Stuck spring objective -- any way to free up?

[PeteM]

One of the microscopes I'm trying to get in shape for a local program has a nice 100x Leitz 160mm "EF" objective lens. Problem is, it came with the spring-loaded portion stuck fully into the barrel. I'd guess from immersion oil - the lens looks otherwise well-cared-for but has a bit of what looks like dried oil. Optically it seems OK -- just with no travel left to be safely used by either parents or kids -- or probably myself. Any way to free this up without trashing the lens?

Knowing little to nothing, I tried to sparingly apply a tiny drop of solvent and gently apply heat. Good news is that I didn't screw the lens up further. Bad news is that it didn't help. Other ideas -- which will probably get me thoroughly laughed at:

- A specific solvent for immersion oil, longer soaking, heat to some specific safe temperature?
- Some way to push from the back of the objective -- however there's a stop at the back with no visible means of removal (e.g. threads inside the barrel, but nothing for a spanner on the stop)?
- Applying maybe 10psi of filtered compressed air to the back of the lens??
- Some miracle solution to use in an ultrasonic tank that will clean things without destroying the lens stack????
- Just living with it as is, and replacing it once trashed?

Any experience, much appreciated.

[zzffnn]

I have only cleaned and released some LOMO (Zeiss Jena clone) spring objectives.

My objective's back disc is screwed onto its back. After the back disc, there is an insert that presses down onto the spring. Both the insert and spring can be easily removed.

Your spring may reside inside of the objective, and not easily accessible from outside (lubricants).

I suggest messaging members Apochronaut, Lorez and Charles and wait for their responses. I know Apochronaut has repaired other spring objectives, though probably not a Leitz one. Charles should have some Leitz objectives. Lorez may be able to help too.

Cover slip correction collar, if stuck, may be released using a TINY amount of lubricant (WD40) soak and a firm twist.

Frozen iris may be difficult, as it can be easily damaged during repair.

Heating is not very safe. I don't do that.

[lorez]

I don't think I would do any of the things you are contemplating. I checked my stock and I have a 100X PL Fluotar, but not one of yours. In the case of the objective I have the entire internal barrel will protrude from the rear of the casing as the spring is on the outside whereas the objective fan is describing is constructed a bit differently. Although dried lubricant is a likely cause of your problem, it is not the only one possible.

A photo of your objective would be helpful.

lorez

[PeteM]

Thanks, Lorez. Attached are some pictures. The back stop appears to be a black plastic with about a 1/4" hole reaching an inch or so into the back of the lens. To me, there's no apparent way to remove it. I probably have some sort of expanding sleeve tool around that I could attempt unscrewing and/or pulling on it.

The spring element, judging from the working 20x and 40x lenses, is the outer of the two diameters; maybe at around 60-70% of the diameter of the objective.

[lorez]

There is no need to remove the back aperture of the objective. The lubricant is on the outside of the protruding barrel, as is the spring.

You could apply the smallest drops of lighter fluid around the protruding inner barrel and let it soak for a while. It may take a couple of applications before it softens the dry lubricant, but patience is a virtue. Once you get it freed you will need to lubricate it properly as the lighter fluid will evaporate and you will be back where you started.

lorez

[PeteM]

Thanks, Lorez. Lighter fluid is what I tried the first time (two tiny applications); based on experience freeing up things like dial indicators. I'll give it a couple more tries. Based on other experience, heating the outside barrel up to, say, 120-150 degrees (what I did before) would help open up a path for the solvent by differential expansion. Bad idea for lens cements, glass, etc. even if I can regulate this to xx degrees??

[lorez]

I recently bought (eBay) a PC telescope in perfect condition, but the seller did not know it was supposed to focus. I was able to get it moving by using my heat gun. I was very nervous and it took enough heat to warm the outer barrel so it was too hot to hold and then enough time to allow the heat to get through the grease. There are only two lenses in the PC telescope. I think allowing enough time for the lighter fluid to work is the key.

lorez

[PeteM]

Just a follow up and a follow up question.

I let the sparingly applied lighter fluid passively soak for a couple days -- but no joy. Then heated the outside of the barrel to warm to the touch to get a bit of thermal expansion, added some lighter fluid to the .0001" or so gap, and fairly quickly worked the cap back and forth and free with no damage to the lens. This allowed me to get four drops of lighter fluid inside (apparently 4 bearings?), freeing the spring action. Took maybe 10 minutes of soaking, light heat, and agitation to get it free, with the cap off and a clear shot to the inner workings.

Added some clock oil and it now works OK except catching a bit when squished fully in (I"ll try not to do that -- there's plenty of free spring extension before it bottoms).

Question is gluing the cap (see pix) back on. The original cement (as well as what may have been a couple decades coating of oxidized immersion oil) seemed to be a pale yellow almost glass-like concoction. It came out in thin slivers and shards.

To get this lens right, I'll need to polish the smallest diameter of the cap a bit (where it contacts the lens insert -- it's a bit rough and mechanically sticky) and then glue it back on to the tip of the lens barrel. Question is, what glue? My present inclination, knowing nothing of lens construction, would be a drop of a low strength Loctite adhesive; reversible with low heat.

[gekko]

Thank you for the update: it is useful to know what worked: it is good to learn from your experience. I personally would have not lubricated it with oil but left it dry, although I'm talking without real knowledge. I hope that lorez might comment.

[PeteM]

I'll be interested in the to-oil-or-not question as well.

My only slightly relevant experience is with dial indicators (think a sort of clock mechanism with a spring plunger). When they're gunked up by ham-handed use of something like WD-40, the use of lighter fluid frees them up only for a while. Unless you wick away as much as you can of the dissolved gunk and apply a tiny drop of oil they'll tend to stick again. In the lens case, I added four tiny drops (hypo needle) at where (I surmised) something like bearing slides were located (?). I've never completely disassembled a Leitz objective -- and pretty much hope never to want or need to -- pretty sure it would only result in a "learning experience."

So far so good, the spring mechanism seems pretty well isolated from the lenses in this Leitz objective; and when the lighter fluid evaporates there should be a tiny bit of fairly stable lube left. The lens looks clear.

Should add that I've been storing the lens nose down in a case; blotting any slight traces of solvent or oil that appeared (only, so far, in the first half hour or so, a couple days ago). Hopefully, neither solvent nor oil will migrate anywhere else over time. Despite this being a several-day effort, maybe only 40 minutes of actual time involved, including asking questions here.

Still hope someone can provided an experienced suggestion on which adhesive to use -- otherwise it's going to be one of the weaker but oil resistant Loctite formulations I have on hand.

[gekko]

The lighter fluid obviously evaporates very quickly, so your point of wicking away the gunk+lighter fluid after repeatedly applying it is what I usually do with my partially sticking spring-loaded objective. If the optics are enclosed and sealed in an inner barrel, this should be safe to do, I think (but avoid getting the solvent on the lens seal). But I'll be looking forward with you to hearing expert opinion.

[lorez]

My experience with lighter fluid as a "dried lubricant" solvent is that it is temporary. If you don't complete the disassembly and re-lubricate the component you may have problems. In the case of this objective a vey light application of "light" oil is sufficient. For the adhesive on the end cap, the loctite will probably work. I have used a very minimal application of 5 minute epoxy.

[gekko]

Thank you, lorez. That is very helpful (and my apologies to PeterM for butting in).

[PeteM]

Thanks, Lorez. Good to have that verified. And, Gekko, thought you added to the conversation.

[PeteM]

Just to close the loop. There was too much clearance between the cap and lens body to feel comfortable using a Loctite low/medium strength thread locker (they don't fill gaps). Ended up using some tiny dabs of a Loctite gel "instant glue." That's holding fine; and the cap appears to be in a position where, if needed, I could drop some acetone into the glue line and remove the cap without any acetone migrating to the lens.

No idea if this was good practice or not; but for now it's working fine.