Author Topic: Rear Element Coating Damage: Remove it all?  (Read 498 times)

karthikrr

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Rear Element Coating Damage: Remove it all?
« on: July 17, 2021, 02:05:12 »
First post, but long time reader ... I recently started building a set of vintage nikkor lenses and finally have a reason to participate here :)

I picked up a Nikkor 28/2.8 yesterday (AI - non-CRC version) with pretty significant coating damage to the rear element. (Image attached : not sure what is the right way to insert an image, somebody please correct me if I am doing this wrong)

I know that the front element can take a severe beating and not affect image quality, but the rear element is more sensitive. Took some sample shots and discovered that this creates a real problem in the bokeh ... (image attached)

Other than this coating issue, the lens is in excellent condition. I have two options as I see it:

1) Wait for a cheap 28/2.8 AI with other issues but a good rear element; swap them out
2) Get rid of the coating altogether from the rear element

Since 2 does not preclude 1 from happening, I see no reason not to get rid of the coating completely. Is there a reason not to do this?

If I do go ahead with this plan, what is the best way to do this? I see MANY sources on the internet that talk about using everything from toothpaste to metal polish to sand to "grind" away the coating, but I would prefer to try a less "abusive" method first, if possible. The same internet sources also have plenty of people talking about the dangers of letting optical elements sit in solvents and cleaners, specifically citing coating damage. Can I simply leave the element in a bowl of vinegar or H202 or IPA overnight and expect results?

Also, as long as I am going to be doing this, any other mods to try and turn this lens into an "art lens"?

Thanks,
Karthik

Zang

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Re: Rear Element Coating Damage: Remove it all?
« Reply #1 on: July 17, 2021, 06:34:49 »
Was photo 2 taken using the lens?

David H. Hartman

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Re: Rear Element Coating Damage: Remove it all?
« Reply #2 on: July 17, 2021, 08:02:27 »
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Hugh_3170

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Re: Rear Element Coating Damage: Remove it all?
« Reply #3 on: July 17, 2021, 08:17:43 »
A third, albeit more expensive and longer shot kind of an option, is to speak to a Nikon repairer and see if Nikon can still supply and fit a replacement rear element.
Hugh Gunn

Snoogly

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Re: Rear Element Coating Damage: Remove it all?
« Reply #4 on: July 17, 2021, 09:44:14 »
To be honest, I'd just live with it, and consider it as an art lens.

The price difference between mint and dodgy with such old lenses is about half a supermarket shop.

Chris Betson

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Re: Rear Element Coating Damage: Remove it all?
« Reply #5 on: July 17, 2021, 11:10:48 »
Getting it polished and recoated will cost more than a better example of the same lens.

If you want to remove the coating yourself then get hold of some jewellers rouge - very fine powder used for polishing glass - it will take a while but I would not soak a lens in anything overnight as the rear group may contain cemented elements.

Hugh_3170

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Re: Rear Element Coating Damage: Remove it all?
« Reply #6 on: July 17, 2021, 11:58:48 »
From Roland Vink's web site (http://www.photosynthesis.co.nz/nikon/lenses.html#28), this lens is a 7 group/7 element design, so cemented lens element groups will not be an issue.  However the rearmost lens element may or may not be practically easy to separate from the rest of the lens cell.  I have a copy of this particular 7/7 lens, but without pulling it apart I cannot comment further on its disassembly.

A good secondhand copy may be the best solution - as others have commented.


Getting it polished and recoated will cost more than a better example of the same lens.

If you want to remove the coating yourself then get hold of some jewellers rouge - very fine powder used for polishing glass - it will take a while but I would not soak a lens in anything overnight as the rear group may contain cemented elements.
Hugh Gunn

pluton

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Re: Rear Element Coating Damage: Remove it all?
« Reply #7 on: July 17, 2021, 19:42:47 »


A good secondhand copy may be the best solution - as others have commented.
This is my thought as well.  I bought one of these a few years ago, here in the USA;  not expensive and flawless glass surfaces.
Keith B., Santa Monica, CA, USA

David H. Hartman

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Re: Rear Element Coating Damage: Remove it all?
« Reply #8 on: July 17, 2021, 19:44:13 »
Getting it polished and recoated will cost more than a better example of the same lens.

If you want to remove the coating yourself then get hold of some jewellers rouge - very fine powder used for polishing glass - it will take a while but I would not soak a lens in anything overnight as the rear group may contain cemented elements.

karthikrr,

I'll agree on both above.

The first and best option is get a better copy and don't spend time on this lens, let it run free on the range. If you wish to make a project of the lens the second option should work. I wonder about internal reflections with an uncoated rear element and a digital sensor. The way to find out is do it.

Dave
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Zang

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Re: Rear Element Coating Damage: Remove it all?
« Reply #9 on: July 18, 2021, 04:44:07 »
I would try reversing the lens to see how it performs as a macro lens.

karthikrr

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Re: Rear Element Coating Damage: Remove it all?
« Reply #10 on: July 19, 2021, 03:55:31 »
Was photo 2 taken using the lens?

Yes! I had just received the lens and was simply trying to see how sharp it was when I noticed something funky going on in the bokeh. I got it cheap because of the coating damage, and was only expecting some loss of contrast issues. To see the pattern in the bokeh was unexpected...

A third, albeit more expensive and longer shot kind of an option, is to speak to a Nikon repairer and see if Nikon can still supply and fit a replacement rear element.

Probably not for THIS lens. I have been buying up boxes and boxes of old M42 primes, mostly to explore adapting lenses, but also to learn to repair them myself. It is only after I became confident about my ability to fix lenses that I turned towards Nikkors. I bought this one because the price was good (reduced due to coating damage) .. I already have a 28/3.5 in excellent condition, and would rather hold out and spend money on a CRC version of the 2.8. I don't want to spend any more money on this lens :)

To be honest, I'd just live with it, and consider it as an art lens.

The price difference between mint and dodgy with such old lenses is about half a supermarket shop.

YES, the "art lens" is what I am going for as well. BUT, I am curious if removing the coating from the rear element will make it more "artistic" ... Plenty has been written about coating damage on the front element, but not much about the rear, other than "its probably a bad idea" ... I wonder if I should test this... Worst case, I prove with pictures just how bad an idea this is :P


Getting it polished and recoated will cost more than a better example of the same lens.

If you want to remove the coating yourself then get hold of some jewellers rouge - very fine powder used for polishing glass - it will take a while but I would not soak a lens in anything overnight as the rear group may contain cemented elements.

DEFINITELY not spending any more money on this lens... Anything I do, it will be done by myself. I don't think this is a cemented element, and the next post from @Hugh_3170 seems to confirm that. My concern mainly revolves around the extreme imprecision that accompanies the use of any kind of abrasive, be it toothpaste or jewellers rouge or metal polish! The solvent soak seems, at least on paper, to be a safer bet. But I have no experience with this, so for now its still just an academic discussion. I will spend some more time shooting with this lens in different kinds of lighting before I do something as irreversible as this.


From Roland Vink's web site (http://www.photosynthesis.co.nz/nikon/lenses.html#28), this lens is a 7 group/7 element design, so cemented lens element groups will not be an issue.  However the rearmost lens element may or may not be practically easy to separate from the rest of the lens cell.  I have a copy of this particular 7/7 lens, but without pulling it apart I cannot comment further on its disassembly.

A good secondhand copy may be the best solution - as others have commented.

I also got a 24/2.8 AIS from the same seller in "defective condition". The focus ring was completely frozen, but everything else was perfect. I used Richard Haw's guide to take that lens apart, praying that the issue would be the main helicoid and not the CRC group. Nope, it was the CRC helicoid that was frozen stiff. It took a few days but the lens can now be listed as "mint" ... So I do feel quite confident that I can handle this disassembly. What I am less confident about is my ability to remove the coating through physical means.

This is my thought as well.  I bought one of these a few years ago, here in the USA;  not expensive and flawless glass surfaces.

karthikrr,

I'll agree on both above.

The first and best option is get a better copy and don't spend time on this lens, let it run free on the range. If you wish to make a project of the lens the second option should work. I wonder about internal reflections with an uncoated rear element and a digital sensor. The way to find out is do it.

Dave

"Make a project of the lens" is exactly what I am leaning towards. I have the 28/3.5, and will at some point buy the CRC 2.8. This lens was cheap and the damage was not of my making, I figure it might be fun to experiment by taking the coating off fully. Now, internal reflections from a digital sensor - thats an interesting question ... I would like to find out :)

Also, I got into adapted lenses (on m4/3) mainly to make videos (not a professional or anything, just for youtube) ... I am curious how the "character" of a nikkor will change if I take the coating off.


I would try reversing the lens to see how it performs as a macro lens.

Funny you mention this, I just dug out my reverse adapter a few hours ago :) Will experiment and report back when I have images to share!

Nasos Kosmas

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Re: Rear Element Coating Damage: Remove it all?
« Reply #11 on: July 19, 2021, 15:57:21 »
You have a very unique  flying bird bokeh, live with it ;)
Unless you use some very fine powder to polish and  remove the  coating then you have slight lower contrast maybe so slight someone cannot recognize

karthikrr

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Re: Rear Element Coating Damage: Remove it all?
« Reply #12 on: July 20, 2021, 01:23:21 »
You have a very unique  flying bird bokeh, live with it ;)
Unless you use some very fine powder to polish and  remove the  coating then you have slight lower contrast maybe so slight someone cannot recognize

Hehe, maybe I should "adjust" the shape a little bit, throw up a bat signal in all my pics!!! Probably can sell the lens for a pretty penny if I did that properly!!!