Removal of the penultimate element in a Zeiss incident light objective

[Jane Newman]

I have damaged an expensive Zeiss incident light dry objective - the cement holding the bottom lens has broken and the lens is now floating and out of position. I have been able to carefully remove a large number of elements from inside the objective, starting at the back (see image) but there is one tubular element remaining inside, above the bottom lens, and I can't see how to remove it. I'm wondering if it is cemented in?

[Hobbyst46]

From my very humble experience with old Zeiss Standard eyepieces, elements are not cemented. Rather, they are precisely arranged, with spacer rings in between, and threaded parts. So, my first guess is that they are not cemented. And I would avoid introducing any potential cement-solvent liquid.

[Adam Long]

The only good resource I'm aware of is:

https://www-funsci-it.translate.goog/sc ... r_pto=wapp

I can't see any Zeiss infinites there unfortunately but some of the other examples might be helpful.

[apochronaut]

I have had many objectives apart for repair but never that one. Usually, the front lens elements are in a precise unique alignment both longitudinally and laterally. The rest of the lens cells then stack in behind. With spring loaded objectives, there is a lock screw into an inner barrel, the head of which runs in a sealed channel in an outer sleeve, allowing up and down movement while not allowing the barrel to drop out. The screw is revealed by removing a further outer shrould, which more often than not threads off or drops off after removal of a retaining ring.
Once the objective is stripped down, it is often easier to determine how the front elements are retained in the barrel.

[Jane Newman]

Thankyou all so much, I will proceed with caution and report the outcome in due course, good or bad.

[Jane Newman]

Hullo and thankyou again for your help. We now have this objective completely dis-assembled (the final internal tubular sleeve pushed out) and we have removed the residues of the epoxy cement that held the bottom (final) lens in position. That cement had failed due to misuse. I will update the original photo when all the lens elements are back at the same location. We now have to choose a cement to reattach the bottom lens into the metal nosepiece of the objective. Do you have any recommendations? We usually have a brass ferrule over the nose of this objective which, incidentally, protects it from damage. For this reason the cement doesn't need to be particularly strong for normal use. It might actually be helpful if it could be easily removed in the event that we don't get the alignment exactly right on our first try. Acetone is effective on many epoxy resins.