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cyberjunkie
29-Sep-2014, 00:40
Please let me know if you have any "secret recipe" for stubborn dirt.
Recently i acquired a recent multicoated lens. It is damaged and it was priced accordingly.
The seller told me that the front glass was damaged by a firecracker, which exploded close to the camera on New Year eve.
From the pictures i thought that it was impact damage, some small dots caused by tiny objects hitting the lens at high speed.
When i had the lens in my hands i realized that there is no missing material. The small dots are in relief!
I think that during the explosion of the firecracker, some molten particles hit the glass and got stuck to it!
At close inspection the dots look glass-like. Nothing comes out if scratched with a nail.
Normally i use isopropilic alcohol or ROR. I am not at home, and i don't have them at hand, but i gave the lens to a friend of mine, who will try with the alcohol and with a commercial lens cleaner.
I am almost sure that it won't be enough. Before trying to pry off the particles with warmth (hair dryer), i'm trying my luck on this forum. Maybe some member has an idea that could work...
Somebody gave me the advice to use WD-40 or Svitol (a locally made oily spray, used to loosen rusted screws), but i'm not sure it won't affect the modern multi coating.

I will try any suggested solvent :) ... the only limitation: it must not eat the coating.

ciao

Paolo

resummerfield
29-Sep-2014, 08:11
...The small dots are in relief!
I think that during the explosion of the firecracker, some molten particles hit the glass and got stuck to it!
At close inspection the dots look glass-like. Nothing comes out if scratched with a nail......

I suspect that is exactly right. I have had glass damaged by welding sparks, and the only way I could minimize this damage was to gently scrape off the particle. I used a 10x microscope and a very sharp and smooth exacto knife blade. Good luck!

BrianShaw
29-Sep-2014, 08:12
I suspect that is exactly right. I have had glass damaged by welding sparks, and the only way I could minimize this damage was to gently scrape off the particle. I used a 10x microscope and a very sharp and smooth exacto knife blade. Good luck!

Did it make a difference? I would think that just leaving the sleeping dog lie would be the more prudent thing to do.

jp
29-Sep-2014, 08:13
If you're at a point with nothing to loose, I'd try a car cleaning "clay kit". They remove stubborn stuff by particles sticking to the clay. Chances are good if the small dots are dark, they will not affect the image and could be left alone. try shooting with it.

vinny
29-Sep-2014, 08:49
Like Brian said, Leave it alone. Most folks are WAY to obsessed with dirty lenses or defects which won't make an appearance on film. In this case, it sounds like anything you do may remove the particles and/or multicoating, but leave holes behind.

Alan Gales
29-Sep-2014, 09:25
If it's melted to the glass wouldn't removing it remove the coating?

I'm with Brian and Vinny on this one. Try shooting it as is and see what your results are before messing with it.

8x10 user
29-Sep-2014, 09:58
I would wait and use ROR. When you do, do not use a lot of force. Let the cleaner melt the particles free and carefully "mop" them away.

cyberjunkie
29-Sep-2014, 23:57
If the particles were dark, i would leave them alone. They are glass-like, and behave as small crazy lentils scattering the light around. It makes a difference. Plenty of it.
While we were examining the damage, a friend told me that an old 55mm Micro Nikkor was damaged by a child with a screwdriver blade. Lots of scratches. After that the lens was still performing very well, taking wonderful detailed pictures! :)
Not all damages are alike. Unfortunately in this case the performance of the lens is definitely affected.
As a last resort, if i can't clean the spots, or find a replacement front glass, i will blacken the affected areas with china ink, and see how it works.... but i hope to find a way to melt (or pry off) the particles glued to the glass.

cheers

Paolo

Doremus Scudder
30-Sep-2014, 03:11
If the particles were dark, i would leave them alone. They are glass-like, and behave as small crazy lentils scattering the light around. It makes a difference. Plenty of it.
Paolo

Paolo,

A possible solution is to use opaque black paint to cover the small bead-like particles, thus preventing them from scattering light. It was/still is common practice to black out a scratch in a lens for exactly the same reason.

Even if you manage to get the particles off the lens, you may still end up with defects in the glass or coating that may require blacking out.

Best,

Doremus

Jim Galli
30-Sep-2014, 12:44
Hoppe's nitro powder solvent is what gun owners use to loosen similar stuff. Might be worth a try.

resummerfield
30-Sep-2014, 20:00
Did it make a difference? I would think that just leaving the sleeping dog lie would be the more prudent thing to do.

I was able to scrape off the particles, but the damage to the glass surface remained. In my case, the bubbles were light colored, and in bright light they would sparkle, and removing them helped slightly. If the particles are dark, I think I would agree with Brian and leave them alone.

cyberjunkie
2-Oct-2014, 07:02
I left the lens in the hands of friend, who's a retired repairman. i try to refrain from asking his help, cause he does not want to be payed, and he saved my bottom way too many times... :)
Whatever... the particles went away (AFAIK he uses isopropilic alcohol and some product for dishwashing machines), but the impact was strong enough to produce some small cavities on the surface of the front glass.
The damage is all over the map: some particles cleaned, others left damaged coating, 3 of them left a visible indent on the surface of the glass.
My best guess? I think that the cleaned lens will perform much better than before, and that the reduction of contrast and the increased flare will be barely noticeable.
If i'm right, i will not do the china ink stuff. Being also a collector, i'm probably too sensible to the "beauty" of my preferred/beloved optics. Therefore i think i'l do my best to find a replacement glass in due time. Placing spots of black ink on the front of the objective would be like defacing it. Can't help but feeling that way... :)

Thanks to all those who offered their advice.

cheers

Paolo

Donald Qualls
5-Oct-2014, 12:27
The particles are most likely aluminum oxide: the stuff inside a firecracker that make the "bang!" is flash powder, usually aluminum powder with a strong oxidizer such as potassium perchlorate. If the cracker was close enough to the lens, particles of aluminum oxide formed in the flash might have arrived still hot enough to melt to coating, and thus effectively welded themselves to the lens. Removing them will be virtually impossible, and completely impossible without leaving craters in the coating. The best results you can get would be to individually paint each particle black (extremely tedious, but possible with something like India ink and a "brush" made of a splinter of wood) or to chip each one off and fill the remaining crater with something black (India ink is a good choice here, too). Given the extremely high risk of adding scratches to the craters if you try to chip the particles off, I'm going to suggest either leaving the particles alone, or blackening them in place.

If the lens is valuable enough, it might be worth having it disassembled and the coating stripped from the front element and reapplied (this might or might not require separating it from the next element if cemented); there used to be a service (in Russia, as I recall) that would do that kind of work for cost low enough to be cheaper than replacing a top-end lens, but who knows if they're still operating, or what if any loss of performance there would be due to their coating not being identical to the original.

Edit: Woops, just reread your last post, Paolo, and realized the "cleaning" is already done, and the craters present. You'll get some flare (that will fill in shadows a bit), but probably little or no loss of resolution; the flare is the only thing likely to be noticeably changed by blacking in the craters. Replacing the front group might or might not give a perfect match with the rear group (in other words, it might be worse than leavin the lens as it is now). Recoating the front element is the course most likely to fully restore the lens performance, but still without any guarantee, because the new coatings won't be the same as the original.

Harold_4074
6-Oct-2014, 13:18
New coatings will also not correct the refraction occurring due to the shape of the craters. But India ink is water-based, so spotting out the worst damage and removing it if the lens ever goes on sale would be an option.

Donald Qualls
6-Oct-2014, 14:44
New coatings will also not correct the refraction occurring due to the shape of the craters. But India ink is water-based, so spotting out the worst damage and removing it if the lens ever goes on sale would be an option.

IF the damage is only to the coating, stripping the old coating will remove it, and the new coating will have (approximately) the same optical surface as the original. If the damage goes through into the glass underneath, new coating will only reduce the visibility of the damage, while doing nothing optically to improve it.