Polishing a lens with damaged coating

[escuta]

Hi forum,

I recently purchased a CLA'd Kiev 4 which produced photos with a halo around bright (mainly white) objects and regions. I initially thought the lens was in excellent condition, however when I shone a torch at the rear element and inspected the front, I could see that the front element is covered in fine scratches. The lens is a Jupiter 8M, by the way, which I believe has a coated front element.

The seller is to send me a replacement lens. Once that's confirmed, I thought it would be worthwhile trying to polish the front element to remove the damaged coating and also thought it would be worthwhile getting some opinions here on this forum!

My city doesn't have many specialist stores to buy correct polishing equipment and mail-order can be very slow, so I thought I would use an improvised polishing agent like cigarette ash. What do people here think of this approach? Also, what kind of cloth can I use, is a lens cloth OK? A finger tip? Perhaps too oily?

Please let me know your opinions.

Thanks!

 

[02Pilot]

Cerium oxide is the proper material to polish it; it's easily available online. Other stuff may work to remove the coating, but the scratches will not come out easily. When I rehabbed a badly scratched Summar I used damp cotton swabs, changed frequently. Work evenly and without pressure. There is a tendency to overpolish in the center, which needs to be avoided lest you alter the shape of the element.

 

[escuta]

Cerium oxide is the proper material to polish it; it's easily available online. Other stuff may work to remove the coating, but the scratches will not come out easily. When I rehabbed a badly scratched Summar I used damp cotton swabs, changed frequently. Work evenly and without pressure. There is a tendency to overpolish in the center, which needs to be avoided lest you alter the shape of the element.

I found cerium oxide online locally in powder form. Do you know what it should be dissolved into and in what concentration? Did you use cotton swabs dampened with this cerium oxide mixture or something else?

Thanks a lot!

 

[Bill Clark]

My 2 cents.

When I made a couple of reflector (Newtonian) telescopes (I ground the pyrex blank) it didn’t take too much effort to change the focal point of the lens. I ground the blank into a parabolic shape. Even when making the final polish to get a mirror finish, it would change the focal point. The final was getting it coated, I had a source that vapirized aluminum in a vacuum in St. Paul.

At any rate, a camera lens is very small compared to a 8” or 10” telescope. If the telescope mirror was easy to change, I would imagine a small camera lens would be critical when dealing with the dimensions. And if it’s off just a hair little in a spot or two then I would think it would be ready to use as a doorstop.

Have some fun with it and maybe it will turn out ok.

 

[Harry Lime]

Just leave it alone. Lenses are ground to extremely precise tolerances on specialized machines. Depending on the size of the lens we are taking hundreds or thousands of an inch or more. If you do it by hand you will ruin the lens.

I would either sell it or use it as your 'artistic glow lens'

 

[Phil_F_NM]

Can you inspect the interior of the lens for any haze before cutting into the glass? A good cleaning will probably do wonders. There are many a Summitar and Summarit that have a ton of scratches but still deliver great images.

Phil Forrest

 

[Steve M.]

The front of the lens is only one piece of the lens's optics. I wouldn't think a small amount of polishing on that alone would have much, if anything, to do with changing things noticeably.

My guess is that the coating defect you described may not cause the halo you are seeing on photos unless you are pointing the lens directly into the sun. I have owned lenses with coating problems, scratches, and even gouges in the front element, and they never flared nor caused any sort of problems.

Here's a photo of a Leica R 90 Summicron I purchased for a good price that has a LOT of coating issues on the front element. Photos from it have been sharp as a tack with nary a sign of flare. Internal haze is usually a much more serious problem when it comes to flaring or ghosting, but the lens below, in addition to the coating issue being much worse that the photo shows, also has some serious internal haze inside that front element. It takes tack sharp photos and has never flared (note, I always use the built in hood). My suspicion is that all the other elements inside my lens have coatings that take care of the front element's problems. Still, I would normally suspect internal haze to be a flare issue.

 

[Larry Cloetta]

I have a Canon 50mm f/1.2 ltm rf lens which has (very common) coating damage to one specific internal element due to (it is said) long term exposure to outgassing of the lubricants used at the time. It is bad enough that it is causing image degradation, and I would like to get it 'fixed' if that turns out to be practical, by removing the remains of the old coating and repolishing and recoating. I do get a little confused by contradicting opinions on the feasibility of doing this. On the one hand, there was much concern after Focal Point quit offering this service, as if they were the only option. On the other hand, there are quite a few companies which seem to be offering polishing and recoating service for telescope lenses, and other optical lenses (google). Every eyeglass lab in the country grinds, polishes, and coats lenses every day. Is it really that difficult? If dealing with glass substrates, is it really that difficult to carefully polish off a thin layer of compromised coating without changing the curvature of the glass underneath in any meaningful way?

I am not challenging the opinions of anyone here which have already been posted, I honestly don't know and am just asking.

In the case of the lens element in the 50+ year old ltm Canon lens, I don't know if this would be considered a soft coating or a hard coating, but the ease with which it was degraded by the presence of lubricant vapor might (?) be an indicator that it is a soft coating which can be easily removed, something someone else here probably knows.(I was once able to get lens polishing supplies from Edmund Scientific, back when kids were interested in things like that, DIY things. The market changed, as they euphemistically put it, and company and the mindset which supported it, has been gone for quite a while now).

 

[escuta]

Thanks everyone, perhaps I'll leave it and wait for the replacement to arrive (i'd hoped to travel with this camera in a week or so). The lens looks perfectly clear, no fog and the only thing i notice is the worn looking front lens.

I'll post 3 shots taken anyway with the lens. All have white things in the them. The first 2 are with no adjustment. This last photo of my dog came out really well, I guess because it was taken in the shade, but even with this I had to bring down the brightness a lot on the computer. I hope these images appear.

All the best!

 

[Sarcophilus Harrisii]

There is a recent classified ad here by a person offering affordable lens re-coating. I noted it a few days ago as I have an otherwise lovely Rolleiflex with ugly defects in the front coating. Single glass pieces only are taken on according to the ad—no cemented doublets etc. I’m writing this on my phone, so I won’t try and link the advert but it’s quite recent and you’ll find it easy enough. Why not get it fixed properly?
Cheers
Brett