Help disassembling a Zeiss objective

[BramHuntingNematodes]

So here I have a pretty good-looking Zeiss Epiplan HD 40x objective except something is terribly wrong with the front lens assembly. I don't know exactly what, but it's all fogged up and crystallized looking in there, why not take it apart and see what we can see. Luckily, the lens design is pretty simple so far, consisting of a rear lens assembly and a front assembly. The rear one just slid right out. The front one won't budge. I have tried heating it, spraying solvent between the cylinders, tapping it with a mallet with a plastic spacer underneath. Is there some trick I am missing? Some sort of reverse thread trickery?

[MicroBob]

Hi Bram,
I can't help you but my impression is that incident lighting objecties are more often severely damaged than transmitted light objectives. I have seen dents, scratches and glass corrosion that are not often seen on transm. objectives. This may be the result of rough workshop use and use of chemicals around specimens and microscope.
Typical stuff for etching steel surfaces e.g. is Nital, alcohol with a couple % of nitric acid.

Bob

[BramHuntingNematodes]

Yeah I thought it must have acid etched but the outer surface of the front lens is still smooth, the coatings all intact. The problem is between two or more surfaces so I have some hope it might be just some severe separation

[Hobbyst46]

If there is no slotted retaining ring inside, perhaps external set-screws on the barrel (not that I have ever seen any such fixture) ?

Also - did you try just wiping with a moist (water, not solvent) Q-tip from the inside ?

[BramHuntingNematodes]

There are four indentations filled with paste but I think those are for some concentricity jig at the factory. A q tip won't help. I checked the assembly using the sz7 coaxial illuminator I just fixed. The problem is definitely between two surfaces

[Element 56]

There are four indentations filled with paste but I think those are for some concentricity jig at the factory. A q tip won't help. I checked the assembly using the sz7 coaxial illuminator I just fixed. The problem is definitely between two surfaces

Those four little holes and the small amount of what you called past is likely what is keeping you from disassembling your lens. Its actually epoxy and there's always a little between the sides of the lens assembly and the housing or sleeve it slides into. When I first started working on objectives I thought there's no way this little bit of epoxy was keeping me from disassembling my lens. It was junk so I took it over to the hydraulic press and pumped and pumped until I heard a loud snap noise. It was the epoxy seal breaking. All was well!

There are two ways that I have use to overcome this, the first I already mentioned but I do not recommend it. I now remove all the epoxy from the little holes and then press out the lens. I use a micromotor and a wood stick sharpened to a point to "grind" or "polish" away the ALL of the epoxy.

Just a fair warning I have never rebuilt the lens you're working on and I can't really see much in the photo you posted so proceed with caution. For all I know there's a set screw or something in the little holes that is covered in the epoxy. I know Zeiss likes really tiny set screws!!

Good luck,
Kirby

BTW heating a lens is never a good idea!

[BramHuntingNematodes]

There are four indentations filled with paste but I think those are for some concentricity jig at the factory. A q tip won't help. I checked the assembly using the sz7 coaxial illuminator I just fixed. The problem is definitely between two surfaces

BTW heating a lens is never a good idea!

says the guy that put a lens into a hydraulic press! I did notice some spalling on the inside of the top surface of the front assembly which may have already been there or maybe I caused when tapping it with the mallet-- the heat source is a 15w bulb and doesn't get much above 130 F but alas

I have cut out as much epoxy as I can. If you enjoy scraping gunk out of crevices-- and who doesn't?-- this is a fine job for you. It's still stuck! Maybe I will try some drops of limonene into the holes and come back to it later.

[Element 56]

[/quote]
says the guy that put a lens into a hydraulic press! I did notice some spalling on the inside of the top surface of the front assembly which may have already been there or maybe I caused when tapping it with the mallet-- the heat source is a 15w bulb and doesn't get much above 130 F but alas

I have cut out as much epoxy as I can. If you enjoy scraping gunk out of crevices-- and who doesn't?-- this is a fine job for you. It's still stuck! Maybe I will try some drops of limonene into the holes and come back to it later.
[/quote]


Yes I put it in a press but as stated in that case the lens was junk. However a hydraulic press is still employed on occasion with the proper jigs to keep things straight. It can be done with no strain on the optic. I'm no expert but I think I've rebuilt 20 or more objectives now and I never broke anything.

I remove all the epoxy I can because even a little will give disassembly trouble. This is done under the microscope with a micromotor as mentioned. It's not difficult. There's always some epoxy that seeps in-between the lens assembly and the housing. You need to push the lens through the remaining epoxy which my require a significant amount of force. With a hydraulic press and a jig to keep things from moving and keep everything aligned this can be safely done.

A hammer is not a good idea. The shock no matter how light can crack the glass or facilitate future lens delamination. If you don't have access to a press use steady hand pressure with some sort of tube to straddle the optic. Press with firm and steady hand pressure and stay on it until it goes. Or set it up in a bench vice. Make sure there's something underneath to absorb the shock when it lets go.

Again this is all said assuming you haven't missed a set screw or retaining ring. I cannot see everything in your pic. If you're confident there's nothing else in the way all that is left is epoxy and a snug fit.

Kirby

[BramHuntingNematodes]

I, on the other hand, have broken everything at least once. I wouldn't fret about the fate of this poor little lens.

Well this was a mystery for sure and still is. Thanks for the tip about the epoxy. We scraped all the crud out and there was still some crunchy pars getting out the tube but we made it. Would not have been able to with the epoxy still, that's for sure. So here's the optics lineup for the front assembly:



Now, there's your problem. As you can see, the third element from the left is an opaque white crusty crystalline substance.


No idea what that is, or if there's a lens under there, or what.


I don't know if you can see it too good but some of that crust dripped onto the backside of the front lens. I cleaned it off with soap and water, but where it was remains an etch in the glass. Booger.


Here is the spall damage which may have existed before or perhaps I instigated with my crude jostles. Honestly, of the several faults in the optical train, this off center spalling is maybe the third most deleterious after the front lens etching and the OPAQUE CRUST ELEMENT

[Element 56]

Glad you got it apart.

I think that white crust is the same that you see on fluorescent filter cube filters. I asked a manufacturer what it was and what can be done and they said it has to do with the coating on the lens reacting with the metal the filter is mounted in. So I guess that is two dissimilar metals reacting with each other. The solution, they said, is to clean it with soap and water as best you can and scrape the hard crust with a razor blade. I did that and on a filter cube it worked although I there was some permit etching.

Kirby

[BramHuntingNematodes]

Hmm progress on this front is slow this muck is quite thick and stubborn. Questions remain as to the removal of it on the recessed convex side. It's my thinking at this point that this element is more or less completely destroyed as the surface is not exactly smooth when the material is removed. I may set this lens aside for awhile. The case is in beautiful shape, maybe some experimentation on converting a cheap BF epi lens to darkfield could be explored at some point. Well anyway I learned a lot and there's the inside of a finite tube length Epiplan HD 40x for you if anyone was curious. Thanks everybody!

[Element 56]

I went back and looked at my conversation again. It was with Omega Optics. They actually recommended using vinegar as a solvent to clean it but I now recall I used ammonia which worked better. I think I tried other acids as well. Might be worth trying.
Kirby

[BramHuntingNematodes]

The story continues to amaze me: I tried ammonia and then vinegar and the lens disintegrated!

It was more crust than glass I guess.

[Element 56]

Yup the lens was probably gone and you dissolved what took it's place. . That is quite interesting how bad it got. I guess my filter cubes would eventually suffer the same fate had I not cleaned them. Funny how this type of reaction occurs over time.

Kirby