Cleaning the Immersion Objective

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linuxusr
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Cleaning the Immersion Objective

#1 Post by linuxusr » Sat Apr 24, 2021 4:21 am

For sure, great microscopy is possible without an immersion objective. But since I chose a 100x, I want to make the best use of it. I almost never use it and that's because hesitancy holds me back. I want to solve my hesitancy problem and start using it much more. In time, I will learn when it's useful to use and when it's not . . .

What's holding me back is uncertainty around cleaning the oil from the objective and what to do if I make a mistake and contaminate a non-immersion objective.

Net search: First, some suggest just wiping the 100x with a Kimwipe and not bothering with a solvent at all. Sure, that will remove excess, but what happens with the oil that remains? Does it harden? If it hardens, does that degrade the light path? And, of course, if you contaminate another objective, you must use a solvent.

If everyone agreed on a "go to" solvent, it'd be easy. But some recommend xylene; others acetone; others various grades and types of alchohols; others "plain vanillla" lens cleaning solutions; others detergents and water, 1:99.

So my head is swimming. Nobody seems to agree and I don't know if it matters.

Let me cut to the chase and make a choice. Tell me if you think this is a good choice and if it is not, why not, and what is a better choice.

I bought my scope at microscopeworld.com I have received excellent tech support. They recommend acetone as being less corrosive than xylene. It also has low toxicity; it will dissolve paint if you drop it on your scope's body. Now, I understand that acetone is everyday nail polish remover which I could grab anywhere, and as I live in the Dominican Republic, this might be a no brainer. But I don't know if there are grades of acetone and I don't know if nail polish remover contains other ingredients.

If acetone is a "go" in your judgement, after every use of my 100x, I would remove excess with a dry Kimwipe, then rotate in a circular motion with one drop on a Kimwipe. Ditto for a contaminated objective.

Looking forward to hearing your judgements and points-of-view.

Oh, for cleaning my slides, I will have one jar marked "oil." for those slides only. For those I will try a bath of 1:99 liquid detergent/water. I could compare two slides (my stage fits two) at 4x, one an oil-cleaned and the other a non-oil cleaned, to ensure that they are identical.
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dtsh
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Re: Cleaning the Immersion Objective

#2 Post by dtsh » Sat Apr 24, 2021 5:14 am

I'm not a pro by any means, but for cleaning I start with the most mild thing I can and work my way up through solvents as needed. Thus far I have found plain distilled water is frequently effective alone or with a drop of soap and rarely reach for anything more. As I understand it, one of the problems with using acetone or xylene is that it may attack the cement between lens elements or remove some coatings, especially on older instruments.

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Re: Cleaning the Immersion Objective

#3 Post by PeteM » Sat Apr 24, 2021 6:19 am

This is one of those questions where different users with long experience may give somewhat different advice. The good thing about that is that it more or less demonstrates that people have managed different cleaning tissues (lens tissue, delicate task Kimwipes, foam swabs, clean cotton, clean microfiber cloths . . .) and different cleaning solutions and still have such excellent oil immersion views years later they swear by whatever has been working for them.

Here's my take:

1) You want to use the lens tissue more to blot up the excess oil on the objective than rub it off and risk grinding a bit of dust or grit into the lens or wearing off the lens coating. Delicate task Kimwipes are cheap and work fine to blot up most of the oil. All the others mentioned (good quality foam swabs, microfiber, cotton etc.) earlier are fine - with some like tiny cleanroom foam swabs better for cleaning a used oil immersion objective that arrives with some devil's brew of long-congealed oil and grit.

2) As far as I can tell the main reason to clean off oil ASAP is to avoid contamination of other objectives or the slide - or allow globs of it to accumulate and seep past lens seals. A good quality immersion oil is formulated to take ages to oxidize and dry. It's not going to turn into something like varnish in minutes or even hours. Even objectives left for years with eventually dried immersion oil can usually be cleaned with aggressive solvents though usually at some risk to the lens coatings. I do think you'll want to clean off the oil from both objectives and slides after every session - if only so that it doesn't attract and trap dust. But you don't have to worry that minutes count.

3) You need to use a solvent that can actually dissolve oil. Plain distilled water is a great start for dry objectives, but it's not the cleaner for immersion oil.

At the same time you don't want a super dissolving solvent for three reasons. First, some can attack lens cements and sealants. Second, some can dissolve whatever mix of oil and perhaps traces of water solulble contaminants and leave streaking. Third, some of the "best" solvents solvent-wise are dangerous in high concentrations - both fire danger and long-term skin transmission or respiratory effects. So, most of the recommended cleaners often include a moderate solvent. Zeiss recommends a mix of 85% hexane and 15% isopropyl alcohol. Many commercial formulas contain a soap as well as a solvent -- and just simple soaps (Dawn etc.) and water are one approach for things like cover slips.

The cleaner I like for general use is "ROR" - Residual Oil Cleaner. It works. It's affordable in three packs from somewhere like Amazon. It comes in handy 1 oz. squeeze bottles that you can forget to close for quite a while and not lose anything detectable to evaporation. Others like "Sparkkle" or the Zeiss formula, or just something like hexane or IPA (cleaning up streaks later) and so on. Note that ROR isn't a high solvent. It does a good job of removing fresh immersion oil from both objectives and slides in my experience. Seriously dried oil might be better served by the Zeiss mixture or straight hexane to start.

So, apply a single drop of a good (non-drying) immerson oil. Blot 95% of it up when you're ready to move on to another view or specimen. Clean off the oil with something like "ROR" when you're done for the day. If you're not sure you've done a good job, remove the objective or objective turret and take a look through a reversed eyepiece.

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Re: Cleaning the Immersion Objective

#4 Post by PeteM » Sat Apr 24, 2021 6:45 am

To add, if you do get some oil on a dry objective - just clean it off ASAP. Same approach. Blot up most of the oil. Then carefully use a bit of lens cleaner on a tissue to remove what little is left. Use multiples and avoid soaking the front element with any solvent or cleaner. Good quality objectives, even dry ones, will be somewhat well sealed at the ends. The problems are mainly when so much oil soaks the last element that it wicks up into the lens assembly. This might easily happy when class after class of kids start slathering on immersion oil to a slide or objective. Less likely with a bit of care.

A few other things to reduce the chances of cross-contamination of dry and oil immersion objectives:

- Have your objectives parfocal, using parfocal shims if necessary. Many makes will have the oil immersion objective designed so it has to be focused a bit further toward the slide - so back up a bit and blot when done.

- Use just a single drop of immersion oil, and rotate the objective into it to make air bubbles less likely. Blot the objective dry when moving on for a while and clean off the slide.

- If your oil immersion objective has a lock-up mode (some better ones do), lock it up when moving to the dry objectives.

- If you have four objectives on a five hole nosepiece or five on a six hole nosepiece, leave the extra space between your highest dry objective and the oil immersion objective. Helps concentrate the mind and provide space for easily cleaning things.

- If you have removable objective turrets, perhaps have one dedicated to high power work - maybe with a finder (plenty of clearance) and a 60x or 100x oil or a fuller complement of objectives but spaces between. Removable nosepieces also simplify cleaning, inspection, and storage out of dust and harm's way.
Last edited by PeteM on Sat Apr 24, 2021 6:50 am, edited 1 time in total.

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Re: Cleaning the Immersion Objective

#5 Post by Hobbyst46 » Sat Apr 24, 2021 6:47 am

1. Do not hesitate to use immersion oil where the specimen and the optics call for it. Immersion oil has been used since many ages ago.
2. To avoid contact of dry, non-immersion objectives with oil, arrange the objective on the nosepiece turret sequentially: 10x, then 20x, then 40x, then 100x, and rotate the turret in one direction only, so that after the 100x immersion, the next objective in place is the 10x. The working distance of the 10x is several millimeters so it will not touch the oil drop on the slide. Then, immediately clean the 100x objective. If no further immersion is planned, clean the slide top as well.
3. Nail polish remover is not acetone, but a similar chemical; however they resemble each other sufficiently that none of them should be used for microscopy (see below).
4. There are indeed several chemicals and household materials that remove immersion oil efficiently. Alcohols, xylene, toluene, gasoline, lighter fluid, and specific sprays. That is why you read many recommendations. It does not matter which one to use as long as it is OK for the job.
Now:
4-1. Xylene is very effective, experts have been using it, but it is toxic, so for home microscopists should be avoided.
4-2. Acetone is very effective, but it can dissolve adhesives and dull paints.
DO NOT USE ACETONE on optical parts. Do not let acetone approach the microscope.
4-3. Wiping the immersion oil off the glass surface with a KimWipe - not rubbing it, just gently wiping - is effective and sufficient. Modern immersion oil does not harden, at least on a time scale of days and weeks.
4-4. Nevertheless, if you decide that further cleaning is necessary, dip a good grade Q-tip in either of the following liquids: heptane; octane; petrol ether; gas lighter fluid; isopropanol (named IPA for short); and wipe the glass just once with it, not to and fro. Then, to remove any fibers if they are there, breath on the glass to make it foggy and wipe with a Kimwipe. Alternatively, fro the start, place a drop of the cleaning liquid on a piece of KimWipe and wipe the glass with it.
Never ever wipe a glass surface with a dry tissue.
4-5 Ethyl alcohol (ethanol, 95%, or methylated spirit) is less effective than IPA.
5. From the above liquids, IPA is usually very good and easy to apply and rarely leaves marks on the glass; the other liquids do leave marks. That is why a final finish with foggy cloth is suggested.
A dedicated lens tissue, sold by microscopy supply houses, is as good as Kimwipe, but I have met some weird looking and feeling lens tissues; so prefer a good quality grade. They are not cheap.

The reason that Kimwipe has been popular is because unlike many other paper tissues, it leaves no fibers on the glass.

P.S. According to my experience, nail polish, which is popular for slides (adhesive, ringing, mounting) is, incompatible with immersion oil. Oil attacks it within hours.

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Re: Cleaning the Immersion Objective

#6 Post by linuxusr » Sat Apr 24, 2021 11:58 pm

@PeteM
@Hobbyst46

Thanks for your detailed reports. Before you posted I found a detailed lens cleaning article at microscopeworld.com The following is a synthesis of some of those ideas, your posts, and my recent thinking:

1. Except for immersion objectives (special case), don't clean lenses "just because they might be dirty." Avoid frequent "what if" cleaning.
2. Ocular lenses. Using 4x, focus on a specimen. Observe debris in the field. Rotate the diopter rings. If field debris rotates, cleans the eyepiece lenses, if not, not. Blow out the lens in the tube end with a bulb syringe. Use a Kimwipe for the external lenses. Recheck debris field.
3. Non-immersion objectives: (Experiment)
I've been playing with a clean test. Still working on it. Mount a clean slide without coverglass. Mark a dot with a marker in the center of the light beam. This is the focus reference point. Focus the dot with 4x and check the field for debris. If the field is pure white, the slide is very clean and so is the objective. Move up to the next power. If the field has debris, it could be the slide or the objective or both. Use lens solution to get the slide very lean. Any remaining "debris" assume objective artifacts and clean the objectives (non-immersion only). So far my little clean test is not working because I cannot get my slide clean enough--neither do I have all my equipment at this moment.

a. (non-immersion) First blow with air. If you need more: do not use a lens brush that may gather grit. Instead, roll a Kimwipe into a tube and tear in half. Use the brush end of the tube to sweep the lens and dispose. If you look at a torn piece of paper at 40x, and you look at the cut edge, you will see a wide range of fibers at different angles and lengths--indeed, a brush. If you need more, distilled water as solvent.
4. Immersion objective: Gently place a Kimwipe on lens after each use, hold for some seconds (osmosis). That is sufficient as the oil will remain stable. If you need more and/or you have contaminated a non-oil objective, use Kimwipe, then ROR, then Kimwipe. If you need more, here I defer to your list of stronger solvents.

I think I should be fine with the above. It's pretty conservative. As I mentioned, I will pull every slide with oil after each use and put it in my "oil" jar. Slides are cheap. So I will not waste ROR on a slide. I may use some ROR for cleaning my oil slides if my soap bath does not work . . .

Observation: It's kind of a problem that we're cleaning objectives (not the oculars) against gravity and being mostly blind, since they are pointed down at roughly 45 degrees. Why not simply remove the objective, set it on a clean and stable and well-lit surface, and examine it through the tube end of the ocular, or even a high power hand lens? That way, you can apply the exact cleaning measures you need and maybe nothing at all. The same would go for immersion oil. What? Pipette one drop against gravity and hope to stick it on the tiny nearly upside down lens? Why not get that drop dead center on the lens while it rests on a table?
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Re: Cleaning the Immersion Objective

#7 Post by 75RR » Sun Apr 25, 2021 10:10 am

linuxusr wrote:
Sat Apr 24, 2021 11:58 pm
Observation: It's kind of a problem that we're cleaning objectives (not the oculars) against gravity and being mostly blind, since they are pointed down at roughly 45 degrees. Why not simply remove the objective, set it on a clean and stable and well-lit surface, and examine it through the tube end of the ocular, or even a high power hand lens? That way, you can apply the exact cleaning measures you need and maybe nothing at all. The same would go for immersion oil. What? Pipette one drop against gravity and hope to stick it on the tiny nearly upside down lens? Why not get that drop dead center on the lens while it rests on a table?
You haven't said which model microscope you have, some have a removable nosepiece which allows the procedure you mention.

As to oiling the objective - it is a bit of a misnomer as one puts oil on the cover slip and then swings in the objective.
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Re: Cleaning the Immersion Objective

#8 Post by linuxusr » Sun Apr 25, 2021 8:29 pm

My microscope model is in my signature (Zeiss Primostar 3 Full Koehler). Regarding the "misnomer," what I read repeatedly is something like this: a. a drop of oil to the lens, b. a drop of oil to the coverslip, c. swing the objective to and fro, slightly, to merge the two drops.

I guess one could test both ways and see if a drop of oil to the coverslip only is equally effective.
Regarding my nosepiece and if it's removable, good point, thanks. I'm certainly going to check because, if so, I could do this both for oiling my 100x and for inspection and cleaning of all objectives.
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Re: Cleaning the Immersion Objective

#9 Post by dtsh » Sun Apr 25, 2021 10:05 pm

I think you'll find it hard to get a drop of oil on an objective without getting it everwhere else first unless your bottle has an applicator rod or the like, but even then my money is on everywhere you don't want it first. My AO bottle has a dropper and my Cargille has a rod, with the AO bottle I'd empty it before any got onto the lens. Maybe if it's an inverted scope. :P

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Re: Cleaning the Immersion Objective

#10 Post by BramHuntingNematodes » Sun Apr 25, 2021 11:35 pm

I got these big long cotton swabs with wood sticks you can put some oil on the tip of the stick end and apply to coverslip. That's all I ever need above the sample.

After I give the objective and condenser a quick wipe. Hope that's enough as it's all I've ever done.
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Re: Cleaning the Immersion Objective

#11 Post by linuxusr » Wed Apr 28, 2021 3:33 am

Thanks for these options. My tech person at microscopeworld.com recommends putting a drop on a coverslip and raising that coverslip to the objective. Even if the coverslip touched the objective, it would not touch the lens because the lens is recessed by several mm. I will try various.

On a separate note, earlier in this thread, I had mentioned the idea of using the magnification capacity of the microscope to check if objectives (and other lenses) need cleaning, and not to clean them if they don't. I'm thinking about a check every three months unless I can see obvious debris artifacts. I practiced some of these techniques that I learned from publication A507 Zeiss' "The Clean Microscope," about a 20 page document with photographs.

Here's what I did:

a. Check each ocular with the other ocular, looking through the wrong end. Blow out tube if necessary. Front lens: distilled water from breath (!) adds moisture prior to Kimwipe or equivalent (always use blow syringe first).
b. Objectives. Start with 4x. Focus on a specimen. Rotate eyetube. If debris rotates, clean eyetube lenses. If not, debris could be from objective but also could be from slide or coverslip.
c. Loosen 4x. I have a rubber pad for grasping. While viewing specimen, rotate within threads, to and fro. Any debris movement = objective debris.
d. Remove 4x. Sit on aluminum foil (dust free). Examine with ocular.

I tried the above with my 4x and found no dust/debris whatsoever. So no cleaning.

Do you want the URL for this brochure (downloadable)? It's in the New Members sub-forum.
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Re: Cleaning the Immersion Objective

#12 Post by linuxusr » Wed Apr 28, 2021 3:38 am

The recommendation for "The Clean Microscope" was by 75RR:
https://www.zeiss.com/content/dam/Micro ... -zeiss.pdf
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Re: Cleaning the Immersion Objective

#13 Post by carlh6902 » Wed Apr 28, 2021 4:17 am

Just to clarify a previous point, many fingernail polish removers (such as Onyx) are indeed 100% acetone, and are marked accordingly.

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Re: Cleaning the Immersion Objective

#14 Post by linuxusr » Wed Apr 28, 2021 8:39 pm

@carlh6902

Thanks. Good to know that I can grab this off-the-shelf item if need be. And I note that it's best to use distilled water before proceeding to a stronger solvent. My tech person at microscopeworld.com has also noted turpentine as an option, small amount. It appears that xylene is "last resort."
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Re: Cleaning the Immersion Objective

#15 Post by linuxusr » Tue May 04, 2021 11:45 pm

Hello All:

As a side question, I'm trying to figure out the best way to clean immersion oil from prepared, purchased slides that I will use repeatedly and which a. I do not want to immerse and b. do not want to contaminate other objectives.

I am thinking about a diluted soap solution and a lenswipe. In your experience, what's the best option?

It seems to me that if I can remove the obvious oil, even if there is a very thin film, that given my working distances, my dry objectives should be OK. On the other hand, the W.D. for my 40x is 0.66 mm, not much clearance!
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