Unable to clean residue from objective lens

[mikey95]

Hi all,

It's my 1st post here! Glad to be part of this forum.

I have a Leica DMLS and was cleaning my 20x objective. I did multiple rounds of 90% IPA drop on a lens tissue and dragging it across the lens, followed by breathing and wiping with a texwipe (polyester swab). Every time I did that, it feels like I made the objective more and more dirty. There is now a sort of transparent, faint "film" with some more obvious spots on the objective. These spots have a different color (blue-ish/purple-ish) when the light from a flashlight hits the lens in a certain way. I feel like the situation always got worse after every round of breath+wipe, and I was careful to not spit any saliva on the lens.

I really don't know how to clean this anymore, as whatever I do just seems to make things worse. IPA doesn't work, breath doesn't work. What's going on here? Is that film from my saliva perhaps? Can anyone help me out with cleaning whatever it is properly?

[Tom Jones]

Try a drop or two of dish detergent in 50ml or so of water. If the residue on the objective is organic, like a body fluid if it was used clinically, that should take it off nicely when the alcohol won't. If that fails I've used acetone, just don't flood it or leave it on very long to prevent damage to any lens cement that may not appreciate it. I use Q-tips as well. Whatever you use, chase it with DI water to get any solvent residue off for a final cleaning. I've even use xylene a few times to remove residue nothing else would touch.

[Alexander]

I wound never put acetone on a microscope!

To try dish detergent is good advice. In case this does not work try hexane then xylene.

[MichaelG.]

Hi all,

[…] There is now a sort of transparent, faint "film" with some more obvious spots on the objective. These spots have a different color (blue-ish/purple-ish) when the light from a flashlight hits the lens in a certain way. I feel like the situation always got worse after every round of breath+wipe, and I was careful to not spit any saliva on the lens.

Welcome, mikey95

Without actually seeing the surface you describe, it’s difficult know whether there is a persistent film of contamination or whether the coating has failed.
If the former, then repeated cleaning may help … but if the latter then it might remove more of the coating.
The colour that you describe is typical of a coated surface, so the ‘spots’ are almost certainly areas where the coating is both present and clean.

Any chance you could get a photo ? … seeing the ‘geography’ would be informative.

MichaelG.
.

Good explanation of AR coatings here:
https://www.edmundoptics.co.uk/knowledg ... -coatings/

[mikey95]

Tom, Alex - thanks for your suggestions. What solution of distilled water and dishwashing liquid is right? (e.g. 5 drops per 10 ml) Also, how do you use it? By putting a drop on the top of lens tissue and dragging it along the objective, like I normally do?

Michael - I attached the pics. I marked one of the problematic spots in red:

IMG_20230926_095909.jpg (29.5 KiB) Viewed 2729 times

IMG_20230926_095852.jpg (26.73 KiB) Viewed 2729 times

IMG_20230926_095939.jpg (26.94 KiB) Viewed 2729 times

Generally, the entire glass has a thin film of some stuff. As you can see, one of the spots I mentioned earlier has a blue-ish tint when the light hits the lens at a certain angle. This particular streak happened after one round of breathing+swab, and others are similar in look. This makes me think it's not damaged coating, and it just doesn't look like that to me. But curious to hear what you think. Also, what are your ideas for cleaning this off?

[Tom Jones]

Dish soap I use roughly 2 drops/50ml of water.

[MichaelG.]

Michael - I attached the pics. I marked one of the problematic spots in red:
[…]

Generally, the entire glass has a thin film of some stuff. As you can see, one of the spots I mentioned earlier has a blue-ish tint when the light hits the lens at a certain angle. This particular streak happened after one round of breathing+swab, and others are similar in look. This makes me think it's not damaged coating, and it just doesn't look like that to me. But curious to hear what you think. Also, what are your ideas for cleaning this off?

Thanks for posting the pictures … they are quite encouraging … because it just looks ‘undamaged but filthy’ !!

I can only suggest that you try the various solvents that have been recommended, but try to test each on a small area and carefully monitor the results … the one that shows any amount of cleaning is the one you should persevere with.

Without knowing how it got into that state, it will need patient experimentation.

MichaelG.
.
P.S. __ good Vodka is an effective solvent for many greasy substances … and there are obvious fringe-benefits to having a glass by your side.

[mikey95]

Happy ending. Lens is almost as clean as out of factory. Here's what I did:

1. I found a Zeiss lens cleaning solution I have for my DSLR camera. Exactly this kit: https://www.amazon.com/Jar-Cleaning-moi ... C89&sr=8-1

2. Sprayed 1 time onto a fresh texwipe polyester swab.

3. Applied a bit more pressure to the lens with the swab (but not too much, of course), and took much longer to wipe. Around 5 seconds.

4. Finished up with dragging lens tissue with 1 drop of IPA to remove residue where the Zeiss lens cleaning fluid dried up last.

Voila! This is now my go-to method for cleaning objectives. No scratches, no dust, no weird film left. Thanks a lot for your help!

[MichaelG.]

Well done !

I have a box of [what I presume to be] those very wipes, but not the spray.

… must see if we can find the ‘recipe’

MichaelG.

[Hobbyst46]

A few more tips if I may:

First step, prior to anything else, deliver a jet of clean room air on the lens, from a rubber air dust blower pump for photography. Look for remaining dust particles,
if necessary remove them by very gentle wiping using a very soft brush (again, a photography accessory).

Then, start by breathing on the lens to form condensation, and wipe with a lens tissue or Kimwipe. Just wiping, no to and fro sweeps.

If the results are still unsatisfactory, switch to IPA and/or heptane or octane.
Xylene is powerful and should be only sparingly used, on a Q-tip. It is a last resort solution.
I am with Alexander about acetone - avoid it.

In practice, almost all organic solvents, those mentioned above and others, tend to leave foggy residues when they evaporate from the glass surface. Due to traces
of other substances they contain. There are highly distilled, very pure versions of these solvents, but they are extremely expensive and are usually less available for hobby use.

So, after treatment with an organic solvents (or instead of them), it is indeed a good idea to finish with distilled water or a specific dedicated lens-cleaning liquid.

Just my opinion.

[MichaelG.]

This is interesting:
http://cdn.celcen.pl/product_at/0/734/z ... N.Z.PH.pdf

I think it relates to the wipes that mikey95 mentioned

Edit: __ but, alternatively: https://www.zeiss.com/content/dam/Visio ... -wipes.pdf

MichaelG.
.
… and for obfuscation: https://www.zeiss.co.uk/vision-care/nee ... m/cleaning

[Phill Brown]

Zeiss lens spray is relatively inexpensive and about the most effective.
I don't have shares in Zeiss.