What kind of glue is used on the threads of a lens?

[slashmaster]

I've got an Elmo 16 cl that has a lens with 3 elements. The element in the middle is dirty. It seems to be there to help you focus by changing the color and it has some mold or some kind of stain on it. I'd like to remove it completely and use the lens without it. I can see how there are notches to put a tool to unscrew the front of the lens but there is some kind of glue on it. What do I use to remove this glue?

[aj]

Lenses are held in place using rings with screwthreads. Sometimes two lenses are one optical unit and then the parts are glued together on their surfaces using Canadian tree barn, or what is called. I doubt modern lenses are still glued using the same compound

I expect you cannot take out optical parts assuming they are of no influence.
Especially not when others think they cannot take out an optical neutral part like a gelatine filter

Good luck.

[cameratech]

You can't remove an element from a lens and expect it to still function!

If the element has fungus it needs to be professionally cleaned with a fungicide, and even then the surface will most probably still have residual etch marks. You can try leaving the lens in the sun for a week, to stop the fungus spreading. If it's in the glue holding two elements together in a doublet, there's not much you can do (affordably).

The lock rings holding in elements are sometimes secured with paint or lacquer, which can usually be dissolved with acetone. Without the right lens tool though, it's very easy to slip and scratch the glass.

[longlivefilm]

canada balsam is used as an optical adhesive