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Microscope lens face damage

 
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houstontx



Joined: 31 Jul 2015
Posts: 226

PostPosted: Sun Jan 14, 2018 1:36 pm    Post subject: Microscope lens face damage Reply with quote

Hi all,

I have a question about a 20x Leica HCX microscope lens I picked up. It has some kind of sheen or coating on the face. Almost like an oil slick but it won't come off with lens cleaner. I am thinking it may have some kind of metal vapor deposit on it. Does anyone have suggestions on how to clean it, if even possible?

I have very dilute potassium hydroxide and hydrochloric acid both 0.01N solutions in water and alcohol. I was wondering if I put a microliter volume bead on the lens face and let it sit for a while, maybe it would etch it off. I am considering this lens a total loss so any thoughts appreciated...
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5805
Location: Issaquah, WA USA

PostPosted: Sun Jan 14, 2018 6:19 pm    Post subject: Reply with quote

I would first try xylene. It was commonly the recommended cleaning solvent for many microscope objectives, and it gets off all kinds of stuff.

Don't let any liquid of any type "pool" at the edge of the front element.
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houstontx



Joined: 31 Jul 2015
Posts: 226

PostPosted: Sun Jan 14, 2018 9:11 pm    Post subject: Reply with quote

Thanks for the suggestion, I have something called "xysol", probably xylene based. will give it a try.

I'll post a pic of the lens face, and the image through the rear lens, looks like the scale is thick and pitted . Doesn't seem like normal organics based contamination. Came from a scope with 2,10,20 and 40x objectives. All others were in perfect shape, not sure why this one was fouled up. its not an oil objective...
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zzffnn



Joined: 22 May 2014
Posts: 1682
Location: Texas USA

PostPosted: Sun Jan 14, 2018 9:47 pm    Post subject: Reply with quote

Try rubbing repeatedly with a Q tip damped with some xylene (xylol).

I made the mistake by soaking front lens in a xylene + acetone solution and it removed a small amount of coating. http://www.photomacrography.net/forum/viewtopic.php?t=29532&highlight=objective+front+lens+clean+xylene

In my thread, you can see that I had some film on my 4x objective, which I eventually removed with xylene solution (though my soaking removed some coating as well).
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MarkSturtevant



Joined: 21 Nov 2015
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PostPosted: Mon Jan 15, 2018 9:12 am    Post subject: Reply with quote

Camera lenses will have a distinct sheen because of a lens coating that improves their performance, don't they? My first thought would be to wonder if this coating is similar, and even if not does it effect image quality? If the lens works well, don't fix it.
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houstontx



Joined: 31 Jul 2015
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PostPosted: Mon Jan 15, 2018 9:36 pm    Post subject: Reply with quote

heres the pic of the 20x lens face first and the 40x lens face from the same scope. The xysol wasn't effective at removing the sheen. I think I'll try the KOH solution next.


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Pau
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Joined: 20 Jan 2010
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Location: Valencia, Spain

PostPosted: Tue Jan 16, 2018 1:33 am    Post subject: Reply with quote

First be sure that the damage is at the front lens external surface. A stereomicroscope with very lateral light is what I use to inspect objective surfaces (and I've cleaned lots of them)
KOH seems an aggressive method...never tried it with optics, if you do it be very careful to avoid it entering into the objective
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zzffnn



Joined: 22 May 2014
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Location: Texas USA

PostPosted: Tue Jan 16, 2018 6:56 am    Post subject: Reply with quote

I agree with what Pau said. But first check if your 20x performs okay optically; it does not look that bad from your image. May even be erosion of original lens coating (which won't be removed or repaired easily).
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houstontx



Joined: 31 Jul 2015
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PostPosted: Tue Jan 16, 2018 3:13 pm    Post subject: Reply with quote

Looking through the back lens the image has a pink hue with many visible black flaws around the edges and center. I haven't been able to test since these are M25 threads, but I'm assuming the image quality would be degraded. The KOH solutions is very dilute. Caustic etches glass, so if let to sit for a few hours maybe it will take off the sheen and also some a thin layer of glass? It would remove any AR coating I suppose...Maybe I should try the HCl solution first then caustic...Need to think about this some more...
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zzffnn



Joined: 22 May 2014
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PostPosted: Tue Jan 16, 2018 5:11 pm    Post subject: Reply with quote

If what you have is delamination (which it sounds like), KOH may make it worse. Try to take a photo of those defeats?
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phil m



Joined: 10 Aug 2014
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PostPosted: Thu Feb 15, 2018 7:17 am    Post subject: Reply with quote

houstontx wrote:
Looking through the back lens the image has a pink hue with many visible black flaws around the edges and center. I haven't been able to test since these are M25 threads, but I'm assuming the image quality would be degraded.


It looks bad enough for that to be the case but I would at least test the objective first. The problem appears to be caused by a degraded coating. I have had several objectives with a similar problem and in all cases there was a loss of contrast . I managed to get rid of some of the film with various solvents( i think 100% ethanol did the most) and the image quality seems little affected , now. In one case, the problem was on the back lens of a 100X planfluor objective and cleaning it off removed a large part of the coating, to the periphery. In this case, removing the murky coating was preferable to leaving it. In comparing the objective with a brand new one, there seems little difference in the image...maybe a smidgen of contrast but it is hard to tell with most specimens. The cleaned objective had 20 years more use than the n.o.s. version, too.
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