verito 18"?

[lungovw]

Hello,

I bought a Wollensak Verito 18". Glass is in mint condition except for an almost 1/2 inch thick ring of balsam oxidation. I have a friend with a small optics workshop (he produces prisms, lenses, doublets for medical equipment, but nothing as big as this lens) and he offered me to re-cement it. But he normally uses that UV type cement and we agreed that Canada Balsam would be more suitable and more forgiving in case of any problem. But there are two types: natural and synthetic. Any insights on which one to pick?

[Nodda Duma]

If you’re going to go to the trouble of using Canada Balsam over UV cure adhesive (which would work just fine), then use natural.

Regards,
Jason

[Mark Sawyer]

I'd strongly recommend Canadian Balsam over UV-cured cement. If you screw up with UV-cured, it's just about impossible to separate the elements and clean off the cement. If you screw up with Canadian Balsam, just separate it and clean it like you did the first time.

Great lens, btw!

[Nodda Duma]

The method for UV cure is to cure it for 3 seconds or so then check alignment. If all is good, then you finish the cure. If not, then it is easy to separate, clean, then rebond. That is standard procedure in the optics industry when curing by hand (vs automated).

[Mark Sawyer]

...If not, then it is easy to separate, clean, then rebond. That is standard procedure in the optics industry when curing by hand (vs automated).

What do you use to remove the UV cement?

[lungovw]

Nodda, thanks for your recommendation. I saw my friend cementing doublets of his production and he does it the way you described. But he said that the solvent is so poisonous that in case of problems he prefers to discard it as scrap and pick another one, as he produces many in a batch. I can't do that with a Verito. So the idea is to stick to balsam and stay on the safe side.

[Steven Tribe]

I have sourced Canada Balsam a couple of times on ebay the last 10 years and have not been disappointed. It is a messy business and there is always plenty of loss during application. The material does become more viscous in storage, but zylol works well to allow better flow. Synthetics have limited life and are a lot more expensive for amateur occasional use.

There are advantages and disadvantages with both simple bottle and "eye drop/mini-pipette" typ containers. Canada Balsam sold for microscope use is totally suitable!

Getting the lens apart and cleaning off insoluble deposited edges is usually 99% of the time involved. The bigger the lens - the easier it is to work with.

[Nodda Duma]

What do you use to remove the UV cement?

Usually just pulled them back apart and then clean-up with Acetone. If I timed the UV pre-cure wrong, then soak overnight in acetone to separate. Keep in mind they didn’t have to be separated often...I usually tried to get the alignment correct the first time.

My go-to adhesive was NOA61 and NOA68 (I’m a chief engineer / system architect now as of last year so I don’t get to play in the lab. Boo ). Dymax adhesives was available as well but I am really familiar with how the NOA stuff handles. Sort of like how you really know a favorite film you’ve been shooting for 20 years.

[Nodda Duma]

Nodda, thanks for your recommendation. I saw my friend cementing doublets of his production and he does it the way you described. But he said that the solvent is so poisonous that in case of problems he prefers to discard it as scrap and pick another one, as he produces many in a batch. I can't do that with a Verito. So the idea is to stick to balsam and stay on the safe side.

Completely understandable. I recently bought a proper bottle of canada balsam dissolved in xylene to rebond a doublet. It was perfect to work with (like perfectly diluted for working with). I’ll post where I sourced it when I get back home later this weekend.

[Mark Sawyer]

Usually just pulled them back apart and then clean-up with Acetone. If I timed the UV pre-cure wrong, then soak overnight in acetone to separate. Keep in mind they didn’t have to be separated often...I usually tried to get the alignment correct the first time.

My go-to adhesive was NOA61 and NOA68 (I’m a chief engineer / system architect now as of last year so I don’t get to play in the lab. Boo ). Dymax adhesives was available as well but I am really familiar with how the NOA stuff handles. Sort of like how you really know a favorite film you’ve been shooting for 20 years.

The only UV-cure cement I'm familiar with is Norland 60. I cemented a number of lenses successfully with it, but had a minor shift on a little rapid rectilinear lens that was too small for my blocks and shifted just a little. I soaked it for months in acetone, which didn't touch it, then months in xylene, which finally separated the elements, but I still can't get the residue off, (and I don't like playing in xylene!) Any further observations on working with the 61 and 68 are most welcome!