Decayed glue ... what now?

[PaulC]

OK, so I finally got the lens with the funny layer on it, like dried dirty water, out of the old Zenobia folding camera, only to find that it isn't surface crud, it is inside the lens. It must be decayed glue between the elements.

The question is, what - if anything - can I do about it? I know it is possible to separate the elements and re-glue them. In theory. I have grave doubts about whether I could do that and still have a functioning lens at the end of it - but there's nothing to lose, is there?

Does anybody know how to disassemble and reconstruct the elements of a lens? I guess it is mostly about the chemistry of dissolving what is left of the glue so it falls apart and then getting the correct substance to glue it back together. Any suggestions (other than "don't bother", which would probably be the most sensible one)?

[estudleon]

I don't like "don't bother", because = don't play.

What lens are you talking about? Pics of it?

Rino.

[PaulC]

It's the one I put a photo of here: http://forum.mflenses.com/in-my-mailbox-today-t13675,start,15.html

It is a 75mm Hesper f3.5 on a 1955-or-so Japanese made Zenobia.

[orly_andico]

Amateur Telescope Makers will try anything.

Including cementing their own lenses. It's a hobby of mine, and I have come across how to do this.

There are still companies which sell lens cement. Since your lens is old, it was cemented with Canada balsam, which is organic, melts, and as you have learned, can rot.

Heating is supposed to be the way to melt the Canada balsam, but extreme care must be taken as differential expansion can crack the cemented element.

After the elements are separated, follow the instructions with your (new, most possibly synthetic) lens cement to glue everything back together.

http://www.skgrimes.com/popsci/index.htm

[PaulC]

Thanks. I've seen somewhere that a couple of days in a solvent might dissolve canada balsam, which seems a harmless way to start, so I think the rear element is going to find itself in a pot of nail varnish remover. Heating does sound risky. If I can get them apart one way or another, then that is half the battle won.

[Photomac]

If you take a look at my thread in the equipment repairs forum, called repairing cemented lenses (sorry don't know how to create a link), you'll see one way to do it

Regards

Angus

[PaulC]

Thanks, Angus, very useful. I'll have to check out the local school science supplies shop for something to cement glass (assuming I get that far!).

[orly_andico]

xylene is supposed to dissolve canada balsam... i don't think nail polish remover will work