What to do about coating damage in Ortholux trinoc head

[DrPhoxinus]

Now that I have a LED flashlight to illumine an Ortholux I, I have found a problem with the trinocular head. With a 10X objective the image looks fine, but with a 20X the background of the image looks like a dusty debris field. Moving the slider moves the "dust"/

Upon looking into the head, the round windows on the slider both have damaged coatings.

Is there anything to do about this? Has anyone encountered this before? How the damage occurred is not known, perhaps over zealous cleaning.

Has anyone had success in removing a damaged coating from a lens?

Gerard

[wporter]

Removing a coating would be a difficult proposition, since typically the coating is harder than the glass it covers. Are you sure it's the coating that is causing the dusty-looking background? I have seen a lot of bad coatings and rarely have they caused a real bad effect on the image. It may indeed be dirt instead.

[Wes]

Try a cotton swab moistened with the cleanest water you can find, move it in a circular motion starting from the center and moving to the periphery of the glass surface you want to clean. That may remove a lot of the dirt you see.

[apochronaut]

Whether you see dust or damage to a coating depends entirely on how close to the conjugate plane it resides. It surprises me that you can see it with the 20X and not the 10X because if they are reasonably parfocal you should see the problem through both.
However contamination in the optical path is usually more visible at lower light levels, so if it shows up with the 20 and not the 10, then it might be that the 10 is much brighter. Try reducing the light with the condenser while using the 10X and see if it shows up. It should also be more evident with the 40X.

Some internal coatings are quite soft and can be removed with solvents. I once had an old Reichert 100X and it was fouled with oil. I broke it down and cleaned the oil up. Partly I used Ethanol and got some on a lens surface. It removed part of the coating. There was nothing to do but continue and remove it all, which the ethanol did well.....100% ethanol.

[DrPhoxinus]

Thanks Apochronaut,

It isn't dirt and reflection of the surface looks like a very uneven and damaged coating.
Perhaps in the past someone was zealous with an alcohol swab.
It may be that the low light level with the 20x exacerbates the problem compared to the 10x

I am cheered that ethanol has the potential to salvage some performance of the trinocular head

Gerard