Front Element Contamination

[cbass]

This is another lens I have picked up. This appears to be on the back of the front element. I have taken out the front element and cleaned with alcohol and it does not seem to have made any difference.

What is this? Is this coating damage from Fungus that has been previously cleaned or something else? It's very difficult to see but looks like a hazy contamination.



Better clue. Focus is a big different but in roughly the same location. It no longer looks hazy. Instead a hair like structure appears.

[RokkorDoctor]

As to the second image; I suspect that is in fact the back-lit reflection of your own hair you are looking at, but I could be wrong

As to the original problem; I have seen this before.

First try some other solvents as well; water (distilled if you have it to hand), and acetone. If that doesn't remove it it is likely permanent damage. I have several optics that have that type of damage. Could be coating damage, but usually it is chemical damage to the glass.

I'm sure on this forum there are some glass experts that can explain better, but as far as I understand, long term exposure to condensation can be one cause of this; Alkali ions diffuse from the glass into small water droplets that have condensed on the surface. The alkaline solutions then erode the silica gel layer of the polished surface. After the condensation evaporates silicon ions and alkali are deposited on the glass surface leaving a hazy film that cannot be removed by wiping (references: H.H. Karow, "Fabrication Methods For Precision Optics",Wiley-Interscience, 2004 & T.S. Izumitani, "Optical Glass", UCRL-Trans-12065, LLNL, 1985 & Hoya Corporation on the phenomenon of "dimming", Japan).

This type of damage can only be removed by re-polishing (and subsequent re-coating).

Hence it is possible the lens was cleaned before, but reassembled under warm & high RH conditions and then sealed & brought into a low temperature environment. You would then get internal condensation along the wipe marks left on the glass surface, with possible damage described as per the above.

But, it could also be something else.

[cbass]

I think you are right. I was surprised to see that hair like structure as I could not see anything like it when I shined a light through the lens. Now I am surprised by my own stupidity. That is a reflection of my own hair. How shameful.

When you say distilled water and acetone do you mean Just distilled water and just acetone or do you mean mix water and acetone? If so, then in what ratio? I do not have any background in cleaning lenses so this is not clear to me.

Anything else I should try?
Dish soap and water?
Hydrogen peroxide?

[RokkorDoctor]

I mean separately.

Some contamination is water soluble, others are soluble in either alcohol or acetone.

You can also get reactions happening where one solvent reacts with the contaminants to leave a residue that is then soluble in another solvent.

On stubborn contamination I usually try a few different solvents in succession, and I usually finish with acetone.

Commercially (in the manufacturing of optics) they use some far more aggressive solvents but they are not usually available to the general public, for good reason. Some of those are due to be phased out anyway because of tightening environmental controls.

If you can get the elements out then I have sometimes found a liquid hand soap to do wonders as well. Just try get one for sensitive hands without perfume.

[cbass]

I think I will try my luck again.

I can use pure acetone or does it need to be diluted?
I also have a product called goof off. Is that safe on optics?

[visualopsins]

[RokkorDoctor]