White sealant on objectives - what is it?

[mneium]

Per title, what is this stuff you find on objectives? I sometimes find objectives where it's in bad shape and think about replacing it, but am not confident about what it is exactly. Liquid latex?

[apochronaut]

It is usually found on objectives that are centered into a spring loaded barrel and is there because of a bit of relief between the inner lens barrel and the outer reflex barrel. With immersion objectives, it provides a seal, so oil can't wick up between the barrels and possible gain entry into the lens column.
It has probably had various formulations over the years. Currently, it is some form of silicone I would guess. I just poked some on a new objective with a probe and it has some give.
If it is truly degraded , probably a little dab of some non-gassing silicone caulking would help, since it is a passive seal.

If it is a dry objective, it doesn't really do too much except keep some dust out of a relatively non-functional space. However, if you are wont to be dipping your dry objectives into immersion oil, it's integrity might be important over time.

[Element 56]

Nikon uses (or used to) a hard epoxy-like seal. The closest thing I've found to it is JB Weld. However, I've been using Permatex Ultra Black Advanced Formula on all my objectives. It's an oil resistant silicon sealer. So far so good!

Kirby