How to remove coating from front lens element?

[PHOTOTONE]

I've got a rather common LF lens in shutter that has a front coating that is too abraded to use. The abrasions appear to just be in the coating. What would be the recommended method to just remove the coating? Any ideas?
I don't mind using elbow grease, but there must be some chemical or very, very mild abrasive that would help. This lens is worthless now, not worth a professional polish and recoat, as the front element is a cemented pair, and the cost would exceed the value of the lens. Now, don't tell me to just use the lens "as is". I have a perfect one to use, just like it. I like "sharp" photos.

 

[Mark Sawyer]

Now, don't tell me to just use the lens "as is". I have a perfect one to use, just like it. I like "sharp" photos.

Before doing anything to the damaged lens, I'd take the opportunity to make two exposures, one with the "perfect" lens and one with the blemished lens, if only for personal knowledge and curiousity.

My experience is that even very bad coating flaws make very little, if any, difference to the contrast of a lens, and no difference to the sharpness. I have an old Dagor that is VERY badly scratched and pitted well into the glass, front and back, and it is very, very sharp. It's lost only contrast, as far as I can tell...

My guess is that removing the coating will lower the contrast but not affect the sharpness of the lens. (Then again, it might be nice having one lens coated and the other uncoated. I'm rather fond of the softness of an uncoated lens...)

 

[Kilgallb]

Removing the coatings from a lens will change such things as chromatic aberration, and lens flare. Also, the coatings can be used to control distortion and focus field, especially in the corners.

If you remove the outer coating, the lens might be toast, but it seems from your description, it already is.

 

[resummerfield]

Before doing anything to the damaged lens, I'd take the opportunity to make two exposures, one with the "perfect" lens and one with the blemished lens, if only for personal knowledge and curiousity.

My experience is that even very bad coating flaws make very little, if any, difference to the contrast of a lens, and no difference to the sharpness. I have an old Dagor that is VERY badly scratched and pitted well into the glass, front and back, and it is very, very sharp. It's lost only contrast, as far as I can tell...

My guess is that removing the coating will lower the contrast but not affect the sharpness of the lens. (Then again, it might be nice having one lens coated and the other uncoated. I'm rather fond of the softness of an uncoated lens...)

I'll agree with Mark on this one. The coating on the front cell of my Heliar is worn/polished off in spots, with numerous cleaning scratches on the remainder of the coating. Compared with a pristine Heliar of similar vintage, the results are very similar. I would use it as is.

 

[Dan Fromm]

photone, I'm with Mark and Eric. I have a couple of lenses with positively pustulent front front coatings -- 210/6.3 Prinz = Commercial Congo and 210/5.6 Zircon -- that both shoot extremely well. Try your lens out before trying to damage it more.

But since you already have a good 'un, where's the problem?

Kilgallb, can you document a connection between chromatic aberration and coating? AFAIK there isn't any.

photone, take a look at the coating service offered by araxfoto.com. I don't know if they can do just one surface of a cemented doublet, but their prices are amazingly low.

 

[PHOTOTONE]

photone, take a look at the coating service offered by araxfoto.com. I don't know if they can do just one surface of a cemented doublet, but their prices are amazingly low.

If I can't remove the coating, I am going to throw away the elements, and save the shutter. The coating has absolutely nothing to do with the correction of optical aberrations, that is in the shape of the glass elements and the overall design of the lens.

I have used Arax several times for single glass elements, and the results were fine. Arax will not deal with a cemented pair that is swage mounted into a metal shell....

So, I guess nobody on this list knows how to remove a lens coating??? I may try some brasso or Bon-Ami.

 

[sanking]

If I can't remove the coating, I am going to throw away the elements, and save the shutter. The coating has absolutely nothing to do with the correction of optical aberrations, that is in the shape of the glass elements and the overall design of the lens.

I have used Arax several times for single glass elements, and the results were fine. Arax will not deal with a cemented pair that is swage mounted into a metal shell....

So, I guess nobody on this list knows how to remove a lens coating??? I may try some brasso or Bon-Ami.

I don't know of any way to remove the coating with re-grinding the lens.

Brasso and Bon-Ami may remove the coating but they will leave the lens in need of re-polishing. Better just save your time and just discard the elements without putting them through that treatment because it will not result in a smooth, clear surfce. I think you would get better results by spraying the lens with a coat of clear acrylic. With the emphasis on "better" as a relative term of comparison.

Sandy King

 

[JG Motamedi]

I would try a very mild abrasive like tooth paste, rouge, or whiting.

I don't know of any chemical which will remove the coating, but perhaps you could ask John van Stelton of Focal Point Lens (http://www.focalpointlens.com/), who specialize in this sort of work.

 

[roodpe]

If the coating is an older "cold" coating, then you can use cerium oxide to remove it. I have never tried it but the guys at lens and repro have done it and they say it works.

I would not try to remove a modern multi-coating that would have been applied at higher temperatures. These coatings do contribute to the correction of optical aberrations, and are an important part of the optical design and resulting performance of the lens.

Pete

 

[Sparky]

The only problem is that using mechanical means to remove the coating (polishing) is basically going to change the shape of the front surface - and THAT will affect many other characteristics of the lens. Perhaps not by much - but I can't guarantee that. If you had some means of making it consistent, it might be good - such as covering the front element with some sort of very very thin but colorful dye marker first (hell - maybe a sharpie) so that you have a gauge as to how much surface you're taking off and where - otherwise you run the risk of an uneven job.

It also might be worth your while to find a friendly renegade optician who can give you a few pointers...

 

[phfitz]

PHOTOTONE,

the product is called "Mother's Mag & Aluminum Polish" and will take the coating off the front of your element. Use it with a soft paper towel and go over it 2 or 3 times. Available at any US auto store.

This will DEFINITELY remove lens coating, there's no going back once you start. It will leave the glass very nicely polished.

Good luck with it.

 

[steven_e007]

Without knowing the age and make of this lens we don't know what type of coating is on it.

If it is a modern sublimated metallic coating then it is extremely thin and extremely well bonded!

If the front of the lens is visibly abraded, then surely these abrasions are right through the coating and into the glass element?

Will not removing the coating just leave you with an abraded glass element with no coating plus a lot of extra scratches from the efforts to remove the coating?

I reckon it is already toast...


Steve

 

[razzledog]

roodpe is absolutely correct....cerium oxide applied to felt (I used and old felt hat) will remove the coatings and at the same time highly polish the glass.
Problem is it damages the lens ability to resolve and the results will look like mud.

I have tried it several times with terrible consequences, so better to use it as is.

I once had a Nikon 24mm lens on a 35mm camera that looked like an ice skater had performed pirouettes on its surface, but the image quality was still awesome.

Keep an eye on ebay for a lone front element, you never know......

 

[roodpe]

roodpe is absolutely correct....cerium oxide applied to felt (I used and old felt hat) will remove the coatings and at the same time highly polish the glass.
Problem is it damages the lens ability to resolve and the results will look like mud.

I have tried it several times with terrible consequences, so better to use it as is.

I once had a Nikon 24mm lens on a 35mm camera that looked like an ice skater had performed pirouettes on its surface, but the image quality was still awesome.

Keep an eye on ebay for a lone front element, you never know......

Razzledog makes a good point. I assummed you tried the lens and were ready to toss the elements because of it's performance. If the coating damage degraded the performance that much, then you would have nothing to loose.

Pete

 

[GeorgesGiralt]

Hi !
I may be late on this one, but I wear glasses. These are (were) coated. One day I had an accident with aWD40 spray. THe glasses get a large spray. The coating went away at every spot the WD40 has touched.
Later, I tried this on an old Russian KMZ 50mm F:2 front lens element which was showing really bad cleaning mars. The coating went totally away (to my eyes, but not to the guy to which I sent the lens to be re-coated. He used a really destructive method to remove the remains of the coating. Now the lens i s gone..)
So give WD40 a try. If it's not good at the optic job, it will help in the garage....

 

[steven_e007]

Hi !
I may be late on this one, but I wear glasses. These are (were) coated. One day I had an accident with aWD40 spray. THe glasses get a large spray. The coating went away at every spot the WD40 has touched.
.

I know a bit about the coating on eye glasses from my day job.

Spectacal lenses are chemically coated. They are dipped in a bath of goo which is cooked onto the glass.

Very early coated camera lenses (starting around WW2) used similar techniques. In this case the coating will be fairly easy to remove.

Later photographic lens coatings are very thin metallic deposits which are deposited onto the lens by sublimation methods (Putting the lens in a chamber with a blob of alloy and zapping it with a huge current so is vapourises and re-condenses on the lens, for example...). These are a very different proposition altogether and are not going to be removed very easily and probably not at all without damaging the lens. A chemical coating can be dissolved with a suitable solvent, such as some of those suggested in this thread.

A metallic coating needs to be scrubbed off with an abrasive.

We really need to know which lens this is and how old to be sure what type of coating it is.


Steve

 

[GeorgesGiralt]

Steve,
The company to which I sent the lens to re-coat had used a chemical method to remove the trace coating the WD40 had left. The lens now looks like an orange (less the color) and upon closer inspection, it seems to have melted on some places. As the 2 sides and the border show the same aspect, I suspect they used some "nasty" chemical.... It was not a valuable lens, so I don't care, but... take care with chemicals and lenses.

 

[Dan Fromm]

Since when is MgF metallic?

 

[Kilgallb]

Kilgallb, can you document a connection between chromatic aberration and coating? AFAIK there isn't any.

Lens coatings can suppress certain wave lenghts. If a lens has not corrected for certain blue or red wavelengths, the coatings can simply reduce or eliminate the energy and thereby sharpen the image, especially in the corners.

If you have an old lens made in the colour blind film days, using a pan-chromatic film such as TMX or Delta could be problematic if the coatings are removed. I have an old uncoated Kodak lens that has this problem. Putting a yellow or red filter in front of it dramatically sharpens the image when shooting TMX or Delta.

 

[Dan Fromm]

Kilgallb, you're confusing helping a lens with severe chromatic aberration by giving it monochromatic light with redesigning it to reduce chromatic aberration. And the old lenses to which you refer weren't coated when new because coating hadn't been invented yet. As a practical matter, coating came in in the mid-1940s.

I don't know which "old uncoated Kodak lens" you have -- a meniscus, perhaps -- but the better grade of Kodak lenses are just fine even today. As are my pre-WWI Tessars and Unos, all as coated as they were when shipped, i.e., not coated at all.

 

[MartinB]

Bjorn Rorslett has a section on his website where he describes removing the coating from a Nikon Series E lens to improve its use for UV and IR photography. I have not tried this so have no idea how well it works.

The design of his website http://www.naturfotograf.com/index2.html makes it difficult to paste a link directly to the page. Use the link above, scroll down below the photo "mission accomplished" to the link "all about D#$#^* UV and IR Photography" Once at the UV/IR article, go to page 7 "Which Lenses?" for his description of removing the lens coating. The last page (13 - final cut) has a photo taken with a 28mm Series E lens.

Good luck and let us know what you decided to do.

 

[Kilgallb]

Dan

You are probably correct. The lens is an old Kodak 127mm. I think it is WW II vintage for 3x4 press cameras. On 4x5 it has barely enough coverage due to poor focus in the corners. It is just amazing how the corners sharpen with a RED or Yellow filter. It is a terrible lens on colour film.

 

[John Kasaian]

Bon Ami? "Hasn't scratched yet" they say.

 

[George]

Phototone, why do you assume the lens is worthless now? What is the reason that you want to remove the rest of the coating?

 

[Murray@uptowngallery]

Someone on f295.org (John F. ?) found a stateside source for single coating elements that was surprisingly cheap (like $3-4 per surface??!?). Don't know anything about ability to work on mounted or cemented. With sputtering I think cement doesn't matter, but a conductor around the perimeter of glass, a dielectric, may be a reason why Arax couldn't do it.

I didn't think AR coatings had anything to do with distortion or chromatic aberration either, from what I've read. But reading is the extent of my knowledge there.