Removing coating from a lens

Cholentpot · Nov 28, 2016

I have a Nikkor 35 2.8 that I bought and it came pretty dinged up. I got it back up to working condition but the front element's coating is toast. Anything light just becomes a mess out of an 80's music video.

Is there any practical way to remove the coating completely? Once the lens is flaring I might as well go all the way.

fstop · Nov 28, 2016

A sand blaster will remove the coating quite effectively.

Sirius Glass · Nov 28, 2016

fstop said:
A sand blaster will remove the coating quite effectively.

Sand paper, a hammer and chisel, placing it under a steam roller, throwing off a cliff ...

faberryman · Nov 28, 2016

When I was young and impressionable, I was told by the editors of Popular Photography that if I didn't protect my lens with a Skylight 1A or UV filter, the multi-coating would spontaneously fall off. You might want to give that a try.

Fixcinater · Nov 28, 2016

Polish it off with a load of cotton swabs like Q-Tips and chrome polish. Brasso is pretty rough, Simichrome is gentler so I prefer it but you do have to be patient sometimes to see results. Softer (older) coatings come off faster than more modern name-brand coatings like Nikon or Canon.

Nodda Duma · Nov 28, 2016

To properly remove the coating, polish it off. That's what an optical shop would do. Use a harder pitch like Gugolz 82 on a suitably-radiused polishing block and your favorite polisher slurry. I.e. Cerium oxide, titanium oxide (my favorite), or red rouge.

Cholentpot · Nov 28, 2016

Fixcinater said:
Polish it off with a load of cotton swabs like Q-Tips and chrome polish. Brasso is pretty rough, Simichrome is gentler so I prefer it but you do have to be patient sometimes to see results. Softer (older) coatings come off faster than more modern name-brand coatings like Nikon or Canon.

You've done this before? Is there a practical way of knowing when you've finished? When it's gone to far?

By the way yes, I've found a lot of the answers here funny. No, I don't think I'll sandblast or go at it with a pick and axe. Maybe I'll fail but I like going the DIY direction before I give up. I can always take it to the beach during a hurricane.

Helios 1984 · Nov 29, 2016

APUGuser19 said:
Put it aside and wait for another junker to come along and steal the glass out of it.

+1

Gerald C Koch · Nov 29, 2016

You can buy lens polishing powders from sites that sell telescope making supplies. What you need is a very fine polish like cerium oxide. This will remove the coating without damaging the lens element.

Nodda Duma · Nov 29, 2016

You have to be careful how you strip the coating off, because you can easily ruin the surface figure / deviate from spherical or the correct radius.

The best way is to polish with pitch tool and polishing slurry made out of one of the polishers listed above (And that should be zirconium oxide, not titanium oxide, available from Universal Photonics). Why? Because the pitch tool can be pressed to come into full, complete contact with the surface and maintain the curvature while polishing. This prevents flattening the surface or turning the edge down, either of which can degrade the optical performance.

Use polishing media as a slurry to prevent health issues.

That's what an optical shop would do to strip the coating for you.

pdeeh · Nov 29, 2016

I'd guess anyone contemplating doing this to a junker lens isn't going to worry too much about retaining sphericality (is that a word?) or correct radius

But good info as ever Jason.

AgX · Nov 29, 2016

Nodda Duma said:
Use a harder pitch like Gugolz 82 on a suitably-radiused polishing block.

How to obtain a "suitably-radiused" one?
I think of casting a negative form, but all materials that come to my mind have some shrinkage. The ideal polishing cup should be a bit larger to take the layer of grinding medium.

Grif · Nov 29, 2016

I'd go find a good telescope DIY site/forum. They resurface mirrors and do all sorts of that kind of thing. The member mentioning the pitch block must have some contacts in the mirror grinding and resurfacing world.

Nodda Duma · Nov 29, 2016

I might have a few contacts in that world (I'm a lens designer by profession, with a fair amount of practical experience in optical shops)

AgX said:
How to obtain a "suitably-radiused" one?
I think of casting a negative form, but all materials that come to my mind have some shrinkage. The ideal polishing cup should be a bit larger to take the layer of grinding medium.

You don't have to hit the radius of curvature exactly with your tool base. Use a thicker layer of pitch (I'd start at 3/8" thick), and press the pitch long enough to form. For a one-off job I'd buy a cheap COTS lens (like a plano-concave) from Edmund Optics or whatever with similar radius of curvature to use as the tool base. Pour the pitch, scribe it, then attach a wooden dowel to the back of the tool with epoxy or optician's wax. Voila! Easy-peasy.

BTW, it's easy enough to send off to a place that will strip the coating for you. The OP mentions DIY. For the DIY'er, going through this exercise will provide very interesting experience in the world of pouring pitch and polishing optics. One tip: Don't use your wife's favorite kitchen pot to melt pitch.

P.S. Texereau's book "How to Make a Telescope" is a very good reference on polishing techniques. The second half of the book on mounts is kind of dated, but the first half is pure gold. His description of making the pitch lap and polishing strokes has relevance here.

BMbikerider · Nov 29, 2016

Depending of course how much you paid for it, you could consider having the front element replaced by a repairer who specialises in lenses. I had one done years ago on an Olympus 21mm/F3.5. I cannot remember how much it cost me but certainly a lot less than a good quality similar lens with no faults. This of course is all depending on the designation of the lens, and the optical design. You can also have a lens re-coated for a reasonable price.

anfenglin · Nov 29, 2016

You could always use toothpaste, that's what I used on a totally trashed Meopta Belar's coating.

thuggins · Nov 29, 2016

Either Simichrome or toothpaste will work. I believe Simichrome is the best. Pay no attention to the comments about needing special tools or compounds. I've polished an number of eyeglass lenses with Simichrome and my fingers, both to remove scratches and damaged coating. It takes some time and patience, but they come out fine.

tedr1 · Nov 29, 2016

You can do it the professional way, spend $$ order the materials and tools, wait a week or two, spend many hours learning to use them. Or you can use the amateur methods perhaps better suited to lens that didn't cost much. Or if you have $150 there are used lenses available ready for work Dead Link Removed

Cholentpot · Nov 29, 2016

thuggins said:
Either Simichrome or toothpaste will work. I believe Simichrome is the best. Pay no attention to the comments about needing special tools or compounds. I've polished an number of eyeglass lenses with Simichrome and my fingers, both to remove scratches and damaged coating. It takes some time and patience, but they come out fine.

So tell me about the toothpaste method. Fingers or cotton balls?

Fixcinater · Nov 29, 2016

It's pretty obvious when you have gotten through the coating. I had a junker third party zoom that I started with and you can see where the coating is and where the reflections lose their color. I don't have the tools to measure if I impacted the radius, but then it took a good amount of polishing to get the coating off by itself so I don't believe I actually took glass off.

I've done it on a couple of hazed Minolta lenses, one in particular went from a terrible 58/1.2 to an acceptable example of same after polishing the inside of the rear element. Canon RF lenses like the 50/1.8 haze need something more advanced like what Nodda Duma is taking about as they need material removed to get through the haze.

I wouldn't do it on something rare or super expensive, but if it is fairly cheap/easy to find and already junk, what do you have to lose?

I tried a fair number of different polishes and toothpastes, settled on Simichrome. YMMV.

Cholentpot said:
You've done this before? Is there a practical way of knowing when you've finished? When it's gone to far?

By the way yes, I've found a lot of the answers here funny. No, I don't think I'll sandblast or go at it with a pick and axe. Maybe I'll fail but I like going the DIY direction before I give up. I can always take it to the beach during a hurricane.

John Koehrer · Nov 29, 2016

thuggins said:
Either Simichrome or toothpaste will work. I believe Simichrome is the best. Pay no attention to the comments about needing special tools or compounds. I've polished an number of eyeglass lenses with Simichrome and my fingers, both to remove scratches and damaged coating. It takes some time and patience, but they come out fine.

Agree with this 100% There's technically correct and then, hey that works.

I've used toothpaste, Flitza, and Simichrome. Q-tips, cotton balls and fingers just to break up the monotony.
Find someplace where you can zone out & rub a dub dub.

Cholentpot · Nov 29, 2016

Fixcinater said:
It's pretty obvious when you have gotten through the coating. I had a junker third party zoom that I started with and you can see where the coating is and where the reflections lose their color. I don't have the tools to measure if I impacted the radius, but then it took a good amount of polishing to get the coating off by itself so I don't believe I actually took glass off.

I've done it on a couple of hazed Minolta lenses, one in particular went from a terrible 58/1.2 to an acceptable example of same after polishing the inside of the rear element. Canon RF lenses like the 50/1.8 haze need something more advanced like what Nodda Duma is taking about as they need material removed to get through the haze.

I wouldn't do it on something rare or super expensive, but if it is fairly cheap/easy to find and already junk, what do you have to lose?

I tried a fair number of different polishes and toothpastes, settled on Simichrome. YMMV.

John Koehrer said:
Agree with this 100% There's technically correct and then, hey that works.

I've used toothpaste, Flitza, and Simichrome. Q-tips, cotton balls and fingers just to break up the monotony.
Find someplace where you can zone out & rub a dub dub.

Thanks, off to the zone for me.

Gerald C Koch · Nov 30, 2016

Tooth enamel is made of fluoroapatite which is a very hard mineral. Many optical glasses can be rather soft. It is possible for tooth paste to scratch some glasses. It all depends on how much value the OP puts on his lens.

As to changing the optical properties of the lens by changing its curvature in reality there is no chance of doing thing. You cannot do it with the polishes mentioned. Perhaps with a power sander.

Cholentpot · Nov 30, 2016

Gerald C Koch said:
Tooth enamel is made of fluoroapatite which is a very hard mineral. Many optical glasses can be rather soft. It is possible for tooth paste to scratch some glasses. It all depends on how much value the OP puts on his lens.

As to changing the optical properties of the lens by changing its curvature in reality there is no chance of doing thing. You cannot do it with the polishes mentioned. Perhaps with a power sander.

Not much value to this lens. When I got it I could have given it to a baby as a rattle.

Dali · Nov 30, 2016

Nodda Duma said:
P.S. Texereau's book "How to Make a Telescope" is a very good reference on polishing techniques. The second half of the book on mounts is kind of dated, but the first half is pure gold. His description of making the pitch lap and polishing strokes has relevance here.

I fully agree even if Texereau is more focused on mirror making but it worth reading it for sure.

Removing coating from a lens

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